WO1998018842A1

WO1998018842A1 - Lldpe copolymers

Info

Publication number: WO1998018842A1
Application number: PCT/US1997/015518
Authority: WO
Inventors: Subrahmanyam Cheruvu; Frederick Yip-Kwai Lo; Shih-May Christine Ong
Original assignee: Mobil Oil Corporation
Priority date: 1996-10-31
Filing date: 1997-09-04
Publication date: 1998-05-07
Also published as: AU4248797A

Abstract

A linear low density copolymer of ethylene (LLDPE) of a density of at least 0.900 g/cc, having excellent processability, optical properties and impact strength.

Description

LLDPE COPOLYMER8

This application is a continuation-in-part of copending application Serial No. 08/632,968 filed April 16, 1996, a Rule 62 application of prior Serial No. 08/218,159 filed March 25, 1994 (now abandoned) , which in turn was a continuation in part of then copending application Serial No. 08/036,796, filed March 25, 1993, now U.S. Patent No. 5,420,220, each of said prior applications being relied upon and incorporated by reference herein.

The invention relates to linear polyolefins; such as linear low density copolymers of ethylene (LLDPE) of improved processability and improved properties. The linear polyolefin resins can be processed readily on commercial film extruders without modifications. The resins exhibit low melt pressure and excellent bubble stability. The invention also relates to films which exhibit improved optical, tensile and impact properties, low heat seal temperature and low extractables .

The invention relates to a composition comprising, in the as-synthesized form, dry and solvent-free spherical, particles having a high settled bulk density (in lb/ft³) . The particles comprise a linear polymer or copolymer of ethylene which exhibits narrow molecular weight distribution. Preferably, the MFR is 15 to 20 and M„/M_n ranges preferably from 2.0 to 3.5. In film production, the linear products exhibit excellent bubble stability despite the very narrow molecular weight distribution.

The invention relates to films consisting of the linear polyolefin. The films exhibit a haze value as measured by ASTM D-1003 of less than 20, preferably from 3 to 10, most preferably from 5 to 7. By comparison, the haze value of conventional LLDPE is greater than 10. Furthermore, the LLDPE of the invention exhibits Dart Drop Impact values as measured by ASTM D-1709 of greater than 800. The olefin resin can also be used in rotational or injection molding processes, to produce articles of manufacture.

The catalytically produced products of the invention are unique in various ways . The products contain 0.1 to 2 ppm of zirconium. The products also contain 5 to 100 ppm, preferably 10-50 ppm, of aluminum. The products do not contain hafnium or titanium. The zirconium and aluminum content of the products is attributable to catalyst residues. The catalysts used to make the products of the invention are metallocenes of zirconium activated by aluminoxane.

In the as-synthesized form, the composition comprises dry and solvent-free spherical, particles. The product has an average particle size of 0.015-0.045 inches, preferably 0.015- 0.035 inches and more preferably from 0.02 to 0.035. The particles have spherical shape and are non-porous in the sense that the particles exhibit significantly less voids than are typical of products produced with titanium based catalysts. In a preferred embodiment the composition is produced in a gas phase catalytic process. The composition has a high settled bulk density which increases reactor throughout; the settled bulk density generally ranges from 25 to 36 lb/ft³.

Moreover, the products are linear, exhibiting no detectable long chain branching. This aspect of the product is attributable to the catalyst. The bubble stability, in blown film processing, is excellent compared to other linear polyolefins, and despite the fact that the products are linear.

Preferably, the products are low density products characterized by a density as low as 0.88 and up to less than 0.965 and preferably less than 0.93 g/cc. For applications herein, the density is greater than about 0.88, generally greater than 0.900 up to less than 0.965, preferably ranging from 0.902 to 0.929 g/cm³, and most preferably ranging from 0.903 to 0.922.

Significantly, the narrow molecular weight distribution low density copolymers have been produced with MI of one (1) and less than 1, down to 0.01. The products of the invention exhibit a MI which can range up to 150 and up to 300; however, when low MI is desired, resins can be produced which exhibit MI from 0.01 to 5, generally from 0.1 to 5, and preferably from 0.5 to 4, and most preferably 0.8 to 2.0. For blown film, the MI of the copolymers is conventionally lower than those used for cast film, (e.g. a MI value of 0.5 to 1.5 versus 2 to 4 , respectively) .

The low density products of the invention exhibit a melt flow ratio (MFR) range of 15 to 25, preferably from 15 to 20, and most preferably from 15 to 18. In products of the Examples the MFR ranges from 16 to 18. MFR is the ratio I₂₁/I₂ [wherein I₂₁ is measured at 190°C in accordance with ASTM D- 1238, Condition F and I₂ is measured at 190°C in accordance with ASTM D-1238, Condition E.]

Melting points of the products range from 95°C to 130°C. Furthermore, the hexane extractables content is very low, typically ranging from 0.3 to 2.0 wt.%.

