KR20010106466A - Polyethylene Film Composition - Google Patents

Abstract

The present invention includes a mixture of first and second ethylene / α-olefin copolymers, wherein the α-olefin has 3 to 8 carbon atoms, the first copolymer having a density of 0.9035 to 0.908 g / cm ³ and about Having a roll mill-flow index of 1.4 to 2.6 g / 10 minutes, the second copolymer having a density of 0.925 to 0.945 g / cm ³ and a melt index in the range of about 200 to 400 g / 10 minutes; The weight ratio of the first copolymer to the second copolymer ranges from about 45:55 to 60:40, and the in situ blend has a density in the range of 0.919 to 0.924 g / cm ³ and a melt in the range of 85 to 115 It relates to an in situ blend which has a flow ratio and has a flow index of 65 to 90 g / 10 minutes.

Description

Polyethylene Film Composition

Polyethylenes having various density ranges have been produced and are converted into films having excellent tensile strength, high elongation, impact strength, and bread composition according to each property. Such properties are further enhanced when the polyethylene has high molecular weight with toughness. However, as the molecular weight of polyethylene increases, the processability of the resin tends to decrease. Thus, blending high molecular weight polymers with low molecular weight polymers retains the advantages of high molecular weight resins while also improving processability, particularly extrudability (advantages of low molecular weight compositions).

Blends of such polymers can be achieved by staged reactor processes similar to those described in US Pat. Nos. 5,047,468 and 5,149,738. In brief, the process relates to a process for preparing a high molecular weight ethylene copolymer in one reactor and a low molecular weight ethylene copolymer in another reactor to in situ blending the polymer. . The process typically consists of continuously contacting ethylene and one or more α-olefins in series with a catalyst in two gaseous fluidized bed fluidized bed reactors connected in series under polymerization conditions, the catalyst being (i) supported magnesium / titanium A catalyst precursor based thereon, (ii) an activator composition containing one or more aluminum; And (iii) hydrocarbyl aluminum cocatalyst.

Although the in situ blends prepared from the above and the films produced therefrom have the above advantages, the application of polymers having a broad molecular weight distribution of such granularity to high quality films has limited commercial use by the degree of gelation. do. Such gels adversely affect extrudability and physical properties, including the aesthetic appearance of the product. The gelation degree of the film product is a subjective scale of film appearance rating (FAR), which varies from -50 (low quality; high gel) to +50 (high quality; no gel or trace amounts). Determined by Commercially available levels preferably have a FAR value of at least +20.

The present invention relates to a polyethylene copolymer blend, wherein the film extruded therefrom relates to a polyethylene copolymer blend that is substantially free of gel (or fish eyes).

It is an object of the present invention, therefore, to provide an in situ blend which can be converted into a film with a particularly high FAR value.

Such a blend is provided by the present invention. In situ blends of the present invention comprise a mixture of first and second ethylene / α-olefin copolymers, wherein the α-olefins have 3 to 8 carbon atoms and the first copolymers have 0.9035 to Having a density of 0.908 g / cm ³ and a roll-mill flow index of about 1.4 to 2.6 g / 10 minutes, the second copolymer having a density of 0.925 to 0.945 g / cm ³ and a range of about 200 to 400 g / 10 minutes Has a melt index of; The weight ratio of the first copolymer to the second copolymer has a range of about 45:55 to 60:40, and the in situ blend has a density in the range of 0.919 to 0.924 g / cm3, 65 to 90 g / 10 min. The flow index and the melt flow ratio are in the range of 85 to 115.

Description of Preferred Embodiments

The film is generally formed by extrusion. The extruder is conventional using a die to provide the desired gauge. The gauge of the film in the present invention is in the range of about 0.4 to about 10 mils, preferably about 0.5 to about 6 mils. An example of an extruder capable of forming a film is a blown film die and a single screw extruder adapted to an air ring and a continuous take-up device. An example of a typical single screw extruder is a form with a hopper at the upstream end and a die at the downstream end. The material is fed from the hopper to the barrel, which contains a screw. There is a screen pack and a breaker plate between the downstream end, the screw end and the die. The screw section of the extruder is divided into three zones: the feeding section (solid resin conveying section), the compression section, the metering section (melting conveying section), and the rear heating zone and the front heating zone. The sections and zones run from upstream to downstream. If there is more than one barrel, the barrels are connected in series. The ratio of length to diameter of each barrel is in the range of about 16: 1 to 30: 1. Extrusion is preferably carried out at a temperature range of about 160 to 270 ° C, preferably about 180 to 240 ° C.

