MXPA99008934A - Lldpe blends with an ethylene-norbornene copolymer for resins of improved toughness and processibility for film production - Google Patents

Abstract

This invention is for LLDPE blends with an ethylene-norbornene copolymer for resins of improved toughness and processibility for film production. This invention provides LLDPE based resins which are significantly improved with respect to their capability to be fabricated into a film layer, particularly by a blown bubble extrusion technique. Films prepared of the LLDPE/E-NB melt blended resins of this invention are significantly improved with respect to certain of their film properties, such as tear strength, without detracting from the beneficial properties that a LLDPE otherwise provides to a film.

Description

PHYSICAL MIXTURES OF LLDPE WITH A NON-NORBORNENE ETILE COPOLYMER FOR INCREASED TENACITY RESINS AND PROCESSING CAPACITY FOR FILM PRODUCTION Background of the Invention Polyolefins and other types of polymer can be manufactured into films by any of two general techniques for forming film. The molten polymer can be emptied by extrusion through a slot die to form a film layer, and the films thus formed are generally referred to as cast films. Or the molten polymer can be extruded through an annular die to form a gas-tight enclosure of the extrudate, which is then blown by filling it with air to expand the extrudate to a bubble of air-supported film, and the films thus formed They are generally referred to as blown bubble films. The technique for forming polymeric resins in films by a blown bubble extrusion technique is widely practiced, and presents different simplifications and processing conveniences, compared to that of film forming by, extrusion casting techniques in slot die. . However, in order to successfully practice film formation using a blown bubble extrusion technique, the polymeric resin from which the film layer is formed must possess certain minimum physical-mechanical properties, the principal one of which is a resistance to its extrusion temperature (ie, "melt strength") sufficient to withstand the formation of a film bubble during its blowing and expansion by air. Now, certain types of polymeric resins that otherwise possess physical / mechanical / chemical properties that are desirable in a film for different end uses, have exhibited melt-resistance properties that make these resins problematic to be produced in films by a Blown bubble extrusion technique One type of problematic polymer resin is that of linear low density polyethylenes. A linear low density polyethylene, conventionally referred to as LLDPE, is a copolymer of ethylene with a minor amount of an olefinic hydrocarbon co-monomer, typically an alpha-olefin of 3 to 8 carbon atoms, acyclic, such that the ethylene comprises at least about 80% by weight of the polymer, while the co-monomer content comprises less than about 20% by weight of the polymer mass. The copolymerization of ethylene with these minor amounts of acyclic olefinic hydrocarbon co-monomer introduces short chain branching along the base structure of the polymer to produce an ethylene-based polymer having a scale density of about 0.910 to about 0.940. grams / cubic centimeter, with lower densities associated with higher contents of co-monomer; and higher densities associated with contents. lower co-monomer. Accordingly, a linear low density polyethylene possesses many attributes of mechanical / chemical properties that are similar to a low density, highly branched homopolyethylene produced by polymerization of free radicals with high pressure, while also possessing certain mechanical properties. / chemical and rheological like those of a linear high density homopolyethylene produced by the low pressure Ziegler-Natta polymerization processes. Accordingly, this ethylene-alpha-olefin copolymer with ethylene high agreed upon is referred to as a "low density" linear polyethylene; that is, LLDPE. The linear low density polyethylenes are used as such, or as a component mixed with yet other polymers, for the formation of films, which are designed for a variety d. end-use purposes, such as movies for the consumer market, such as garbage bags and disposable household wraps; wrapping films and bags for laundry items and dry cleaning; and shipping and take-away bags, to store merchandise. Linear low density polyethylene is desirable as a resin for films of these end-use designs, due to its relatively low cost compared to other types of resin, such as polyvinyl chloride, and so on, and because it has, in combination with this low cost, an excellent set of mechanical / physical / chemical properties, such as tensile strength, secant modulus, resistance to tearing by traction, resistance to perforation, elongation to breakage, etcetera. For this purpose, the linear low density polyethylene resins have so far been extruded into film layers by both film forming techniques - slot die and blown bubble extrusion techniques. However, due to the relatively low melt strength and relatively low dynamic viscosity at low shear rates of a linear low density polyethylene resin, compared to other types of polymer, a linear low density polyethylene is more difficult to be used as such to be manufactured in a film layer by the blown bubble extrusion technique. Therefore, when a linear low density polyethylene resin is used in a blown bubble extrusion technique for film formation, the processing conditions should be controlled more carefully within a narrower window of operating conditions, and should be observed certain limitations