MXPA01002520A - Polyethylene film composition - Google Patents

Abstract

An in situ blend comprising a mixture of first and second ethylene/alpha-olefin copolymers wherein the alpha-olefin has 3 to 8 carbon atoms, the first copolymer having a density in the range of 0. 9035 to 0.908 gram per cubic centimeter and a roll-milled flow index in the range of about 1.4 to about 2.6 grams per 10 minutes and the second copolymer having a density in the range of 0.925 to 0. 945 gram per cubic centimeter and a melt index in the range of about 200 to about 400 grams per 10 minutes;the weight ratio of the first copolymer to the second copolymer being in the range of about 45:55 to about 60:40 and the in situ blend having a density in the range of 0.919 to 0.924 gram per cubic centimeter, a melt flow ratio in the range of about 85 to about 115 and a flow index of 65 to 90 grams per 10 minutes.

Description

COMPOSITION OF POLYETHYLENE FILM Technical Field This invention relates to a mixture of polyethylene copolymers such that a film extruded therefrom essentially has no gels (or fish eyes).

Basic Information Polyethylenes of various densities have been prepared and converted into films that are characterized by excellent tensile strength, high final elongation, good impact resistance and excellent puncture resistance. These properties together with the rigidity improve when the polyethylene is of high molecular weight. However, when the molecular weight of the polyethylene increases, the processability of the resin usually decreases. By providing a mixture of high molecular weight and low molecular weight polymers, the proper characteristics of the high molecular weight resins can be conserved and the processability, particularly spreadability (a characteristic of the low molecular weight component) can be improved. The mixing of these polymers is carried out with good results in a phase reactor process similar to those described in U.S. Patent Nos. 5,047,468 and 5,149,738. Briefly, the process is one for the polymer site where it prepares a high molecular weight ethylene copolymer in a reactor and a low molecular weight ethylene copolymer is prepared in another reactor. The process usually comprises the continuous contact, under polymerization conditions, of a mixture of ethylene and one or more alpha-olefins with a catalyst system in two gaseous phases, fluidized bed reactors in series, said catalyst system comprising: (i) ) a catalyst precursor based on magnesium / titanium with support; (ii) one or more activating compounds containing aluminum; and (iii) a hydrocarbyl aluminum cocatalyst. although in situ combinations prepared as above and the films produced therefrom, the commercial application of these granular polymers of wide molecular weight distribution for high quality film applications was found to have the advantageous characteristics hitherto mentioned. often limited by the levels of gels obtained. These gels adversely affect the aesthetic appearance, extrusion capacity, and physical properties of the product. The gel characteristics of a film product are usually designated by a subjective scale of Film Appearance Rating (FAR) ranging from minus 50 (very poor, these films have a large number of large gels) to more than 50 ( very good, these movies have a small amount, or essentially no, of gels). For commercial acceptability, the FAR must be more than 20 or better.

Description of the Invention An object of this invention, therefore, is to provide a combination in situ, which can be converted into a film having an exceptionally high FAR. Other objects and advantages will be evident from now on. In accordance with the present invention, such a combination has been discovered. The in situ combination of this invention comprises a mixture of first and second ethylene / alpha-olefin copolymers wherein the alpha-olefin has 3 to 8 carbon atoms, the first copolymer having a density in the range of 0.9035 to 0.908 grams per centimeter cubic centimeter and a flow rate in the roller mill in the range of about 1.4 to about 2.6 grams per 10 minutes and the second copolymer has a density in the range of 0.925 to 0.945 grams per cubic centimeter and a melt index in the range from about 200 to about 400 grams per 10 minutes; the weight ratio of the first copolymer for the & - ^ - ^ a_ £ -ÍM-Í ---_ B _------- Hwi Sfg ^ nym second copolymer being in the range of about 45:55 to about 60:40, and the combination in Sodium has a density in the range of 0.3 to 0.924 grams per cubic centimeter, a flow index in the range of 65 to 90 grams per 10 minutes and a melt flow ratio in the range of about 85 to about 115.