The M„/M_n of these products ranges from 2.0 to 2.8 and from 2.5 to 3.0; M„ is the weight average molecular weight and M_n is the number average molecular weight, each of which is calculated from molecular weight distribution measured by GPC (gel permeation chromatography) . Products have been produced with M„/M_n lower than 2.5, in the range of 2.0 to 3.5 preferably in the range of 2 to 3. [Parenthetically, conventional LLDPE, produced with Ziegler type titanium containing catalysts, which are not single site catalysts exhibit M_n of greater than 3. ] In the products of the invention, the numerical value of I₁₀/I₂ ~ 4.63 is less than M_w/M,,. I₂, or melt index is measured in accordance with ASTM D-1238; and I₁₀ is measured in accordance with ASTM-D 1238. Products have been made with I₁₀/I₂ ranging from 5.5 and greater. The products exhibit excellent bubble stability characteristics, compared to conventional linear polyolefins. The reference to bubble stability is material to use of the copolymers in blown film production processes in which bubble stability is prerequisite. Bubble stability can be correlated to die swell response, which is also referred to as I₂ swell. Specifically, as explained below, I₂ swell can be correlated to elasticity which in turn can be correlated to bubble stability. It is well established that "die swell" is a measure of the elasticity of polymer melts (Ref: Polymer Rheology, L.E. Nielsen, pages 111-117, Marcel Dekker, Inc., 1977.). In fact, J. E. Guillet et al. (Journal of Applied Polymer Science _f pages 757-763, vol 8, 1963) used I₂ swell to characterize the rheology of polyethylene resins. The I₂ swell test used for illustrating properties of the invention resin is similar to the reported test. Specifically, I₂ swell is defined as the percentage increase in swell during I₂ measurement:

100 x (D/Do-1) where D = diameter of solid polymer extrudate during

I₂ measurement

Do = diameter of die orifice in the melt indexer

The above illustrates the I₂ swell of metallocene resins of the invention. Based on this plot, it is apparent that the elasticity of invention metallocene resins is consistently high. The high elasticity of invention resin provides significant advantage in terms of increased bubble stability for blown film production. These advantages are unobvious because it is the common thought that linear olefin resins, free of long chain branching, with narrow MWD (low Iι₀/I₂) [and produced by single site catalyst] possess low elasticity which limits their processability and bubble stability. The higher elasticity of the invention resin despite the narrow MWD is thus unobvious. The higher elasticity of the invention resins may be a result of their slightly broader MWD and the presence of HMW tails which are known to have a strong influence on the elasticity of a resin. As discussed below, this high elasticity is not a result of the presence of long chain branching.

To explain the uniqueness of the invention metallocene resin, when compared to other gas phase metallocene resins, it may be helpful to discuss factors that control I₂ swell. Example 6 clearly demonstrates that modifiers (C0₂, 0₂ etc.) are necessary to increase the I₂ swell of the resins. Since prior art metallocene products do not use modifiers, it is reasonable to expect that they would not possess the unique swell characteristics of invention metallocene resins.

Long chain branching (LCB) in a polyethylene resin may render the resin highly elastic. The presence of LCB's is detected by the difference in the I1₀/I₂ ratio and Mw/Mn. For all the metallocene resins of the present invention, I₁₀/I₂- 4.63 is less than Mw/Mn (see Example 5). These criteria establish that the resins of the invention are distinctly linear and contain no detectable long chain branching.

The results show that the I₂ swell of resins of the invention is greater than 5% and preferably greater than 10%. Conventional LLDPE formed with conventional Zieger catalysts containing titanium as the active metal may exhibit comparable I₂ swell values but also exhibit much greater Mw/Mn values than those of the resin of the invention. By comparison, the literature reports that resins produced by other single site catalysts exhibit no long chain branching and narrow molecular weight distribution; this, it is the common thought, makes them less elastic and difficult to process. Such resins would exhibit I₂ swell of less than or around 5% [and obviously, less than those of conventional LLDPE formed from titanium containing Ziegler catalysts.]

When fabricated into films, the films of the copolymers exhibit balanced tear strength, as measured by ASTM D1922, which ranges from 50 to 600, preferably from 220 to 420 for machine direction and from 200 to 700, preferably from 200 to 600 for the transverse direction. They also give high modulus, as measured by ASTM D-882 which ranges from 1.0 x 10⁴ to 6.0 x 10⁴ psi, preferably from 2.2 to 4.5 x 10⁴ psi; high tensile yield, as measured by ASTM D-882 which ranges from 1.0 to 3.0 x 10³ psi, preferably from 1.8 to 2.3 x 10³ psi.

When fabricated into films, the films of the copolymers exhibit excellent optical qualities as determined by haze studies, measured by ASTM D-1003 which means that haze is preferably between 3 to 20, preferably from 4 to 10. Films of inferior haze properties exhibit a haze of greater than 10. The importance of the optical properties of LLDPE depend on the intended application of the LLDPE resin. It is generally accepted that the poor optical properties of normal LLDPEs (haze >10 and gloss <50) severely limits their use in applications where film opticals are important. The invention LLDPEs with their improved opticals (haze <10 and gloss >70) significantly broaden the application areas.

When fabricated into films, the films exhibit dart impact properties as measured by ASTM D-1709, Method A. For example, the films of the present invention exhibit superior dart drop over the films prepared with such previously-known catalysts. Films of the invention exhibit Dart Drop Impact values as measured by ASTM D-1709 from 100 to 2000, preferably from 150 to 1500. The most preferred films exhibit densities of .902 to .918 and dart drops of greater than 800, generally from 800 to 1500, and up to a measurement which characterizes the product as unbreakable, e.g., a dart drop of 2000.

