Films comprising metallocene catalyzed polyethylene

A high clarity film containing three layers wherein the polymer of each outer layer is the same or different polyethylene selected from polyethylenes having a density of at least 0.925 g/cc, and a molecular weight distribution of less than 4, and being further characterized by being substantially free of branches having 6 or more carbon atoms, polyethylenes of the outer layers optionally containing a fluoroelastomer.

FIELD OF THE INVENTION
 This invention relates to film of polymers produced from a monomer
 consisting essentially of ethylene. In another aspect, the present
 invention relates to polyethylene film having a good balance of physical,
 processing, and optical properties.
 BACKGROUND OF THE INVENTION
 In its broadest sense, the term "film" as used herein refers to
 self-supporting materials having a wide range of thicknesses. Examples
 would include thicknesses in the range of 0.05 to about 40 mils, more
 typically about 0.25 to about 5 mils (1 mil equals 1/1000 of an inch).
 Films can be made using a variety of techniques such as casting, blowing,
 and extrusion.
 Good clarity in polyethylene blown film as indicated by low Haze and high
 Gloss has been noted in the past to be dependent upon several factors.
 Typically the Haze increases (and the Gloss decreases) as the polymer
 density and molecular weight distribution increases. Also, it has been
 noted that typically the surface roughness increases as the molecular
 weight distribution and density increases. Film stiffness on the other
 hand, which is often a desired property of the blown film dependent upon
 the actual application, has been noted to increase as density increases.
 Therefore, there has usually been a trade-off between film clarity and
 stiffness in polyethylene blown film.
 Often in forming multi-layered films, a base layer of high molecular weight
 high density polyethylene or medium molecular weight high density weight
 polyethylene has been employed to provide strength and a low density
 polyethylene or linear low density polyethylene layer has been provided to
 provide other properties. Often, however, it has been noted that the low
 density polyethylene and linear low density polyethylene layers are tacky
 and sticky unless antiblock agents are included. Such antiblock agents,
 however, generally also have an adverse effect upon the clarity and
 physical properties.
 An object of the present invention is to provide a method for producing
 films of ethylene polymers having a density of at least about 0.925 g/cc
 which have a good balance of processing, physical, and optical properties.
 Other aspects, objects, and advantages of the present invention will be
 apparent from the following comments.
 SUMMARY OF THE INVENTION
 In accordance with the present invention, there is provided a unusually
 clear self-supporting film comprising at least one layer having a percent
 haze of less than 17.8 wherein the polymer of said layer consists
 essentially of polyethylene having a density of at least about 0.925 g/cc
 and a molecular weight distribution of no more than 4. The narrow
 molecular weight polyethylene having a density of at least about 0.925
 g/cc is preferably selected from polyethylenes which can be formed into a
 1 mil blown film having a percent haze of less than 17.8, or most
 preferably no more than 10.
 In one preferred embodiment, the film has only one layer of polymer
 consisting essentially of polyethylene having a density in the range of
 0.93 to about 0.945 g/cc and a molecular weight distribution in the range
 of about 1.5 to about 4, or more preferably about 1.5 to about 3.5. In
 another preferred embodiment the film is multilayered and at least one
 layer has a percent haze of less than 17.8, more preferably a percent haze
 of less than 10, and comprises polyethylene having a density of at least
 0.925 g/cc and a molecular weight distribution no more than 4.
 DETAILED DESCRIPTION OF THE INVENTION
 The polyethylene useful for producing the inventive films can be produced
 using a suitable metallocene-containing polymerization catalyst system. In
 a particularly preferred embodiment the polyethylene is produced in a
 slurry, i.e. particle form, type process wherein the polymer is formed
 under conditions such that the polymer is produced in the form of solid
 particles that can be readily separated from the liquid polymerization
 diluent. In such particle form polymerizations it is preferable that the
 metallocene-containing catalyst system be employed in a form that is
 substantially insoluble in the polymerization diluent during the
 polymerization process. Various techniques are known for producing such
 relatively insoluble catalyst systems. Some examples are shown in U.S.
 Pat. Nos. 5,354,721; 5,411,925; and 5,414,180.
