MXPA99004381A - Shrink film having balanced properties or improved toughness and methods of making the same - Google Patents

Abstract

This invention relates to an improved shrink film obtained by selectively controlling and optimizing the density differential between at least two polyolefin polymer components to provide narrow density splits. One aspect of this invention relates to a biaxially oriented polyolefin shrink film having balanced properties and another aspect of this invention relates to an oriented shrink film having improved toughness. This invention also relates to a biaxial orientation method of making an improved shrink film using elaborate shrink orientation techniques such as tenter framing, double-bubble, trapped bubble, tape orientation or combinations thereof. Most preferably, the first polyolefin polymer component is a lower density, substantially linear ethylene/&agr;-olefin interpolymer and the second polyolefin polymer component is a higher density, heterogeneously branched ethylene/&agr;-olefin interpolymer.

Description

CONTRACTION FILM THAT HAS BALANCED PROPERTIES OR IMPROVED RIGIDITY AND METHODS TO FORM THE SAME This invention relates to an improved shrink film obtained by selectively controlling and optimizing the differential density between at least two polyolefin polymer components to provide narrow density separations. One aspect of the invention relates to a biaxially oriented polyolefin shrink film having balanced properties comprising a polymer composition, the polymer composition comprising and formed of (A) a first ethylene polymer component having a single peak Differential Scanning Calorimetry (CBD) Fusion and Single Peak Elution Fractional Analytical Temperature Elevation (FEETA) and (B) a second component of ethylene polymer having one or more melting peaks of CBD, where The density differential between component (A) and component (B) is on the scale from 0 to 0.03 g / cc. Another aspect of the invention relates to an oriented shrink film having improved rigidity and comprising a polymer composition, the polymer composition comprising and made of at least a lower density, a homogeneously branched ethylene polymer (C) and at least one higher density molecular weight ethylene polymer of higher density (D) wherein the density differential between the two polymer components are in the range of 0.001 to 0.05 g / cc. This invention also relates to a method of biaxial orientation by forming a shrink film having balanced properties, a method for forming an oriented shrink film having improved stiffness. Food products such as poultry, fresh red meat and cheese, as well as non-food industrial and retail items, are packaged by various methods of heat shrink film. Heat shrink films can be oriented monoaxially or biaxially and are required to have a variety of film tributes. For example, in addition to a high shrinkage response, for successful use in hot fill and bake applications, shrink films should also have a relatively high smoothing point. There are two main categories of heat shrinkage films, heat shrink shrink film and shrink film oriented. Heat shrink shrink film is formed by a simple hot-blow bubble film process and, conversely, the shrink film oriented is made by elaborate biaxial orientation processes known as double bubble, bubble construction of tape, trapped bubble or tension. Both amorphous and semi-crystalline polymers can be formed into oriented shrink films using elaborate biaxial orientation processes. For amorphous polymers, the orientation is carried out at a temperature immediately above the glass transition temperature of the polymer. For semi-crystalline polymers, the orientation is carried out at a temperature below the peak melting point of the polymer. Shrink packaging generally involves placing an article in a bag (or sleeve) made of a heat shrink film, then closing or heat sealing the bag and then exposing the bag to sufficient heat to cause shrinkage of the bag and the bag. intimate contact between the bag and the item. The heat inducing shrinkage can be provided by conventional heat sources, such as hot air, infrared radiation, hot water, hot oil burning flames or the like. The heat compression wrapping of food products helps to preserve freshness, its attractiveness, hygiene and allows the narrower insertion of the quality of the packaged food item. Heat compression wrapping of industrial and retail items, which are alternatively referred to in the art and in the present, as industrial and retail packages, preserves the cleanliness of the product and is also a convenient means of packaging and intercalating for accounting and transportation purposes. The biaxial heat compression response of the compression film is obtained by initially