WO2000015712A1

WO2000015712A1 - Polyethylene film composition

Info

Publication number: WO2000015712A1
Application number: PCT/US1998/019186
Authority: WO
Inventors: Michael William Tilston; Stephanie Marie Upham; William James Michie, Jr.; George Edward Ealer; Jorge Oscar Buhler-Vidal
Original assignee: Union Carbide Chemicals & Plastics Technology Corporation
Priority date: 1998-09-11
Filing date: 1998-09-11
Publication date: 2000-03-23
Also published as: CN1358215A; CA2343375A1; KR20010106466A; BR9816010A; AU9568898A

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

Polyethylene Film Composition

Technical Field

This invention relates to a blend of polyethylene copolymers such that a film extruded therefrom has essentially no gels (or fish eyes).

Background Information

Polyethylenes of various densities have been prepared and converted into film characterized by excellent tensile strength, high ultimate elongation, good impact strength, and excellent puncture resistance. These properties together with toughness are enhanced when the polyethylene is of high molecular weight. However, as the molecular weight of the polyethylene increases, the processability of the resin usually decreases. By providing a blend of polymers of high molecular weight and low molecular weight, the properties characteristic of high molecular weight resins can be retained and processability, particularly extrudability (a characteristic of the lower molecular weight component) can be improved.

The blending of these polymers is successfully achieved in a staged reactor process similar to those described in United States patents 5,047,468 and 5,149,738. Briefly, the process is one for the in situ blending of polymers wherein a high molecular weight ethylene copolymer is prepared in one reactor and a low molecular weight ethylene copolymer is prepared in another reactor. The process typically comprises continuously contacting, under polymerization conditions, a mixture of ethylene and one or more alpha-olefins with a catalyst system in two gas phase, fluidized bed reactors connected in series, said catalyst system comprising: (i) a supported magnesium/titanium based catalyst precursor; (ii) one or more aluminum containing activator compounds; and (iii) a hydrocarbyl aluminum cocatalyst,

While the in situ blends prepared as above and the films produced therefrom are found to have the advantageous characteristics heretofore mentioned, the commercial application of these granular broad molecular weight distribution polymers for high quality film applications is frequently limited by the level of gels obtained. These gels adversely effect the aesthetic appearance, extrudability, 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) varying from minus 50 (very poor; these films have a large number of large gels) to plus 50 (very good; these films have a small amount of, or essentially no, gels). For commercial acceptability, the FAR should be plus 20 or better.

Disclosure of the Invention

An object of this invention, therefore, is to provide an in situ blend, which can be converted into a film having an exceptionally high FAR. Other objects and advantages will become apparent hereinafter.

According to the present invention such a blend has been discovered. The in situ blend 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 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 .925 to .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 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 the Preferred Embodiment(s)

The film is generally formed by extrusion. The extruder is a conventional one using a die, which will provide the desired gauge. The gauge of the films of interest here 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 forming the film, is a single screw type modified with a blown film die and air ring and continuous take off equipment. A typical single screw type extruder can be described as one having a hopper at its upstream end and a die at its downstream end. The hopper feeds into a barrel, which contains a screw. At the downstream end, between the end of the screw and the die, is a screen pack and a breaker plate. The screw portion of the extruder is considered to be divided up into three sections, the feed section, the compression section, and the metering section, and multiple heating zones from the rear heating zone to the front heating zone, the multiple sections and zones running from upstream to downstream. If it has more than one barrel, the barrels are connected in series. The length to diameter ratio of each barrel is in the range of about 16:1 to about 30:1. The extrusion can take place at temperatures in the range of about 160 to about 270 degrees C, and is preferably carried out at temperatures in the range of about 180 to about 240 degrees C.

The blend is produced by the in situ blending of two polymers. The flow index of the first copolymer 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. The melt index of the second copolymer can 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 copolymers are copolymers of ethylene and one alpha-olefin comonomer having 3 to 8 carbon atoms, for example, propylene, 1- butene, 1-hexene, 4-methyl-l-pentene, or 1-octene. The preferred comonomers are 1-butene and 1-hexene.