 One particularly preferred type of relatively insoluble solid metallocene
 catalyst system can be produced by prepolymerizing a mixture of a
 metallocene, preferably a metallocene having olefinically unsaturated
 substituents, and a suitable cocatalyst in the presence of an olefin,
 generally containing 2 to 8 carbon atoms. In particularly preferred
 embodiment the solid catalyst system is obtained by polymerizing ethylene
 in the presence of an alkane liquid diluent under slurry polymerization
 conditions using a special type of metallocene-based catalyst system The
 catalyst system is a solid catalyst prepared by (a) combining
 5-(9-fluorenyl)-5-(cyclopentadienyl)-hexene-1 zirconium dichloride and
 methylaluminoxane in a liquid, (b) prepolymerizing ethylene in the
 resulting liquid, and (c) separating the resulting solid prepolymerized
 catalyst system from the liquid. It is preferred that the liquid employed
 in step (a) be an organic liquid in which the methylaluminoxane is at
 least partially soluble. Preferably some aromatic solvent is employed in
 step (a). Examples of aromatic solvents include benzene, toluene,
 ethylbenzene, diethylbenzene, and the like. Preferably the amount of the
 liquid should be such as to dissolve the product of reaction between the
 metallocene and the aluminoxane, provide desirable polymerization
 viscosity for the polymerization, and to permit good mixing. During the
 mixing, the temperature would preferably be kept below that which would
 cause the metallocene to decompose. Typically the temperature would be in
 the range of about -50.degree. C. to about 150.degree. C. Preferably, the
 metallocene, the aluminoxane, and the liquid diluent are combined at room
 temperature, i.e. around 10.degree. C. to 30.degree. C. The reaction
 between the aluminoxane and the metallocene is relatively rapid. The
 reaction rate can vary over a wide range, however, it is generally desired
 that they be contacted for an amount of time in the range of about 1
 minute to about 1 hour.
 It is also within the scope of the invention to carry out the step (a) in
 the presence of a particulate solid. Any number of particulate solids can
 be employed. Typically this solid would be any inorganic solid that does
 not interfere with the desired end results. Examples include porous
 supports such as talc, inorganic oxides, resins to support material such
 as particulate polyolefins. Examples of inorganic oxide materials include
 metal oxides of Groups II-V, such as silica, alumina, silica-alumina, and
 mixtures thereof Other examples of inorganic oxides are magnesia, titania,
 zirconia, and the like.
 If a solid is employed, it is generally desirable for the solid to be
 thoroughly dehydrated prior to use. Preferably it is dehydrated so as to
 contain less than 1 percent loss on ignition. Thermal dehydration may be
 carried out in a vacuum or while purging with a dry inert gas such as
 nitrogen at a temperature of about 20.degree. C. to about 1000.degree. C.
 and preferably from about 300.degree. C. to about 870.degree. C. Pressure
 considerations are not viewed as critical. The duration of the thermal
 treatment can be from about 1 to about 24 hours as needed.
 Dehydration can also be accomplished by subjecting the solid to a chemical
 treatment in order to remove water and reduce the concentration of surface
 hydroxyl groups. Chemical treatment is generally capable of converting all
 water hydroxyl groups in the oxide surface to relatively inert species.
 Useful chemical agents are for example, carbon monoxide, carbonyl sulfide,
 trimethylaluminum, ethyl magnesium chloride, chloro silanes such as
 SiCl.sub.4, disilazane, trimethylchlorosilane, dimethylamino
 trimethylsilane, and the like.
 The amount of aluminoxane and metallocene used in forming a liquid catalyst
 system for the prepolymerization can vary over a wide range. Typically,
 however, the molar ratio of the aluminum in the aluminoxane to the
 transition metal of the metallocene is in the range of about 1:1 to about
 20,000:1, more preferably a molar ratio of about 50:1 to about 2,000:1 is
 used. If a particulate solid, i.e. silica, is used, generally it is used
 in an amount such that the weight ratio of the metallocene to the
 particulate solid is in the range of about 0.00001/1 to 1/1, more
 preferably 0.0005/1 to 0.2/1.
 The prepolymerization is conducted in the liquid catalyst system, which can
 be a solution, a slurry, or gel in a liquid. A wide range of olefins can
 be used for the polymerization. Typically, however, the prepolymerization
 will be conducted using an olefin, preferably selected from ethylene and
 non-aromatic alpha olefins, such as propylene. It is within the scope of
 the invention to use a mixture of olefins, for example, ethylene and a
 higher alpha olefin can be used for the prepolymerization. The use of a
 higher alpha olefin, such as 1-butene, with ethylene, is believed to
 increase the amount of copolymerization occurring between the olefin
 monomer and the olefinically unsaturated portion of the metallocene.
 The prepolymerization can be conducted under relatively mild conditions.
