MXPA98001244A - Films that include catalyticed polyethylene with metaloc - Google Patents

Abstract

A self-supporting film having one or more layers is described wherein at least one layer has a percentage of optical clarity of less than 17.8 and the polymer of this layer consists essentially of a polyethylene having a density of at least 0.925 grams per cc. , a molecular weight distribution of not more than 4, optionally containing a fluoroelastomer, and methods for making such a film

Description

FILMS THAT INCLUDE CATALYTIC POLYETHYLENE WITH METALOCENE Field of the Invention This invention relates to a film of polymers produced from a monomer consisting essentially of ethylene. In another aspect, the present invention relates to a 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 that have a wide range of thicknesses. Examples would include thicknesses in the range of 0.05 to approximately 40 mils, more typically approximately 0.25 to approximately 5 mils (1 thousand equals 1/1000 of an inch). The films can be made using a variety of techniques such as molding, blowing and extrusion.

REF .: 26810 Good clarity in blown polyethylene film as indicated by low Optical Clarity and High Brightness has been observed in the past that is dependent on various factors. Typically, Optical Clarity increases (and Brightness decreases) as the density and molecular weight distribution of the polymer increases. Also, it has been observed that typically the roughness of the surface increases as the molecular weight distribution and density increase. The smoothness of the film, on the other hand, which is often a desired property of the blown film dependent on the current application, has been observed to increase as the density increases. Therefore, there has usually been a relationship between clarity and smoothness of the film in a polyethylene blown film. Frequently in the formation of multilayer films, a base layer of high density polyethylene, high molecular weight or high density polyethylene, medium molecular weight has been used to provide strength and a layer of low density polyethylene has been provided. or low density, linear polyethylene to provide other properties. However, it has often been observed that the layers of low density polyethylene and linear low density polyethylene are viscous and sticky unless antiblocking agents are included. However, such antiblock agents generally also have an adverse effect on clarity and physical properties. An object of the present invention is to provide a method for producing polyethylene polymer films having a density of at least about 0.925 g / cc having a good balance of processing, physical and optical properties. Other aspects, objectives and advantages of the present invention will be apparent from the following comments.