The linear polyethylene blend components can be produced using various transition metal catalysts. The polyethylene blend of subject invention is preferably produced in the gas phase by a low pressure process. The blend can also be produced in the liquid phase in solutions or slurries by conventional techniques, again at low pressures. Low pressure processes are typically run at pressures below 1000 psi whereas high pressure processes are typically run at pressures above 15,000 psi. Typical transition metal catalyst systems, which can be used to prepare the blend, are magnesium/titanium based catalyst systems, which can be exemplified by the catalyst system described in United States patent 4,302,565; vanadium based catalyst systems such as those described in United States patents 4,508,842; 5,332,793; 5,342,907; and 5,410,003; a chromium based catalyst system such as that described in United States patent 4,101,445; and metallocene catalyst systems such as those described in United States patents 4,937,299; 5,317,036; and 5,527,752. Many of these catalyst systems are often referred to as Ziegler-Natta catalyst systems. Catalyst systems, which use chromium or molybdenum oxides on silica-alumina supports, are also useful. Preferred catalyst systems for preparing the components for the blends of this invention are magnesium/titanium catalyst systems and metallocene catalyst systems.

The magnesium/titanium based catalyst system will be used to exemplify the process, e.g., a catalyst system in which the precursor is formed by spray drying and is used in slurry form. 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 mineral oil to provide the slurry form. This catalyst system is described in United States patent 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 of an aliphatic or aromatic carboxylic acid, an aliphatic ketone, an aliphatic amine, an aliphatic alcohol, an alkyl or cycloalkyl ether, or mixtures thereof, each electron donor having 2 to 20 carbon atoms. Among these electron donors, the preferred are alkyl and cycloalkyl ethers 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.

While an excess of electron donor is used initially to provide the reaction product of titanium compound and electron donor, the reaction product finally contains about 1 to about 20 moles of electron donor per mole of titanium compound and preferably about 1 to about 10 moles of electron donor per mole of titanium compound.

An activator compound, which is generally used with any of the titanium based catalyst precursors, can have the formula AlR_aX_DH_c wherein each X is independently chlorine, bromine, iodine, or OR'; each R and R' is independently a saturated aliphatic hydrocarbon radical having 1 to 14 carbon atoms; b is 0 to 1.5; c is 0 or 1; and a+b+c = 3. Preferred activators include alkylaluminum mono- and dichlorides wherein each alkyl radical has 1 to 6 carbon atoms and the trialkylaluminums. Examples are diethylaluminum chloride and tri-n- hexylaluminum. About 0.10 to about 10 moles, and preferably about 0.15 to about 2.5 moles, of activator are used per mole of electron donor. The molar ratio of activator to titanium is in the range of about 1:1 to about 10:1, and is preferably in the range of about 2:1 to about 5:1. The hydrocarbyl aluminum cocatalyst can be represented by the formula R3AI or R2AIX wherein each R is independently alkyl, cycloalkyl, aryl, or hydrogen; at least one R is hydrocarbyl; and two or three R radicals can be joined to form a heterocyclic structure. Each R, which is a hydrocarbyl radical, can have 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- hexylaluminum, isobutyl dihexylaluminum, trimethylaluminum, triethylaluminum, tripropylaluminum, triisopropylaluminum, tri-n- butylaluminum, trioctylaluminum, tridecylaluminum, tridodecylaluminum, tribenzylaluminum, triphenylaluminum, trinaphthylaluminum, tritolylaluminum, dibutylaluminum chloride, diethylaluminum chloride, and ethylaluminum sesquichloride. The preferred cocatalyst is trimethylaluminum. The cocatalyst compounds can also serve as activators and modifiers.

It is preferred not to use a support. However, in those cases where it is desired to support the precursor, silica is the preferred support. Other suitable supports are inorganic oxides such as aluminum phosphate, alumina, silica/alumina mixtures, silica modified with an organoaluminum compound such as triethylaluminum, and silica modified with diethyl zinc. A typical support is a solid, particulate, porous material essentially inert to the polymerization. It is used as a dry powder having an average particle size of about 10 to about 250 microns and preferably 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 about 100 angstroms and preferably at least about 200 angstroms. Generally, the amount of support used is that which will provide about 0.1 to about 1.0 millimole of titanium per gram of support and preferably about 0.4 to about 0.9 millimole of titanium per gram of support. Impregnation of the above mentioned catalyst precursor into a silica support can be accomplished by mixing the precursor and silica gel in the electron donor solvent or other solvent followed by solvent removal under reduced pressure. When a support is not desired, the catalyst precursor is generally used in liquid form.