Description of preferred mode (s) The film is generally formed by extrusion. The extruder is a conventional one that uses a nozzle that will provide the desired thickness. The thickness of the films of interest in this case can be in the range of about 0.4 to about 10 mils and is preferably in the range of about 0.5 to about 6 mils. An example of an extruder, which can be used in the formation of the film, is a type of modified le screw with a film blowing nozzle and air ring and continuous collection equipment. A common extruder of the le screw type can be described as having a feeder tank at its upper end and a nozzle at its lower end. The tank feeds a barrel, which contains a screw. At the lower end, between the end of the screw and the nozzle, is a packed screen and a plate j ^ ítóí ^^ _ ^^ i ^ __ groundbreaking. The screw portion of the extruder considered to be divided into three sections, the feeding section, the compression section measuring section, and multiple zones of heating déset ^ the heating zone of the front, the multiple sections and zones that run from the top to bottom So it has more than one barrel, the barrels are connected in series. The length-to-diameter ratio of each barrel is in the range from about 16: 1 to about 30: 1. the extrusion can take place at temperatures in the range from about 160 to about 270 degrees C, and preferably it is carried out at temperatures in the range from about 180 to about 240 degrees C. The combination is produced by in situ mixing of two polymers. The flow rate of the first copolymer can be in the range from about 1.4 to about 2.6 grams per 10 minutes, and is preferably in the range from about 1.7 to about 2.4 grams per 10 minutes. The melt index of the second copolymer can be in the range of from about 200 to about 400 grams per 10 minutes, and is preferably in the range from about 250 to about 350 grams per 10 minutes.