The blend is made by in situ blending of two polymers. The flow index of the first polymer is preferably in the range of about 1.4 to 2.6 g / 10 minutes, preferably about 1.7 to 2.4 g / 10 minutes. The melt index of the second polymer is in the range of about 200 to 400 g / 10 minutes, preferably about 250 to 350 g / 10 minutes.

The copolymer is a copolymer of ethylene and a C _3-8 α-olefin comonomer such as propylene, 1-butene, 1-hexene, 4-methyl-1-pentene or 1-octene. Preferred comonomers include 1-butene and 1-hexene.

Linear polyethylene blend compositions are prepared using various transition metal catalysts. The polyethylene blends of the present invention are preferably prepared by low pressure processes in the gas phase. The blend can also be produced at low pressure likewise by solution or slurry polymerization, which is usually the polymerization process in the liquid phase. Low pressure processes operate at pressures up to 1000 psi, while high pressure processes typically operate at pressures of 15,000 psi. Typical transition metal catalyst systems used to make such blends include those based on magnesium / titanium as disclosed in US Pat. No. 4,302,565; Vanadium based catalyst systems disclosed in US Pat. Nos. 4,508,842, 5,332,793, 5,342,907 and 5,410,003; Chromium-based systems disclosed in US Pat. No. 4,01,445; Metallocene catalyst systems disclosed in US Pat. Nos. 4,937,299, 5,317,036, and 5,527,752. Most of these catalyst systems are often referred to as Ziegler-Natta catalyst systems. Catalyst systems using chromium or molybdenum oxides on silica-aluminum supports are also usefully employed. Preferred catalyst systems for preparing the compositions used in the blends of the present invention are magnesium / titanium catalyst systems and metallocene catalyst systems.

The magnesium / titanium based system is a good example of such a process, for example a catalyst system in which precursors are formed by spray drying and used in slurry form. Such catalyst precursors contain, for example, titanium, magnesium, electron donors, and optionally aluminum halides. The precursor is introduced into a hydrocarbon medium such as mineral oil and provided in the form of a slurry. Such catalyst systems are described in US Pat. No. 5,290,745.

The electron donor is an organic Lewis base, is liquid in the temperature range of about 0 to 200 ° C., and the magnesium and titanium compositions are soluble. The electron donors may be alkyl esters of fatty acids or aromatic carboxylic acids, aliphatic ketones, aliphatic amines, aliphatic alcohols, alkyl or cycloalkyl ethers, or mixtures thereof, each electron donor having 2 to 20 carbon atoms. Alkyl and cycloalkyl ethers of C _2-20 in the electron donor; C _3-20 dialkyl, diaryl and alkyl aryl ketones; And alkyl, alkoxy and alkylalkoxy esters of alkyl and aryl carboxylic acids of C _2-20 are most preferred. Most preferred electron donor is tetrahydrofuran. Other suitable electron donors include methyl formate, ethyl acetate, butyl acetate, ethyl ether, dioxane, di-n-propyl ether, dibutyl ether, ethyl formate, methyl acetate, ethyl aniseate, ethylene carbonate, tetra Hydropyrane and ethyl propionate.

An excess electron donor is used at the beginning of the reaction to produce a reaction product of the electron donor and the titanium compound, but the reaction product finally contains about 1 to 20 moles of electron donor per mole of the titanium compound, preferably about 1 to 20 It contains moles.

Activators commonly used with titanium based catalyst precursors have a structure of AlR _a X _b H _c , wherein X is independently chlorine, bromine, iodine or OR '; R and R 'are each independently C _1-14 saturated aliphatic hydrocarbon radicals; b is 0 to 1.5; c is 0 or 1; And a + b + c = 3. Preferred activators include mono- and di-alkyl aluminum chlorides and trialkyl aluminums where each alkyl radical is C _1-6 . Examples are diethylaluminum chloride and tri-n-hexylaluminum. About 0.10 to 10 moles, preferably about 0.15 to 2.5 moles of activator per mole of unit electron donor are used. The molar ratio of activator to titanium is in the range of about 1: 1 to 10: 1, preferably in the range of about 2: 1 to 5: 1.