Activators can be added to the precursor either before and/or during polymerization. In one procedure, the precursor is fully activated before polymerization. In another procedure, the precursor is partially activated before polymerization, and activation is completed in the reactor. Where a modifier is used instead of an activator, the modifiers are usually dissolved in an organic solvent such as isopentane and, where a support is used, impregnated into the support following impregnation of the titanium compound or complex, after which the supported catalyst precursor is dried. Otherwise, the modifier solution is added by itself directly to the reactor. Modifiers are similar in chemical structure and function to the activators as are cocatalysts. For variations, see, for example, United States patent 5,106,926. The cocatalyst is preferably added separately neat or as a solution in an inert solvent, such as isopentane, to the polymerization reactor at the same time as the flow of ethylene is initiated.

The polymerization is, preferably, conducted in the gas phase using a continuous fluidized process. A relatively low density copolymer is prepared in the first reactor (the first copolymer) and a relatively high density copolymer in the second reactor (the 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 can be in the range of about 45:55 to about 60:40.

The low density copolymer:

The flow index 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. Note that this is a roll-milled flow index, which provides a more accurate flow index. This is accomplished by taking a sample from the reactor in which the low density copolymer is made, and roll-milling it before the flow index is measured. The molecular weight of this polymer is, generally, in the range of about 275,000 to about 230,000 Daltons. The density of the copolymer can be in the range of 0.9035 to 0.908 gram per cubic centimeter, and is preferably in the range of 0.9035 to 0.908 gram 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 about 3.5 to about 5.5.

Melt index is determined under ASTM D-1238, Condition E (also referred to as 190/2.16). It is measured at 190 degrees C and 2.16 kilograms and reported as grams per 10 minutes. Flow index is determined under ASTM D-1238, Condition F (also referred to as 190/21.6). It 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 roll-milled technique is described above. Melt flow ratio is the ratio of flow index to melt index.

The high density component:

The melt index can 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 molecular weight of the high density copolymer is, generally, in the range of about 25,000 to about 20,000 Daltons. The density of the copolymer can be in the range of 0.925 to 0.945 gram per cubic centimeter, and is preferably in the range of 0.930 to 0.940 gram 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 about 3.5 to about 5.5.

The in situ blend or final product 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 blend can be in the range of 0.919 to 0.924 gram per cubic centimeter, and is preferably in the range of 0.919 to 0.923 gram per cubic centimeter. The melt flow ratio of the blend can be in the range of about 85 to about 115, and is preferably in the range of about 90 to about 110. The blend can have an Mw/Mn ratio of about 12 to about 18, and preferably has an Mw/Mn ratio of about 12 to about 17. Mw is the weight average molecular weight; Mn is the number average molecular weight; and the Mw/Mn ratio can be referred to as the polydispersity index, which is a measure of the breadth of the molecular weight distribution.

The low density component (process conditions): The mole ratio of alpha-olefin to ethylene can 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 mole ratio of hydrogen (if used) to ethylene can 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 ethylene partial pressure in the low density (high molecular weight) reactor can be in the range of about 25 to about 50 psi, but it is found that high FARs are more easily obtained when the ethylene partial pressure is in a preferred range of about 40 to about 50 psi. The total pressure is generally in the range of about 250 to 320 psig.

The high density component (process conditions):

The mole ratio of alpha-olefin to ethylene can be in the range of about 0.2:1 to about 0.4:1, and is preferably in the range of about 0.25:1 to about 0.35:1. The mole ratio of hydrogen to ethylene can be in the range of about 1.4:1 to about 2.5:1, and is 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 ethylene partial pressure can be in the range of about 75 to about 150 psi and is preferably in the range of about 90 to about 120 psi. The total pressure is generally in the range of 400 to 450 psig.