Brief Description of the Invention In accordance with the present invention, there is provided an unusually clear self-supporting film comprising at least one layer having a percent optical clarity of less than 17.8 where the layer polymer consists essentially of polyethylene having a density of at least about 0.925 g / cc and a molecular weight distribution of not more than 4. The reduced molecular weight polyethylene having a density of at least about 0.925 g / cc is preferably selected from polyethylenes which can be forming into a 1 mil blown film having a percent optical clarity of less than 17.8, or more preferably no more than 10. In a preferred embodiment, the film has only one layer of polymer consisting essentially of polyethylene which has 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 in m-form s preferably about 1.5 to about 3.5. In another preferred embodiment, the film is multilayer and at least one layer has a percentage of optical clarity of less than 17.8, more preferably one percent of optical clarity of less than 10, and comprises polyethylene having a density of at least 0.925 g / cc and a molecular weight distribution of 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-type process, ie, a particle form wherein the polymer is formed under conditions such that the polymer is produced in the form of solid particles that can be easily separated of the polymerization diluent, liquid. In particle form polymerizations of this kind 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 the production of such relatively insoluble catalyst systems. Some examples are shown in U.S. Patent Nos. 5,354,721; 5,411,925 and 5, 414, 180. A particularly preferred type of solid, relatively insoluble 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, in general containing 2 to 8 carbon atoms. In a particularly preferred embodiment, the solid catalyst system is obtained by the polymerization of ethylene in the presence of a liquid alkane diluent under thick slurry polymerization conditions using a special type of metallocene-based catalyst system. The catalytic system is a solid catalyst prepared by (a) the combination of 5- (9-fluorenyl) -5- (cyclopentadienyl) -hexen-1-zirconium dichloride and methyl aluminoxane in a liquid, (b) the prepolymerization of ethylene in the resulting liquid; and (c) the separation of the catalytic, prepolymerized, solid system resulting from the liquid. It is preferred that the liquid employed in step (a) is an organic liquid in which the methyl aluminoxane is at least partially soluble. Preferably, some aromatic solvents are used 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 reaction product between the metallocene and the aluminoxane, provide the desired polymerization viscosity for the polymerization and allow good mixing. During mixing, the temperature in would preferably be maintained below that which would cause the metallocene to decompose. Typically, the temperature would be in the range of about -50 ° C to about 150 ° C. Preferably, the metallocene, the aluminoxane and the liquid diluent are combined at room temperature, i.e., about 10 ° C to 30 ° C. The reaction between the aluminoxane and the metallocene is relatively fast. The reaction rate may vary over a wide range, however, it is generally desired that these are contacted for a time in the range of about 1 minute to about 1 hour. It is also within the scope of the invention to carry out step (a) in the presence of a particulate solid. Any number of particulate solids can be used. Typically, this solid would be any inorganic solid that does not interfere with the final, desired results. Examples include porous supports such as talc, inorganic oxides, resins for supporting the 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 used, it is generally desirable for the solid to be completely dehydrated before use. Preferentially, dehydrates to contain less than 1 percent loss in ignition. The thermal dehydration can be carried out in a vacuum or while purging with an inert, dry gas such as nitrogen at a temperature of from about 20 ° C to about 1000 ° C and preferably from about 300 ° C to about 870 ° C. C. Pressure considerations are not observed as critical. The duration of the heat treatment may be from about 1 to about 24 hours as necessary. Dehydration can also be performed by holding the solid to a chemical treatment in order to remove the water and reduce the concentration of hydroxyl groups on the surface. The chemical treatment in general is capable of converting all the hydroxyl groups of water on the oxide surface to relatively inert species. Useful chemical agents are, for example, carbon monoxide, carbonyl sulphide, trimethylaluminum, magnesium chloride of ethyl, chloro silanes such as SiCl 4, disilazane, trimethyl-chlorosilane, dimethylamino-trimethylsilane, and the like. The amount of aluminoxane and metallocene used in the formation of a catalyst system, liquid for prepolymerization can vary over a wide range. However, typically, the molar ratio of the aluminum in the aluminoxane to the metallocene transition metal 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. If a particulate solid, i.e. silica, is used, it is generally 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 catalyst system, liquid, which can be a solution, a slurry, or gel in a liquid. A wide range of olefins can be used for polymerization. However, typically, the prepolymerization will be conducted using an olefme, 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 may be useful for prepolymerization. The use of a higher alpha-olefin, such as 1-butene, with ethylene is believed to increase the amount of copolymerization that occurs between the olefin monomer and the olefinically unsaturated portion of the metallocene. The prepolymerization can be conducted under relatively moderate conditions. Typically, this would involve the use of low olefin pressures and relatively low temperatures, designed to prevent decomposition of the site resulting from high localized heat concentrations. Prepolymerization typically occurs at temperatures in the range of about -15 ° C to about + 15 ° C, more typically in the range of about 0 ° C to about + 30 ° C. The amount of prepolymer may be varied but would typically be in the range of about 1 to about 95 weight percent of the resulting solid, prepolymerized catalyst system, even more preferably, about 5 to about 80 weight percent. In general, it is desirable to carry out the prepolymerization to at least one point where substantially all of the metallocene is in the solid state rather than in the liquid state, since it maximizes the use of the metallocene.