The alpha-olefin comonomer copol having 3 to 8 carbon atoms, for example, propylene, 1-butene, 1-hexene, 4-methyl-1-pentene, or 1-octene; The preferred comonomers are 1-butene and 1-hexene. The components of the linear polyethylene blend can be produced using various transition metal catalysts. The polyethylene mixture of the intention is preferably produced in the gas phase by a low pressure process. The mixture can also be produced in liquid phase in solutions or slurries by conventional techniques, again at low pressures. Low pressure processes are typically run at pressures below 1000 psi (6,897 Pa) while high pressure processes are typically run at pressures above 15,000 psi (103.45 Pa). The common transition metal catalyst systems, which can be used to prepare the mixture, are magnesium / titanium based catalyst systems, which can be exemplified by the catalyst system described in US Pat. No. 4,302,565; vanadium-based catalyst systems such as those described in U.S. Patent Nos. 4,508,842; 5,332,793; 5,342,907 and 5,410,003; a chromium-based catalyst system, such as the one described in US Pat. No. 4,101,445; and systems described in U.S. Patent Nos. 4,937,299; 5,317,036 and 5,527,752. Many of these catalyst systems are often referred to as a Ziegler-Natta catalyst system. Catalyst systems, which use chromium or molybdenum oxides in silica-alumina supports, are also useful. The preferred catalyst systems for preparing the components of the mixtures of this invention are magnesium / titanium catalyst systems and metallocene catalyst systems. The catalyst system based on magnesium / titanium will be used to exemplify the process, for example, a catalyst system in which the precursor is formed by spray drying and is used in the form of a slurry. Such a catalyst precursor, for example, contains titanium, magnesium, an electron donor, and optionally, an aluminum halide. The precursor is then introduced into a hydrocarbon medium such as a mineral oil to provide the slurry form. This catalyst system is described in U.S. Patent No. 5,290,745. The electron donor is an organic Lewis base, liquid at temperatures in the range of about 0 degrees C to about 200 degrees C, in which the magnesium and titanium compounds are soluble. The electron donor can be an alkyl ester or an aliphatic or aromatic carboxylic acid, *, an aliphatic aliphatic ketone, an aliphatic alcohol, an alkyl ether, or mixtures thereof, each electron donor having 2 to 20 electron atoms, Preferred ^ fon alkyl and cycloalkyl esters having 2 to 20 carbon atoms; dialkyl, diaryl, and alkylaryl ketones having 3 to 20 carbon atoms; and alkyl, alkoxy, and alkylalkoxy esters of alkyl and aryl carboxylic acids having 2 to 20 carbon atoms. The most preferred electron donor is tetrahydrofuran. Other examples of suitable electron donors are methyl formate, ethyl acetate, butyl acetate, ethyl ether, dioxane, di-n-propyl ether, dibutyl ether, ethyl formate, methyl acetate, ethyl anisate, ethylene carbonate. , tetrahydropyran and ethyl propionate. Although an excess of electron donor is used initially to supply the reaction product of the titanium compound and the electron donor, the reaction product finally contains about 1 to about 20 moles of electron donor per mole of titanium compound and preferably from 1 to 10 moles of electron donor per mole of titanium compound. An activating compound, which is generally used with any of the titanium-based catalyst precursors, may have the formula AlRaXbHc, wherein each X is independently chloro, bromo, iodo or OR '; each R and independently a saturated aliphatic hydrocarbon radical having 1 to "*" carbon atoms, b is 0 to 1.5, c is 0 or 1, and a + b + c = 3. Preferred activators * 5 include mono- and alkyl aluminum dichlorides wherein each alkyl radical has 1 to 6 carbon atoms and the trialkylaluminums, examples are diethylaluminum chloride and tri-n-hexylaluminum, from 0.10 to about 10 moles, and preferably from 0.15 to about 2.5. moles of activator per mole of electron donor. The molar ratio of activator for titanium is in the range of about 1: 1 to about 10: 1, and is preferably in the range of 2: 1 to about 5: 1. The hydrocarbyl aluminum cocatalyst can be represented by the formula R3A1 or R2A1X, wherein each R is independently alkyl, cycloalkyl, aryl, or hydrogen; at least one R is hydrocarbyl; and two or three radicals R can be linked to form a heterocyclic structure. Each R, which is a hydrocarbyl radical, can having 1 to 20 carbon atoms, and preferably has 1 to 10 carbon atoms. X is a halogen, preferably chlorine, bromine or iodine. Examples of hydrocarbyl aluminum compounds are as follows: triisobutylaluminum, tri-n-hexylaluminum, di-isobutyl aluminum hydride, dihexylaluminum hydride, di-isobutyl-ahexylaluminum, isobutyl dihexylaluminum, trifpefcylaluminum, tripropylaluminum, triisopropylaluminum, tri-n-butylaluminum, trioctylaluminum, tridecylaluminum, dibutylaluminum, diethylaluminum chlorido, and ethylaluminum sesquichloride. The preferred cocatalyst is trimethylaluminum. The cocatalyst compounds can also serve as activators and modifiers. It is preferred not to use support. However, in those cases where it is desired to support the precursor, silica support is preferred. Other suitable supports are inorganic oxides such as aluminum phosphate, alumina, silica / alumina mixtures, silica modified with an organoaluminum compound such as t-butylaluminum, and silica modified with zinc diethyl. A common support is a solid particulate porous material, essentially inert to the polymerization. This is used as a dry powder having an average particle size of from about 10 to about 250 microns and preferably from about 30 to about 100 microns; a surface area of at least 200 square meters per gram and preferably at least about 250 square meters per gram; and a pore size of at least 100 angstroms and preferably at least about 200 angstroms. Generally, the amount of -_. ^? ^^ * ^? J ^^^^^^^ ^ ^ ^ ^ ^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Sß? Kjg support used is such that it provides up to about 1.0 millimole of titanium per gram of support and preferably from 0.4 to about 0.9 millimole of titanium per gram of support. Impregnation of the aforementioned catalyst precursor 5 in the silica support can be relaxed by mixing the precursor and silica gel in the electron donor solvent or other solvent followed by removal of the solvent under reduced pressure. When a support is not desired, the catalyst precursor generally is used in liquid form. The activators can be added to the precursor in any case before and / or during the polymerization. In one procedure, the precursor is fully activated before polymerization. In another procedure, the precursor is partially activated before polymerization and complete activation in the reactor. Where a modifier is used in place of an activator, the modifiers are usually dissolved in an organic solvent such as isopentane and, where a support is used, impregnated in the support after impregnation of the titanium compound or complex, after which the supported catalyst precursor is dried. Otherwise, the modifier solution adds itself directly to the reactor. Modifiers have a chemical structure and function similar to activators such as cocatalysts. For i fftí ^ variations, see, for example, U.S. Patent No. 5,106,926. The cocatalyst is preferably added separately pure or as a solution in an inert solvent, such as isopentane, to the polymerization reactor at the same time when the ethylene flow begins. The polymerization is preferably carried out in the gas phase using a continuous fluidized process. In the first reactor a copolymer of relatively low density (the first copolymer) is prepared and in the second reactor a copolymer of relatively high density (the second copolymer). The first copolymer has a relatively high molecular weight and the second complier has a relatively low molecular weight. The weight ratio of the first copolymer for the second copolymer can be in the range from about 45:55 to about 60:40. The low density copolymer: The flow rate can be in the range of about 1.4 to about 2.6 grams per 10 minutes and is preferably in the range of about 1.7 to about 2.4 grams per 10 minutes. It is noted that this is the flow index of the roller mill, which provides a more accurate fluid index. This is obtained by taking a sample from the reactor in which the low density copolymer is made, and is ground into rolls before measuring the flow rate. The polymer molecular weight is generally in the range of about 275,000 to about 230,000 Daltons. The copolymer density may be in the range of 0.9035 to 0.908 grams per cubic centimeter, and is preferably in the range of 0.9035 to 0.908 grams per cubic centimeter. The Mw / Mn ratio can be in the range of about 3.5 to 8, and is preferably in the range of about 3.5 to about 5.5. The Melt Index is determined in accordance with ASTM D-1238, Condition E (also known as 190 / 2.16). This is measured at 190 degrees C and 2.16 kilograms and reported as grams per 10 minutes. The Flow Index is determined in accordance with ASTM D-1238, Condition F (also known as 190 / 21.6). This is measured at 190 degrees C and 10 times the weight used in determining the Melt Index, and reported as grams per 10 minutes. The roller milling technique is described above. The melt flow ratio is the ratio of the Flow Index to the Melt Index. The high density component: The Melt Index may be in the range of about 200 to about 400 grams per 10 minutes, and is preferably in the range of about 250 to about 350 grams per 10. minutes The weight is, generally, in the range of approximately 25,000, up to about 20,000 Daltons. The density of the copolymer can be in the range of 0.925 to 0.945 grams per cubic centimeter, and is preferably in the range of 0.930 to 0.940 grams per cubic centimeter. The Mw / Mn ratio can be in the range of about 3.5 to about 8, and is preferably in the range of 3.5 to about 5.5. The in situ or final product mix can have a Flow Index in the range of about 65 to about 90 grams per 10 minutes. The molecular weight of the final product is generally in the range of about 160,000 to about 200,000. The density of the mixture may be in the range of 0.919 to 0.924 grams per cubic centimeter, and is preferably in the range of 0.919 to 0.923 grams per cubic centimeter. The melt flow ratio of the mixture may be in the range of about 85 to about 115, and is preferably in the range of about 90 to about 110. The mixture may have a Mw / Mn ratio of about 12 to about of 18, and preferably has a Mw / Mn ratio of about 12 to about 17. Mw is the weighted average molecular weight; Mn is the numerical average molecular weight; and the Mw / Mn ratio can be referred to as the Polydispersity Index, which measure the amplitude of the molecular weight distribution.