The hydrocarbyl aluminum cocatalyst is represented by the formula R ₃ Al or R ₂ AlX, wherein each R is independently alkyl, cycloalkyl, aryl, or hydrogen; At least one R is hydrocarbyl; In addition, two or three R radicals combine to form a heterocyclic structure. Each R which is a hydrocarbyl radical has C _1-20 , preferably C _1-10 . X is 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-hexylaluminum, isobutyl di Hexyl aluminum, trimethyl aluminum, triethyl aluminum, tripropyl aluminum, triisopropyl aluminum, tri-n-butyl aluminum, trioctyl aluminum, tridecyl aluminum, tridodecyl aluminum, tribenzyl aluminum, triphenyl aluminum, trinaphthyl Aluminum, tritorylaluminum, dibutylaluminum chloride, diethyl aluminum chloride and ethyl aluminum sesquichloride. Of these, trimethylaluminum is preferred. The cocatalyst compound also acts as an activator and modifier.

In this invention, it is preferable not to use a support body. However, when it is necessary to support the precursor, it is preferable to use silica as a support. Other suitable supports include aluminum phosphate, alumina, silica / alumina mixtures, silica modified with organoaluminum compounds such as triethyl aluminum, and silica modified with diethyl zinc. Typical supports are solid, particulate, porous materials which in particular need to be inert to the polymerization reaction. It has an average particle size of about 10 to 250 μm, preferably 30 to 100 μm; The surface area is at least 200 m ² / g, preferably 250 m ² / g; It is used as a dry powder with a pore size of at least 100 mm 3, preferably 200 mm 3.

Generally, the amount of the support to be used is an amount that can provide about 0.1 to 1.0 mmole Ti / g carrier, preferably about 0.4 to 0.9 mmole Ti / g carrier. Impregnation of the above-mentioned catalyst precursor with the silica support can be carried out by mixing the precursor and silica gel in an electron donor solvent or other solvent, and then removing the solvent under reduced pressure. When no support is used, the catalyst precursor is used in liquid form.

An activator may be added to the precursor before and / or during the polymerization process. In some processes, the precursor is sufficiently active before the polymerization process. In other processes, the precursor is only partially activated before the polymerization process and is fully activated in the reactor. When a modifier is used instead of an activator, the modifier is generally dissolved in an organic solvent such as isopentane and, if a support is used, the supported catalyst precursor is only after impregnation of the titanium compound or complex followed by impregnation with the support. To dry. Otherwise the modifier solution is added directly to the reactor alone. Modifiers, like cocatalysts, have a similar chemical structure and action to activators. See, for example, US Pat. No. 5,106,926. The cocatalyst is preferably added to the polymerization vessel at the same time as the flow of ethylene is initiated either individually in pure state or in the form of a solution dissolved in an inert solvent such as isopentane.

The polymerization is preferably carried out in the gas phase using a continuous fluidized process.

Relatively low density copolymers are made in the first reactor (first copolymer), and relatively high density copolymers are made in the second reactor (second copolymer). The first copolymer has a relatively high molecular weight and the second copolymer has a relatively low molecular weight. The weight ratio of the first copolymer to the second copolymer ranges from about 45:55 to 60:40.

The low density copolymer is:

The flow index is in the range of about 1.4 to 2.6 g / 10 minutes, preferably 1.7 to 2.4 g / 10 minutes. The flow index is a roll-milled flow index which provides a more accurate flow index. The roll mill flow index is performed by taking a sample from a reactor in which a low density copolymer is prepared and performing a roll mill before measuring the flow index. The molecular weight of the polymer is generally in the range of about 275,000 to 230,000 Daltons. The density of the copolymer is in the range of 0.9035 to 0.908 g / cm ³ , preferably 0.9035 to 0.908 g / cm ³ . The ratio of M _w / M _n is in the range of about 3.5 to 8, preferably 3.5 to 5.5.

Melt index was measured under conditions of ASTM D-1238, E (190 / 2.16). Measured at 190 ° C. at 2.16 kg and reported in g / 10 min. Flow index was measured under conditions of ASTM D-1238, F (190 / 21.6). The flow index was measured at 10 times the mass used at 190 ° C. and recorded in g / 10 min. The roll-mill method is as mentioned above. Melt flow ratio refers to the ratio of the flow index to the melt index.