 Typically this would involve using low pressures of the olefin and
 relatively low temperatures designed to prevent site decomposition
 resulting from high concentrations of localized heat. The
 prepolymerization typically occurs at temperatures in the range of about
 -15.degree. C. to about +150.degree. C., more typically in the range of
 about 0.degree. C. to about +30.degree. C. The amount of prepolymer can be
 varied but typically would be in the range of from about 1 to about 95
 weight percent of the resulting prepolymerized solid catalyst system,
 still more preferably about 5 to about 80 weight percent. It is generally
 desirable to carry out the prepolymerization to at least a point where
 substantially all of the metallocene is in the solid rather than in the
 liquid, since that maximizes the use of the metallocene.
 After the prepolymerization, the resulting solid prepolymerized catalyst is
 separated from the liquid reaction mixture. Various techniques known in
 the art can be used for carrying out this step. For example, the material
 could be separated by filtration, decantation, or vacuum evaporation. It
 is currently preferred, however, not to rely upon vacuum evaporation since
 it is considered desirable to remove substantially all of the soluble
 components in the liquid reaction product of the prepolymerization from
 the resulting solid prepolymerized catalyst before it is stored or used
 for subsequent polymerization. After separating the solid from a liquid,
 the resulting solid is preferably washed with a hydrocarbon and dried
 using a high vacuum to remove substantially all the liquids or other
 volatile components that might still be associated with the solid. The
 vacuum drying is preferably carried out under relatively mild conditions,
 i.e. temperatures below 100.degree. C. More typically the prepolymerized
 solid is dried by subjection to a high vacuum at a temperature of about
 30.degree. C. until a substantially constant weight is achieved. A
 preferred technique employs at least one initial wash with an aromatic
 hydrocarbon, such as toluene, followed by a wash with a paraffinic
 hydrocarbon, such as hexane, and then the vacuum drying.
 It is also within the scope of the present invention to add a particulate
 solid to the liquid catalyst system after it has been formed and then to
 carry out the prepolymerization in the presence of that solid. Another
 option is to add a particulate solid of the type aforementioned after the
 prepolymerization or after the solid prepolymerized catalyst system has
 been separated from the liquid.
 This resulting solid prepolymerized catalyst system is capable of preparing
 polymers of ethylene having a fairly wide range of densities. Typically,
 in preparing the lower density versions, the ethylene is polymerized in
 combination with a smaller amount, generally less than 20 mole percent, of
 at least one other alpha olefin, generally containing about 3 to about 10
 carbon atoms, examples of which include aliphatic hydrocarbons such as
 butene-1, pentene-1, hexene-1, 4-methylpentene-1, octene-1, and the like.
 The solid prepolymerized catalyst system can be employed using slurry
 polymerization conditions. Typically the polymerization temperature would
 be selected so as to provide slurry polymerization conditions in the
 particular liquid diluent selected. Typically the temperature would be in
 the range of about 20.degree. C. to about 130.degree. C. With isobutane as
 the liquid diluent, temperatures in the range of about 60.degree. C. to
 about 110.degree. C. have been found desirable. For producing polymers for
 film applications, it is generally desirable to produce a polymer having a
 melt index of less than 5. This can be accomplished by adjusting the molar
 ratio of hydrogen to ethylene in the polymerization process, changing the
 reactor temperature, and/or changing the ethylene concentration.
 When the polymerization is carried out in a continuous loop slurry process,
 it is generally desirable to include in the reaction mixture a small
 amount of an antistatic agent. An example of such as antistatic agent is
 the material sold by DuPont Chemical Co. under the trade name Stadis 450.
 In a particle form type polymerization the above described type of catalyst
 system is capable of producing polyethylene homopolymers and copolymers
 having densities of 0.925 g/cm or higher with molecular weight
 distributions of no more than 4 that are useful for making films having
 percent haze of less than 17.8, especially preferred polyethylenes having
 densities in the range of 0.925 to 0.95 g/cc. The polymers produced in
 that manner have low flow activation energies, i.e. below about 25
 kJ/mole, and a critical shear stress at the onset of melt fracture of less
 than 4.times.10.sup.6 dyne/cm.sup.2. This is considered to indicate that
 the polymers are substantially linear polymers substantially free of long
 chain branching. The number of long chain branches in such polymers is
 considered to be less than 0.01/1000 carbon atoms. The term "long chain
 branching" as used herein refers to branches having a chain length of at
 least 6 carbon atoms. A method of determining long chain branching is
 disclosed in Randal, Rev. Macromol. Chem. Phys., C29 (243), 285-297.
 The ethylene polymers produced in a particle form process with that
 catalyst system are also believed to have a very uniform distribution of
 short chain branches both at the intramolecular level (monomer sequence
 distributions along the chain) and at the intermolecular level (monomer
 distribution between polymer chains of different molecular weights).