on the dimensions up to which the film layer of a linear low density polyethylene can be produced, particularly that of its film thickness. The limitations that should be observed with a linear low density polyethylene as used in a blown bubble extrusion technique for film formation, further limit the speed of film production, compared with that at which other types could be produced. of polymer on film using a blown bubble extrusion technique. SUMMARY OF THE INVENTION This invention provides resins based on linear low density polyethylene which are significantly better with respect to its ability to be manufactured in a film layer, particularly by means of a blown bubble extrusion technique. The linear low density polyethylene based resins of this invention comprise a melt mixture composed of 50 to 90, preferably 70 to 90% by weight of a linear low density polyethylene resin, with 10 to 50, preferably of 10 to 30% by weight of an ethylene-norbornene copolymer (E-NB), with a norbornene content of > 10% molar and of < 20% molar, and a glass transition temperature (Tg) of less than 60 ° C. In accordance with this invention, the linear low density polyethylene component is melt mixed under high shear conditions, with an amount of ethylene-norbornene copolymer component (E-NB), to produce a molten composite resin mixed with a norbornene content of > 1 mole% and < . 10 mole%, and preferably a norbornene content of > 2 and < 6% molar. These mixed fused resins of LLDPE / E-NB are significantly better with respect to their processability and hardness for the production of film layers, particularly for the production of film layers by a blown bubble extrusion technique, and therefore, overcome the inherent processability / hardness deficiencies in linear low density polyethylene for film production. In addition, it has been found that the films prepared from the fused resin blends of LLDPE / E-NB of this invention are significantly better with respect to certain film properties, such as tear strength., without harming the beneficial properties that a linear low density polyethylene otherwise provides to a film. In accordance with the foregoing, the. subject matter of this invention is the mixed molten resin of LLDPE / E-NB, and the films produced therefrom, wherein at least one film layer thereof is comprised of the mixed molten resin of LLDPE / E-NB. Brief Description of the Drawings Figure 1 illustrates the sample configurations used for film tear tests described by the examples herein. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS This invention comprises a blended cast resin of a linear low density polyethylene which can be easily processed, and of sufficient hardness for convenient production in a film layer by a blown bubble extrusion technique. The main polymer component of the mixed molten resin is a linear low density polyethylene comprising more than 50% by weight of the molten mixture, and preferably 70 to 90% by weight thereof. The second component for the molten mixture resin is a copolymer of ethylene (E) with norbornene (NB), to the extent that the ethylene-norbornene copolymer (E-NB) has a content of norbornene >; 10 mol%, preferably equal to, or greater than, approximately 12 mol%, and less than 20 mol%. The components of linear low density polyethylene and ethylene-norbornene copolymer (E-NB) are mixed in a weight ratio with one another, such that the composite material has a norbornene content that is less than 10% molar, and the components of the mixture are mixed under high shear conditions, at a temperature higher than the peak melting temperature of the highest melting point component of the mixture, to form a homogeneous molten mixture of the two components. The incorporation by the molten mixture of an amount of an E-NB copolymer having a NB content of 10 to 20 mol%, with a linear low density polyethylene in an amount sufficient to impart the mixture of LLDPE / E-NB a NB content of 1 to 10 mole%, has been found to provide the composite mixing resin with non-linear elongation characteristics. This provides the LLDPE / E-NB blend with properties of resistance to melting and elasticity, which allow rapid processing by blown bubble extrusion techniques to a bubble of excellent stability, bubble film that is susceptible to the rapid stretches. In addition, the films formed from the LLDPE / E-NB blend exhibit remarkably superior tear resistance properties - both with respect to the notched and notched resistance to tear propagation - compared to a comparable film formed only of linear polyethylene of low density. The Low Density Linear Polyethylene Mixing Component The low density linear polyethylene polymer component for the blend can be any of the linear low density polyethylene polymers described hitherto by the art, or now available to any other producer. In accordance with the foregoing, the linear low density polyethylene polymer component for the blend may be one that is produced from a conventional Ziegler-Natta catalyst system, or, and preferably, the polyethylene polymer component. Low density linear may be one that occurs with the most recently described metallocene-based catalyst systems. For the purposes of this application, the preferred linear low density polyethylene polymers include ethylene copolymers made using a metallocene catalyst, wherein the ethylene is the monomeric constituent greater in weight percent or molar; specifically, ethylene comprises at least and preferably more than 94% of the linear low density polyethylene polymer, while the co-monomer content thereof