After the prepolymerization, the resultant bristling solid prepoly catalyst is separated from the liquid reaction mixture. Various techniques known in the art can be used to carry out this step. For example, the material could be separated by filtration, decantation or vacuum evaporation. However, it is currently preferred not to adhere to vacuum evaporation since it is considered desirable to remove substantially all of the components soluble in the reaction product, liquid from the prepolymerization of the prepolymerized, solid catalyst, resulting before it is stored or used for the subsequent polymerization. After removing the solid from a liquid, the resulting solid is preferably washed with a hydrocarbon and dried using a high vacuum to remove substantially all liquids or other volatile components that could still be associated with the solid. Vacuum drying is preferably carried out under relatively moderate conditions, that is, temperatures below 100 ° C. More typically, the prepolymerized solid is dried by subjecting it to a high vacuum at a temperature of about 30 ° 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 vacuum drying. It is also within the scope of the present invention to add a particulate solid to the catalyst system, liquid after it has been formed and then carry out the prepolymerization in the presence of that solid. Another option is to add a particulate solid of the type mentioned above after the prepolymerization or after the prepolymerized, solid catalyst system of the liquid has been separated. This catalytic, prepolymerized, solid, resulting system is capable of preparing ethylene polymers having a fairly wide range of densities. Typically, when 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, in general, they contain about 3 to about 10 carbon atoms. carbon, examples of which include aliphatic hydrocarbons such as 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene and the like. The prepolymerized, solid catalytic system can be employed using slurry polymerization conditions. Typically, the polymerization temperature would be selected to provide thick slurry polymerization conditions in the particular, selected liquid diluent. Typically, the temperature would be in the range of about 20 ° C to about 130 ° C. With isobutane as the liquid diluent, temperatures in the range of about 60 ° C to about 110 ° C have been found desirable. In order to produce polymers for film applications, it is generally desirable to produce a polymer having a melt index of less than 5. This can be done by adjusting the molar ratio of hydrogen to ethylene in the polymerization process, changing the temperature of the polymer. reactor and / or change the ethylene concentration. When the polymerization is carried out in a thick, continuous loop suspension process, in general, it is desirable to include a small amount of an antistatic agent in the reaction mixture. An example of such an antistatic agent is the material sold by DuPont Chemical Co. under the trade name Stadis 450. In a polymerization of the particle form type, the type described above of the catalyst system is capable of producing polyethylene homopolymers and copolymers having densities of 0.925 g / cm or greater with molecular weight distributions of no more than 4 that are useful for making films that have a percent optical clarity 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 this manner have low flux activation energies, ie, below about 25 J / mol, and a critical shear stress at the beginning of the melt fracture of less than 4 x 106 dynes / cm2. 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 for determining long chain branching is described in Randal, Rev. Ma cromol. Chem. Phys. , C29 (243), 285 -29 7. Ethylene polymers produced in a particle-like process with that catalyst system are also believed to have a very uniform distribution of short-chain branches at both the intramolecular level (monomer sequence distributions along the chain) and at intermolecular level (monomer distribution between polymer chains of different molecular weights). The hexene-hexene homopolymers and copolymers produced with such catalysts are particularly unusual in that they contain ethylene branching even when a butene comonomer was not used in the polymerization. It is theorized that butene is formed in situ in the polymerization and that such results in a very uniform distribution of the ethylene branches. The shear 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 stabilization packages suitable in the art are known. The stabilizers can be incorporated into the polymer during a pelletizing step or by the reextrusion of pellets previously produced. An example of a stabilizer would be the Irganox® 1010 antioxidant which is believed to be an hindered or opposing polyphenol stabilizer containing tetracis [3- (3,5-di-tert-butyl-4-hydroxy-phenylpropionate methylene)] methane produced by Ciba-Geigy Corporation. Another example is the PEP-Q additive which is a product of Sandoz Chemical, the primary ingredient of which is believed to be tetracis (-2,4-di-tert-butyl-phenyl) -4,4'-biphenyl phosphonite. Other common stabilizer additives include calcium stearate or zinc stearate. Still other commonly used stabilizers include the antioxidant Ultranox 626 which is a product of GE, the primary ingredient of which is believed to be diphosphite of bis (2, -di-t-butylphenyl) -pentaerythritol, and the antioxidant Ultranox 627A which is believed to be Ultranox 626 containing about 7 weight percent of a magnesium aluminum hydrocarbonate. Such stabilizer additives can be employed, in general, in any suitable amount. The amounts used in general are the same as they have been used for other polyethylene polymers. Frequently, the amounts for each additive is less than 0.2 weight percent based on the weight of the polymer. The molecular weight of the polyethylene used to make the inventive film can vary over a wide range. Typically, to form 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. In general, if the melt index of the polymer is less than about 1, it is often desirable to incorporate an amount that increases the processing of a fluoroelastomer processing aid. An example is the fluoroelastomer sold under the trade name Viton by E. I. DuPont de Nemours & amp;; 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 on 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 on the weight of the polyethylene. In some cases, the luoroelastomer is used in the form of a masterbatch in which the fluoroelastomer is dispersed in a polymer such as the copolymer of butene and ethylene LLDPE. An example of such material is the masterbatch, processing aid, Ampecet 10919 available from AMPACET Corp. In some applications it may be desirable to include in the polymer of one or more of the layers an anti-blocking agent, particularly for the Layers produced from polymers having a density less than 0.925 g / cc. In general, such materials are inorganic compounds. Some examples include mica, talc, silica, calcium carbonate and the like. A typical example would be displacement / antiblocking concentrate Ampacet 10430 available from AMPACET Corp.