The low density component (process conditions): The molar ratio of the alpha-olefin to ethylene may be in the range of about 0.12: 1 to about 0.18: 1, and is preferably in the range of about 0.14: 1 to about 0.17: 1. The molar ratio of hydrogen (if used) to ethylene may be in the range of about 0.02: 1 to about 0.06: 1, and is preferably in the range of about 0.03: 1 to about 0.05: 1. The operating temperature is generally in the range of about 65 degrees C to about 75 degrees C. The partial pressure of ethylene in the low density reactor (higher molecular weight) may be in the range of about 25 (172.4 kPa) to about 50 psi (344.85 kPa), but it was found that a higher FAR is easier to obtain when the ethylene partial pressure is in a preferred range of about 40 (275.88 kPa) to about 50 psi (344.85 kPa). The total pressure is generally in the range of approximately 250 to320 psig. The high density component (process conditions) The molar ratio of alpha-olefin to ethylene can be in the range of about 0.2: 1 to about The ggg of 0.4: 1 and is preferably in the range of about 0.25: 1 to about 0.35: 1. The molar ratio of hydrogen to ethylene may be in the range of about 1.4: 1 to about 2.5: 1, and preferably in the range of about 1.6: 1 to about 2.0: 1. The operating temperature is generally in the range of about 80 degrees C to about 90 degrees C. The partial pressure of ethylene may be in the range of about 75 (517 kPa) to about 150 psi (1,034 kPa) and is preferably in the range of about 90 (620.7 kPa) to about 120 psi (820.64 kPa). The total pressure is generally in the range of 400 to 450 psig. A common fluidized bed reactor is exemplified in U.S. Patent No. 4,482,687, and can be described as follows: The bed is made regularly of the same granular resin that is to be produced in the reactor. In this way, during the course of the polymerization, the bed includes particles of the polymer formed, particles of polymer in growth, and particles of catalyst fluidized by the polymerization and modifying gaseous components introduced at a rate or flow rate sufficient to cause the separation of particles and act as a fluid. The fluidizing gas is constituted by the ____ Íss UFA íMílSm ij- J »» "&? 'FFj initial feed, constituted power, and cycling gas (recycling) is de'cir, comonomers and, if desired, modifiers and / or gas carrying The essential parts of the reaction system are the container, the bed, the plate for gas distribution, internal and external piping, a compressor, a recycled gas cooler, and a product discharge system. on the bed, there is a zone speed reduction and, in the bed, a reaction zone. Both are 10 on the plate gas distribution. conventional additives, which can be introduced into the blend, are e emplificados by antioxidants , ultraviolet absorbers, antistatic agents, pigments, dyes, nucleating agents, filler materials 15, slip agents, fire retardants, plasticizers, processing aids, lubricants, stabilizers, smoke inhibitors, agents for viscosity control, crosslinking agents, catalysts, and reinforcers, thickeners, and antiblocking agents. In addition to filler materials, the additives may be present in the mixture in amounts of about 0.1 to about 10 parts by weight of additive per 100 parts by weight of polymer blend. The fillers can be added in amounts of up to 200-25 parts by weight and more per 100 parts by weight of the ^ gú ^^^ te j ^ ^^ A. ^^^^^^^^^^ mixture. The advantage of the prepared film of the in situ mixture of this invention is the consistently high FAR. All molecular weights mentioned in this specification are weighted average * 1molecular weights unless otherwise indicated. The patents mentioned in this specification are incorporated as the reference. The invention is illustrated by the following examples.

