MXPA96005406A - Movie extruded from an in-situ mix of ethylene copolymers - Google Patents

Abstract

The present invention relates to a shrinkable film comprising a mixture of copolymers of ethylene and one or more alpha-olefins having from 3 to 12 carbon atoms formed in situ, the mixture having a melt index within the range of about 0.2 to about 3.5 grams per 10 minutes, a melt flow ratio within the range of about 50 to about 1775, a molecular weight within the range of about 90,000 to about 225,000, a ratio of Mw / Mn of at least about 8 and a density within the range of 0.910 to 0.940 grams per cubic centimeter, the shrinkable film is formed at a blow ratio within the range of about 2: 1 to about 6: 1 and has the following properties: (i) at a temperature of about 135 degrees centigrade, a shrinkage of at least about 50 percent in the machine direction and a zero or positive shrinkage or in the transverse direction, (ii) the melting voltage is zero kilopascals or positive, and (iii) a cooling voltage of at least about 0.35 x 10 3 kilopascal

Description

"EXTRUDED FILM FROM AN IN-SITU MIX OF ETHYLENE COPOLYMERS" This application claims the benefit of United States Provisional Application Number 60 / 006,270 filed on November 7, 1995.

TECHNICAL FIELD This invention relates to a shrinkable film extruded from a mixture of ethylene copolymers prepared in a series of polymerization reactors.

BACKGROUND INFORMATION For many years, high pressure, low density polyethylenes, which are highly branched polymers, were considered to be the select resin for commercial shrinkable film applications. The key property that facilitates the use of high pressure, low density polyethylene for these applications is the long chain branching. The long chain branching makes possible the development of high melting tension, which can be frozen in the film in the freezing line during the extrusion of the tubular film. In other words, sufficient strain hardening occurs during extrusion of the tubular film, for example, to generate in the film the frozen stresses that are required for shrinkable film applications. Under shrinkage tunnel conditions, frozen stresses cause the film to shrink around the article to be packaged, thus securing it securely. These resins also have a relaxation regime of j. ú relatively low tension, which facilitates a retention of the shrink forces necessary to provide support for the packaged items. Unlike high pressure, low density polyethylene, the linear low density polyethylene of The limited molecular weight distribution commonly used for the extrusion of the tubular film has only short chain branching, the branching in length corresponding to the alpha-olefin which is copolymerized with ethylene to produce it. Without long chain or branching, however, the stresses of linear low density polyethylene of limited molecular weight distribution relaxes too rapidly during melt extrusion to provide high melting efforts, which can freeze in the film. This is particularly the case for the transverse direction of the linear low density polyethylene film of limited molecular weight distribution, which is much less elongated than in the machine direction during extrusion of the film and, therefore, it has virtually no shrinkage in that direction. As a result, the linear low density polyethylene of limited molecular weight distribution is unacceptable for a shrinkable film application because it would bump around the material to be packaged, rather than retaining it securely. The manufacturers of linear low density polyethylene (LLDPE) were therefore trying to identify an LLDPE, which was appropriate for shrink film applications; that it was easier to process and the polyethylene resins of low density, high pressure; and, finally, that would result in a film that exceeds the performance of the high pressure resin films in terms of those more desirable properties in the shrink films. This was achieved in U.S. Patent No. 4,814,135. In this patent, it was found that, in order to achieve a shrinkage of at least about 10 percent in the important transverse direction, a high average weight molecular weight of at least 250,000, together with a small amount of the species of Molecular weight of at least about 500,000 was necessary among other defined parameters. It would be economically advantageous to be able to provide a shrinkable film having a shrinkage in the transverse direction of at least about 10 percent at a limited blowing ratio, but at a much lower molecular weight, due to the reason that the processability of extrusion is facilitated in this way.

EXHIBITION OF THE INVENTION An object of this invention, therefore, is to provide a shrinkable film of relatively low molecular weight having a shrinkage in the transverse direction of at least about 5 percent at a limited blowing ratio. Other objects and advantages will become evident below. In accordance with the present invention, these shrinkable films have been discovered, the films being extruded from a mixture of polymers in situ, produced in two reactors connected in series. The steps and conditions, which can be used to provide the mixture in situ, will be described below. The shrinkable film comprises a mixture of copolymers of ethylene and one or more alpha-olefins having from 3 to 12 carbon atoms formed in situ, the mixture having a melt index within the range of about 0.2 to about 3.5 grams per 10. minutes, and preferably from about 0.5 to about 3.5 grams per 10 minutes; a ratio of melt flow within the range of about 50 to about 175; a molecular weight within the range of about 90,000 to about 225,000; a ratio of Mw / Mn of at least about 8; and a density within the range of 0.910 to 0.940 gram per cubic centimeter id, the shrinkable film being formed at a blow ratio within the scale of approximately 2: 1 to approximately 6: 1 and having the following properties: (i) at a temperature of approximately 135 ° C, a shrinkage of at least about 50 percent in the machine direction, and a zero or positive shrinkage in the transverse direction; (ii) the melting tension is zero kilopascals or positive; and 0 (iii) a cooling voltage of at least about 0.35 x 10- ^ kilopascals.