By the use of the term "consisting essentially of" it is proposed that the polyethylene used to produce the inventive films may contain various other additives normally included in polyethylenes, such as heat stabilizers, climate stabilizers, lubricants, etc., in amounts not they unduly impact the objectives of the present invention. It is also proposed that this term includes mixing the required reduced molecular weight polyethylene having a density of at least about 0.925 with other polymers while the amount of the other polymers does not unduly decrease the beneficial properties of the required polyethylene, i.e. Low optical clarity properties and good handling. In general, the polyethylene required is greater than about 50 weight percent of the polymer, more typically at least 90 weight percent of the polymer, and even 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 an optical clarity 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. Such are considered to be Films can be produced by casting, blowing or extruding. It is also within the scope of the present invention to use a film layer of this kind to form a multilayer film. The polymers used in the other layers can be selected in general from any of the polymeric materials generally used in the production of films. In this way, the other necessary layers are not limited to the ethylene polymers but could contain other polymers such as propylene-butene copolymer, poly (1-butene), styrene-acrylonitrile resin, acrylonitrile-butadiene-styrene resin, polypropylene, ethylene vinyl acetate resin, polyvinyl chloride resin, poly (4-met il-1-pentene), and the like. Multiple layers can be formed using techniques generally known in the art, such as, for example co-extrusion. A particularly preferred example of a multilayer film includes a layer having an optical clarity percentage of less than 17.8 which comprises a polyethylene having a density in the range of about 0.925 to about 0.945 g / cc and a molecular weight distribution of not more than 4 and another layer comprising a second polyethylene having a molecular weight distribution greater than 4, more preferably greater than 6, and even more preferably greater than 10, such as polyethylenes produced using Phillips chrome or Ziegler-Natta type catalysts. For some applications it is also desirable for polyethylene with the broadest molecular weight distribution to have a higher density than polyethylene having the lowest 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 an optical clarity 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 distribution of molecular weight of no more than 4, 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 an optical clarity of less than 17.8 percent and consist essentially of polyethylene having a density in the range of about 0.925 to about 0.945 g / cc and a weight distribution molecular weight of at least 4, and an inner layer comprises polyethylene having a molecular weight distribution of at least 10 and a density of less than 0.93 g / cc, more preferably a density in the range of 0.91 to 0.929 g / cc with an HLMI in the range of about 12 to about 24 dg / min. The most preferred multilayer films are those in which the multilayer film itself has a percentage of optical clarity of less than 17.8, even more preferably a percentage of optical clarity of less than 10. In the film of three layers currently preferred, the outer layers each have a thickness in the range of about 5 to about 25 weight percent of the total thickness of the three-layer 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-layer film, with the polymer of that inner layer being a linear copolymer of low density of ethylene and 1- hexene produced using a Cr, Phillips catalyst in a particulate polymerization process, particularly a copolymer having a density in the range of about 0.91 to about 0.929 g / cc, an HLMI in the range of about 12 to 24 dg per minute and a molecular weight distribution greater than 10. It is also within the scope of the present multi-layer, inventive films to have a polyethylene layer having a wider molecular weight distribution and a lower density than polyethylene in the layer that has a percentage of optical clarity of less than 17.8, for example a layer could have a percentage of optical clarity of meno s of 17.8 and be composed of a polyethylene having a density of at least 0.925 g / cc and a 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 multilayer film in which a layer has a percentage of optical clarity of less than 17.8 where 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 broader molecular weight distribution and good clarity. In this case, the inventive polyethylene layer provides inflexibility that can not be provided by the low density polyethylene without decreasing the clarity of the lower density polyethylene much as would a polymer of similar density produced by a Phillips chromium catalyst or a catalyst of coordination containing titanium of the Ziegler-Natta type. A layer having a percentage of optical clarity of less than 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 the coordination catalysts, transition metal, conventional or Phillips chromium catalysts. If a lower melting temperature layer is desired, it may be advantageous for it 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 optical clarity of less than 17.8. In a particularly preferred embodiment, all polyethylene layers are polyethylenes produced using metallocene catalysts having molecular weight distributions of less than 4. Further understanding of the present invention and its objectives and advantages will be provided by the following examples.