Examples 1 and 2 Example 1 is one embodiment of the invention and Example 2 is a Comparative Example. Both examples use the same steps and conditions except as stated in the Table. The preferred catalyst system is one in which the precursor is formed by spray drying and used in the form of a slurry. Such a catalyst precursor, for example, contains titanium, magnesium, aluminum halides and an electron donor. The precursor is then introduced into a hydrocarbon medium, such as mineral oil, to provide the form of grout. See U.S. Patent No. 5,290,745. The catalyst composition and method of preparation thereof, used in this example, is of the same composition and method of preparation as in Example 1 of 5.29Q 745 except that 0.25 mol of hexylaluminum per mole of tetrahydrofuran is used instead of 0.2 mol. The polyethylene is produced using the following model procedure. The ethylene is copolymerized with 1-hexene in the first reactor, and the addition of 1-butene in the second reactor. The trimethylaluminum cocatalyst (TMA) is added to each reactor during the polymerization as a 50 percent by weight solution in hexane. The temperature in the first reactor is 70 degrees C and the temperature in the second reactor is 85 degrees C. Each polymerization is carried out continuously after equilibrium is reached under the conditions stated here and in the Table. The polymerization is initiated in the first reactor by continuous feeding of the catalyst precursor above and fluidized bed cocatalyst of polyethylene granules together with ethylene, 1-hexene, and hydrogen. The resulting copolymer mixed with active catalyst is removed from the first reactor and transferred to the second reactor using gas as a transfer medium to the second reactor. The second reactor also contains a fluidized bed of polyethylene granules. The ethylene, 1-butene, and hydrogen are introduced into the second reactor where they come into contact with the copolymer and the catalyst. a ^ a ^ * a * ^ l ^ fn first reactor. Additionally, cocatalyst is also introduced. The product mixture is continuously removed. Variable polymerization conditions, ream properties, film extrusion conditions and film properties are also shown in the Table and Notes.