A typical fluidized bed reactor is exemplified in United States patent 4,482,687, and can be described as follows:

The bed is usually made up of the same granular resin that is to be produced in the reactor. Thus, during the course of the polymerization, the bed comprises formed polymer particles, growing polymer particles, and catalyst particles fluidized by polymerization and modifying gaseous components introduced at a flow rate or velocity sufficient to cause the particles to separate and act as a fluid. The fluidizing gas is made up of the initial feed, make-up feed, and cycle (recycle) gas, i.e., comonomers and, if desired, modifiers and/or an inert carrier gas.

The essential parts of the reaction system are the vessel, the bed, the gas distribution plate, inlet and outlet piping, a compressor, cycle gas cooler, and a product discharge system. In the vessel, above the bed, there is a velocity reduction zone, and, in the bed, a reaction zone. Both are above the gas distribution plate.

Conventional additives, which can be introduced into the blend, are exemplified by antioxidants, ultraviolet absorbers, antistatic agents, pigments, dyes, nucleating agents, fillers, slip agents, fire retardants, plasticizers, processing aids, lubricants, stabilizers, smoke inhibitors, viscosity control agents, crosslinking agents, catalysts, and boosters, tackifiers, and anti-blocking agents. Aside from the fillers, the additives can be present in the blend in amounts of about 0.1 to about 10 parts by weight of additive for each 100 parts by weight of polymer blend. Fillers can be added in amounts of up to 200 parts by weight and more for each 100 parts by weight of the blend.

The advantage of the film prepared from the in situ blend of this invention is the consistently high FAR.

All molecular weights mentioned in this specification are weight average molecular weights unless otherwise designated.

Patents mentioned in this specification are incorporated by reference herein.

The invention is illustrated by the following examples. Examples 1 and 2

Example 1 is an embodiment of the invention and example 2 is a comparative example. Both examples use the same steps and conditions except as set forth in the Table.

The preferred catalyst system is one where the precursor is formed by spray drying and is used in slurry form. 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 slurry form. See United States patent 5,290,745. The catalyst composition and method of preparing same used in this example is of the same composition and preparation method as example 1 of 5,290,745 except that 0.25 mol of tri-n-hexylaluminum per mol of tetrahydrofuran is used instead of 0.2 mol.

Polyethylene is produced using the following standard procedure.

Ethylene is copolymerized with 1-hexene in the first reactor, and the addition of 1-butene in the second reactor. Trimethylaluminum (TMA) cocatalyst is added to each reactor during polymerization as a 50 weight percent 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 continuously conducted after equilibrium is reached under the conditions set forth here and in the Table.

Polymerization is initiated in the first reactor by continuously feeding the above catalyst precursor and cocatalyst into a fluidized bed of polyethylene granules together with ethylene, 1-hexene, and hydrogen. The resulting copolymer mixed with active catalyst is withdrawn from the first reactor and transferred to the second reactor using second reactor gas as a transfer medium. The second reactor also contains a fluidized bed of polyethylene granules. Ethylene, 1- butene, and hydrogen are introduced into the second reactor where they come into contact with the copolymer and catalyst from the first reactor. Additional cocatalyst is also introduced. The product blend is continuously removed.

Variable polymerization conditions, resin properties, film extrusion conditions, and film properties are set forth in the Table and Notes.

Table

Example 1 2

Reactor I II I II pressure 296 431 298 433

(psig)

C2 PP(psi) 44.5 112.5 42.4 118.8

H2/C2 0.043 1.79 0.033 1.78

(mole ratio)

C4/C2 0 0.248 0 0.320

(mole ratio)

C6/C2 0.152 0.018 0.143 0.011

(mole ratio)

N2 (%) 74.1 19.4 76.5 14.5

H2 (%) 0.62 45.09 0.45 47.11

C2H4 (%) 14.33 25.23 13.59 26.53

C4H8 (%) 0 6.26 0 8.48

IC5 (%) 6.81 2.58 7.00 2.02

C6H12 (%) 2.18 0.46 1.94 0.28

TMA flow 9.72 4.83 10.05 3.35

(lbs/hr) production 36.1 41.3 35.9 47.6 rate (1000 lbs/hr) catalyst feed 17.5 0 16.9 0

(lbs/hr)

C2 feed 30.0 38.5 30.5 43.6

(1000 lbs/hr) Example 1 (continued) 2 (continued)

Reactor I II I II

C4 feed 0 4.00 0 5.88

(1000 lbs/hr)