stretching the manufactured film to an extension several times its original dimensions in the directions of the machine and transverse to orient the film. Stretching is usually achieved while the manufactured film is sufficiently smooth or cast, although contraction films by cold extraction are also known in the art. After the fabricated film is stretched and while still in a stretched condition, the stretch or orientation is frozen or fixed by rapid cooling of the film. Subsequent heat application will then cause the oriented film to relax and, depending on the actual shrinkage temperature, the oriented film can essentially return to its original unstretched dimensions, i.e., shrink in relation to its stretched dimension. The orientation window and the shrinkage response of oriented films are affected by resin properties and manufacturing parameters. The orientation window depends on the amplitude of the resin melting scale and, as such, directly refers to the short chain branching distribution of the resin. In general, the ethylene alpha-olefin interpolymers having a broad short chain branching distribution and broad melting scale (e.g., heterogeneously branched ultra low density polyethylene resins such as ATTAN E ™ resins supplied by The. Dow Chemical Company) exhibit a wide orientation window compared to the ethylene alpha-olefin interpolymers characterized by having a narrow short chain branching distribution and narrow melting scale (e.g., homogenously branched linear ethylene polymers such as EXCEED ™ and EXACT ™ resins supplied by Exxon Chemical Corporation). The shrinkage of the polyolefin film depends on the shrinkage tension and film density. The film shrinkage decreases as the orientation temperature is increased due to the lower shrinkage pressure. The shrinkage of film at lower densities (lower crystallinity) is increased because the crystallites provide topological constraints and, as such, hide free shrinkage. Conversely, for a given extraction ratio, the stress depends on the crystallinity of the resin at the orientation temperature. While the temperature at which the particular polymer is soft enough or melts is a critical factor in various orientation techniques, such temperatures are not well defined in the art. The descriptions pertaining to oriented films that describe various types of polymers (which invariably have varying crystallinity and polymer melting points) simply do not define the shrinkage or orientation temperatures used for the reported comparisons. The Patent of E. U.A. 4,863,769 to Lustig et al., WO 95/00333 to Eckstein et al., And WO 94/07954 to Garza et al. Are two examples of such descriptions. The direct effect of density or crystallinity on the shrinkage response and other desired shrink film properties such as, for example, resistance to shrinkage. impact, for example, in WO95 / 08441, the description of which is incorporated herein by reference. That is, even when the orientation temperature is presumably constant, the lower density polymer films will show a superior shrinkage response and improved impact strength. However, the effects of density and other resin properties of the orientation temperature are not well understood. In the prior art, there are only general rules of practical or generalized teachings that refer to proper stretching or orientation conditions. For example, in commercial operations, it is often that the temperature at which the film temperature is adequately soft or melts is just above its respective glass transition temperature in the case of amorphous polymers, or below its respective melting point, in the case of semi-crystalline polymers. While the effects of density and other resin properties of the optimum orientation temperature of the polyolefins are generally unknown, it is clear that heterogeneously branched ethylene polymers such as ATTAN E ™ and DOWLEX ™ have relatively large orientation windows (ie. say, the temperature scale at which the resin can stretch substantially when melted or softened). It is also clear that softening temperatures and other film properties such as, for example, drying modulus, tend to decrease at lower polymer densities. Because of these relationships, films with high shrinkage response, wide orientation windows, high modulus and high smoothing temperatures (i.e. shrinkage films with balanced properties) are unknown in the prior art. That is, polymer designers invariably have to sacrifice high smoothing temperatures and high modulus to provide films with high shrinkage response and wide orientation windows. The importance of the upper module belongs to, for example, the need for good handling capacity during automatic packing operations and good handling during bag forming operations. An example of