High Density Ingredients:

The melt index is in the range of about 200 to 400 g / 10 minutes, preferably 250 to 350 g / 10 minutes. The molecular weight of the high density copolymer is generally in the range of about 25,000 to 20,000 Daltons. The density of the copolymer is in the range of 0.925 to 0.945 g / cm ³ , preferably 0.930 to 0.940 g / cm ³ . The ratio of M _w / M _n is in the range of 3.5 to 8, preferably 3.5 to 5.5.

The in-situ blend or final product has a flow index in the range of 65 to 90 g / 10 minutes. The molecular weight of the final product is generally in the range of 160,000 to 200,000. The density of the blend is 0.919 to 0.924 g / cm ³ , preferably in the range of 0.919 to 0.923 g / cm ³ . The melt flow rate of the blend is 85 to 115, preferably 90 to 110. The blend has a M _w / M _n ratio in the range of about 12 to 18, preferably about 12 to 17. M _w is a weight average molecular weight; M _n is a number average molecular weight; The M _w / M _n ratio is a criterion for measuring the degree of dispersion of the molecular weight distribution as a polydispersity index.

Low Density Components (Process Conditions):

The molar ratio of α-olefins to ethylene ranges from about 0.12: 1 to 0.18: 1, preferably from about 0.14: 1 to 0.17: 1. The ratio of hydrogen (if used) to ethylene is about 0.02: 1 to 0.06: 1, preferably about 0.03: 1 to 0.05: 1. The operating temperature is generally 65 ° C to 75 ° C. The ethylene partial pressure in the low density (high molecular weight) reactor is 25 to 50 psi, and in order to obtain higher FAR values, it is preferred to operate the ethylene partial pressure to 40 to 50 psi. The voltage is operated in the range of 250 to 320 psi.

High Density Components (Process Conditions):

The molar ratio of α-olefin to ethylene is in the range of about 0.2: 1 to 0.4: 1, preferably in the range of 0.25: 1 to 0.35: 1. The ratio of hydrogen to ethylene is in the range of about 1.4: 1 to 2.5: 1, preferably in the range of 1.6: 1 to 2.0: 1. The operating temperature is generally 80 ° C to 90 ° C. The ethylene partial pressure is 75 to 150 psi, preferably in the range of 90 to 120 psi. The voltage is in the range of 400 to 450 psi.

Typical fluidized bed reactors are illustrated in US Pat. No. 4,482,687, as follows.

The bed consists of the same granular resin as the resin produced in the reactor. Thus, during the polymerization process the bed is composed of polymer particles, growth polymer particles and catalyst particles formed and fluidized by polymerization and reforming gas components introduced at a flow rate or speed sufficient to disperse the particles and behave like a fluid. The fluidizing gas consists of initial feed gas, make-up gas and circulating (recirculating) gas, ie comonomers and, if necessary, modifiers and / or inert transport gases.

Important parts of the reaction system are vessels, beds, gas distribution plates, inlet and outlet tubes, compressors, circulating gas coolers and product discharge systems. In the vessel there is a speed reduction zone above the bed and a reaction zone in the bed. All of these are formed on the gas distribution plate.

Common additives that may be added to the blend include antioxidants, ultraviolet absorbers, antistatic agents, pigments, dyes, nucleating agents, fillers, antiskids, flame retardants, plasticizers, processing aids, lubricants, stabilizers, smoke inhibitors, viscosity modifiers, crosslinkers, Catalysts, boosters, pressure-sensitive adhesives, and antiblocking agents. Additives other than fillers may be present in the blend at about 0.1 to 10 parts by weight relative to 100 parts by weight of the polymer blend. The filler can be added up to 200 parts by weight or more based on 100 parts by weight of the blend.

An advantage of films made from the in situ blends of the present invention is that they have high FAR values.

All molecular weights herein refer to weight average molecular weights unless otherwise specified.

The above patent is referred to in the present invention.

The invention is explained in detail in the following examples. This embodiment is for illustration only and is not intended to limit the claims.

Example

Examples 1 and 2

Example 1 is a specific example of the present invention, and Example 2 is a comparative example. The following examples were all performed at the same steps and conditions except as indicated in the table.

Preferred catalyst systems are those in which the precursor is formed by spray drying and is used in the form of a slurry. Such catalyst precursors include, for example, titanium, magnesium, aluminum halides and electron donors. The precursor is then introduced into a hydrocarbon medium, such as mineral oil, to form a slurry. See US Pat. No. 5,290,745. The catalyst composition used in this example and its preparation method are the same as in Example 1 of No. 5,290,745, except that tri-n-hexylaluminum / mol tetrahydrofuran was used at 0.25 mol instead of 0.2 mol.