 Homopolymers and ethylene-hexene copolymers produced with such catalysts
 are particularly unusual in that they contain ethylene branches even
 though no butene comonomer was employed in the polymerization. It is
 theorized that butene is formed insitu in the polymerization and that such
 results in a very uniform distribution of the ethylene branches. The shear
 stress response of such polymers is essentially independent of the
 molecular weight distribution.
 It is typically desirable to add stabilizers to the polymer recovered from
 the polymerization process. A number of suitable stabilization packages
 are known in the art. Stabilizers can be incorporated into the polymer
 during a pelletization step or by reextrusion of previously produced
 pellets. One example of a stabilizer would be Irganox.RTM. 1010
 antioxidant which is believed to be a hindered polyphenol stabilizer
 containing tetrakis [methylene 3-(3,5-di
 tertbutyl4-hydroxy-phenylpropionate)] methane produced by Ciba-Geigy
 Corporation. Another example is the PEP-Q.RTM. additive which is a product
 of Sandoz Chemical, the primary ingredient of which is believed to be
 tetrakis-(2,4-di-tertbutyl-phenyl)-4,4' biphenyl phosphonite. Other common
 stabilizer additives include calcium stearate or zinc stearate. Still
 other stabilizers commonly used include Ultranox 626 antioxidant which is
 a product of GE, the primary ingredient of which is believed to be
 bis(2,4-di-t-butylphenyl) pentaerythritol diphosphite, and Ultranox 627A
 antioxidant which is believed to be Ultranox 626 containing about 7 weight
 percent of a magnesium aluminum hydrocarbonate. Such stabilizer additives
 can be employed in generally any suitable amount The amounts used are
 generally the same as have been used for other polyethylene polymers.
 Often the amounts for each additive is less than 0.2 weight percent based
 upon the weight of the polymer.
 The molecular weight of the polyethylene used to make the inventive film
 can vary over a wide range. Typically for forming films by blowing it is
 desirable for the polymer to have a melt index in the range of about
 0.1-10 dg/min, more preferably about 0.2-5 dg/min. Generally if the melt
 index of the polymer is less than about 1, it is often desirable to
 incorporate a processing enhancing amount of a fluoroelastomer processing
 aid. One example is the fluoroelastomer sold under the trade name Viton by
 E. I. DuPont de Nemours & Co. Another example is the fluoropolymer sold
 under the trade name Dynamar FX-9613 by 3M Company. The amount of
 fluoropolymer employed can vary over a wide range depending upon the
 particular results desired. Typically it would be employed in an amount in
 the range of about 0.01 to about 1 weight percent based upon the weight of
 the polyethylene. In some cases the fluoroelastomer is employed in form of
 a masterbatch in which the fluoroelastomer is dispersed in a polymer such
 as LLDPE copolymer of butene and ethylene. One example of such a material
 is Ampacet 10919 processing aid masterbatch available from AMET Corp.
 In some applications it may be desirable to include in the polymer of one
 or more of the layers a slip/anti-block agent, particularly for layers
 produced from polymers having a density of less than 0.925 g/cc. Generally
 such materials are inorganic compounds. Some examples include mica, talc,
 silica, calcium carbonate, and the like. A typical example would be
 Ampacet 10430 slip/antiblock concentrate available from AMET Corp.
 It is also within the scope of the present invention for the polyethylene
 used to produce the inventive films to contain various other additives
 normally included in polyethylenes, such as heat stabilizers, weather
 stabilizers, lubricants, etc, in amounts that do not impact unduly on the
 objects of the present invention. It is also within the scope of the
 present invention to blend the required narrow molecular weight
 polyethylene having a density of at least about 0.925 with other polymers
 so long as the amount of the other polymers does not unduly detract from
 the beneficial properties of the required polyethylene, i.e. low haze and
 good handling properties. Generally the required polyethylene is greater
 than about 50 weight percent of the polymer, more typically at least 90
 weight percent of the polymer, and still more preferably at least about
 99.5 weight percent of the polymer.
 It is within the scope of the present invention to prepare single layer
 films having a haze of less than 17.8 using polyethylene having a density
 of at least 0.925 and a molecular weight distribution of no more than
 about 4. It is considered that such films can be produced by casting,
 blowing, or extrusion.
 It is also within the scope of the present invention to use such a layer of
 film to form a multilayered film. The polymers employed in the other
 layers can be selected from generally any of the polymeric materials
 generally used in producing films. Thus the other layers need not be
 limited to polymers of ethylene but could contain other polymers such as
 propylene-butene copolymer, poly(butene-1), styrene-acrylonitrile resin,
 acrylonitrile-butadiene-styrene resin, polypropylene, ethylene vinyl
 acetate resin, polyvinylchloride resin, poly(4-methyl-1-pentene), and the
 like. Multilayers can be formed using techniques generally known in the
 art, such as, for example co-extrusion.