C6 feed 6141 0 5382 0

(lbs/hr)

H2 feed 0.47 177 0.33 233

(lbs/hr)

N2 feed 504 0 626 0

(lbs/hr)

IC5 feed 1730 0 1599 0

(lbs/hr)

Bed weight 95 173 94 172

(1000 lbs)

Residence 2.6 2.2 2.6 2.1

Time (hrs)

Split 0.47 0.53 0.43 0.57

(weight fraction)

Resin

Analysis

Ti (ppm) 3.49 1.90 3.37 1.69

Al Ti (molar 22.4 33.1 28.9 34.6 ratio)

Melt index 0.80 0.63

(g/10 min) Example 1 2

Resin

Analysis

(continued)

Flow index 1.85 83.7 1.23 81.4

(g/10 min) (roll-milled) (roll-milled)

MFR 104 130

Density 0.9057 0.9216 0.9067 0.9216

(g/cc)

Film

FAR plus 50 minus

Notes to Table: psig = pounds per square inch gauge.

C2 PP = partial pressure of ethylene reported in psi (pounds per square inch).

H2/C2, C4/C2, and C6/C2 are mole ratios of hydrogen, 1-butene, and 1- hexene, respectively, to ethylene.

N2, H2, C2H4, C4H8, IC5, C6H12, are nitrogen, hydrogen, ethylene, 1- butene, isopentane, and 1-hexene, respectively. % is percent by mole .

TMA = trimethylaluminum.

Split = weight fraction of individual component

Ti ppm = parts per million by weight of titanium in the resin.

Al/Ti = molar ratio of aluminum to titanium in the resin. Density is measured by producing a plaque in accordance with ASTM D-1928, procedure C, and then testing as is via ASTM D-1505. It is reported in gram per cubic centimeter.

FAR = film appearance rating as explained above. The films are prepared by extrusion in a 3.5 inch Gloucester™ blown tubular film extruder having a length to diameter ratio of 24:1; a linear low density polyethylene screw; a 6 inch die; and a die gap of 60 and 120 mils. FAR is determined for each film.

Roll Milling Procedure: Granular resin from the reactors is placed on a two roll mill that is commonly available in the industry. The rolls are set at a temp of 148 C and initially set at the closet spacing. The resin is placed on the rolls for about 5 minutes and then roll milled at low RPM's (< 5) for about 5 minutes with a gap of 0.008 inches. The milled crepe should be removed and refed approximately 3 times during the period. The sample is then removed and the flow properties measured.

Claims

1. 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 and a melt flow ratio in the range of about 85 to about 115.

2. The in situ blend defined in claim 1 wherein the first copolymer has 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 1.7 to about 2.4 grams per 10 minutes and the second copolymer has a density in the range of 0.930 to 0.940 gram per cubic centimeter and a melt index in the range of about 250 to about 350 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 50:50 and the in situ blend having a density in the range of 0.919 to 0.924 gram per cubic centimeter and a melt flow ratio in the range of about 90 to about 110.

3. The in situ blend defined in claim 1 wherein the alpha-olefin is 1-hexene and/or 1-butene.

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

5. The in situ blend defined in claim 4 wherein the ethylene partial pressure in the first reactor is in the range of about 35 to about 50 psi.

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

7. An in situ blend comprising a mixture of two ethylene/alpha- olefin copolymers wherein the alpha-olefin comonomer has 3 to 8 carbon atoms, said blend having a flow index in the range of about 65 to about 90 grams per 10 minutes; a melt flow ratio in the range of about 85 to about 115; and a density in the range of .919 to 0.924 gram per cubic centimeter, said blend having been prepared, under catalytic polymerization conditions, in two reactors connected in series wherein, in the first reactor, the copolymer has a roll milled flow index 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 gram per cubic centimeter, and ,in the second reactor, said copolymer has a melt index in the range of about 200 to about 400 grams per 10 minutes; a density in the range of 0.925 to 0.945 gram per cubic centimeter; the weight ratio of the copolymer prepared in the first reactor to the copolymer prepared in the second reactor 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 mole 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 to about 50 psi, 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 mole ratio of hydrogen to ethylene is in the range of about 1.4:1 to about 2.5:1.

8. The in situ blend 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 blend defined in claim 1.