teaching that is beyond the ordinary practical rules (but which have never been well generalized) is provided by Golike in the U.A. 4,597,920. Golike teaches that the orientation should be carried out at temperatures between the lower and higher melting points of an ethylene copolymer with at least one α-olefin of C 8 -C 8. Golike specifically teaches that the temperature differential is at least 10 ° C, however, Golike also specifically describes the full scale that the temperature differential may not be practical, because, depending on the particular equipment and technique used , can be presented based on the polymer film at the lower end of the scale. At the upper limit of the scale. Golike teaches that the structural integrity of the polymer film begins to suffer during stretching (and eventually fails at higher temperatures) because the polymer film is then in a soft, molten condition. See, the Patent of E. U.A. 4,597, 920, Col. 4, lines 52-68 that join Col. 5, lines 1-6. The orientation temperature scale defined by Golike (which is based on upper and lower peak melting points) is generally applied to other mixtures of heterogeneously branched ethylene / α-olefin polymers and interpolymers, ie, compositions having two or more CBD melting points and generally do not apply to homogeneously branched ethylene / α-olefin interpolymers having only one melting point of CBD. Golike also indicates that a person of ordinary skill can determine the tearing temperature of a particular polymer and discloses that for heterogeneously branched polymers having a density of about 0.920 g / cc, the tearing temperature occurs at a temperature above the Lower peak melting point. See, Patent of E. U.A. No. 4,597,920, Col. 7, Example 4. However, Golike does not teach or suggest how to optimize the orientation process as in terms of the stretching temperature at a given rate and stretch ratio to maximize the contraction response and achieve the balanced properties. Hideo and others, in EP 0259907 A2 teaches that the surface temperature of the film at the starting point of the stretch should be within the range of 20 ° C to about 30 ° C or below the melting temperature of the polymer determined with respect to the peak endothermic of main CBD. While such teaching is considered applicable to homogenously branched ethylene / α-olefin interpolymers having a single peak of CBD, the prescribed scale is both general and broad. Furthermore, Hideo and others do not provide any specific teaching as to the optimum orientation temperature for a particular polymer with respect to the heat shrinkage response, nor for any other desired shrink film property. WO 95/08441 provides generalized teachings pertaining to homogenously branched ethylene / α-olefin interpolymers. In the examples of this disclosure, several homogeneously branched, substantially linear ethylene / α-olefin interpolymers were studied and compared with the heterogeneously branched ethylene / α-olefin interpolymers. Although the homogeneously branched, substantially linear ethylene / α-olefin polymers had densities ranging from 0.896 to 0.906 g / cc, all interpolymers (including the heterogeneously linear ethylene / α-olefin interpolymer, ATTAN E ™ 4203, supplied by The. Dow Chemical Company, which had a density of 0.905 g / cc) was oriented essentially at the same orientation temperature. The results reported in WO 95/08441 describe three general findings: (1) at an equivalent polymer density, the substantially linear ethylene / α-olefin ether polymers and homogeneously branched linear ethylene / α-olefin interpolymers have shrinkage responses essentially equivalent (compare Example 21 and Example 39 on pages 15-16), (2) the shrinkage responses increase at lower densities and constant orientation temperatures, and (3) as the orientation temperature increases, they increase the orientation regimes. In addition, a careful study of the Examples and CBD melting point data not reported for the interpolymers reported in WO 95/08441 indicate that the Examples described in WO 95/08441, which at a given draw ratio regime, are a preference for orienting the multilayer film structures at orientation temperatures above the respective CBD melting point of the cooled polymer as the shrinkage control layer. Furthermore none of the teachings or examples in WO 95/08441 suggests that a shrink film with balanced properties is obtained. Other descriptions that exhibit orientation information with respect to homogeneously branched ethylene polymers (do not specify orientation conditions in relation to the lower shrinkage temperatures) teach the specific requirements of the balanced shrink film properties) include EP 0 600425 A1 from Babrowicz et al. and EP 0 587502 A2 from Babrowicz et al.