 One particularly preferred example of a multilayered film includes one
 layer having a percent haze of less than 17.8 comprising a polyethylene
 having a density in the range of about 0.925 to about 0.945 g/cc and a
 molecular weight distribution of no more than 4 and another layer
 comprising a second polyethylene having a molecular weight distribution
 greater than 4, more preferably greater than 6, and still more preferably
 greater than 10, such as polyethylenes produced using Phillips chromium
 catalysts or Ziegler-Natta type catalysts.
 For some applications it is also desirable for the polyethylene with the
 broader molecular weight distribution to have a higher density than the
 polyethylene having the narrower molecular weight distribution, for
 example a density of at least about 0.945 g/cc. In a preferred embodiment
 of this type there are at least three layers and the outer layers have a
 haze of less than 17.8 percent and comprise a polyethylene having a
 density in the range of about 0.925 to about 0.945 g/cc and a molecular
 weight distribution of no more than 4, and and the inner layer comprises a
 polyethylene having a density of at least about 0.945 g/cc.
 In another preferred embodiment there are at least three layers and the
 outer layers have a haze of less than 17.8 percent and consists
 essentially of polyethylene having a density in the range of about 0.925
 to about 0.945 g/cc and a molecular weight distribution of no more than 4,
 and and the inner layer comprises polyethylene having a molecular weight
 distribution of at least 10 and a density of less than 0.93 g/cc, most
 preferably a density in the range of 0.91 to 0.929 g/cc with a HLMI in the
 range of about 12 to about 24 dg/min.
 The most preferred multilayered films are those in which the multilayered
 film itself has a percent haze of less than 17.8, even more preferably a
 percent haze of less than 10. In the currently preferred three layer film
 the outer layers each have a thickness in the range of about 5 to about 25
 percent of the total thickness of the three layered film. A particularly
 preferred inner layer is one having a thickness equal to about 50 to about
 90 percent of the total thickness of the three layered film, with the
 polymer of that inner layer being a low density linear copolymer of
 ethylene and 1-hexene produced using a Phillips Cr catalyst in a particle
 form polymerization process, particularly a copolymer having a density in
 range of about 0.91 to about 0.929 g/cc, an HLMI in the range of about 12
 to 24 dg/min. and a molecular weight distribution greater than 10.
 It is also within the scope of the present inventive mutilayered films to
 have a layer of polyethylene having a broader molecular weight
 distribution and a lower density than the polyethylene in the layer having
 a percent haze of less than 17.8, for example one layer could have a
 percent haze of less than 17.8 and be composed of a polyethylene having a
 density at least 0.925 g/cc and molecular weight distribution of at least
 4 and a second layer could be composed of a polyethylene having a density
 of less than 0.925 g/cc, such as for example a low density polyethylene
 produced by a high pressure process.
 It is also within the scope of the present invention to have a multilayered
 film in which one layer has a percent haze of less than 17.8 wherein the
 polymer consists essentially of a polyethylene having a density of at
 least 0.925 g/cc and a molecular weight distribution of less than 4 and
 another layer composed of a low density polyethylene having a narrow
 molecular weight distribution and good clarity. In that case the inventive
 layer of polyethylene provides stiffness that may not be provided by the
 lower density polyethylene without detracting from the clarity of the
 lower density polyethylene as much as would a similar density polymer
 produced by a Phillips chromium catatalyst or a Ziegler-Natta type
 titanium-containing coordination catalyst.
 A layer having a percent haze of less 17.8 made of a polyethylene having a
 density of less than 0.935 g/cc typically has a much lower melting point
 than polymers of the same density and molecular weight produced by
 conventional transition metal coordination catalysts or Phillips chromium
 catalysts. If a lower melt temperature layer is desired it may therefor be
 advantageous to use the polyethylenes having a density in the range of
 0.925 to 0.935 g/cc and a molecular weight distribution of less than 4 to
 form the layer having the haze of less than 17.8.
 In a particularly preferred embodiment all the polyethylene layers are
 polyethylenes produced using metallocene catalysts which have molecular
 weight distributions of less than 4.
 A further understanding of the present invention and its objects and
 advantages will be provided by the following examples.

EXAMPLES
 Example I
 A large batch of solid particulate metallocene-based catalyst was prepared.