The above properties are for a 1 mil film made under a standard fabricating condition outlined in the Examples, on a 3/4 inch Brabender extruder, 2-1/2" Brampton Film Extruder or a 3-1/2" Glouster Film Extruder. It is apparent to those familiar to the field that the film properties may be further modified by optimizing the fabricating conditions or by addition of LDPE or nucleating agents. Fabrication of the Products

The products of the invention are produced by an olefin polymerization. The monomers used in the polymerization are ethylene and C₃-C₁₀ alpha-olefins. Preferably, the products are copolymers which contain at least 80 wt.% ethylene units. The comonomers used with the ethylene in the present invention preferably contain 3 to 8 carbon atoms. Suitable alpha olefins include propylene, butene-1, pentene-1, hexene-1, 4- methylpentene-1, heptene-1 and octene-1. Preferably, the alpha-olefin co onomer is 1- butene, 1-hexene, and 1- octene. The most preferred alpha olefin is hexene-1. Thus, copolymers having two monomeric units are possible as well as terpolymers having three monomeric units. Particular examples of such polymers include ethylene/1-butene copolymers, ethylene/1- hexene copolymers, ethylene/4-methyl-l-pentene copolymers, ethylene/1-butene/l-hexene terpolymers, ethylene/propylene/1- hexene terpolymers and ethylene/propylene/1-butene terpolymers. Hydrogen may be used as a chain transfer agent in the polymerization reaction of the present invention. Any gas inert to the catalyst and reactants can also be present in the gas stream.

These products are prepared in the presence of a unique catalyst, described below, preferably under either slurry or more preferably under fluid bed gas phase catalytic polymerization conditions described below. When made in the gas phase fluid bed process, on pilot plant scale, the product is dry and solvent-free and comprises spherical , non-porous particles, which has an average particle size of 0.015 to 0.045 inches and a settled bulk density of from 25 to 36 lb/ft³. Moreover, under these conditions, the copolymer produced is linear without long chain branching. The Catalyst

The catalyst compositions employed to produce resins and films of the present invention contain one transition metal in the form of a metallocene which has an activity of at least 2,000 g polymer/g catalyst or 1,000 kg polymer/g transition metal .

The catalysts comprise a carrier, an aluminoxane and at least one metallocene. The carrier material is a solid, particulate, porous, inorganic or organic materials, but preferably inorganic material, such as an oxide of silicon and/or of aluminum. The carrier material is used in the form of a dry powder having an average particle size of from 1 micron to 250 microns, preferably from 10 microns to 150 microns. If necessary, the treated carrier material may be sieved to insure that the particles have an average particle size of preferably less than 150 microns. This is highly desirable in forming narrow molecular weight LLDPE, to reduce gels. The surface area of the carrier is at least 3 square meters per gram (m²/gm) , and preferably at least 50 m²/gm up to 350 m²/gm. When the carrier is silica, it is heated to preferably 100°C to 850°C and most preferably at 250°C. The carrier material must have at least some active hydroxyl (OH) groups to produce the catalyst composition of this invention.

In the most preferred embodiment, the carrier is silica which, prior to the use thereof in the first catalyst synthesis step, has been dehydrated by fluidizing it with nitrogen and heating at 250°C for about 4 hours to achieve a surface hydroxyl group concentration of 1.8 millimoles per gram (mmols/gm) . The silica of the most preferred embodiment is a high surface area, amorphous silica (surface area = 300 m²/gm; pore volume of 1.65 cm³/gm) , and it is a material marketed under the tradenames of Davison 952-1836, Davison 952 or Davison 955 by the Davison Chemical Division of W. R. Grace and Company. To form the catalysts, all catalyst precursor components can be dissolved with aluminoxane and reacted with a carrier. The carrier material is reacted with an aluminoxane solution, preferably methylaluminoxane, in a process described below. The class of alu inoxanes comprises oligomeric linear and/or cyclic alkylalu inoxanes represented by the formula:

R-(Al(R)-0)_n-AlR₂ for oligomeric, linear aluminoxanes and (-Al(R)-0-)_m for oligomeric cyclic aluminoxane wherein n is 1-40, preferably 10-20, m is 3-40, preferably 3- 20 and R is a Cx-Cg alkyl group and preferably methyl. Methylaluminoxane (MAO) is a mixture of oligomers with a very wide distribution of molecular weights and usually with an average molecular weight of 1000. MAO is typically kept in solution in toluene.

In a previously preferred embodiment, of aluminoxane incorporation into the carrier, one of the controlling factors in the aluminoxane incorporation into the carrier material during catalyst synthesis is the pore volume of the silica. In that previously preferred embodiment, the process of impregnating the carrier material is by infusion of the aluminoxane solution, without forming a slurry of the carrier material, such as silica, in the aluminoxane solution. The volume of the solution of the aluminoxane is sufficient to fill the pores of the carrier material without forming a slurry in which the volume of the solution exceeds the pore volume of the silica; accordingly and preferably, the maximum volume of the aluminoxane solution is and does not exceed the total pore volume of the carrier material sample. [It has been recently discovered that up to 30% excess of solvent volume based on the silica pores can be used without producing a silica slurry during impregnation. ] That maximum volume of the aluminoxane solution insures that no slurry of silica is formed. Accordingly, if the pore volume of the carrier material is 1.65cm³/g, then the volume of aluminoxane will be equal to or less than 1.65 cm³/gram of carrier material. As a result of this proviso, the impregnated carrier material will appear dry immediately following impregnation although the pores of the carrier will be filled with inter alia solvent. Solvent may be removed from the aluminoxane impregnated pores of the carrier material by heating and/or under a positive pressure induced by an inert gas, such as nitrogen. If employed, the conditions in this step are controlled to reduce, if not to eliminate, agglomeration of impregnated carrier particles and/or crosslinking of the aluminoxane. In this step, solvent can be removed by evaporation effected at relatively low elevated temperatures of above 40^CC and below 50°C. Although solvent can be removed by evaporation at relatively higher temperatures than that defined by the range above 40°C and below 50°C, very short heating times schedules must be employed.