Polyethylene is prepared from the following conventional process.

Ethylene is copolymerized with 1-hexane in the first reactor and with 1-butene in the second reactor. Trimethylaluminum (TMA) cocatalyst is added to each reactor during the polymerization process in 50% by weight hexane solution. The temperature of the first reactor is 70 ° C and the temperature of the second reactor is 85 ° C. Each polymerization takes place continuously after reaching equilibrium under the conditions indicated above and under the conditions shown in the table below.

Polymerization in the first reactor is initiated by continuously injecting the catalyst precursor and cocatalyst into a fluidized bed of polyethylene particles and ethylene, 1-hexane and hydrogen. The resulting copolymer mixed with the active catalyst is withdrawn from the first reactor and sent to the second reactor using the second reactor gas as the transfer medium. The second reactor also includes a fluidized bed of polyethylene particles. Ethylene, 1-butene and hydrogen are introduced into the second reactor to come into contact with the copolymer and catalyst from the first reactor. Additional cocatalysts may also be introduced. The product blend is removed continuously.

Various polymerization conditions, resin properties, film extrusion conditions and film properties are shown in the table and footnote below.

Example One 2 Reactor I Ⅱ I Ⅱ Pressure (psig) 296 431 298 433 C ₂ PP (psi) 44.5 112.5 42.4 118.8 H ₂ / C ₂ (molar ratio) 0.043 1.79 0.033 1.78 C ₄ / C ₂ (molar ratio) 0 0.248 0 0.320 C ₆ / C ₂ (molar ratio) 0.152 0.018 0.143 0.011 N ₂ (%) 74.1 19.4 76.5 14.5 H ₂ (%) 0.62 45.09 0.45 47.11 C ₂ H ₄ (%) 14.33 25.23 13.59 26.53 C ₄ H ₈ (%) 0 6.26 0 8.48 IC ₅ (%) 6.81 2.58 7.00 2.02 C ₆ H ₁₂ (%) 2.18 0.46 1.94 0.28 TMA flow (lbs / hr) 9.72 4.83 10.05 3.35 Generation rate (1000 lbs / hr) 36.1 41.3 35.9 47.6 Catalyst feed (lbs / hr) 17.5 0 16.9 0 C ₂ supply (1000 lbs / hr) 30.0 38.5 30.5 43.6 C ₄ supply (1000 lbs / hr) 0 4.00 0 5.88 C ₆ (lbs / hr) 6141 0 5382 0 H ₂ (lbs / hr) 0.47 177 0.33 233 N ₂ (lbs / hr) 504 0 626 0 IC ₅ (lbs / hr) 1730 0 1599 0 Bed weight (1000 lbs) 95 173 94 172 Retention time (hr) 2.6 2.2 2.6 2.1 Split (weight fraction) 0.47 0.53 0.43 0.57

Balance analysis

Example One 2 Reactor I Ⅱ I Ⅱ Ti (ppm) 3.49 1.90 3.37 1.69 Al / Ti (molar ratio) 22.4 33.1 28.9 34.6 Melt Index (g / 10min) - 0.80 - 0.63 Flow index (g / 10 minutes) 1.85 (roll mill) 83.7 1.23 (roll mill) 81.4 MFR - 104 - 130 Density (g / cc) 0.9057 0.9216 0.9067 0.9216 Film FAR - +50 - -30

footnote

psig = lb / in ²

C ₂ PP = partial pressure of ethylene psi (lb / in ² )

H ₂ / C _2, C ₄ / C ₂ and C ₆ / C ₂ are the molar ratios of hydrogen, 1-butene and 1-hexane to ethylene, respectively.

N ₂ , H ₂ , C ₂ H ₄ , C ₄ H ₈ , IC ₅ , C ₆ H ₁₂ are nitrogen, hydrogen, ethylene, 1-butene, isopentene and 1-hexene, respectively,% means mol% .

TMA = trimethylaluminum

Split = weight fraction of each component

Ti ppm = weight of Ti in resin

Al / Ti = molar ratio of Al to Ti in the resin

Density was made according to ASTM D-1928, C method and then tested according to ASTM D-1505. The unit is expressed in g / cm ³ .