 The preparation involves reacting the metallocene (but-3-enyl)
 (cyclopentadienyl) (fluorenyl) (methyl) methane zirconium dichloride which
 is also known as (5-cyclopentadenyl) (5-fluorenyl) hex-1-ene zirconium
 dichloride with a 10 weight percent solution of methylaluminoxane in
 toluene to give a soluble olefin polymerization catalyst system. Davison
 948 silica, dried thermally and treated with trimethylaluminum, was added
 to the liquid catalyst system. To heterogenize this system the terminal
 unsaturated group of the metallocene was copolymerized with ethylene by
 adding ethylene to maintain a pressure in the reaction vessel at 3 to 4
 psig and stirring while the temperature was maintained at about 20.degree.
 C. After about two hours, the ethylene addition was stopped and the slurry
 was filtered. The solid was washed with toluene and then with hexane and
 dried overnight using a membrane pump until no more solvent appeared on
 the condenser. The resulting pink powder was dried an additional 5 hours
 in a high vacuum. The solid was sieved through a 60 mesh screen and
 combined with Cabosil HS-5, a fumed silica which had been dried thermally
 and treated with trimethylaluminum.
 The resulting solid metallocene-based catalyst system was then employed in
 a pilot plant scale continuous loop reactor under slurry type
 polymerization conditions. The feedstocks to the reactor were passed
 through alumina drier beds prior to being sent to the reactor. The reactor
 was a stainless steel pipe loop reactor. Circulation was achieved by a
 propeller within the reactor. Reactant concentrations were monitored by
 flash gas analysis using two on-line gas chromatographs.
 The polymerizations were conducted in isobutane as a liquid diluent using
 varying amounts of ethylene and hexene-1 comonomer to obtain a number of
 lots of polyethylene fluff. Copolymers of ethylene and hexene-1 having
 densities varying from 0.9179 to 0.9402 g/cc were produced using the solid
 metallocene based catalyst system. The polyethylene copolymers of various
 densities were compounded with a typical stabilization package comprising
 0.06 weight percent Irganox 1010, 0.12 weight percent PEP-Q, and 0.05
 weight percent zinc stearate based upon the weight of the polymer.
 The resulting polymers were then evaluated for various physical properties
 and were employed in the production of films using a 4 inch Sano blown
 film line having a 1.5 inch single screw extruder. The film die is a
 spiral mandrel die with four entry ports and is 4 inches in diameter. The
 die had a dual lip air ring mounted on it which was used to cool and
 stabilize the extruded bubble. Film blowing parameters were employed that
 are typical of linear-low density polyethylene type processing conditions,
 including a 0.06 inch die gap, 190.degree. C. extruder barrel and film die
 set temperatures, 2.5:1 blowup ratio, no stalk, i.e. "in-pocket extrusion"
 in 1 mil film thickness. The screw rotation was adjusted to keep the
 extrusion rate between 55 and 60 pounds per hour, so that the film
 properties so obtained would scale directly (i.e., be the same as or at
 least very similar) with those obtained from larger, commercial scale
 equipment.
 For some of the polyethylene copolymers runs were also made where the
 copolymer had been compounded with 0.07 weight percent of FX-9613
 fluoropolymer. As controls films were also produced using the commercially
 available Dow 2045A copolymer, which is believed to be a linear low
 density polyethylene copolymer produced using a non-metallocene
 titanium-based catalyst system. Also, films were made using a copolymer
 produced by a Phillips chrome resin.
 Various characteristics of the polymer and the polymerization were
 characterized. Examples of characteristics determined in various cases
 include Haze (ASTM D-1003 using an XL-211 Hazeguard System from
 Garder/Neotec Instruments Division); density in grams/mL (ASTM D 1505-68);
 High Load Melt Index (HLMI) in grams of polymer/10 minutes 190.degree. C.
 (ASTM D1238-86, Condition 190/21.6); Melt Index (MI) in grams of
 polymer/10 minutes 190.degree. C. (ASTM D1238-86, Condition 190/2.16);
 Shear Stress Response (SR) determined by diving HLMI by MI; Molecular
 weights by size exclusion chromatography, i.e. weight averge molecular
 weight referred to herein as M.sub.w and number average molecular weight
 referred to herein as M.sub.n ; and Heterogenity index (HI) or molecular
 weight distribution (MWD) being determined by dividing M.sub.w by M.sub.n.
 The (SEC) size exclusion chromatography was conducted using a linear
 column capable of resolving the wide range of molecular weights generally
 observed in polyolefins, such as polyethylene.