In a preferred embodiment, the metallocene is added to the solution of the aluminoxane prior to reacting the carrier with the solution. Again the maximum volume of the aluminoxane solution also including the metallocene is the total pore volume of the carrier material sample. The mole ratio of aluminoxane provided aluminum, expressed as Al, to metallocene metal expressed as M (e.g. Zr) , ranges from 50 to 500, preferably 75 to 300, and most preferably 100 to 200. An added advantage of the present invention is that this Al:Zr ratio can be directly controlled. In a preferred embodiment the aluminoxane and metallocene compound are mixed together at a temperature of 20°C to 80°C, for 0.1 to 6.0 hours, prior to reaction with the carrier. The solvent for the metallocene and aluminoxane can be appropriate solvents, such as aromatic hydrocarbons, halogenated hydrocarbon or halogenated aromatic hydrocarbons, preferably toluene.

In a more recent preferred embodiment for silica impregnation of the alu oxane or alumonoxane activated metallocene, the solution of alumoxane in an aromatic or halogenated solvent is dispersed in an aliphatic solvent, to form a slurry of the silica. Accordingly, although the alumoxane solvent volume is insufficient to form a slurry, together with the aliphatic solvent a slurry will be formed. This modification tends to enhance dispersion of metals throughout the catalyst carrier.

The metallocene compound has the formula Cp„,MA_nB_p in which Cp is an unsubstituted or substituted cyclopentadienyl group, M is zirconium or hafnium and A and B belong to the group including a halogen atom, hydrogen or an alkyl group. In the above formula of the metallocene compound, the preferred transition metal atom M is zirconium. In the above formula of the metallocene compound, the Cp group is an unsubstituted, a mono- or a polysubstituted cyclopentadienyl group. The substituents on the cyclopentadienyl group can be preferably straight-chain or branched Ci-Cg alkyl groups. The cyclopentadienyl group can be also a part of a bicyclic or a tricyclic moiety such as indenyl, tetrahydroindenyl , fluorenyl or a partially hydrogenated fluorenyl group, as well as a part of a substituted bicyclic or tricyclic moiety. In the case when m in the above formula of the metallocene compound is equal to 2, the cyclopentadienyl groups can be also bridged by polymethylene or dialkylsilane groups, such as -CH₂-, -CH₂-CH₂-, -CR'R"- and -CR'R"-CR^,R"- where R¹ and R" are short alkyl groups or hydrogen, -Si(CH₃)₂-, Si(CH₃)₂-CH₂-CH₂-Si (CH₃)₂- and similar bridge groups. If the A and B substituents in the above formula of the metallocene compound are halogen atoms, they belong to the group of fluorine, chlorine, bromine or iodine. If the substituents A and B in the above formula of the metallocene compound are alkyl or aromatic groups, they are preferably straight-chain or branched Ci-Cβ alkyl groups, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, n-pentyl, n-hexyl or n-octyl.

Suitable metallocene compounds include bis (cyclopentadienyl) metal dihalides, bis (cyclopentadienyl) metal hydridohalides, bis (cyclopentadienyl) metal monoalkyl monohalides, bis (cyclopentadienyl) metal dialkyls and bis (indenyl) metal dihalides wherein the metal is titanium, zirconium or hafnium, halide groups are preferably chlorine and the alkyl groups are Cx-Cg alkyls. Illustrative, but non-limiting examples of metallocenes include bis (cyclopentadienyl) zirconium dichloride, bis (cyclopentadienyl) hafnium dichloride, bis (cyclopentadienyl) zirconium dimethyl, bis (cyclopentadienyl) hafnium dimethyl, bis (cyclopentadienyl) zirconium hydridochloride, bis (cyclopentadienyl) hafnium hydridochloride, bis (pentamethylcyclopentadienyl) zirconium dichloride, bis (penta ethylcyclopentadienyl) hafnium dichloride, bis(n- butylcyclopentadienyl) zirconium dichloride, bis(iso- butylcyclopentadienyl) zirconium dichloride, bis(dimethylcyclopentadienyl) zircomium dichloride, cyclopentadienyl-zirconium trichloride, bis (indenyl) zirconium dichloride, bis (4, 5, 6,7-tetrahydro-l-indenyl) zirconium dichloride, and ethylene- [bis (4 , 5, 6, 7-tetrahydro-l-indenyl) ] zirconium dichloride. The metallocene compounds utilized within the embodiment of this art can be used as crystalline solids, as solutions in aromatic hydrocarbons or in a supported form. The catalyst comprising a metallocene compound and an aluminoxane in particulate form is fed to the fluid bed reactor for gas phase polymerizations and copolymerizations of ethylene and higher alpha olefins. The Process Conditions

When polymerization is undertaken in the gas phase, fluid bed, it is essential to operate the fluid bed reactor at a temperature below the sintering temperature of the polymer particles. To insure that sintering will not occur, operating temperatures below the sintering temperature are desired. For the production of ethylene copolymers in the process of the present invention an operating temperature of 60°C to 115°C is preferred, and a temperature of 75°C to 95°C is most preferred. In accordance with the invention of copending Serial No. 08/154,069, filed November 18, 1993, polymerizations (or copolymerizations) catalyzed by the above-described metallocene catalysts are undertaken to decrease MI of the product by increasing polymerization temperatures and to increase MI of the product by decreasing polymerization temperature.