FAR = refers to the appearance grade of the film as unrolled above. The film has a length to diameter ratio of 24: 1; Has a linear low density polyethylene screw; 6 in die; And extrusion in a 3.5 in Gloucester ^™ blown tubular film extruder with die spacing of 60 and 120 mils. FAR was measured for each film.

Roll Mill Process: The granular resin from the reactor is placed on a commercially available two roll mill. The roll is fixed at 148 ° C. and initially placed to near touch. The resin is placed on a roll for about 5 minutes and roll milled at an interval of 0.008 in at low RPM (<5) for about 5 minutes. The rolled crepe is removed and repeated three times during the process. The sample is then removed and the flow properties measured.

Claims (9)

A mixture of first and second ethylene / α-olefin copolymers, wherein the α-olefin has 3 to 8 carbon atoms, the first copolymer having a density of 0.9035 to 0.908 g / cm ³ and about 1.4 to 2.6 a roll mill-flow index of g / 10 min, the second copolymer having a density of 0.925 to 0.945 g / cm ³ and a melt index in the range of about 200 to 400 g / 10 min; The weight ratio of the first copolymer to the second copolymer is in the range of about 45:55 to 60:40, and the in situ blend has a density in the range of 0.919 to 0.924 g / cm ³ and a melt flow in the range of 85 to 115 In situ blends characterized by having a ratio. The method of claim 1, wherein the first copolymer has a density of 0.9035 to 0.908 g / cm ³ and a roll mill-flow index of about 1.7 to 2.6 g / 10 minutes, the second copolymer is 0.930 to 0.940 g / cm ^Has a density of ³ and a melt index in the range of about 250 to 350 g / 10 minutes; The weight ratio of the first copolymer to the second copolymer is in the range of about 45:55 to 50:50, the in situ blend has a density in the range of 0.919 to 0.924 g / cm ³ and the melt flow ratio is 90 to In situ blend, characterized in that it has a range of 110. The in situ blend of claim 1, wherein the α-olefin is 1-hexene and / or 1-butene. The method of claim 1, wherein the blend is prepared under catalytic polymerization conditions in two series connected reactors, wherein the molar ratio of α-olefin to ethylene in the first reactor ranges from 0.12: 1 to 0.18: 1, The molar ratio of hydrogen to ethylene ranges from 0.02: 1 to 0.06: 1, the molar ratio of α-olefin to ethylene in the second reactor ranges from 0.2: 1 to 0.4: 1 and the molar ratio of hydrogen to ethylene is 1.4: In situ blend, characterized in that it ranges from 1 to 2.5: 1. 5. The in situ blend of claim 4, wherein the partial pressure of ethylene in the first reactor is in the range of 35 to 50 psi. 5. The in situ blend of claim 4 wherein the catalyst is a magnesium, titanium and aluminum compound and the cocatalyst is trimethyl aluminum. A mixture of first and second ethylene / α-olefin copolymers, wherein the α-olefin has 3 to 8 carbon atoms, and the blend has a flow index of 65 to 90 g / 10 minutes; Melt flow rate in the range of 85 to 115; And a density ranging from 0.919 to 0.924 g / cm ³ , wherein the blend is prepared under catalytic polymerization conditions in two series connected reactors, in the first reactor the copolymer has a roll mill-flow index of 1.4 to 2.6 g / 10 minutes. And a density of 0.9035 to 0.908 g / cm ³ , and in the second reactor, the copolymer has a melt index in the range of 200 to 400 g / 10 minutes; A density of 0.925 to 0.945 g / cm ³ ; The weight ratio of the copolymer prepared in the first reactor to the copolymer prepared in the second reactor has a range of about 45:55 to 60:40; In the first reactor the mole ratio of α-olefins to ethylene ranges from 0.12: 1 to 0.18: 1, the optional mole ratio of hydrogen to ethylene ranges from 0.02: 1 to 0.06: 1 and the partial pressure of ethylene In the second reactor, the molar ratio of α-olefin to ethylene ranges from 0.2: 1 to 0.4: 1, and the molar ratio of hydrogen to ethylene ranges from 1.4: 1 to 2.5: 1. In situ blends, characterized in that having. 8. The in situ blend of claim 7, wherein the catalysts used in the polymerization process are magnesium, titanium and aluminum compounds and the cocatalyst is trimethylaluminum. A film with a high FAR value made from the in situ blend of claim 1.