DESCRIPTION OF THE PREFERRED MODALITY (ES) The caliper or thickness of the shrinkable film can be within the range of approximately .0127 millimeters to approximately .1524 millimeters, and preferably falls within the range of approximately 5.02424 millimeters to .0635. millimeter. The optimum size is approximately .0305 mm. Shrinkable films can be produced by various extrusion techniques such as blown film extrusion and orientation extrusion j. or biaxial molded in groove. The extrusion of tubular film is preferred, particularly the extrusion of blown tubular film cooled with air. A typical apparatus and method for extruding a blown tubular film will be described below. The values The minimum values for the critical properties of the shrinkable film are the following: (i) Shrinkage at a temperature of approximately 135 ° C (the temperature of the approximate shrink tunnel) in the machine direction is 0 at least about 50 percent , and, in the transverse direction, the shrinkage is zero or positive and preferably from zero to about 40 percent. (ii) The shrinkage forces with respect to the melting voltage is zero kilopascals or positive; preferably from about 14 to about 103 kilopascals; and especially preferably from about 35 to about 69 kilopascals. (iii) The cooling voltage is at least about 0.35 x 103 kilopascals and preferably about 0.85 x 10 ^ to about 2 x 10 ^. The only upper limits for these properties of the film are those that can be achieved in a practical way. The mixture, which is used in the extrusion apparatus, can be produced in two reactors in stages connected in series, wherein a mixture of resin and the catalyst precursor is transferred from the first reactor to the second reactor, where it is prepared and it is mixed in situ with the copolymer of the first reactor. The process is generally described for example in U.S. Patent Nos. 5,047,468 and 5,126,398; however, the conditions have to be adjusted to provide the desired properties in the mixture in situ. The copolymers produced in each of the reactors are copolymers of ethylene and at least one alpha olefin co -omer. The relatively high molecular weight copolymer is produced in one which is referred to as the high molecular weight reactor, and the relatively low molecular weight copolymer is produced in what is referred to as the low molecular weight reactor. The alpha-olefin comonomer (s), which may be present in both reactors, may have from 3 to 12 carbon atoms, and preferably has from 3 to 8 carbon atoms. The alpha-olefins are exemplified by propylene, 1-butene, 1-hexene, 4-methyl-1-pentene, or 1-octene. Any of the aforementioned comonomers can be used in any reactor. Preferred comonomer combinations are 1-butene / 1-butene; 1-butene / l-hexene; 1-hexene-l-butene; and 1-hexene / l-hexene. The magnesium / titanium based catalyst system that can be used to produce the mixture in situ, can be exemplified by the catalyst system described in US Pat. No. 4,302,565 even though the precursor is preferably not supported. Another preferred catalyst system is one in which the precursor is formed by spray drying such as the system described in US Patent Number 5,290,745. The electron donor, if used in the catalyst precursor, is an organic Leis base, liquid at temperatures within the range of about 0 ° C to about 200 ° C, where the magnesium and titanium compounds are soluble. . The electron donor can be an alkyl ester of an aliphatic or aromatic carboxylic acid, an aliphatic ketone, an aliphatic amine, an aliphatic alcohol, an alkyl or cycloalkyl ether, or mixtures thereof, each electron donor having an at 20 carbon atoms. Among these electron donors, the preferred are alkyl and cycloalkyl ethers having from 2 to 20 carbon atoms; the dialkyl, diaryl and alkylaryl ketones having from 3 to 20 carbon atoms; and the alkyl, alkoxy and alkylalkoxy esters of the acids I O alkyl and aryl carboxylic acids having from 2 to 20 carbon atoms. The especially preferred electron donor is tetrahydrofuran. Other examples of suitable electron donors are methyl formate, ethyl acetate, butyl acetate, ethyl ether, dioxane, di-n-propyl, dibutyl ether, ethyl formate, methyl acetate, ethyl anisate, ethylene carbonate, tetrahydropyran and ethyl propionate. Even when an excess of the electron donor is used initially to provide the reaction product of the titanium compound and the electron donor, the reaction product finally contains from about 1 to about 20 moles of the electron donor per mole of the compound of titanium and preferably from about 1 to 10 moles of electron donor per 5 mole of the titanium compound.

An activating compound, which is generally used with any of the precursors of the titanium based catalyst, can have the formula AlRaXkHc wherein each X is independently chlorine, bromine, iodine or OR '; each R and R 'is independently a saturated aliphatic hydrocarbon radical having from 1 to 14 carbon atoms; b is 0 to 1.5; c is 0 or 1; and a + b + c = 3. Preferred activators include alkylaluminum mono- and di-dichlorides wherein each alkyl radical has from 1 to 6 carbon atoms and the trialkylaluminums. A particularly preferred activator is a mixture of diethylaluminum chloride and tri-n-hexylaluminum. They can be used per mole of the electron donor, from about 0.10 to about 10 moles, and preferably from about 0.15 to about 2.5 moles, of the activator. The molar ratio of the activator to titanium may be within the range of about 1: 1 to about 10: 1 and preferably falls within the range of about 2: 1 to about 5: 1. The hydrocarbyl aluminum catalyst can be represented by the formula R3AI or R2 IX wherein each R is independently alkyl, cycloalkyl, aryl or hydrogen; at least one R is hydrocarbyl; and two or three R radicals can be joined to form a heterocyclic structure. Each R, which is a hydrocarbyl radical, can have from 1 to 20 carbon atoms, and preferably has from 1 to 10 carbon atoms. X is a halogen, preferably chlorine, bromine or iodine. Examples of the hydrocarbyl aluminum compounds are the following: triisobutylaluminum, tri-n-hexylaluminum, di-isobutyl aluminum hydride, dihexylaluminum dihydride, di-isobutyl-hexylaluminum, isobutyl dihexylaluminum, trimethylaluminum, triethylaluminum, tripropylaluminum, triisopropylaluminum , tri-n-butylaluminum, trioctylaluminum, tridecylaluminum, tridodecylaluminum, tribencylaluminum, triphenylaluminum, trinaphthylaluminum, tritylaluminum, dibutylaluminum chloride, diethylaluminum chloride and ethylaluminum sesquichloride. The co-catalytic compounds can also serve as activators and modifiers. As mentioned above, it is preferred not to use a support. However, in those cases where it is desired to support the precursor, silica is the preferred support. Other suitable supports are inorganic oxides such as aluminum phosphate, alumina, silica / alumina mixtures, silica modified with an organoaluium compound such as triethylaluminum, and silica modified with diethyl zinc. A typical support is a solid particulate porous material essentially inert to the polymerization. It is used as a dry powder having an average particle size of from about 10 to about 250 microns and preferably from about 30 to about 100 microns; a surface area of at least 200 square meters per gram and preferably at least about 250 square meters per gram; and a pore size of at least about 100 angstrom units and preferably at least about 200 angstrom units. As usual, the amount of support used is that which provides from about 0.1 to about 1.0 millimol of titanium per gram of the support and preferably from about 0.4 to about 0.9 millimole of titanium per gram of the support. Impregnation of the aforementioned catalyst precursor in the silica support can be achieved by mixing the precursor and the silica gel in the solvent of the electron donor or other solvent, followed by removal of the solvent under reduced pressure. When a support is not desired, the catalyst precursor can be used in liquid form. Activators can be added to the precursor either before and / or during polymerization. In one procedure, the precursor is fully activated prior to polymerization. In another process, the precursor is partially activated prior to polymerization, and activation is completed in the reactor. When a modifier is used instead of an activator, the modifiers are usually dissolved in an organic solvent such as isopentane and, when a support is used, they are impregnated in the support after the impregnation of the titanium compound or complex, after which the precursor of the supported catalyst dries. Otherwise, the solution of the modifier is added by itself directly to the reactor. The modifiers are similar in structure and chemical function to the activators. For any of the variations, see, for example, U.S. Patent No. 5,106,926. The cocatalyst is preferably added separately pure or as a solution in an inert solvent, such as isopentane, to the polymerization reactor at the same time as the flow of the ethylene is initiated. U.S. Patent No. 5,106,926 provides another example of a magnesium / titanium based catalyst system comprising: (i) a catalyst precursor having the formula Mg ^ Ti (OR) eXf (ED) g wherein R is a radical of aliphatic or aromatic hydrocarbon having 1 to 14 carbon atoms or COR 'where R' is an aliphatic or aromatic hydrocarbon radical having 1 to 14 carbon atoms, each group of OR is the same or different, X is independently chlorine, bromine or iodine; ED is an electron donor; d is from 0.5 to 56; e is 0, 1 or 2; f is 2 to 116; and g is 1.5d + 2; (ii) at least one modifier having the formula BX3 or AlR (3_e) Xe wherein each R is alkyl or aryl and which is the same or different, and X and e are as defined above for the component (a ) wherein the components (a) and (b) are impregnated in the inorganic support; and (iii) a hydrocarbyl aluminum cocatalyst. The precursor is prepared from a titanium compound, a magnesium compound, and an electron donor. The titanium compounds, which are useful for preparing these precursors, have the formula Ti (OR) eHh wherein R, X and e are as defined above for component (a); h is an integer from 1 to 4; and e + h is 3 or 4. Examples of the titanium compounds are TÍCI3, TÍCI4, Ti (OC2H5) 2Br2, Ti (OC6H5) CI3, Ti (OCOCH3) Cl3, and Ti (OCOC5H5) CI3. The magnesium compounds include magnesium halides such as MgCl 2, MgBr and Mgl 2. Anhydrous MgCl2 is a preferred compound. They are used per mole of the titanium compounds of about 0.5 to 56, and preferably about 1 to 10 moles of the magnesium compounds.