does not exceed 6.0 mol% of the polymer, and the amplitude index of compositional distribution (CDBI) of the linear low density polyethylene polymer exceeds 50%. Preferably, these linear low density polyethylene polymers comprise at least about 96 mol% of monomeric ethylene units, and the content of co-monomer thereof does not exceed 5.0 mol%, and more preferably the content of co-monomer. monomer does not exceed about 4 mol% of the polymer. These linear low density polyethylene polymers made with metallocene can later be referred to herein in general as a "m-LLDPE" polymer. The term linear low density polyethylene, as used herein, will mean copolymers of ethylene and alpha-olefins. These alpha-olefins will generally have from 3 to 20 carbon atoms. Polymers of ethylene and one or more of these alpha-olefins are contemplated. The preferred alpha-olefins are butene-1, pentene-1,4-methyl-1-pentene, hexene-1, octene-1, and decene-1. Butene-1, hexene-1, and octene-1 are especially preferred. The catalyst for the polymerization of the linear low density polyethylene preferred herein, comprises a transition metal component -t having at least one organic ligand containing a cyclopentadienyl anion fraction, through which the organic ligand is coordinated in a ligatable manner with the transition metal cation. These catalyst systems are now commonly referred to as "metallocene" (m) catalysts, and many examples of these metallocene catalyst systems have now been described in the art. In contrast to the catalyst systems known hitherto for the polymerization of alpha-olefin, they utilize a transition metal component that does not have an organic ligand having a cyclopentadienyl anion fraction, now commonly referred to as Ziegler-Natta catalysts (ZN) ) conventional or traditional, the metallocene catalysts are essentially single-site catalysts, while the ZN catalysts are multi-site catalysts that generally produce a polymer resin having a large diversity of polymer species. In contrast, an ethylene-alpha-olefin copolymer produced by a metallocene catalyst is generally much more uniform with respect to the psimérica species comprising the polymer resin m-LLDPE, particularly with respect to the disparity between the different fractions of molecular weight thereof - as indicated by the Mw / Mn value of the polymer resins of m-LLDPE, which is in general <; 3.0- and with respect to the distribution of the alpha-olefin co-monomer between the fraction of different molecular weight thereof -as indicated by a high value of compositional composition amplitude index (CDBI) of 50% and higher. In part, because of the greater uniformity of composition and molecular weight distribution achieved in the m-LLDPE polymer produced by a metallocene catalyst, the density of the resulting m-LLDPE resins is substantially a linear function of its molar percentage of co-monomer content, and densities of linear low density polyethylene resin in the scale of interest of 0.910 to 0.940 grams / cubic centimeter for the films of this invention, can be achieved with an eflene content greater than 94% molar, and a comonomer content no greater than about 6.0 mole%, particularly a co-monomer content that preferably does not exceed about 5.0 mole%, and more preferably e, or less than, 4 mole%. In addition, these densities are achieved in the m-LLDPE resin, while the base structure of the polymer remains substantially linear; that is, the short chain branching (SCB) that occurs along the base structure of the polymer, is due substantially only to the alpha-olefin co-monomer content of the polymer. In accordance with the above, although the final density of m-LLDPE varies somewhat depending on the number of carbon atoms of the co-monomer used, the magnitude of this variation with alpha-olefin co-monomers of 3 to 20 carbon atoms carbon is not substantial; the copolymer densities required of the m-LLDPE resin for the molten composite LLDPE / E-NB blend resins of this invention, can be easily achieved with low comonomer contents, such as alpha-olefins of 4 to 8 carbon atoms. carbon, with butene-1 and hexene-1 being preferred as the co-monomer because of its lower cost. The m-LLDPE polymers having these requirements have recently become commercially available from Exxon Chemical Company in Baytown, Texas, United States, and are now identified by the "Exceed" brand. The linear low density polyethylene polymers preferably for use in the present invention will generally have a narrow molecular weight distribution (MWD), as characterized by the ratio of the heavy average molecular weight (Mw) to the numerical average molecular weight (Mn). , Mw / Mn. These values of Mw and Mn are determined by Gel Permeation Chromatography (GPC). The molecular weight distribution for the m-LLDPE of the present invention is less than, or equal to, 5; preferably < 3.5, more preferably < 3.0; and more preferred < 2.5. The embodiments of these m-LLDPE polymers will have a density preferably in the range of about 0.915 to 0.940, preferably 0.917 to 0.940, and more preferably 0.920 to 0.940 grams / cubic centimeter. Low density linear polyethylene polymers produced from a catalyst system having a single metallocene component have a very narrow composition distribution - most polymer molecules will have only a molar percentage of co-monomer content hardly equal or comparable. The Ziegler-Natta catalysts, on the other hand, generally produce copolymers having a considerably broader composition distribution, meaning that the inclusion of the co-monomer varies widely among the polymer molecules. One