Moreover, in accordance with the invention of Serial No. 08/148,309 filed November 8, 1993, polymerizations (or copolymerizations) catalyzed by metallocene catalysts are undertaken to include introducing to the polymerization or copolymerization reactor a reagent (s) which decreases MI. The reagents which are used to decrease MI are electron donating in effect. A preferred group of reagents include oxygen and/or compounds containing oxygen atoms. Moreover, polymerizations (or copolymerizations) catalyzed by the metallocene catalysts are undertaken to include introducing to the polymerization (or copolymerization) reactor reagent (s) , which are electron withdrawing in effect, to increase MI.

The fluid bed reactor is operated at pressures of 150 to 350 psi, with operation at the higher pressures in such ranges favoring heat transfer since an increase in pressure increases the unit volume heat capacity of the gas. A "diluent" gas is employed with the comonomers. It is nonreactive under the conditions in the polymerization reactor. The diluent gas can be nitrogen, argon, helium, methane, ethane, and the like. In fluidized bed reactors, the superficial gas velocity of the gaseous reaction mixture through the bed must exceed the minimum flow required for fluidization, and preferably is at least 0.2 feet per second above the minimum flow. Ordinarily the superficial gas velocity does not exceed 5.0 feet per second, and most usually no more than 2.5 feet per second is sufficient. The feed stream of gaseous monomer, with or without inert gaseous diluents, is fed into the reactor at a space time yield of 2 to 10 pounds/hour/cubic foot of bed volume. The copolymer product produced in the presence of the preferred catalysts, described above, in a gas phase fluid bed process are linear and contain no long chain branching; the products so produced do not satisfy the equation Mw/Mn is less than or equal to I₁₀/I₂-4.63. A particularly desirable method for producing linear low density polyethylene polymers according to the present invention is in a single fluid bed reactor unit which is shown and is also described in U.S. Patent No. 4,481,301.

For film production, the products may contain any of various additives conventionally added to polymer compositions such as lubricants, microtalc, stabilizer, antioxidants, compatibilizers, pigments, etc. These reagents can be employed to stabilize the products against oxidation. For example, additive packages comprising 400-1200 ppm hindered phenol(s); 700-2000 ppm phosphites; 250 to 1000 ppm antistats and 250-1000 ppm stearates, for addition to the resin powders, can be used for pelletization. The polymers can be added directly to a blown film extruder, e.g., a Sterling extruder, to produce films having a thickness, for example, of 0.5 to 5 mils.

The following Examples further illustrate the essential features of the invention. However, it will be apparent to those skilled in the art that the specific reactants and reaction conditions used in the Examples do not limit the scope of the invention.

The properties of the polymers produced in the Examples were determined by the following test methods:

Density ASTM D-1505 - a plaque is made and conditioned for one hour at 100°C to approach equilibrium crystallinity. Measurement for density is then made in a density gradient column; reported as gms/cc.

Melt Index ASTM D-1238 - Condition E (MI) , I₂ Measured at 190°C - reported as grams per 10 minutes.

Melt Index, ASTM D-1238, measured at 190°C, using 10 kg

Iio weight

High Load ASTM D-1238 - Condition F Melt Index Measured at 10.5 times the weight used in (HLMI) , I₂₁ the melt index test above.

Ratio (MFR)

EXAMPLES

Example 1

This example is of the catalyst used to make products for films described later in the Examples.

Raw materials used in catalyst preparation included 504 g of Davison 952-1836 silica, 677 g of methylaluminoxane in toluene solution (30 wt.% MAO), 7.136 g of bis(n- butylcyclopentadienyl) zirconium dichloride. The steps of the catalyst preparation are: 1. Dehydrate the 952-1836 silica at 250°C for 4 hours using air to purge. Then purge with nitrogen on cooling.

2. Transfer the silica to a mix-vessel. 3. Add 7.136 g of bis (n-butylcyclopentadienyl) zirconium dichloride and 677 g of methylaluminoxane to a bottle. 4. Agitate the catalyst solution in the bottle until the metallocene dissolves in the MAO solution. 5. Transfer the MAO and metallocene solution into the mix-vessel containing the dehydrated 952-1836 silica slowly while agitating the silica bed vigorously to make sure that the catalyst solution is well dispersed into the silica bed. 6. After the addition, continue to agitate the catalyst for 1/2 hours.