EXAMPLES Example I A large batch of catalyst was prepared based on metallocene, particulate, solid. The preparation involves reacting the metallocene zirconium dichloride (but-3-enyl) (cyclopentadienyl) - (fluorenyl) (methyl) methane which is also known as zirconium dichloride of (5-cyclopentadenyl) (5-fluorenyl) hex- 1-ene with a 10 weight percent solution of methyl aluminoxane in toluene to give a soluble olefin polymerization catalyst system. Davison 948 silica was added, thermally dried and treated with trimethylaluminum, to the liquid catalyst system. To homogenize this system, the terminal unsaturated metallocene group was copolymerized with ethylene by adding ethylene to maintain a pressure in the reaction vessel at 0.211 to 0.281 kg / cm2 (3 to 4 psig) and stir while the temperature was maintained at approximately 20 ° C. After about 2 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 in 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 fume-free or vapor-free silica that had been thermally dried and treated with trimethylaluminum. The resulting solid metallocene catalyst system was then used in a continuous loop reactor, at the scale of an experimental station, under polymerization conditions of the slurry type. The raw materials were passed to the reactor through alumina drying beds before being sent to the reactor. The reactor was a circuit reactor, of stainless steel conduits. The circulation was achieved by an impeller inside the reactor. The concentrations of the reagents were monitored by gas analysis using two in-line gas chromatographs. The polymerizations were conducted in isobutane as a liquid diluent using varying amounts of ethylene and 1-hexane comonomer to obtain a number of polyethylene fine powder portions. Copolymers of ethylene and 1-hexene having densities ranging from 0.9179 to 0.9402 g / cc were produced using the catalyst system based on metallocene, solid. The polyethylene copolymers of various densities were composites 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 on the weight of the polymer. The resulting polymers were then evaluated for various physical properties and used in the production of films using a Sano blown film of 10.16 cm (4 inches) having a single screw extruder of 3.81 cm (1.5 inches). The nozzle for the film is a spiral mandrel nozzle with four inlet holes and is 10.16 cm (4 inches) in diameter. The nozzle had an air ring, protruding, mounted on it, which was used to cool and stabilize the extruded bubble. The film blowing parameters which are typical of linear low density polyethylene type processing conditions, which include a 0.15 cm (0.06 inch) nozzle opening, extruder body temperatures and the nozzle for the film set at 190 ° C, blowing ratio of 2.5: 1, without stems, ie, "extrusion in receptacle or insulated" at a film thickness of 1 mil. The rotation of the screw was adjusted to maintain the extrusion rate between 24,947 and 27,215 kg (55 and 60 pounds) per hour, so that the properties of the films thus obtained would be directly classified (ie, it is the same as or less very similar) with those obtained from the larger commercial scale equipment. For some of the runs of polyethylene copolymers were also made where the copolymer had been composed with 0.07 weight percent fluoropolymer FX-9613. As controls, films were also produced using the commercially available Dow 2945A copolymer, which is believed to be a linear, low density polyethylene copolymer produced using a titanium-based, metallocene-free catalyst system. Also, films were made using a copolymer produced by a Phillips chromium resin. Various characteristics of the polymer and the polymerization were characterized. Examples of characteristics determined in various cases include Optical Clarity (ASTM D-1003 using an XL-211 Hazeguard System from Garder / Neotec Instruments Division); density in grams / mL (ASTM D1505-68); Large Load Melt Index (HLMI) in polymer grams / 10 minutes at 190 ° C (ASTM D1238-86, Condition 190 / 21.6); Fusion index (MI) in polymer grams / 10 minutes a. 190 ° C (ASTM D1238-86, Condition 190 / 2.16); Response to the Cutting Effort (SR) determined by dividing the HLMI by the MI; molecular weights by size exclusion chromatography, ie weight average molecular weight referred to herein as Mw and number average molecular weight referred to herein as Mn; and Heterogeneity index (Hl) or molecular weight distribution (MWD) that is determined by dividing Mw by Mn. Size exclusion chromatography (SEC) was conducted using a linear column capable of solving 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 activation energy, i.e., Ea, reflects the sensitivity of a polymer melt viscosity to temperature. This is generally observed as a function of the linear versus crosslinked character of the polymer. Molecular weight and molecular weight distribution are also generally observed as factors that affect the energy of flow activation. The Ea in terms of kJ / mol can be easily determined from the data obtained from a dynamic-rheometer such as a dynamic rheometer from Rheo etrics Inc. (RMS 800). A standard prescription to summarize the temperature dependence of the viscosity of polymer melts has been available for a long time in the scheme known as the Williams-Landel-Ferry Overlay (WLF) which is described in the classic text entitled "Viscoelastic". Properties of Polymers ", 3rd edition (John Wiley &Sons, New York, 1980) by John D. Ferry. The data necessary to establish the temperature dependence of dynamic viscosity versus frequency, or viscosity versus 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 values of the Ea are more accurate, it is desirable to optimize the data to produce master curves, isothermal, optimally uniform according to the superposition of the time-temperature of WLF but using a criterion of accuracy of concordance of the minimum squares based on the parameters of the Carreau-Yasuda model that have been previously shown to give concordances or adjustments-highly accurate for individual temperature polyethylene data. This can be done in various ways. The presently preferred technique involves the clamping of dynamic viscosity frequency curves obtained from a dynamic viscometer from Rheometrics, Inc. for a computer program for internal use entitled "Rheology Analysis Program CY" protected by the copyright of Phillips Petroleum Company , unpublished, which was submitted for registration on January 31, 1995. This computer program for internal use is available for use by others under an authorized program. Discussions of the Carreau-Yasuada model can be found in Dynamics of Polymeric Liquids. Second edition (John Wiley &Sons, New York, 1987) by R. Byron Bird, Robert C. Armstrong, and Ole Hassager; also in C.A. Hieber and H.H. Chiang, "Some correlations involving the shear viscosity of polysyrene 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). Copolymers produced using the catalytic system based on the matalocene have some marked 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 the range of 2.17 to 2.31 and unusually low melting points for their density. of broader molecular weight.The polymer produced using a Phillips chromium catalyst, a molecular weight distribution that was even wider 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 while the Dow resin was 30. From the rheological data and the parameters of Carreau-Yasuda to 190 ° 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 percentage of chains with a terminal vinyl were in the range of 30 to about 42.9 percent, a value that is somewhat lower than that normally observed for copolymers produced using chromium type catalysts. Carbon 13 NMR analysis also indicated that the metallocene-based polymers showed evidence of minute amounts of short chain branching of ethyl and butyl that may have come from oligomers of an olefin, generated in-situ. As determined by FTIR spectroscopy, the total branching of the produced metallocene resins ranged from about 0.4 to about 2.1 mole percent. The number of vinyl groups per 1000 carbon atoms for the resins based on metallocene as determined by FTIR was in the range of 0.087 to 0.145. A summary of the properties of polyethylene and the properties of selected films is shown in the following table.