measure of the distribution of the composition is the "Compositional Distribution Amplitude Index" ("CDBI"), as defined in U.S. Patent No. 5,382,630, which is incorporated herein by reference. The CDBI is defined as the weight percent of the copolymer molecules having a co-monomer content within 50% of the average total molar co-monomer content. The CDBI of a copolymer is easily determined using well-known techniques to isolate the individual fractions from a sample of the copolymer. One technique is the Elution Fraction with Temperature Elevation (TREF), as described in Wild et al., J. Polv. Sci., Poly. Phys. Ed., Volume 20, page 441 (1982) ", and in U.S. Patent No. 5,008,204, which are incorporated herein by reference.The additional details of the CDBI determination of a copolymer are known by experts in this field, see, for example, PCT patent application WO 93/03093, published February 18, 1993. The m-LLDPE polymers employed in the films of this invention have CDBIs equal to or greater than that, 50 percent, and on the scale of 50 to 98 percent, usually on the scale of 50 to 70 percent, and more typically on the scale of 55 to 60 percent.The m-LLDPE that are the resins Preferred, have a melt index (MI) on the scale of about 0.5 to about 10, preferably on the scale of about 1.0 to 5.0, and more preferably 1 to 4.0 decigram / minute.The Mi scale for the mixed resin cast of LLDPE / E-NB for the production of film by medium of a blown bubble technique, preferably it is from about 0.8 to about 2.0 decigrams / minute; for the production of cast film, the MI scale of the molten mixed resin of LLDPE / E-NB is preferably about 0.75 to 4.0 decigram / minute; preferably from 1 to 5.0 decigrams / minute; more preferably from 1 to 4 decigrams / minute. The choice of melt index for the molten mixed resin of LLDPE / E-NB will generally be driven by the type of extrusion process and the specific equipment used, as well as the final use for the films and / or the subsequent use in the conversion operations. The EXCEED® polymer resin product now available from Exxon Chemical Company is an ethylene-based copolymer produced with metallocene catalyst. One grade of EXCEED® is a copolymer of ethylene and hexene-1, and is a linear polymer and a single type of linear low density polyethylene. This m-LLDPE produced with metallocene has a narrow molecular weight distribution (Mw / Mn), normally less than 3.0, while having useful mean heavy molecular weights (Mw) greater than 10,000 and less than 500,000, and a branching scale of short chain (SCB) close to about 12 and smaller # of 30 SCB / 10Q0 atom? of carbon. The class of polyethylenes EXCEED® (where the co-monomer is an alpha-olefin of 4 to 8 carbon atoms), have a substantial absence of molecules of low molecular weight and high content of co-monomer, a substantial absence of molecules of high molecular weight and low co-monomer content, as indicated by CDBI J > fifty%; a narrow molecular weight distribution, and a slightly lower melt strength than traditional linear ethylene polymers, and a slightly flatter shear rate viscosity curve. The Ethylene-Norbornene Component of the Copolymer Blend The ethylene-norbornene copolymer which is suitable as a blending component for the purposes of this invention, can be prepared by the copolymerization of ethylene and norbornene in the presence of a catalyst system which comprises an activated cyclopentadienyl transition metal compound; that is, a metallocene catalyst system. The ethylene-norbornene copolymer is of a substantially uniform composition, and incorporates norbornene into the copolymer in an amount of 10 to 30 molar percent norbornene, preferably 10 to 20 molar percent norbornene. Preferably, the ethylene-norbornene copolymer has a weight average molecular weight (Mw) of from about 30,000 to about 1,000,000, and more preferably from about 60,000 to about 600,000, and a molecular weight distribution (Mw / Mn) substantially less than about 4, more preferably from about 1.2 to about 2.0. The ethylene-norbornene copolymer is generally amorphous, as reflected by the absence of a well-defined melting point by differential scanning calorimetry (DSC), and the substantial absence of a crystalline phase transition. That is, the differential scanning calorimetry trace may exhibit a broad hump, but in general it does not exhibit a sharp-narrow peak as a maximum of the melting point. The ethylene-norbornene copolymer preferably has a glass transition temperature between -50 ° C and +50 ° C. The norbornene can generally comprise from about 5 to about 30 mol% of the E-NB copolymer, but preferably comprises from about 10 to about 20 mol%. In more incorporation rates. low, norbornene does not substantially affect the properties of the ethylene-based co-polymer. Conversely, at higher rates of incorporation, the E-NB copolymer would behave in a manner similar to the cyclic poly (olefin). Accordingly, the ratio of norbornene is essential to obtain an E-NB copolymer having the rubberized and memory retention properties required to be used in the formation of the molten LLDPE / E-NB blend resins of this invention. The norbornene and ethylene content of the E-NB copolymer is generally directed to obtain the desired properties of the copolymer. For example, the glass transition temperature (Tg) generally increases as the norbornene content increases, because the norbornene homopolymers generally have a higher Tg than the ethylene homopolymers. The E-NB copolymer preferably has a Tg of about -50 ° C to 50 ° C, more preferably of about -10 ° C to about 30 ° C. As used herein, Tg is determined by differential scanning calorimetry (DSC) or dynamic mechanical thermal analysis (DMTA), in accordance with procedures well known in the art. Preferred E-NB copolymers for use in the present invention have a number of properties that make them desirable. E-NB copolymers generally have good hardness and optical clarity; as the homopolymers of ethylene, propylene, and higher olefins; but they also tend to have greater elasticity and recovery after elongation. However, the preferred E-NB copolymers also have hardness * and excellent tensile properties. As used herein, ultimate tensile strength, elongation to breaking, and recovery, are determined at 25 ° C using procedures in accordance with ASTM D-1708, unless noted otherwise. t The E-NB copolymer preferably has an elongation? breakage of 300% or more, more preferably greater than 400%, and especially greater than 500%; a tensile strength with an elongation of 150% of at least 56 kg / cm2. of preference at least 70 kg / cm2; an elastic recovery of at least 75% after 10 minutes of relaxation from an elongation of 150%, more preferably a recovery of at least 85%, and especially 90%. The E-NB copolymer preferably has a final tensile strength of at least 175 kg / cm2, more preferably greater than 280 kg / cm2. The elasticity of the E-NB copolymers can be extended over a relatively wide temperature scale, by controlling the Mw and the MWD. In general, the combination of a higher Mw with a lower Mw tends to result in an E-NB copolymer remaining coiled at temperatures greater than the approximate Tg (measured by DSC or DMTA) of the copolymer, e.g. Tg (from -50 ° C to 50 ° C) to more than 100 ° C, preferably more than 150 ° C, as reflected by a storage module packed on this temperature scale. To achieve this relatively high use temperature, the Mw of the E-NB copolymer is at least 30,000, preferably at least 60,000, and especially at least 90,000; while the Mw / Mn ratio is less than 2, preferably from 1.2 to 1.8. The modulated storage module of the E-NB copolymer is easily observed as a flatness between approximately 1 and approximately 100 MPa by dynamic mechanical thermal analysis (DMTA) at a frequency of 1 or 10 Hz, with a temperature ramp of 2 ° C / minute, using commercially available DMTA equipment, for example, from Polymer Laboratories, Inc. The polymerization methodology employed to produce an E-NB copolymer as used in this invention, can be practiced in the manner and with the catalysts of metallocene referents, disclosed, and described in the following references: U.S. Patent Nos. 5,055,438; 5,057,475; 5,096,867; 5,017,714; 5,153,157; 5,324,800; 5,198,401; 5,278,119, and pending United States patent application, Serial No. 08 / 412,507, filed March 29, 1995. See also the pending United States patent application, Serial No. 09 / 005,676, filed on January 19, 1993, and international application WO 94/17113; all of which are incorporated herein by reference. In general, the preferred catalyst systems employed in the preparation of the E-NB copolymer, as used in this invention, may comprise a complex formed by mixing a metallocene transition metal component of Group 4 with an activating component. . The catalyst system can be prepared by the addition of the required transition metal components and alumoxane, or a metallocene * cationically activated transition metal component, to an inert solvent in which the olefin polymerization can be performed by a process of polymerization in solution, in paste, or in bulk phase. Generally optimum results are obtained where the Group 4 transition metal compound is present in the polymerization diluent, in a concentration preferably from about 0.00001 to about 10.0 millimoles / liter of diluent, and the activating component is present in an amount to provide a molar ratio of the activator component to the transition metal from about 0.5: 1 to about 2: 1 or greater, and in the case of alumoxane, the molar ratio of the alumoxane to the transition metal can be high, such as 20,000: 1. Normally enough solvent is used to provide adequate heat transfer from the catalyst components during the reaction, and to allow good mixing. The ingredients of the catalyst system, i.e., the transition metal, it alumoxane, and / or the ionizing activators, and the polymerization diluent, can be added to the 4 'reaction vessel in a rapid or slow manner. The temperature maintained during the contacting of the catalyst components can vary widely, such as, for example, from -100 ° C to 300 ° C. Preferably, during the formation of the catalyst system, the reaction is maintained at a temperature of about 25 ° C to 140 ° C, more preferably about 25 ° C to 120 ° C. In a preferred process for the production of the E-NB copolymer, the catalyst system is used in the liquid phase (paste phase, solution, suspension, or bulk, or a combination thereof), in the high pressure fluid phase, or in the gas phase. The liquid phase process comprises the steps of contacting ethylene and norbornene with the catalyst system in a suitable polymerization diluent, and reacting these monomers in the presence of the catalyst system for a time and at a temperature sufficient to produce an E-polymer. -NB of sufficient molecular weight. The most preferred conditions for ethylene copolymerization are those in which ethylene is subjected to the reaction zone at pressures from about 0.00133 kg / cm2 to about 3500 kg / cm2, and the reaction temperature is maintained from about -100 ° C to approximately 300 ° C. The reaction time can be from about 