7. Start drying the catalyst by purging with nitrogen for 5 hours at 45°C.

8. Sieve the catalyst to remove particles larger than 150 micron.

9. The catalyst has the following analysis: Yield = 767 g catalyst (from 500 g of silica)

Al = 9.95 wt.% Zr = 0.19 wt.% Example 2

To produce a polymer for low density film, 0.918 g/cc, 1 MI, 17 MFR, in a fluid bed gas phase reactor the following process conditions were employed. Process Conditions: Fluidization velocity 1.7 ft/sec

Residence time 2.5 hours

Temperature 84°C

Ethylene 220 psi

Hexene 3.6 psi Isopentane 50 psi

Carbon dioxide 3 ppm

Ash 200 to 250 ppm The catalyst was that of Example 1. Example 3

To produce a polymer for cast film of 0.918 g/cc density, 2.5 MI, 16 MFR, the following process conditions were employed:

Fluidization velocity 1.7 ft/sec Residence time 2.5 hours

Temperature 77.5°C

Ethylene 180 psi Hexene 3.6 psi

Isopentane 38 psi

Ash 100 ppm

The catalyst was that of Example 1. Example 4 A variety of resins were produced with the catalyst formulation described in example 1 and the process of example 2. The resins were characterized for their I₂ swell and compared to prior art metallocene resins. It is clearly shown that the Mobil resins have significantly higher swell (elasticity) compared to prior art resins. It is because of this high elasticity that the invention resins could be blown into film without encountering bubble instability problems. Example 5

A set of resins with the catalyst of example 1 and process similar to example 2 were characterized for their MWD using I₁₀/I₂ and Mw/Mn measurements. The I₁₀/I₂ values were compared to other metallocene resins. The results are summarized in the following table:

Table II

LLDPE In n/I, Characteristics

Sample. Density I₂ MEB I10ZI2 IιoZI₂-4 . 63 Mw/Mn B 0. 917 1. 2 16. 7 5. 58 0. 95 2 . 6

C 0. 904 0. 7 17 . 4 6. 07 1. 44 2 . 9

The invention Zr LLDPE resins showed a narrow MWD (Mw/Mn < 3.0) and gave values of I₁₀/I₂-4.63 ranged from 0.95-1.44 less than the 2.6-2.9 for Mw/Mn. In contrast, the resins of U.S. Patent No. 5,272,236 have an I₁₀/I₂ which is greater than the Mw/Mn of the same resin. Example 6 The swell characteristics of LLDPE copolymers made from catalyst described in Example 1 and process similar to Example 2 and 3 can be carefully controlled by selecting the proper levels of process modifier:

Table III

Effect of Modifier on resin Swell

Sample Modifier Density I₂ J-2-. Swell

D 0. 2 ppm 0₂ 0. 917 2 . 8 14

E none 0. 917 2 . 8 6 . 7

The presence of the process modifiers contributes the high elasticity (I₂ swell) of metallocene resins of the application. Example 7

This example relates to a slurry product which can be used to form cast film. 493 g of silica (Davison 955) was dehydrated at 250°C.

6.986 g of bis (n-butylcyclopentadienyl) zirconium dichloride was dissolved in 670 g of methylalumoxane in toluene which contained 13.7 wt.% Al. The zirconcene solution was then added to the silica slowly while agitating the silica bed vigorously. The reaction between the methylalumoxane and the silica is highly exothermic and the reaction temperature must be controlled carefully. After the addition, the powder was dried under flowing nitrogen at 45°C for 5 hours, and was sieved to remove any particles larger than 150 microns. The catalyst was designated RV-92-110 and contained 9.2 wt.% Al and 0.17 wt.% Zr.

This catalyst was evaluated in either a 2.5 liter or a 4 gallon slurry reactor. Ethylene, hexene, and hydrogen partial pressure were adjusted to give the products with the corresponding hexene content and melt index. Catalyst was added to the reactor using high pressure ethylene. The polymer yield, the reaction temperature, the hexene content in the polymer, and the melt index of the products are listed in the following table.

Because of the high bulk density (about 0.37 to 0.44 g/cc) and the granular morphology of these resins, very high polymer contents per liquid volume can be produced in these slurry reactor. The solid/liquid ratios in the above table represent the minimum level achieved during each of the polymerization run. Even higher solid polymer to liquid ratio can be achieved by letting the polymerization reaction to continue for longer period. Example 8

Davison 955 silica was dehydrated at 250°C. 10.0 grams of this dehydrated silica were added to a 300 ml flask; and 50 cc of heptane were added to the silica to form a slurry mixture. In a separate bottle, 0.142 grams of bis(n- butylcyclopentadienyl) zirconium dichloride was dissolved in 13.41 grams of a 30 wt.% methylalumoxane solution in toluene. This solution was added slowly to the silica over a period of 30 minutes. The slurry mixture was then dried at 45 °C with nitrogen purge for 16 hours. 13.7 grams of free flowing catalyst were obtained and analyzed to contain 13.2 wt.% Al and 0.23 wt.% Zr. Example 9 (comparative example)

The same procedures was used as in example 1 except no silica was used. 3.235 grams of solid were collected and analyzed to contain 32.8 wt.% Al and 0.65 wt.% Zr. Example 10

Davison 955 silica was dehydrated at 250°C. 20.07 grams of this dehydrated silica were added to a 500 ml flask with an addition funnel and equipped with a pedal stirrer. 100 cc isohexane were added through the addition funnel into the silica to form a slurry mixture. In a separate bottle, 0.284 grams of bis(n-butylcyclopentadienyl) zirconium dichloride was dissolved in 32.08 cc of a 30 wt.% methylalumoxane solution in toluene. This solution was added slowly over a period of 30 minutes. The slurry was mixed thoroughly, and 20 cc of the clear solvent were decanted from the slurry for analysis of Al and Zr. The slurry mixture was then dried at 45 °C with nitrogen purge for 16 hours. 27.8 grams of free flowing catalyst were collected and analyzed to contain 12.0 wt.% Al and 0.22 wt.% Zr.