The electron donor, the support and the cocatalyst are the same as those described above. As can be seen, the modifier can be similar in chemical structure to activators containing aluminum. The modifier has the formula BX3 or AlR (3_e) Xe wherein each R is independently alkyl having from 1 to 14 carbon atoms; each X is independently chlorine, bromine or iodine; and e is 1 or 2. One or more modifiers can be used. Preferred modifiers include alkylaluminum mono- or di-chlorides wherein each alkyl radical has from 1 to 6 carbon atoms; boron trichloride; and trialkylaluminium. It can be used per mole of the electron donor, from about 0.1 to about 10 moles, and preferably 0.2 to about 2.5 moles of the modifier. The molar ratio of the modifier to titanium may be within the range of about 1: 1 to about 10: 1 and preferably falls within the range of about 2: 1 to about 5: 1. The entire catalyst system, which includes the precursor or the activated precursor and the cocatalyst, is added to the first reactor. The catalyst is mixed with the copolymer produced in the first reactor, and the mixture is transferred to the second reactor. As far as the catalyst is concerned, only the cocatalyst is added to the second reactor from a source or external source. The polymerization in each reactor is preferably carried out in the gas phase using a continuous fluidized process. A typical fluidized bed reactor is described in the North American Patent Number 4,482, 687. A relatively low melt index (or high molecular weight) copolymer is preferably prepared in the first reactor and the relatively high melt index (or low molecular weight) copolymer is prepared in the second reactor. This can be referred to as the direct mode. Alternatively, the relatively low molecular weight copolymer can be prepared in the first reactor, and the relatively high molecular weight copolymer can be prepared in the second reactor. This is referred to as the inverse mode. The first reactor is generally smaller in size than the second reactor because only a portion of the final product is manufactured in the first reactor. The mixture of polymer and an active catalyst is usually transferred from the first reactor to the second reactor through an interconnection device using nitrogen or the recycle gas from the second reactor as a transfer medium.

In the high molecular weight reactor: Due to the low values instead of the melt index, the flow index is determined from those values used in this specification. The flow rate may be within the range of about 0.01 to about 30 grams per 10 minutes, and preferably falls within the range of about 0.2 to about 6 grams per 10 minutes. The molecular weight of this polymer, in general, falls within the range of about 400,000 to about 480,000. The density of the copolymer can be from 0.860 to 0.940 grams per cubic centimeter, and preferably falls within the range of 0.900 to 0.930 grams per cubic centimeter. The melt flow ratio of the polymer can be within the range of about 20 to about 70, and preferably is about 22 to about 45. In the low molecular weight reactor: A copolymer of the relatively high melting (or low molecular weight). The high melt index can be within the range of about 50 to about 3000 grams per 10 minutes, and preferably falls within the range of about 100 to about 1500 grams per 10 minutes. The molecular weight of the high-lime copolymer melt index is generally within the scale of approximately 14, 000 to approximately 30,000. The density of the copolymer prepared in this reactor can be from 0.900 to 0.970 gram per cubic centimeter, and preferably falls within the range of 0.905 to 0.945 gram per cubic centimeter. The melt flow ratio of this copolymer can be within the range of about 20 to about 70 and preferably is about 20 to about 45. The mixture or the final product as removed from the second reactor, can have an index of melting within the range of about 0.2 to about 3.5 grams per 10 minutes, and preferably have a melt index within the range of about 0.5 to about 3.5 grams per 10 minutes. The melt flow ratio is within the range of about 50 to about 175. The molecular weight of the final product may be within the range of about 90,000 to about 225,000, and preferably falls within the range of about 120,000 to about 200,000. The density of the mixture can be within the range of 0.910 to 0.940 gram per cubic centimeter and preferably falls within the range of 0.918 to 0.926 gram per cubic centimeter.