10 seconds to about 4 hours. A process for the polymerization for the production of the E-NB copolymer is as follows: in a stirred vessel reactor, liquid 2-norbornene is introduced. The catalyst system is introduced by means of the nozzles, either in the vapor or liquid phase. The feed ethylene gas is either introduced into the vapor phase of the reactor, or dispersed in the liquid phase, as is well known in the art. The reactor contains a liquid phase composed substantially of liquid 2-norbornene, together with dissolved ethylene gas, and a vapor phase containing vapors of all monomers. The temperature and pressure of the reactor can be controlled by co-monomer reflow in vaporization (self-cooling), as well as by cooling coils, jackets, and so on. The polymerization rate is generally controlled by the concentration of the catalyst. The ethylene and norbornene contents of the polymer product are determined by the ratio of ethylene to norbornene in the reactor, which are controlled by manipulating the relative feed rates of these components to the reactor. As noted above, any suitable coordination catalyst system can be used. However, preferably the catalyst has a relatively low ethylene: norbornene reactivity ratio, less than about 300, more preferably less than 100, and especially about 25 to about 75. In accordance with the above, the selection of the transition metal, and other components of the catalyst system, is a parameter that can be used as a control over the ethylene content of the E-NB copolymer, with a reasonable ratio of ethylene to norbornene feed rates. Formation of the LLDPE / E-NB Mixture As noted above, the linear low density polyethylene can comprise as little as 50% by weight of the mixture, the remainder being E-NB. However, it is preferred to use a larger amount of linear low density polyethylene component, an amount sufficient for the E-NB to become in essence completely comparable with the amorphous phase of the linear low density polyethylene component, as evidenced by the disappearance of a melting point peak (or hump) in the mixture ^ fused compound, which would otherwise be ascribed, to the E-NB component. Accordingly, in the preferred embodiment, the molten mixture exhibits LDSC melting point peaks that can be ascribed only to linear low density polyethylene. Accordingly, it is preferred to employ the linear low density polyethylene component in an amount comprising at least about 70 percent by weight of the final blend, more preferably in an amount to provide 75% by weight of the mixture, and most preferably in such a way that the linear low density polyethylene comprises at least about 80% by weight of the mixture. The rest of the polymer components of the mixture is then the E-NB copolymer, and the norbornene content of this E-NB copolymer is selected such that the final mixture has a norbornene content of about 1 to about less than 10 mol%, preferably from about 2 to about 6 mol%. The final melt index of the mixture can vary up to a desired scale by selecting the LLDPE and E-NB components of different melt index values. Accordingly, the final blend can be designed to have the desired melt index value for the film forming technique within which the blend will be employed. Conventional additives, such as anti-oxidants, Irganox® 1076 or Weston® 399, and the like, can be incorporated with the mixture in their typical amounts as desired. The molten mixture is essentially a physical mixing process, and, as opposed to a chemical reaction process, the conditions of time and temperature of the molten mixture are not especially critical. With respect to the temperature for the molten mixture, it is only necessary to employ as a mixing temperature, one greater than that of the higher melting peak of the higher melting point polymer component, and lower than the temperature at the that any component of the mixture would degrade thermally. Mixing components, in their molten state, need to be subjected to a high shear mixing only during the time that the mixing components enter a relatively uniform mixture, as judged by visual appearance and / or properties. of melt flow of the molten mixture. In this regard, the molten mixture can be prepared as an aspect of an extrusion process that forms an article, wherein a previously mixed dry blend of the LLDPE and E-NB components in appropriate proportions is added to the supply hopper of resin from an extruder, and the molten mixture of these components occurs during its transit driven by screw through the barrel of the extruder into the hollow of the die that forms the article. Alternatively, the blend components can be premixed melted in a static mixer, and then ground to a granule or other suitable particle form as a dry feed resin material for an extrusion operation. With respect to the tear-resistance properties of a film formed of the LLDPE / E-NB blend resin of this invention, notched tensile tear strength (NTTS) seems to have its peak in the region where the component of E-NB comprises from about 20 to about 30% by weight of the mixed resin, although the compatibility limits of the E-NB with the amorphous phase of the linear low density polyethylene component are reached when one approaches "the loading level of 30% by weight of E-NB.The improvement in Elmendorf Tear Resistance is noted and is means across the entire loading region of 10 to 50% by weight of E-NB, Elmendorf Tear Resistance peak in the loading region of 20 to 50% by weight of E-NB, and focusing in the region of 25 to 30% by weight of E-NB. This region of 25 to 30% by weight of