 The property referred to herein as flow-activation energy, also sometimes
 referred to as energy of activation, i.e. Ea, reflects the sensitivity of
 a polymer melt viscosity to temperature. This is generally viewed as a
 function of the linear vs network character of the polymer. The molecular
 weight and the molecular weight distribution are also generally viewed as
 factors affecting the flow activation energy. The Ea in terms of kJ/mol
 can be readily determined from data obtained from a dynamic rheometer such
 as Rheometrics Inc. (RMS 800) dynamic rheometer. A standard prescription
 for summarizing the viscosity-temperature dependence of polymer melts has
 long been available in the scheme known as the Williams-Landel-Ferry (WLF)
 superposition which is described in the classic text entitled
 "Viscoelastic Properties of Polymers", 3rd Edition (John Wiley & Sons, New
 York, 1980) by John D. Ferry. Data needed for establishing the temperature
 dependence of dynamic viscosity versus frequency, or viscosity vs shear
 rate, are not difficult to obtain at various temperatures in a range
 between melting and the onset of chemical degradation. In order to ensure
 that the Ea values are most accurate, it is desirable to optimize the data
 to produce optimally smooth isothermal master curves according to the WLF
 time-temperature superposition but using a least squares closeness-of-fit
 criterion based on Carreau-Yasuda model parameters that have been shown
 previously to give highly precise fits to single temperature polyethylene
 data. This can be done in various ways. The currently preferred technique
 involves subjecting the dynamic viscosity frequency curves obtained from a
 Rheometrics, Inc. dynamic viscometer to a proprietary computer program
 entitled "Rheology Analysis Program CY" covered by Phillips Petroleum
 Company unpublished copyright which was filed for registration on Jan. 31,
 1995. This proprietary computer program is available for use by others
 under a licensing program.
 Discussions of the Carreau-Yasuada model can be found in Dynamics of
 Polymeric Liquids, Second ed. (John Wiley & Sons, New York, 1987) by R.
 Byron Bird, Robert C. Armstrong, and Ole Hassager; as well in C. A. Hieber
 and H. H. Chiang, "Some correlations involving the shear viscosity of
 polystryrene melts," Rheol. Acta, 28, 321-332 (1989) and C. A. Hieber and
 H. H. Chiang, "Shear-rate-dependence modeling of polymer melt viscosity,"
 Polym. Eng. Sci. 32, 031-938 (1992).
 The copolymers produced using the metallocene-based catalyst system have
 some distinct differences from the Dow 2045A polymer and the polymer
 produced using a Phillips chromium catalyst. Specifically, the polymers
 produced using a metallocene-based catalyst had molecular weight
 distributions in a range of 2.17 to 2.31 and unusually low melting points
 for their density. The Dow polymer had a broader molecular weight
 distribution. The polymer produced using a Phillips chromium catalyst a
 molecular weight distribution that was even broader than that of the Dow
 polymer. In addition, the SR or HLMI/MI for the polymers produced using
 the metallocene-based catalyst were in the range of 17 to 18 whereas the
 Dow resin was 30. From rheological data and Carreau-Yasuda parameters at
 190.degree. C., the flow activation energies of the polymers were
 compared. The polymers produced from the metallocene-based system had flow
 activation energies in the range of 20.48, to 23.71 kJ/mol. The Dow 2045A
 polymer in contrast had a flow activation energy, Ea, of 25.47 kJ/mol. The
 metallocene-based polymers were also evaluated to determine the
 concentration of terminal vinyl groups. The percent of chains with a
 terminal vinyl were in the range of 30 to about 42.9 percent, a value of
 which is somewhat lower than that normally observed for copolymers
 produced using chromium type catalysts. Carbon .sup.13 NMR analysis also
 indicated that the metallocene-based polymers showed the evidence of trace
 amounts of ethyl and butyl short chain branches which may have come from
 in-situ generated one olefin oligomers. As determined by FTIR
 spectroscopy, the total branching of the metallocene produced resins
 varied from about 0.4 to about 2.1 mole percent. The number of vinyl
 groups per 1000 carbon atoms for the metallocene based resins as
 determined by FTIR was in the range of 0.087 to 0.145.
 A summary of the polyethylene properties and the properties of selected
 films is shown in the following table.