It will be understood that in situ mixing can generally be characterized as a multimodal resin, usually bimodal or trimodal. In some cases, however, the two components constituting the mixture are sufficiently similar in average molecular weight that there is no discernible discontinuity in the molecular weight curve. The properties of these resins are strongly dependent on the proportion of the high molecular weight component, i.e., the low melt index component. For a staged reactor system, the proportion of the high molecular weight component is controlled through the relative production rate in each reactor. The relative production rate in each reactor in turn can be controlled by a computer application program, which monitors the production regime in the reactors (measured by thermal equilibrium) and then manipulates the partial pressure of the ethylene in each reactor and the regime of catalyst feed in order to fill or satisfy the production rate, the separation of the production rate, and the catalyst productivity requirements. The broader molecular weight distribution is reflected in a Mw / Mn ratio of at least about 8, and preferably is at least about 10. The only upper limit is the restrictions of the practical. Mw is the weight average molecular weight; and one can refer to the Mn relation as the polydispersity index, which is a measure of the latitude of the molecular weight distribution. The weight ratio of the copolymer prepared in the high molecular weight reactor to the copolymer prepared in the low molecular weight reactor can be within the range of about 0.5: 1 to about 2: 1. The catalyst system, ethylene, allyloolefin, and hydrogen are continuously fed to the first reactor; the polymer / catalyst mixture is transferred continuously from the first reactor to the second reactor, the ethylene, the alpha-olefin and the hydrogen, as well as the cocatalyst are continuously fed to the second reactor. The final product is continuously removed from the second reactor. In the low melt index reactor as reflected in a flow index: The molar ratio of alpha-olefin to ethylene can be within the range of about 0.05: 1 to about 0.4: 1, and preferably falls within the scale from about 0.09: 1 to about 0.26: 1. The molar ratio of hydrogen (if used) to ethylene can be within the range of about 0.001: 1 to about 0.3: 1, and preferably falls within the range of about 0.0001: 1 to about 0.18: 1. . The operating temperature usually falls within the range of about 60 ° C to about 100 ° C. Preferred operating temperatures vary depending on the density desired, that is, lower temperatures for lower densities and higher temperatures for higher densities. In the high melt index reactor: The molar ratio of alpha-olefin to ethylene can be within the range of about 0.1: 1 to about 0.6: 1, and preferably falls within the range of about 0.2: 1 to approximately 0.45: 1. The molar ratio of hydrogen to ethylene may be within the range of about 1: 1 to about 3: 1, and preferably falls within the range of about 1.6: to about 2.2: 1. The operating temperature generally falls within the range of about 70 ° C to about 100 ° C. As mentioned above, the temperature is preferably varied with the desired density. The pressure is usually the same in both the first and the second reactors. The pressure may be within the range of about 14.06 to about 31.27 kilograms per square centimeter preferably falling within the range of about 19.68 to about 24.60 kilograms per square centimeter gauge. A typical fluidized bed reactor can be described as follows: The bed is usually constituted of the same granulated resin that is to be produced in the reactor. Thus, during the course of the polymerization, the bed comprises formed polymer particles, growing polymer particles and catalyst particles fluidized by polymerization and the gaseous modification components are introduced at a rate of flow or sufficient velocity to cause the particles Separate and act like a fluid. The fluidizing gas is constituted by the initial feed, the replacement feed and the cycle gas (recycle), ie comonomers and if desired modifiers and / or an inert carrier gas. The essential parts of the reaction system are the vessel, the bed, the gas distribution plate, the inlet and outlet piping, a compressor, a cycle gas cooler and a product discharge system. In the container, above the bed, there is a zone of speed reduction, and, in the bed, a reaction zone. Both are above the gas distribution plate.

A typical and preferred catalyst system is one in which the precursor is formed by spray drying and used in the form of a slurry. This catalyst precursor, for example, contains titanium, magnesium, and an electron donor, and, optionally, an aluminum halide. The precursor is then introduced into the hydrocarbon medium such as a mineral oil to provide the slurry form. See U.S. Patent Number 5,290,745. The in situ polyethylene mixture can be produced using the following typical procedure: Ethylene is copolymerized with 1-hexene and 1-butene. The trimethylaluminum cocatalyst (TMA) is added to each reactor during the polymerization. The pressure in each reactor is 21.09 kilograms per absolute square centimeter. Each polymerization is carried out continuously after reaching equilibrium. Polymerization is initiated in the first reactor by continuously feeding the aforementioned TMA catalyst and cocatalyst precursor into a fluidized bed of polyethylene granules together with ethylene, 1-hexene, and hydrogen. The TMA is first dissolved in isopentane (5 weight percent TMA). The resulting copolymer mixed with the active catalyst is removed from the first reactor and transferred to the second reactor, using nitrogen as a transfer medium. The second reactor also contains a fluidized bed of polyethylene granules. The ethylene, the 1-butene and the hydrogen are introduced into the second reactor, where they are brought into contact with the copolymer and the catalyst from the first reactor. The additional cocatalyst is also introduced. The mixture produced is continuously stirred. A typical process for preparing the shrinkable film by extrusion of blown tubular film is as follows: The extrusion apparatus is equipped with a fluted mixing screw capable of providing the level of melt homogeneity found in current commercial tubular film extrusions. They are used to extrude the polymer or copolymer a lower feed of 7.62 centimeters and 15.24 centimeters, dies of tubular film of spiral mandrel and each equipped with a pin of matrix of 1.02 millimeters. The size of the orifice of the matrix is maintained at .914 millimeter. Films are extruded at a matrix circumference matrix regime of 1.42 kilograms / hour / centimeter using a blow ratio (BUR) varying (in the present invention) from about 2: 1 to about 6.1 :, and preferably from about 2.5: 1 to about 4.5: 1, temperatures melt within the range from about 175 ° C to about 210 ° C; and a height of freezing line of 30.48 centimeters. Variations in these extrusion conditions to optimize the properties of the film for specific applications can be made by any person who is aware of the technique in the extrusion of a shrinkable film. The extrusion apparatus, for example, can be an extrusion apparatus of 3.81 centimeters or 8.89 centimeters having a 75 millimeter matrix and a 1.0 millimeter space. The thickness of the film provided and tested is 25 microns except for examples 1, 2 and 3 where it is 35, 50 and 65, respectively. The temperatures are as follows: tubular body profile = 190 ° C; adapter = 200 ° C; Matrix = 210 ° C; and fusion = 250 ° C. The screw speed is 120 revolutions per minute (rpm); the fusion pressure is 158 bars; the extrusion regime is 22 kilograms per hour; and the driving impulse is 10 amperes. The terms and properties mentioned are defined or determined as follows: The direction of the machine is the direction in which the continuous tape of the film is pulled from the die of the film extrusion apparatus.