* "*" ^ T ^^^^^^^ l ^^^^ f ^^ rí ^^^^^ -.1? ^ Table Table Notes: psig = effective pounds per square inch. C2PP = partial pressure of ethylene reported in psi (pounds per square inch) H2 / C2, C4 / C2, and C6 / C2 are molar ratios of ^^ M ^^. ^^^ - ^^^^^. ^ -?. ^^^. hydrogen, 1-butene and ethylene. N2, H2, C2H4, C4H8, IC5, C6H12, are nitrogen, hydrogen, ethylene, 1-butene, isopentane and 1-hexene, respectively. It's a mole percent. TMA = trimethylaluminum. Fraction = fraction of weight of the individual component. Ti ppm = parts per million by weight of titanium in the resin. 10 Al / Ti = molar ratio of aluminum to titanium in the resin. The density is measured by the production of a plate in accordance with ASTM D-1928, procedure C, and then testing as per ASTM D-1505. It is reported in grams per 15 cubic centimeter. FAR = classification of the appearance of the film as already explained. The films are prepared by extrusion in a 3.5-inch Gloucester ™ tabular film extruder and has a length-to-diameter ratio of 20-24: 1; a linear low density polyethylene screw; a 6-inch nozzle; and a nozzle opening of 60 and 120 mils. FAR is determined for each movie. The roller milling process: the granular resin of the reactors is placed in a mill of two rolls that is commonly available in the industry. The two rollers are set at a temperature of 148 C [if < initially the most closed separation is arranged. The resin is placed on the rollers for approximately 5 minutes and then ground at low RPM (<5) for approximately 5 minutes with an opening of 0.008 inches. The ground crepe should be removed and reformed approximately 3 times during the period. The sample is then removed and the flow properties are measured. ^ g ^^^ _ ^ _ ^^ _ ¿^ _ ^ __; ____ ^ ____ ^ _ 3_?

Claims (9)

1. An in situ mixture that contains a mixture of first and second ethylene / alpha-olefin copolymers wherein the alpha olefin has 3 to 8 carbon atoms, the first copolymer has a density in the range of 0.9035 to 0.908. grams per cubic centimeter and a milled flow rate in rolls in the range of about 1.4 to about 2.6 grams per 10 minutes and the second copolymer has a density in the range of 0.925 to 0.945 grams per cubic centimeter and a melt index in the interval from about 200 to about 400 grams per 10 minutes. The weight ratio of the first copolymer for the second copolymer is in the range of about 45:55 to about 60:40 and the in situ mixture has a density in the range of 0.919 to 0.924 grams per cubic centimeter and a flow ratio of melt in the range of about 85 to about 115.