Polyethylene Properties Film Properties
 Density Dart, MD TD Haze,
 Gloss,
 Film g/cc MI MWD g Tear, g Tear, g % %
 1A 0.9179 1.06 2.17 388 200 398 4.06
 119.7
 1B 0.9179 1.06 2.17 708 299 429 3.73
 134.3
 2A 0.9216 1.36 2.24 169 237 411 5.9
 111.5
 3A 0.9222 1.89 2.21 256 253 429 -- --
 3B 0.9222 1.89 2.21 145 174 453 5.66
 118.2
 4A 0.9256 0.98 2.31 153 170 422 -- --
 4B 0.9256 0.98 2.31 152 222 355 -- --
 5A 0.9402 0.87 2.31 30 19 147 -- --
 5B 0.9402 0.87 2.31 &lt;30 24 168 5.74 121.4
 Dow 0.9200 1.00 4.17 216 461 755 17.8 --
 2045
 Cr 0.9230 -- 24.0 -- -- -- 27.08 30
 Resin
 In the above table if there is an A after the film number, it refers to a
 film prepared without any fluoroelastomer, whereas if there is a B after
 the number, it refers to a film produced using a polymer containing 0.07
 weight percent fluoroelastomer. No fluoroelastomer was used in the control
 runs where films were produced from the Dow resin and the Phillips
 chromium resin.
 The table demonstrates that in some cases the addition of fluoropolymer
 improved the dart impact strength. It is important to note that the
 metallocene based resin was much clearer and smoother than the film of the
 resin with lower density that was produced with a Phillips chromium
 catalyst. While the metallocene resin having a density of 0.9402 g/cc had
 somewhat lower values for dart impact and tear resistance, the fact still
 remains that the copolymer produced using the metallocene is capable of
 producing very clear films at densities much higher than that normally
 employed in making films. In addition films made from the higher density
 resins have the additional property of greater stiffness than the films
 made from lower density polymer, a definite advantage in some
 applications.
 It was further noticed that the films produced from the lower density
 metallocene based resins, i.e. those having a density of less than 0.925
 g/cc exhibited significant friction in the wooden take-up slats. In
 addition, the tackiness and blocking decreased as resin density increased.
 Accordingly, for the best balance of processing and clarity properties,
 the metallocene produced resins having a density of at least about 0.925
 g/cc were preferable. Additional runs were made that demonstrated that it
 was possible to produce 0.5 mil films using the special polyethylene
 copolymers having a density of at least about 0.925 g/cc and a narrow
 molecular weight distribution.
 Example II
 A coextruded blown film having three layers was produced using a medium
 density metallocene prepared using the same type of catalyst system
 described in Example I and a low density linear polyethylene produced
 using a Phillips chromium catalyst process. Both ethylenes were copolymers
 of ethylene and 1-hexene. The medium density metallocene-produced polymer
 had a density of 0.9309 g/cc and a melt index of 0.87 dg/min. The low
 density linear polyethylene produced with the Phillips chromium catalyst
 process had a density in the range of 0.919 to 0.923 and a HLMI in the
 range of 15 to 21 dg/min. If one produced a 1 mil film using the chromium
 low density linear polyethylene, it is possible to obtain good physical
 properties, however, the optical properties are less than would be
 desirable for clear film applications, i.e. the percent haze is greater
 than 17.8 in such a film. A 1 mil film produced using the metallocene
 catalyst system had lower tear resistance than the low density linear
 polyethylene produced using the chromium catalyst. The 1.5 mil coextruded
 film was extruded using a Sano coextrusion dye. Processing parameters
 included 3.0:1 blow up ratio, 0.060 inch die gap at 200 lb/hour rate. The
 bubble configuration was "pocket". The process was carried out to produce
 a product in which 60 percent of the thickness was the low density linear
 polyethylene and the two outer layers each were 20 percent of the
 thickness, the two outer layers being the metallocene polyethylene. The
 metallocene polyethylene was compounded with 1 weight percent of Ampacet
 10919, which is believed to be a butene-ethylene linear low density
 polyethylene containing about 3 weight percent of the fluoroelastomer
 processing aid. A comparison of various properties of approximately 1 mil
 films of each of the two resins and of the 1.58 mil coextruded film are
 set forth in the following table.

Comparison of Films
 Metallocene
 Property Tested Coextruded Cr Polymer Polymer
 Gauge mil 1.58 1.01 1.08
 E. Tear MD g 101 103 58
 E. Tear TD g 685 323 272
 T.E.D.D. ft-lbs 1.23 1.45 0.886
 Dart g 96 216 110
 Ten. @ Yield Md psi 1800 -- 2150
 Ten. @ Yield TD psi 1850 -- 2300
 Ten. @ Break MD psi 4450 -- 3750
 Ten. @ Break TD psi 4350 -- 4150
 Elongation MD % 517 -- 506
 Elongation TD % 723 -- 630
 Haze - 7.4 &gt;17.8 4.4
 Gloss - 115.6 -- 129
 The data shows that the coextruded film has improved optical properties as
 compared to the low density linear chromium based polyethylene and
 improved properties in toughness as compared to the films made only from
 the metallocene polymer. Of particular note is the fact that the haze of
 the coextruded film is significantly lower than that of the polymer of the
 inner layer.