The transverse direction is the direction of the continuous belt, which is perpendicular to the machine direction and parallel to the continuous belt. The shrinkage (the percentage of change in the dimension of the film) is determined as follows: Shrinkage in the machine direction (percentage) = LiMD - LsMD x 100 LiMD Shrinkage in the transverse direction (percentage) = L TD _ LsTD x 10Q LiMD where LiMD = initial length in the machine direction LsMD = length in the machine direction after shrinkage LiTD = initial length in the transverse direction LsTD = length in the transverse direction after shrinkage. Another method to determine the shrinkage is the following: A specimen of 7.62 centimeters by 7.62 centimeters was cut so that the directions MD and TD were parallel to the sides of the specimen. The specimen is placed in a circulating oil bath at 124 ° C for - 21 - S seconds using an appropriate film holder in such a way that the film can shrink freely but not roll up. The specimen is removed from the bath and briefly cooled briefly in water. MD and TD shrinkage is obtained by measuring the specimen in the MD and TD directions and making the following calculation: Initial Width Percentage less Shrinkage = Final Width X 100 Initial Width The melting tensions are frozen stresses in the film in the first freezing line. The cooling tensions are the crystalline tensions that remain in the solidified film. The melting tension and the cooling tension are determined as follows: A specimen of the 2.54 cm wide film is held in a set of "Instron" jaws so that they are separated at a distance of 15.24 centimeters. With the stationary "Instron" jaws, a radiant heater of 500 watts is oscillated at a certain distance from the film causing the film to melt and begin to shrink. The tension in the fusion state is recorded as a load on the "Instron" chart. As the melting tension begins to decrease, the heater is removed and the film allowed to cool. MD and TD addresses. The values are given in kilopascals (KPa). The melting strength is the resistance to deformation in fusion. It can be defined as that property that resists thinning and subsequent hole formation when subjected to shrinkage stresses and released while the film is in the molten state in the oil bath at an elevated temperature (usually 12 ° C). Then, the time for the film to come off under the set weight is recorded as the melting resistance in seconds. For example, for a sample of .0102 millimeter, a weight of 18 grams is usually used which provides a tension of .565 kilogram per square centimeter in oil. The time to failure is usually between 10 and 70 seconds. Temperatures and weights are varied according to the thickness of the film and the melting temperature. The Fusion Flow is determined under Method D-1238-79 of the American Society for the Test of Materials in grams for 10 minutes. It is similar to the melting index. The melt index is determined under Method D-1238, Condition E of the American Society for the Testing of Materials. It is measured at 190 ° C and 2.16 kilograms, and is reported as grams per 10 minutes. The flow rate is determined under method D-1238, Condition F of the American Society for the Testing of Materials. It is measured at 190 ° C and 10 times the weight used to determine the melt index and is reported as grams per 10 minutes. The melting flow ratio is the ratio of the flow index to the melt index. The density is determined under Method D-1505 of the American Society for the Testing of Materials. A plate is made in accordance with method D-1928, Procedure C, of the American Society for the Testing of Materials, and conditioned for one hour at 100 ° C to approximate equilibrium crystallinity. The measurement for the density is then made in a density gradient column and the density values they are released in kilograms per cubic meter. The caliber of the film is the thickness of the film. The value can be provided in microns or millimeters. The blowing ratio is the ratio of the diameter of the matrix to the diameter of the bubble. The diameter of the bubble is determined as follows: 2 X flat / TT '. The term "flat" refers to the width of the flattened bubble. The molecular weight distribution is determined through Size Exclusion Chromatography using Waters ^ M 150C with trichlorobenzene as the solvent at 140 degrees centigrade with a broad molecular weight distribution standard and a wide molecular weight distribution calibration method. The matrix regime is defined as kilograms per hour per centimeter of the circumference of the matrix. The height of the freezing line is that distance away from the base of the matrix during which the polymer undergoes a phase transformation from a viscous liquid to a solid. Conventional additives, which can be introduced into the mixture, are exemplified by antioxidants, ultraviolet light absorbing agents, antistatic agents, pigments, dyes, nucleating agents, fillers or fillers, glidants, flame retardants, plasticizers, processing aids, lubricants, stabilizers, smoke inhibitors, viscosity control agents and crosslinking agents, catalysts and reinforcers, tackifiers, and antiblocking agents. In addition, of the filler or filler materials, the additives may be present in the mixture in amounts of about 0.1 to about 10 parts by weight of the additive per 100 parts by weight of the polymer blend. The filler or filler materials may be added in amounts of up to 200 parts by weight and more per 100 parts by weight of the mixture. The additives can be added to the reactor (s) or the extrusion apparatus through an appropriate medium such as a conventional hydrocarbon diluent. In addition, the mixture in turn can be mixed with other polyethylenes such as low density, high pressure polyethylene (HP-LDPE), for use in shrinkable films in varying amounts depending on the desired properties. The melt index of the HP-LDPE may be left within the appropriate scale for blown films and groove films preferably from about 0.15 gram to about 6 grams per 10 minutes. The shrinkable film of the invention, in addition to Having frozen stresses that are so important in shrinkable film applications have the following advantages: (i) excellent shrinkage properties of in situ blends, particularly those containing 0 significant amounts of 1-butene and / or 1-hexene; (ii) the mixtures can be extruded in a normal LLDPE line or a conventional high pressure (HP) LDPE line using narrow matrix spaces, eg, .889 millimeter, and at normal blow ratios, 5 v .gr. , 2: 1 to 4: 1; and (iii) there is an economic advantage through the shrinkage of the film compared to the shrinkable film produced from HP-LDPE blends or HP-LDPE / LLDPE blends. This economic advantage is retained in the shrink film market by capitalizing on the tenacity of the inherent film characterized by extruded films from an in situ blend of ethylene copolymers. The patents mentioned in this specification are incorporated by reference herein. The invention is illustrated by the following examples.