E-NB is also the center for the peak NTTS, and therefore, is a preferred blend composition. Film Formation from LLDP Mixing Resin? /? - NB Blown films produced with an annular die, and air cooling, and cast films using a slot die and an ice roller for cooling, are both techniques acceptable to make a film layer of the molten mixed composite resin of LLDPE / E-NB in accordance with the present invention. Additionally, various additives are also contemplated, including pigments, viscosifiers, anti-static agents, anti-fog agents, anti-oxidants, or other additives, and may be included in the resins and / or films made therefrom. Structures in multiple layers can be preferred in some applications. These structures include, but are not limited to, co-extruded films, and laminated films. Laminated films may include not only one or more film layers based on the molten mixed resins of LLDPE / E-NB of the present invention, but also other film layers, including, but not limited to, polyester, polyamide, polypropylene, other polyethylenes, Saran®, ethylene-vinyl alcohol, and the like. Lamination methods include extrusion lamination, adhesive lamination, heat lamination, and the like. The films produced from the resins of the present invention preferably have a higher NTTS than an otherwise comparable film formed only from the above linear low density polyethylene. More preferably, the NTTS of the film is greater than a mathematically weighted average of a contribution to the NTTS which is represented by the percentage by weight of the proportions of the LLDPE and the E-NB in sum. For a further preferred embodiment, the film has an Elmendorf Tear Strength (ETS) that is greater than a mathematically weighted average of a contribution to the ETS that is presented by the weight percentage proportions of the LLDPE and the E-NB in sum. . EXAMPLES Example 1 - Copolymerization of Ethylene-Norbornene Activation of the Catalyst 4.0 grams of Cp2ZrMe2 (0.0159 mole) were weighed into the dry box, and added to 12.0 grams of tetraperfluoropheropyl boron of N, N-dimethyl dimethylaniline (DMAH B (pfp )4; 0.0150 moles, 1.06: 1 molar excess of Zr complex). 2.0 liters of dry toluene was added, and the mixture was allowed to stand with occasional stirring until activation was complete. The resulting solution was transferred to a 2.25 liter pump fitted with ball valves, and sealed to be transferred to the reactor. Reactor Conditions 749.50 liters of toluene were transferred to a clean and dry batch reactor of 946.35 liters. The reactor was cleaned with 1496 kilograms of a 25% by weight solution of tri-isobutyl aluminum (TIBAIJ in toluene (1.95 moles), 40.188 kilograms of a solution of norbornene at 80.7% by weight in toluene were transferred to the reactor (345.3 moles). Finally, ethylene was introduced under a regulated pressure of 2.66 kg / cm 2. The mixture was stirred until the solution was saturated with ethylene (approximately 320 moles), and equilibrated at 60 ° C. The previously activated catalyst solution discussed above. It was pressurized in the reactor in dps lots in rapid succession, until an exotherm was presented.A controlled exotherm of 3 ° C to 5 ° C was presented after the addition of approximately 62 percent of a catalyst solution "( 9.3 millimoles of Zr, Al / Zr = 210: 1) The temperature was controlled at 60 ° C by circulating refrigerant oil at room temperature through the reactor jacket as required Ethylene was refilled as needed sario to maintain 2.66 kg / cm2 ,. the reaction was monitored by ethylene recovery. The reaction was turned off after 2 hours. The resulting copolymer solution was pumped in batches of 37.85 liters to a precipitation unit filled with hot water. Steam was used at a high pressure to separate the solvent and the remaining co-monomer. After cooling, the solid white copolymer was removed, cut into small pieces, ground, extruded through a devolatilizing extruder, quenched in ice water, and minced into granules. The granules were blown dry with nitrogen. The yield was greater than 45.36 kilograms. The melting temperature was 63 ° C by differential scanning calorimetry, MI = 1.8 decigrams / minute, Mw = 73,000, and an incorporation of 11.8 mol% of norbornene by HNMR. Example 2 - Production of Film and Properties In the following example, a series of thin films (from 76.2 to 127 microns thick) were prepared by compression molding of 14 kg / cm2 at 180 ° C, and different properties were determined of the resulting films. The resins Polymers used in the production of these films were:?: (A) a 10% by weight linear ethylene-hexene low density polyethylene, with a density of 0.917 grams / cubic centimeter, a melt index (MI) of 1.0 decigram / minute, a molecular weight distribution (Mw / Mn) of approximately 2.13, and a first melting point temperature of 120 ° C, and a second temperature of 110 ° C (by differential scanning calorimetry analysis) - film A; (B) an E-NB or ethylene-norbornene copolymer, having a norbornene content of 11.8 mole percent (31% by weight), of a density of 0.950 grams / cubic centimeter, and a melting index of 1.2 decigrams / minute, and an Mw / Mn (80,200 / 43,800) of 1.83 that exhibited, by means of differential scanning calorimetry analysis, _ a melting point temperature (Tm) of 63 ° C, and a crystallization temperature (Tc) of 40 ° C, a heat value of fusion ((?) Hf) of 35 J / g, and a Young's modulus (G) of 137.62 kg / cm2 - film B; and (C) fused composite mixtures of the above copolymer of LLDPE and E-NB in weight proportions of LLDPE / E-NB of (1) 90/10, (2) 80/20, (3) 70/30, and ( 