2. The in situ mixture defined in claim 1 wherein the first copolymer has a density in the range of 0.9035 to 0.908 grams per cubic centimeter and a flow index of the grind. in rolls in the range of about 1.7 to about 2.4 grams per 10 minutes and the second copolymer has a density in the range of 0.930 to 0.940 grams per cubic centimeter and a Melt Index in the range of about 250 to about 350 grams for 10 minutes, the weight ratio of the first copolymer for the second copolymer being in the range of about 45:55 to about 50:50 and mixing in situ having a density in the range of 0.919 to 0.924 grams per cubic centimeter and a melt flow ratio in the range of from about 90 to about 110.

3. The in situ mixing defined in claim 1, in where the alpha-olefin is 1-hexene and / or 1-butene.

4. The in situ mixture defined in claim 1, wherein the mixture is prepared in two reactors connected in series under conditions of catalytic polymerization comprising: in the first reactor, a molar ratio of alpha-olefin to ethylene in the range of about 0.12: 1 to about 0.18: 1 and a molar ratio of hydrogen, which is optional, for ethylene in the range of about 0.02: 1 to about 0.06: 1, and, in the second reactor, a molar ratio of alpha ethylene olefin in the range of about 0.2: 1 to about 0.4: 1 and a molar ratio of hydrogen to ethylene in the range of about 1.4: 1 to about 2.5: 1.

5. The in situ mixture defined in claim 4 in A & amp; m * ¡& ^ M ^ where the ethylene partial pressure of the first reactor is in the range of about (241.4 kPa) to about 50 psi (344.85 kPa).

6. The in situ mixture defined in claim 4, wherein the catalyst comprises magnesium, titanium and aluminum compounds and the cocatalyst is trimethylaluminum.

7. A mixture in situ comprising a mixture of two ethylene / alpha-olefin copolymers in which the alpha-olefin comonomer has 3 to 8 carbon atoms, said mixture having a flow index in the range of about 65 to about of 90 grams for 10 minutes; a melt flow ratio in the range of about 85 to about 115; and a density in the range of 0.919 to 0.924 grams per cubic centimeter, said mixture having been prepared, under conditions of catalytic polymerization, in two reactors connected in series where, in the first reactor, the copolymer has a flow rate of the grind in rolls in the range of about 1.4 to about 2.6 grams per 10 minutes and a density in the range of 0.9035 to 0.908 grams per cubic centimeter and, in the second reactor, said copolymer has a melt index in the range of about 200. up to about 400 grams per 10 minutes, a density in the range of 0.925 to 0.945 grams per cubic centimeter; the weight ratio of the copolymer prepared in the first reactor for the copolymer prepared in the second being in the range of about 45:55 to about 60:40, and wherein, in the first reactor, the mole ratio of alpha-olefin to ethylene is in the range of about 0.12: 1 to about 0.18: 1; the molar ratio of hydrogen, which is optional, to ethylene is in the range of about 0.02: 1 to about 0.06: 1; and the partial pressure of ethylene is in the range of about 40 (275.88 kPa) to about 50 psi (344.85 kPa) and, in the second reactor, the mole ratio of alpha-olefin to ethylene is in the range of about 0.2: 1 to about 0.4: 1 and the molar ratio of hydrogen to ethylene is in the range of about 1.4 : 1 to about 2.5: 1.

8. The in situ mixture defined in claim 7 wherein the catalyst used in the polymerization comprises magnesium, titanium and aluminum compounds and the cocatalyst is trimethylaluminum.

9. A film having a high FAR, prepared from the in situ mixture defined in claim 1. ^ _ ^