Examples Two in situ mixing resins were prepared, i.e., Resin A and Resin B. The reaction conditions for the preparation of Resin A are disclosed in Table I and the reaction conditions for the preparation of Resin B are disclosed in Table II, Resin A was prepared in the reverse mode. Resin B was prepared in the normal mode. In the reverse mode, the low molecular weight copolymer is prepared in the first reactor; it is transferred together with the active catalyst to the second reactor; and it is mixed in situ with the high molecular weight copolymer, which is prepared in the second reactor. In the normal mode, the high molecular weight copolymer is prepared in the first reactor; it is transferred together with the active catalyst to the second reactor, and is mixed in situ with the low molecular weight copolymer, which is prepared in the second reactor. The catalyst precursor is formed by spray-drying and is used in the form of a slurry. It contains titanium, magnesium and aluminum halides, and an electron donor, and is fixed to the surface of the silica. The precursor is then introduced into the hydrocarbon medium such as mineral oil to provide the slurry form. See U.S. Patent 5,290,745 ('745). The catalyst precursor and the method for preparing the same used in the examples is the same composition and method of preparation as in Example 1 of '745. For low density operation, as described herein, a reduced catalyst precursor is used. Typically, the molar ratio of diethylaluminum chloride (DEAC) to tetrahydrofuran (THF) is 0.45, and the molar ratio of tri-n-hexylaluminum to tetrahydrofuran is 0.20. The addition of diethylaluminum chloride and tri-n-hexylaluminum (TnHAl) is achieved by an in-line reduction system in which diethylaluminum chloride and tri-n-hexylaluminum are fed to the reactor simultaneously with the catalyst precursor, in order of producing a reduced catalyst. The ethylene is copolymerized with a comonomer in each of the two fluidized bed reactors. Each polymerization is carried out continuously after reaching equilibrium under the conditions indicated in the Tables. Polymerization is initiated in the first reactor by continuously feeding the aforementioned catalyst precursor and the cocatalyst, trimethylaluminum (TMA), to a fluidized bed of polyethylene granules together with ethylene, a comonomer and hydrogen. The cocatalyst is first dissolved in isopentane (5 weight percent cocatalyst). Higher concentrations of the cocatalyst in solution can also be used as well as using the pure cocatalyst. The resulting copolymer mixed with the active catalyst is removed from the first reactor and transferred to the second reactor using either hydrogen or a cyclic gas from the second reactor as a transfer medium. The second reactor also contains a fluidized bed of polyethylene granules. Again, ethylene, a comonomer and hydrogen is introduced into the second reactor where the gases are contacted with the copolymer and catalyst of the first reactor. Additional cocatalyst is also introduced. The product mixture is continuously stirred. Resin A has a melt index of 0.7 gram per 10 minutes; a flow rate of 68.0 grams per 10 minutes; a melt flow ratio of 98.0; and a density of 0.923 gram per cubic centimeter. Resin B has a melt index of 0.7 gram per 10 minutes; a melt index of 69.0 grams per 10 minutes; a melt flow ratio of 98.0; and a density of 0.922 gram per cubic centimeter. Resin C is a low density, high pressure polyethylene (HP-LDPE). It is an ethylene homopolymer prepared by a conventional high pressure process. Resin C has a melt index of 2 grams per 10 minutes; a flow rate of 120 grams per 10 minutes; a melt flow ratio of 60; and a density of 0.920 gram per cubic centimeter. Resin D is also an HP-LDPE, and is an ethylene homopolymer prepared by a conventional high-pressure process. Resin D has a melt index of 0.9 gram per 10 minutes; a flow rate of 73 grams per 10 minutes; a melt flow ratio of 80; and a density of 0.920 gram per cubic centimeter. In addition to the polymerization conditions for Resin A in Table I and Resin B in Table II, the extrusion conditions of films and the properties of the film are given in Tables III and IV. The equipment to extrude the blends into a film in Table III is a 40 mm Old Sterling ™ extrusion apparatus that has a Barrier ™ screw; a 50-millimeter matrix; and a matrix space of 1 millimeter. The revolutions per minute of the screw is a variable. The equipment to extrude the blends in the film in Table IV is a 90 millimeter Gloucester ™ extrusion apparatus having a DSB II screw, a 150 millimeter matrix, and a 0.9 millimeter matrix space. The matrix regime is 1.78 kilograms per hour per centimeter.