Analysis of the 20 cc solvent decanted from the slurry mixture was shown to contain 3.30 mg of Al and 0.060 g of Zr. Calculation showed that 99.4% of the total Al from the MAO reacted with the silica, and only 0.56% of the total Al from MAO remained in the solvent. Similarly, 99.4% of the total Zr from metallocene was in the silica and 0.60% of the total Zr from metallocene remained in the solvent phase. Example 11

Davison 955 silica was dehydrated at 250°C. 20.162 grams of this dehydrated silica were added to a 500 ml flask equipped with an addition funnel and a pedal stirrer. 100 cc isohexane and 0.5 cc of 15 wt.% trimethylaluminum in heptane were added into the addition funnel. This solution was then added to the silica to form a slurry mixture. In a separate bottle, 0.473 grams bis (n-butylcyclopentadienyl) zirconium dichloride was dissolved in 32.2 cc of a 30 wt.% methylalumoxane solution in toluene. This solution was then added slowly over a period of 30 minutes. The slurry was mixed thoroughly for 30 minutes and 20 cc of the clear solvent was decanted from the slurry for Al and Zr analysis. The slurry mixture was then dried at 45 °C with nitrogen purge for 16 hours. 27.412 grams of free flowing catalyst were collected and analyzed to contain 11.8 wt.% Al and 0.35 wt.% Zr.

Analysis of the 20 cc solvent decanted from the slurry mixture was shown to contain 0.53 mg of Al and 0.014 mg of Zr. Calculation showed that 99.9% of the total Al from the MAO reacted with the silica and 0.09% of the total Al from MAO remained in the solvent. Similarly, 99.9% of the total Zr from metallocene were inside the silica pore and 0.09% of the total Zr from metallocene remained in the solvent phase. Example 12 (Comparative example)

Davison 955 silica was dehydrated at 600°C. 15.63 grams of this dehydrated silica were added to a 500 ml flask equipped with an addition funnel and a pedal stirrer. 75 cc isohexane and 0.4 cc of 15 wt.% trimethylaluminum in heptane were added into the addition funnel. This solution was then added to the silica to form a slurry mixture. In a separate bottle, 0.367 grams bis (n-butylcyclopentadienyl) zirconium dichloride was dissolved in 22.74 cc of a 30 wt.% methylalumoxane solution in toluene. This solution was then added slowly over a period of 30 minutes. The slurry was mixed thoroughly for 30 minutes and 15 cc of solvent were then decanted from the slurry for Al and Zr analysis. The solvent phase was cloudy and white in color, indicative of excessive amount of methylalumoxane that did not react with the silica. The slurry mixture was then dried at 45 °C with nitrogen purge for 16 hours. 20.5 grams of free flowing powder was collected and analyzed to contain 11.4 wt.% Al and 0.32 wt.% Zr.

Analysis of the 15 cc solvent decanted from the slurry mixture was shown to contain 41.2 mg of Al and 1.27 mg of Zr. Calculation showed that 90.7% of the total Al from the MAO reacted with the silica and 9.29% of the total Al from MAO remained in the solvent. Similarly, 89.8% of the total Zr from metallocene were inside the silica pore and 10.23% of the total Zr from metallocene remained in the solvent phase. Example 13

Davison 955 silica was dehydrated at 600°C. 20.06 grams of this dehydrated silica were added to a 500 ml flask with an addition funnel and a pedal stirrer attached. 100 cc isohexane and 0.5 cc of 15 wt.% trimethylaluminum in heptane were added to the addition funnel. This solution was then added to the silica to form a slurry mixture. In a separate bottle, 0.325 grams bis(n-butylcyclopentadienyl) zirconium dichloride was dissolved in 20.84 cc of a 30 wt.% methylalumoxane solution in toluene and additional 7 cc of toluene were added. This solution was then added slowly over a period of 30 minutes to the silica. The slurry was then thoroughly mixed for 30 minutes and 20 cc of solvent were then decanted from the slurry for Al and Zr analysis. The slurry mixture was then dried at 45 °C with nitrogen purge for 16 hours. 26.0 grams of free flowing powder were collected and analyzed to contain 9.51 wt.% Al and 0.27 wt.% Zr. Analysis of the 20 cc solvent decanted from the slurry mixture was shown to contain 1.62 mg of Al and 0.024 mg of Zr. Calculation showed that 99.6% of the total Al from the MAO reacted with the silica and 0.37% of the total Al from MAO remained in the solvent. Similarly, 99.8% of the total Zr from metallocene were inside the silica pore and 0.20% of the total Zr from metallocene remained in the solvent phase. Example 14

Same procedure was used as example 6 except that 16.1 cc of 30 wt.% methylalumoxane and 0.236 gram of bis(n- butylcyclopenta dienyl) zirconium dichloride was used. 23.985 grams of a free flowing powder catalyst were collected and analyzed to contain 7.36 wt.% Al and 0.22 wt.% Zr.