Polyethylene Properties Film Properties Film Density MI MWD Dart, Effort Effort Clarity Brightness, g / cc Cutting Cutter Optics, MD, g TD, g% 1A 09179 106 217 388 200 398 406 1197 1B 09179 106 217 708 299 429 373 1343 2A 09216 136 224 169 237 411 59 1115 3A 09222 189 221 256 253 429 3B 09222 189 221 145 174 453 566 1182 4A 09256 098 231 153 170 422 4B 09256 098 231 152 222 355 5A 09402 087 231 30 19 147 5B 09402 087 231 < 30 24 168 574 1214 Dow 09200 100 417 216 461 755 178 2045 Ream 09230 - 240 - - - 2708 30 Cr In the above table, if there is an A after the film number, it refers to a film prepared without any luoroelastomer, whereas if there is a B after the number, it refers to a film produced using a polymer that contains 0.07 percent in weight of luoroelastomero f. No luoroelastomer was used in the control runs where the films were produced from the Dow resin and the Phillips chromium resin. The table shows that in some cases the addition of the fluoropolymer improved the impact resistance of the dart. It is important to note that the metallocene-based resin was much lighter and more uniform than the lower density resin film 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 the impact resistance of the dart and the shear stress, even though the copolymer produced using the metallocene is capable of producing very clear films in densities much higher than that normally used in the manufacture of films. In addition, films made of higher density resins have the additional property of greater inflexibility or stiffness than films made of the lower density polymer, an advantage defined in some applications. In addition, an observation was made that the films produced from the lower density metallocene-based resins, ie, those having a density less than 0.925 g / cc, exhibited significant friction on wood tensioning strips. In addition, the viscosity and the. Locking decreases as the density of the resin increases. Accordingly, for the best balance of processing properties and clarity, metallocene-produced resins having a density of at least about 0.925 g / cc were preferable. Additional runs were made to demonstrate 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 low 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 the catalyst system described in Example I and a linear low density polyethylene, produced using a Phillips chromium catalytic process. Both ethylenes were copolymers of ethylene and 1-hexene. The polymer produced with metallocene, of medium density, had a density of 0. 9390 g / cc and a melt index of 0.87 dg / min ..

The linear low density polyethylene, produced with the Phillips chromium catalytic process had a density in the range of 0.919 to 0.923 and an HLMI in the range of 15 to 21 dg / min. If one produced a 1 mil film using linear, low density, chromium polyethylene, it is possible to obtain good physical properties, however, the optical properties are lower than would be desirable for clear film applications, ie the percentage of optical clarity is greater than 17.8 in such a film. A 1 mil film, produced using the metallocene catalyst system, had lower shear strength than linear low density polyethylene, produced using the chromium catalyst. The 1.5 thousand movie, coextruded was extruded using a Sano coextrusion die. The processing parameters included the 3.0: 1 blowing ratio, nozzle opening of 0.15 cm (0.060 inches) at a speed of 108.72 kg / hour (200 lb / hour). The bubble configuration was "isolated". The process was carried out to produce a product in which 60 percent of the thickness was linear, low density polyethylene and the two outer layers. each one was 20 percent thick, 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 buten-ethylene linear low density polyethylene containing about 3 weight percent of the fluoroelastomer processing aid. A comparison of various film properties of approximately 1 thousand of each of the two resins and of the coextruded film, of 1.58 mil, are set forth in the following table.