4) 50/50, which were prepared by the melted mixture in a CW mixer Brabender (45 cubic centimeters) at 150 ° C / 60 rpm for 10 minutes - like the Cl, C2, C3, and C4 films. Irganox 1076 antioxidant in an amount of 0.5 grams (1% by weight) was added to all LLDPE / E-NB mixtures during the mixing process. All thin film samples were tested for Notched tensile strength (NTTS, units, energy / thickness, in kilograms), Elmendorf Tear Strength (grams / 25.4 microns), and analyzed by scanning calorimetry. differential for melting point peaks. The determined results are given in Table 1 below. Tear Resistance Two methods were used to evaluate the tear strength of the films: the Elmendorf Tear Test, and the "Notched Strip Tear Test", which was developed during the course of their investigation. The traditional method is the Elmendorf test, but it was found to be deficient for testing high tear strength films and compression molded samples, so a second method was developed, which doubled the "Tensile Strength by Traction with Notch "(or NTTS). The sample configurations used for the tear tests are shown in Figure 1, where A is the Elmendorf, and where B is the NTTS. In blown or emptied films, the initial notch in the sample is made parallel either in the machine direction or in the transverse direction. By convention, the test direction is defined as the axis with which the notch is aligned. The beginning of the Elmendorf test is attached to a sample tab in a fixed jaw, while the other is held in a movable jaw attached to a pendulum. When the pendulum is released, it oscillates downwards, taking with it the movable hold, subjecting the sample to a complex "leg of pants" tear, absorbing energy as it does. Elmendorf tear strength (ETS) is reported as the force required to break the sample in grams / 25.4 microns. In the NTTS or notched strip test, a strip of 1.27 centimeters in width is cut a "notch" of 0.635 centimeters with a razor, perpendicular to its long axis, which may be parallel or perpendicular to the direction of machine. The sample is held by the jaws set to 3.81 centimeters apart, and is subjected to tensile deformation in an Instron tensile test machine, at an elongation speed of 1.27 centimeters per minute. The tear strength (kg) is reported as the energy (kg-cm) required to break the sample, divided by its thickness (cm). The notched strip tear test (NTTS) has the additional advantage that the deformation zone can be observed directly during the course of the test.

Although this invention has been described with reference to its preferred embodiments, upon reading this disclosure, those skilled in the art may appreciate that changes and modifications may be made that are not outside the scope and spirit of this invention as set forth herein. described above or claimed later herein.

Claims (13)

1. CLAIMS 1. A composition for the manufacture of a film having improved mechanical properties, comprising: a resin physically mixed in a molten state, composed of a) from 50 to 90% by weight of an LLDPE formed of acyclic olefin monomers; b) from 50 to 10% by weight of an ethylene-norbornene copolymer having a norbornene content of at least 10 mol% and a Tg of less than 60 ° C; wherein said components of LLDPE and ethylene-norbornene copolymer are present in proportion to each other to result in a composite material having a content of norbornene > 1 mole% and < 10% molar. The composition of claim 1, wherein the LLDPE comprises from 70 to 90% by weight, and the E-NB copolymer comprises from 30 to 10% by weight. The composition of claim 2, wherein the E-NB copolymer has a norbornene content of less than 20 mol% and the physical mixture has a norbornene content of 2 to 6 mol%. 4. The composition of claim 3, wherein the E-NB copolymer comprises from 20 to 30% by weight of the physical mixture. The composition of claim 2, wherein the melted physical mixture exhibits melting point peaks by DSC attributable solely to LLDPE 6. A film, comprising: a film layer composed of a physically blended resin in a molten state, composed of a) from 50 to 90% by weight of an LLDPE formed from acrylic olefin monomers, b) from 50 to 10% by weight of an ethylene-norbornene copolymer having a norbornene content of at least 10 mol% and a Tg less than 60 ° C, where said components of LLDPE and ethylene-norbornene copolymer are present in proportion to each other to result in a physical mixture having a norbornene content of> 1 mol% and <10 mol%. The film of claim 6, wherein the LLDPE comprises from 70 to 90% by weight, and the E-NB copolymer comprises from 30 to 10% by weight 8. The film of claim 7, wherein the copolymer of E-NB has a norbornene content of meno s of 20 mole% and the physical mixture has a norbornene content of 2 to 6 mole%. 9. The film of claim 8, wherein the E-NB copolymer comprises from 20 to 30% by weight of the physical mixture. The film of claim 7, wherein the melted physical mixture exhibits melting point peaks by DSC attributable solely to LLDPE. The film of claim 7, wherein the film has a higher NTTS than a comparable film otherwise formed "only of the LLDPE alone." The film of claim 11, wherein the NTTS of the film is greater than average mathematically weighing a contribution to the NTTS that is represented by the weight percentage proportions of LLDPE and E-NB in a sum 13. The film of claim 11, wherein said film has an Elmendorf tear strength (ETS) which is greater than a mathematically weighted average of a contribution to the ETS that is represented by the percentage proportions by weight of LLDPE and E-NB in a sum.