Table I reaction conditions reactor I reactor II temperature (° C) 85 72 pressure (kg / cm2 absolute) 20.95 17.65 partial pressure of C2 (kg / cm2 / absolute) 4.69 3.73 molar ratio of H2 / C2 1.96 0.018 molar ratio of C4 / C2 0.28 0 molar ratio of C6 / C2 0 0.166 C2 feed (kilograms / hour) 6923.5 4830.1 H2 feed (kilograms / hour) 8.76 .030 C4 feed (kilograms / hour 538.4 or C6 feed (kilograms / hour) 0 1345.7 co-catalyst 10% TMA 10% TMA i'O catalyst feed rate (kg / hour) 4.03 production rate (kilograms / hour ) 7296.7 5777.2 total production rate 15 (kilograms / hour) 13,073.8 ethylene division 0.589 0.411 titanium division 0.591 0.409 fluidized volumetric density (grams / cubic centimeter) 248.64 230.4 20 bed weight (kilograms) 28.243.3 27.342.2 bed level (meters) 11.98 11.34 bed volume (cubic meters) 113.28 118.35 dwell time (hours) 3,871 2,091 5 STY (Kg / hour / cubic cm) 231.58 175.56 Table II reaction conditions reactor I reactor II temperature (° C) 70 85 pressure (Kg / cm2 absolute) 21.44 21.51 partial pressure of C2 (kg / cm2 absolute) 1.65 5.96 molar ratio of H2 / C2 0.057 1.79 molar ratio of C4 / C2 0. 0.23 molar ratio of C6 / C2 0.147 0.006 C2 feed (kg / hour) 5,818.5 7,033.4 H2 feed (kg / hour) .144 26.79 C4 feed (kg / hour) 0 729.1 C6 feed (kg / hour) 107.6 0 co-catalyst 10% TMA 10% of TMA co-catalyst diet (kg / hour) 16.34 5.90 hexane feed rate (kg / hour) 245.2 catalyst feed rate (kg / hour) 8.90 production rate (kilograms / hour) 6,628.4 7, 400.2 diet total production (kilograms / hour) 14,028.6 ethylene division 0.453 0.547 titanium division 0.490 0.50 SGV (meters / second) .631 6.71 fluidized volumetric density (gram per cubic centimeter) 198.72 271.68 bed weight (kilograms) 23, 681.1 33, 124.7 bed level (meters) 11.92 12.10 bed volume (meters c bicos) 118.86 121.61 dwell time (hours) 3,573 2,361 % condensation (by weight) 4.4 STY (kilograms / hour / cubic centimeter) 200.97 218.87 Table III example RESINA BUR CALIBER KILOGRAMS REGIME / (mm) MATRIX HOURS KG / HOUR / CM 1 C 3: 1 .038 1.3 20.88 2 C 3: 1 .051 2.1 34.05 3 A 3.5: 1 .038 1.4 21.79 4 A 4: 1 .038 1.7 26.79 A 4: 1 .051 1.7 26.79 6 A 4: 1 .0.64 1.7 26.79 example RESIN ENCOGY-COGENSION IN TENSION IN HOT BREED MD MD MD MD (%) (Kg / cm2) (Kg / cm2) 1 C 85 23 1.36 18.20 2 C 80 25 0.83 14.64 3 A 80 10 0.42 19.18 4 A 77 17 0.34 16.96 A 73 17 0.34 16.32 6 A 70 20 0.25 17.29 TABLE I I I (continued) Extrusion conditions: example 1 2 3 4 5 6 resin C C A A A A gauge (mm) .04 .05 .04 .04 .05 .06 BUR 3: 1 3: 1 3.5: 1 4: 1 4.0: 1 4.0 Screw speed / min 90 154 120 152 152 152 Fusion temperature (° C) 199 204 210 216 216 216 Upper Pressure (MPa) 8.3 9.0 13.8 15.9 15.9 15.9 Amperes 7.0 8.5 10 11 11.0 11.0 Matrix Regime (kg / hour / cm) 1.3 2.1 1.4 1.7 1.7 1.7 Specific Output Regime (kg / hour / rpm) 0.23 0.22 • 0.18 0.18 .18 .18 Table IV Resin B Resin D MI (gram / 10 minutes) 0.7 0.9 HLMI (gram / 10 minutes) 69.0 73 MFR 98.0 80.0 Density (gram / cc) 0.922 0.920 Extrusion Conditions: Fusing Temperature (° C) 218 207 Higher Pressure (Mpa) 26.9 20.0 Amperes 110 90 Matrix Regime (kg / hr / cm) 1.8 1.8 Specific Output Regime (kg / hr / rpm) 1.7 2.0 Bubble Stability GOOD GOOD Fusion Fracture NONE NONE Table IV (continued) Film Properties: 30 micron film, 2.5: 1 BUR Resistance tension MPa MD 34.5 23.4 TD 24.8 18.6 Elongation at Break (%) MD 560 260 TD 800 540 Secant Module (MPa) MMDD 225555 186 TD 296 228 Elmendorf break (N / mm) M MDD 5 511..22 77.0 TD 385 62.8 Shrinkage (%) M MDD 7 766 %% 78% TD 0% 20% Hot Melt Tension (kPa) M MDD 2 222..88 31.0 Cold Tension (kPa) M MDD 8 85555 1627 Sting (J / mm) 8 899 65.4 Dart Drop (grams) 115500 97 Turbidity (%) 3355..00 5.0 Luster (45 degrees) 1188..00 68.0 Film Properties 55 micron film, 2.5: 1 BUR Stress Resistance (MPa) MD 32.4 20.0 TD 26.9 19.3 Elongation at Break (•%) MD 760 475 TD 900 660 Secant Module (MPa) MD 248 193 TD 290 220 Elmendorf Break (N / millimeter) MD 73.2 54.3 TD 192.5 65.5 Shrinkage (%) MD 66% 68% TD 8% 23% Hot Melt Tension (kPa) M MDD 1 188..66 38.6 Cold Tension (kPa) "M MDD 1 1440000 1434 Sting (J / mm) 8 800..11 62.3 Dart Drop (grams) 223300 170 Turbidity (%) 3344..00 4.7 Luster (45 degrees) 2222..00 81.0 Film Properties: 30 micron film, 3.0: 1 BUR Stress Resistance (MPa) MD 31.7 23.4 TD 26.2 22.8 Elongation at break MD 600 275 TD 800 600 Secant Module (MPa) MD 241 186 TD 303 207 Breakage Elmendorf MD 77.0 48.1 (N / mm) TD 327.3 77.0 Shrinkage (%) MD 75% 80% TD 10% 40% Hot Melt Tension (kPa) M MDD 1 177..99 33.1 Cold Tension M MDD 9 95522 1345 Sting (J / mm) 8 844..66 74.3 Dart Drop (grams) 112255 103 Turbidity (%) 3322..00 4.6 Luster (45 degrees) 2200..00 72.0 Film Properties: 55 micron film, 3.0: 1 BUR Resistance to Tension MD 30.3 26.2 (MPa) TD 28.3 22.1 A Allaarrggaammiieennttoo aa llaro rroottuurraa M MDD 8 80000 430 (%) TD 900 600 Sealing Module MD 248 193 (MPa) TD 262 193 Elmendorf breakage MD 94.3 43.9 ((NN // mmmm)) T TDD 1 19922..55 55.8 Shrinkage (%) MD 63% 70% TD 16% 40% Hot Melt Tension (kPa) MD 13.8 13.8 Cold Tension (kPa) MD 1317 478 Sting (J / mm) 80.1 73.4 Dart Drop (grams) 260 191 Turbidity (%) 33.0 4.2 Luster (45 degrees) 22.0 79.0 Properties of the Film: 30 micron film, 3.5: 1 BUR Resistance to the Tension M MDD 3 311..77 22.8 (MPa) T TDD 2 222..11 22.8 Elongation at break MDD 6 60000 300 TD 700 500 Secant Module M MDD 2 25555 172 (MPa) T TDD 2 28833 206 Elmendorf break (N / mm) M MDD 8 822..88 28.9 T TDD 3 32277 67.4 Shrinkage (%) M MDD 7 755 %% 77% TD 20% 50% Hot Melt Tension (kPa) M MDD 1 144..55 26.2 Cold Tension (kPa) M MDD 3 36655 931 Sting (J / mm) 7 755..77 75.7 Dart Drop (grams) 1 15500 127 Turbidity (%) 3 322..00 4.5 Luster (45 degrees) 2 200..00 72.0 Film Properties: 55 micron film, 3.5: 1 BUR Resistance to Stress (MPa) MD 30.3 20.7 TD 26.2 19.3 Elongation at Break (%) M MDD 8 87755 480 TD 900 580 Secant Module (MPa) M MDD 2 26611 179 T TDD 2 28811 186 Breakdown Elmendorf (N / mm) M MDD 1 10055..8 8 28.1 TD 163. 6 48.1 Shrinkage (%) M MDD 6 600 %% 70% TD 30% 45% Hot Melt Tension (kPa) M MDD 1 133 ..88 50.3 Cold Tension (kPa) M MDD 1 1224411 1489 Sting (J / mm) 7 711..22 71.12 Dart Drop (grams) 3 30000 185 Turbidity (%) 3 333..00 4.8 Luster (45 degrees) 2 222..00 79.0 Notes of the Examples: 1. MI = fusion index 2. HLMI = flow index .3. MFR = melt flow ratio 4. The stability of the bubble is determined by the speed of the line. The faster the speed (before the failure) the better the stability of the bubble. 5. The impact or shock of the dart (fall of the dart) is determined under methods D-1709, of the American Society for the Test of Materials. They are provided in grams. 6. The Elmendorf Break is determined under Method D-1992 of the American Society for Testing Materials. It is provided in N / millimeters. 7. MD = machine direction 8. TD = transverse direction 9. Tension Resistance is measured in accordance with Method D-882 of the American Society for the Testing of Materials. 10. Elongation is measured in accordance with Method D-882 of the American Society for the Testing of Materials.11. The tensile strength at the limit point is measured in accordance with Method D-882 of the American Society for the Testing of Materials. 12. The Secant Module is measured in accordance with Method D-882 of the American Society for Testing Materials. 13. Turbidity is determined under Method D-1003 of the American Society for the Testing of Materials. 14. Luster is determined under Method D-2457 of the American Society for the Testing of Materials. 15. Fusion fracture is determined by visually examining the film. Each film is provided with a value from 1 to 9 with the value 1 being the worst case of the fusion fracture and the value 9 representing that there is essentially no fusion fracture in the following way: 1 = seriously thick 2 = coarse 3 = coarse sand skin 4 = sanding skin serious 5 = sanding skin 6 = rough surface 7 = slightly rough surface 8 = small imperfection, but acceptable 9 = essentially without melting fracture 16. Puncture resistance: the test is carried out end with a metal cylinder, open at both ends that have a diameter of 75 millimeters and length of 100 millimeters. An open end is covered with a film that shows that it is held taut by a metal band that surrounds that end of the cylinder (similar to a drum). The cylinder is placed in a vertical position with the film covered with the end facing up. Then the film is pressed with the pronounced point of a rod similar to a nail (5 millimeters in diameter and 150 millimeters in length) and a force is exerted against the film. When the film is broken, the force exerted is measured in grams. 17. STY (kilogram / hour / cubic centimeter) is the space time yield defined as kilograms per hour of the polymer produced per cubic meter of the fluidized bed.