Film Comparison Proven Property Coextruded Polymer Polymer Metallocene Polymer Width one thousand .58 1 .01 1 .08 MD of Shear Effort E. g 101 103 58 TD of Shear Effort E. g 685 323 272 T. E.D.D. kg per meter 1,828 2.15 1 .31 (Ibs per inch) (1 .23) (1.45) (0.886) Dart g 96 216 1 10 Ten. @ MD Performance 126.39 - 150.96 kg / cm (psi) (1800) (2150) Ten. @ Performance TD 129.90 - 161 .50 kg / cm2 (psi) (1850) (2300) Ten. @ Breakdown MD 312.46 - 263.31 kg / cm2 (psi) (4450) (3750) Ten. @ Break Break TD 305.44 - 291 .40 kg / cm2 (psi) (4350) (4150) MD of Elongation% 517 - 506 TD of Elongation% 723 - 630 Optical Clarity 7.4 > 17.8 4.4 Brightness 1 15.6 • _ 129 The data shows that the co-extruded film has improved optical properties as compared to polyethylene based on chromium, linear, low density and improved firmness properties as compared to films made only of the metallocene polymer. It's attention. particularly the fact that the optical clarity of the coextruded film is significantly lower than that of the polymer of the inner layer.

It is noted that in relation to this date, the best method known by the applicant to carry out the aforementioned invention, is the conventional one for the manufacture of the objects to which it relates.

Having described the invention as above, property is claimed as contained in the following:

Claims (33)

1. A self-supporting film, characterized in that it has one or more layers wherein at least one layer is a layer of low optical clarity having an optical clarity percentage of less than 10% wherein the polymer consists essentially of polyethylene, optionally containing a fluoroelastomer, having a density of at least 0.93 g / cc, a molecular weight distribution of not more than 4, polyethylene that is substantially free of branches having six or more carbon atoms.

2. A film according to claim 1, characterized in that the film consists of a single layer.

3. A film according to claim 2, characterized in that the polyethylene has a molecular weight distribution of no more than about 34.

A film according to any of the preceding claims, characterized in that the polyethylene used to produce the film has a density of at least about 0.94 g / cc.

5. A film according to claim 4, characterized in that the polyethylene has a density in the range of about 0.94 to about 0.945 g / cc.

6. A film according to any of the preceding claims, characterized in that the polyethylene used to produce the film has a molecular weight distribution of at least about 1.5.

7. A film according to any of the preceding claims, characterized in that the polyethylene has a melt index in the range of about 0.2 to about 5 dg / min.

8. A film according to any of the preceding claims, characterized in that the polyethylene has a shear response value in the range of about 16 to about 20.

9. A film according to claim 8, characterized in that the polyethylene has a shear stress, critical at the beginning of the fracture of the molten material of less than 4 x 10 dynes / cm.

10. A film according to claim 9, characterized in that at least about 20 percent of the polyethylene polymer chains contain terminal vinyl groups.

11. A film according to any of claims 1-9, characterized in that the polyethylene has ethyl branches that are uniformly distributed at the intermolecular level.

12. A film according to claim 14, characterized in that the polyethylene is produced by the polymerization of ethylene in the presence of a liquid diluent of alkane under thick slurry polymerization conditions using a catalyst consisting essentially of the solid catalyst-prepared at (a) ) combine 5- (9-f luorenyl) -5- (cyclopentadienyl) -hexene-1-zirconium dichloride and methyl aluminoxane in a liquid, (b) prepolymerize ethylene in the resulting liquid, and (c) separate the catalyst system prepolymerized, solid, resulting from the liquid.

13. A film according to any of claims 1-9, characterized in that the polyethylene contains ethyl branches and butyl branches.

14. A film according to any of the preceding claims, characterized in that it is a blown film.

15. A film according to claim 14, characterized in that it has a thickness in the range of about 0.25 to about 5 mils.

16. A film according to claim 1, which contains three layers wherein the polymer of each outer layer is a layer of low optical clarity having a percent optical clarity of less than 10% wherein the polymer consists essentially of a polyethylene , optionally containing a fluoroelastomer, a density of at least 0.93 g / cc, and a molecular weight distribution of not more than 4, the polymer which is further characterized because it is substantially free of branches having six or more carbon atoms.