Analysis of the 20 cc solvent decanted from the slurry mixture was shown to contain 0.13 mg of Al and 0.0037 mg of Zr. Calculation showed that 99.96% of the total Al from the

MAO reacted with the silica and 0.04% of the total Al from MAO remained in the solvent. Similarly, 99.9% of the total Zr from metallocene were inside the silica pore and 0.04% of the total Zr from metallocene remained in the solvent phase. Example 15

Silica was dehydrated at 250°C. 5.00 grams of this silica were added to a 100 ml Schlenk flask equipped with a magnetic stirrer. 25 cc of isohexane were transferred into the flask to form a slurry mixture. This slurry mixture was chilled in an ice bath at 0°C. In a separate bottle, 0.047 grams of bis(n-butylcyclopentadienyl) zirconium dichloride was dissolved in 7.7 cc of 30 wt.% methylalumoxane in toluene. This solution was then transferred slowly into the silica slurry over a period of 5 minutes while stirring vigorously. The slurry mixture was then dried at 45 °C with nitrogen purge for 4 hours. 6.3 grams of free flowing catalyst were obtained and analyzed to contain 11.9 wt.% Al and 0.15 wt.% Zr. Example 16 Silica was dehydrated at 250°C. 5.0 gram of this silica were added to a 100 ml Schlenk flask equipped with a magnetic stirrer. 25 cc of isohexane were transferred into the flask to form a slurry mixture. In a separate bottle, 0.047 grams of bis(n-butylcyclopentadienyl) zirconium dichloride was dissolved in 5.5 cc of 30 wt.% methylalumoxane in toluene. This solution was then transferred slowly into the silica slurry over a period of 10 minutes with vigorous stirring. The slurry mixture was then dried at 45°C with nitrogen purge for 4 hours. 6.4 grams of free flowing dry catalyst were collected and analyzed to contain 10.3 wt.% Al and 0.16 wt.% Zr. Example 17

Silica was dehydrated at 600°C. 5.0 grams of this silica were weighed into a 100 ml Schlenk flask equipped with a magnetic stirrer. 25 cc of isohexane were transferred into the flask to form a slurry mixture. In a separate bottle, 0.047 gram of bis (n-butylcyclopentadienyl) zirconium dichloride was dissolved in 5.5 cc of 30 wt.% methylaluminoxane in toluene and additional 1.9 cc of toluene was added. This solution was then transferred slowly into the silica slurry over a period of 10 minutes with vigorous stirring. The slurry mixture was then stirred for an additional 30 minutes before the clear solvent layer was decanted off. The remaining mixture was then dried at 45°C with nitrogen purge for 16 hours. 6.3 grams of free flowing dry catalyst were obtained and analyzed to contain 10.4 wt.% Al and 0.18 wt.% Zr.

Claims

CJ ΔIM≤:

1. A cast film, exhibiting a haze value as measured by ASTM D-1003 of less than about 20; a dart drop value measured by ASTM D-1709, Method A, and ranging from 100 to 2000; comprising a linear copolymer of ethylene and an alpha olefin of 3 to 10 carbon atoms, which has a density ranging from

0.900 to 0.929; MFR of 15 to 25; Mw/Mn of about 2.5 to about 3.0; and a melting point of 95 to 135°C; and which comprises a zirconium content of 0.1 to 2 ppm Zr.

2. The cast film of Claim 1, wherein the copolymer comprises residues of a supported catalyst.

3. The cast film of Claim 1, wherein the linear copolymer comprises hexene-1.

4. The cast film of Claim 1, wherein the MFR ratio is 15 to 20.

5. A gas phase produced composition, in the as- synthesized form, which is dry, solvent-free, and is particulate, particles of which have an average particle size of 0.015 to 0.035 inches in the as-synthesized form; which composition comprises a linear copolymer of ethylene and an alpha olefin of 3 to 10 carbon atoms and comprises catalyst residues comprising a zirconium content of 0.1 to 2 ppm Zr (as zirconium content); and wherein the linear copolymer has a density of 0.900 to 0.29, and wherein the copolymer exhibits a Mw/Mn of about 2.5 to 3.0.

6. The composition of Claim 5, wherein the copolymer exhibits MFR ratio of 15 to 20.

7. A polyolefin, in the as-synthesized form in a slurry polymerization, which is particulate, particles of which have an average particle size of 0.015 to 0.035 inches in the as- synthesized form; which composition comprises a linear copolymer of ethylene and at least one alpha olefin selected from the group consisting of 1-butene, 1-hexene, 1-octene and 4- methylpentene-1 and contains catalyst residues of a supported catalyst and thus comprises 0.1 to 2 ppm Zr (as zirconium content) ; and wherein the linear copolymer has a density of 0.900 to 0.29, and exhibits a Mw/Mn of 2.5 to 3.0.

8. The composition of Claim 7, wherein the copolymer exhibits MFR of 15 to 20.

9. A blown film, a dart drop value measured by ASTM D- 1709, Method A, and ranging from 100 to 2000, comprising a linear copolymer of ethylene and an alpha olefin of 3 to 10 carbon atoms, which has a density ranging from 0.900 to 0.929; MFR of 15 to 25; Mw/Mn of 2.5 to about 3.0; and a melting point of 95 to 135°C and which comprises catalyst residues of a supported catalyst and comprises a zirconium content of 0.1 to 2 ppm Zr.

10. The blown film of Claim 9, wherein the linear copolymer comprises hexene-1.

11. The blown film of Claim 9, wherein the MFR ratio ranges from 15 to 20.

12. The blown film of Claim 9 , wherein the dart drop value ranges from greater than 800 up to 2000.

13. The blown film of Claim 10, wherein the dart drop value ranges from greater than 800 up to 2000.