Claims (7)

CLAIMS:

1. A shrinkable film comprising a mixture of copolymers of ethylene and one or more alpha-olefins having from 3 to 12 carbon atoms formed in situ, the mixture having a melt index within the range of about 0.2 to about 3.5 grams per 10 minutes; a melt flow ratio within the range of about 50 to about 175; a molecular weight within the range of about 90,000 to about 225,000; a ratio of Mw / Mn of at least about 8; and a density within the range of 0.910 to 0.940 grams per cubic centimeter, the shrinkable film is formed at a blow ratio within the range of about 2: 1 to about 6: 1 and has the following properties: (i) a temperature of about 135 degrees centigrade, a shrinkage of at least about 50 percent in the machine direction and zero shrinkage or positive in the transverse direction; (ii) the melting tension is zero kilopascals or positive; and (iii) a cooling voltage of at least about 0.35 x 103 kilopascals.

2. The film according to claim 1, wherein the molecular weight of the mixture is within the range of about 120,000 to about 225,000.

3. The film according to claim 1, wherein the copolymer mixture is formed in a high molecular weight reactor and a low molecular weight reactor, the polymer formed in the high molecular weight reactor has a flow index inside. from the scale of about 0.2 to about 6 grams per 10 minutes, and a density within the scale of 0.900 to 0.930 gram per cubic centimeter, and the polymer formed in the low molecular weight reactor has a melt index within the scale from about 100 to about 1500 grams per 10 minutes and a density within the range of 0.905 to about 0.945 gram per cubic centimeter.

4. The film according to claim 1, wherein the mixture has a melt index within the range of about 0.5 to about 3.5 grams per 10 minutes.

5. The film according to claim 1, wherein the mixture has a ratio of Mw / Mn of at least about 10.

6. A shrinkable film comprising a mixture of copolymers of ethylene and one or more alpha-olefins having from 3 to 8 carbon atoms formed in situ, the mixture having a melt index in the range of about 0.5 to about 3.5 grams For 10 minutes; a melt flow ratio within the range of about 50 to about 175; a molecular weight within the range of about 130,000 to about 200,000; a ratio of Mw / Mn of at > "> less than about 10, and a density within the range of 0.918 to 0.926 gram per cubic centimeter, the shrinkable film is formed at a blow ratio within the range of about 2: 1 to about 4.5: 1 and has the following properties: 5 (i) at a temperature of about 135 degrees centigrade a shrinkage of at least about 60 percent in the machine direction, and from 0 to about 40 percent in the transverse direction; (ii) the melting tension of about 14 0 to about 103 kilopascals; and (iii) a cooling tension of about 0.85 x 103 to about 2 x 103 kilopascals, the film has been extruded to a 5 gauge within the range of about .0254 to about .0889 millimeter and has been produced in situ by placing in contact ethylene and at least one alpha-olefin comonomer having from 3 to 8 carbon atoms, with a magnesium / titanium based catalyst system in each of the two reactors connected in series, under polymerization conditions, wherein (a) the polymer formed in the high molecular weight reactor has a flow index within the scale of about 0.2 to about 1 gram per 10 minutes and a density within the scale of 0.900 to 0.930 gram per cubic centimeter, and (b) the polymer formed in the low molecular weight reactor has a melt index within the range of about 100 to about 1500 grams per 10 minutes and a density within the range of 0.905 to 0.945 gram per cubic centimeter , the weight ratio of the polymer of the high molecular weight reactor to the polymer of the low molecular weight reactor is within the range of about 0.5: 1 to about 2: 1. The film according to claim 6, wherein the mixture is produced under the following conditions: (i) in the high molecular weight reactor: the molar ratio of the comonomer (s) to ethylene is within the scale of approximately 0.05: 1 to approximately

0. 4: 1, and the mole ratio of hydrogen, if used, to ethylene is within the range of about 0.0001: 1 to about 0.3: 1; and (ii) in the low molecular weight reactor: the molar ratio of the comonomer (s) to ethylene is within the range of about 0.1: 1 to about 0.6: 1, and the molar ratio of hydrogen to ethylene is within the range of scale from about 1: 1 to about 2.5: 1.