17. A film according to claim 16, characterized in that the polyethylene of the inner layer has a lower density than that of the two outer layers.

18. A film according to claim 17, characterized in that the polyethylene of the inner layer has a molecular weight distribution of at least 10.

19. A film according to claim 18, characterized in that the polyethylene of each of the two outer layers has a density in the range of about 0.94 to about 0.945 g / cc.

20. A film according to claim 19, characterized in that the polyethylene of the inner layer has a density in the range of about 0.91 to about 0.929 g / cc and an HLMI in the range of about 12 to 24 dg / min.

21. A film according to claim 20, characterized in that the polyethylene of the two outer layers is selected from the same or different polyethylene selected from polyethylenes having a melt index in the range of 0.2 to 5 dg / min.

22. A film according to claim 21, characterized in that it is a blown film, coextruded, having a percentage of optical clarity of less than 10 percent and a thickness in the range of 0.25 to 5 thousand.

23. A film according to claim 22, characterized in that at least one of the outer layers contains polyethylene having a melt index of less than about 2 dg / minute and the polyethylene contains about 0.01 to about 1 weight percent of fluoroelastomer.

24. A film according to claim 1, characterized in that it has at least a second layer wherein the polymer of the second layer consists essentially of polyethylene having a density of at least about 0.945 and a molecular weight distribution of greater than 6.

25. A film according to claim 1, having at least a first and a second layer wherein the polymer of the second layer consists essentially of polyethylene having a density of less than 0.925 g / cc and a molecular weight distribution of less than 4 and wherein the polymer of the first layer has a percentage of optical clarity of less than 10% and consists essentially of a polyethylene, optionally containing a fluoroelastomer, a density of at least 0.925 g / cc and a molecular weight distribution of no more than 4 and a melt index in the range of about 0.2 to about 10 dg / minute, and which is further characterized because it is substantially free of branches having six or more carbon atoms.

26. A film according to claim 1, characterized in that the polymer used in the manufacture of the layer with low optical clarity has a melt index of at least about 2 dg / min and does not contain any fluoroelastomer.

27. A film according to claim 1, characterized in that the polyethylene used in the formation of at least one of at least one of the layers of low optical clarity has a melt index of less than 2 dg / min and contains an amount that increases the processing of fluoroelastomer.

28. A film according to claim 1, characterized in that the polyethylene used in the formation of at least one of at least one layer of low optical clarity has a melt index of less than 2 dg / min and contains about 0.01 to about 1 per weight percent fluoroelastomer based on the weight of the polyethylene in the layer.

29. A blown film, co-extruded, having a percentage of optical clarity of less than 17.8% consisting of three layers wherein the polymer of each of the outer layers is the same or different polyethylene selected from polyethylenes having a density of at least 0.93 g / cc, and a molecular weight distribution of less than 4 and which is further characterized because it is substantially free of branches having six or more carbon atoms, and the polymer of the inner layer consists essentially of a copolymer of ethylene and 1-hexene having a density in the range of about 0.91 to about 0.929 g / cc, an HLMI in the range of about 12 to 24 dg / minute and a molecular weight distribution greater than 10 produced using a catalyst containing chromium oxide in a polymerization process in the particle form.

30. A film according to claim 29, characterized in that it has an optical clarity of not more than 10% wherein the polymer of the outer layers is selected from copolymers of ethylene and 1-hexene having a density of at least about 0.93 g / cc, wherein the thickness of each outer layer is in the range of about 5 to about 25 percent of the total thickness of the film, and wherein if the polymer of each of the outer layers was formed into a one mil film , the films each would have a lower optical clarity than a film of one thousand produced from the polymer of the inner layer under the same conditions.

31. A film according to claim 2, characterized in that the polyethylene is produced by the polymerization of ethylene and hexene in the presence of a liquid alkane diluent under thick sy polymerization conditions using a catalyst consisting essentially of the solid catalyst prepared to the a) combine 5- (9-fluorenyl) -5- (cyclopentadienyl) -hexene-1-zirconium dichloride and methyl aluminoxane in a liquid, (b) prepolymerize ethylene in the resulting liquid, and (c) separate the catalyst system prepolymerized, solid, resulting from the liquid.

32. A self-supporting film of low optical clarity, where the polymer consists essentially of a polyethylene, the polyethylene has a density of at least 0.93 g / cc and a MWD of no more than 4, and ethyl branches that are evenly distributed at the intermolecular level, the polyethylene is further characterized because it is substantially free of branches having six or more carbon atoms.

33. A film according to claim 32, characterized in that the polyethylene also has butyl branches.