Although various film compositions have been described in the art as being useful for shrinkage film with heat blow and oriented shrink film applications, these descriptions focus on the provision of films with a high shrinkage response when prepare by any method. However, in addition to the response with high shrinkage, the shrink film should also have a number of important properties such as, for example, relatively high softening points and improved modulus which are particularly suitable for use in heat-filled applications. In addition, for many applications, including heat-filled packing and shrinkage packaging of sharp articles, such as, for example, main drum items and meat knives, the shrink films should also have good abuse or stiffness properties. While the technique has several alleged solutions that meet the particular performance requirements of shrink film applications, it does not provide known shrinkage films with the desired balance of high shrinkage response and improved stiffness. Accordingly, although there are several general rules and general descriptions pertaining to shrinkage film and orientation temperatures suitable for biaxially oriented polyolefins, there is no specific information as to the optimum orientation conditions as a function of the type of polymer and, More importantly, there is no specific information regarding balanced or optimized shrinkage responses, wide orientation windows, high modulus and high smoothing temperatures. As such, it is an object of the present invention to provide an improved shrink film according to a shrinkage response maximally increased, an orientation orientation increased and, for a given polymer modulus or density, a relatively high softening temperature. It is also an object of the present invention to provide a shrink film with a high shrinkage response and improved stiffness. Another object of the invention is to provide a method for forming an oriented shrink film having heat shrink and balanced rigidity properties. Another object of the invention is to provide a method for forming an oriented shrink film having balanced properties of heat shrinkage and stiffness wherein the method includes an elaborate biaxial orientation technique. These and other objectives will be apparent from the following detailed description and several following modalities. In accordance with the present invention, we have discovered that for a polymer composition that is comprised of at least two ethylene polymers, wherein the density differential between the two ethylene polymer components is selectively controlled and optimized, a improved shrink film. The improved shrinkage film will have balanced properties, i.e., a high shrinkage response, a wide orientation window and a relatively high smoothing temperature. We have also found that where the polymer composition is further defined as comprising a second component of higher density ethylene polymer which is characterized by having a molecular weight equal to or greater than the first component of ethylene polymer. of lower density, the shrinkage film will be characterized by having a high shrinkage response and improved film rigidity. The broad aspect of the present invention is a shrink film comprising a polymer composition, the polymer composition characterized by having a density in the scale of 0.88 grams / centimeter (g / cc) to 0.94 g / cc, as determined in accordance with ASTM D-792 and which comprises and is made from 20 to 80 weight percent, based on the total weight of the polymer composition, of at least one first ethylene polymer characterized by having (i) one or more melting peaks as determined using differential scanning calorimetry (CBD), and (ii) a density in the scale of 0.87 (g / cc) to 0.93 g / cc, as determined in accordance with ASTM D-792, and from 20 to 80 weight percent, based on the total weight of the polymer composition, at least one first ethylene polymer characterized by having (i) one or more melting peaks as determined using the differential scanning calorimetry (CB D), and (ii) a density on the scale of 0.89 (g / cc) to 0.96 g / cc, as determined in accordance with ASTM D-792, wherein the density differential between the first and second ethylene polymer components, determined in accordance with ASTM D-792, is on a scale of 0 to 0.05 g / cc. A second aspect of the present invention is a shrink film which comprises a polymeric composition, the polymer composition having a density in the scale of 0.88 grams / centimeter (g / cc) to 0.94 g / cc, determined in accordance with ASTM D-792 comprising and made of (A) from 20 to 80 weight percent, based on the total weight of the polymer composition, of at least one first polymer characterized by having (i) a single peak of fusion, determined using differential scanning calorimetry (CBD), or a single peak of Fractionation of Analitical Temperature Elevation Elution (FEETA), and (¡i) a density on the scale of 0.87 (g / cc) to 0.93 g / cc, determined in accordance with ASTM D-792, and (B) from 20 to 80 percent by weight, based on total weight! of the polymer composition, of at least one second polymer characterized by having (i) one or more melting peaks, determined using differential scanning calorimetry (CBD), and (ii) a density on the scale of 0.89 (g / cc) at 0.96 g / cc, determined in accordance with ASTM D-792, wherein the density differential between the first ethylene polymer component (A) and the second ethylene polymer component (B), determined in accordance with ASTM D-792, is in the range of 0 to 0.03 g / cc. A third aspect of the present invention is a shrink film comprising a polymer composition, the polymer composition having a density on the scale of 0.88 grams / centimeters (g / cc) to 0.94 g / cc, and comprising and made from (C) from 20 to 80 weight percent, based on the total weight of the polymer composition, of at least one first ethylene polymer, wherein at least one first ethylene polymer was manufactured using a single site of metallocene or restricted geometry catalyst system and is characterized by having: (i) one or more melting peaks, as determined using differential scanning calorimetry (CBD), (ii) a short chain ramification index ( I RCC) or composition distribution branching index (I RDC) greater than 50%, determined using an elution fractionation of temperature rise, (i ii) a molecular weight, as indicated by the value a value of ind melting ice determined in accordance with ASTM D-1238, and (iv) a density on the scale from 0.87 (g / cc) to 0.93 g / cc, and (D) from 20 to 80 weight percent, based on the total weight of the polymer composition, of at least one second ethylene polymer characterized by having (i) one or more melting peaks, determined using differential scanning calorimetry (CBD), (ii) a molecular weight equal to, or greater than the molecular weight of the first ethylene polymer (C) as indicated by the melt index values determined in accordance with ASTM B-1238, and (iii) a density on the scale of 0.89 (g / cc) to 0.96. g / cc, wherein the differential between the first and second components of ethylene polymers (C) and (D) is in the range of 0.001 to 0.05 g / cc, the density of at least one first ethylene polymer (C ) is lower than the density of at least one ethylene polymer (D) and where the density of the polymer components (C) and (D) and for the polymer composition is determined in accordance with ASTM D-792. Unexpectedly, the shrinkage film of the present invention shows an improved shrinkage response at a comparatively higher density while normally lower densities are required for said improvement. As another unexpected surprise, the shrink film of the invention also shows a comparatively high softening temperature for its response to the given compression where normally the interpolymer softening temperatures of ethylene alpha-olefin are reduced where Improves response to shrinkage. Specifically, the shrinkage film of the invention surprisingly exhibits superior shrinkage at higher equivalent softening temperatures while for prior art materials, smoothing temperatures must be decreased for superior shrinkage performance. As another unexpected result, the present oriented shrinkage film exhibits improved rigidity when biaxially oriented using an elaborate orientation process (eg, stress marking or double bubble orientation) relative to comparative films made from compositions of polymer ilar. That is, the present invention is surprising in that the film of the invention has superior oriented shrinkage film stiffness in relation to a comparative film wherein the same comparative film shows excellent stiffness of heat blown shrinkage film. In this comparison, the comparative film comprises (1) a first component of ethylene polymer equivalent to the film of the invention and (2) a second component of ethylene polymer that differs from the second polymer component of the film of the invention and its first component of ethylene polymer. The second ethylene polymer component of the comparative film differs from the first ethylene polymer component of the comparative film having a lower molecular weight and higher density. The stiffness performance of the film of the invention is also surprising since it can have a shrinkage film stiffness level which is commonly obtained with heterogeneously branched linear ethylene / α-olefin polymers such as, for example, LLDPE resins of DOWLEX ™ available from The Dow Chemical Company. The excellent stiffness of the film of the invention in comparison with heterogeneously branched linear ethylene / α-olefin interpolymers is considered particularly surprising when at least one first ethylene polymer is a substantially linear ethylene polymer. That is, the impact or stiffness properties of the present invention (as well as for the invention described by Lai et al., In U.S. Patent Nos. 5,272,236 and 5,278,272) are contrary to various teachings in the art ( see, for example, "Enhanced Metallocene PE Terpolymers are Unveiled," Modern Plastic, July 1994, pp. 33-34) suggesting that lower stiffness properties can be expected when long chain branched polymers are used. While the present invention allows practitioners to perform the increased unrestrained compression performance, the benefits of this invention are particularly useful for common commercial cases where the orientation temperature capabilities of the drawing operation are essentially fixed. That is, by providing an increased orientation window, a film composition that could not be successfully stretched within a given type capacity, can now be conveniently oriented. Further, due to the discovery of the excellent shrinkage oriented film stiffness, we think that one of the benefits of the present invention is that now practitioners can use the same film composition to prepare a shrinkage oriented film or blown shrink film. by heat and perform excellent properties of abuse or rigidity in both cases. FIGURE 1 is a first heat CBD curve illustrating the residual crystallinity portion of a heterogeneously branched polymer that remains at 100 ° C whose temperature is below several melting peaks of the polymer illustrated.

FIGURE 2 is an Analytical Temperature Elevation Elution Fraction (FEETA) curve of EXCEED ™ ECD 301 resin (3 g / 10 min I2, density 0.917 g / cc, supplied by Exxon Chemical Company which has a single peak of FEETA FIGURE 3 is a graph of response to the contraction to 90 ° C in water and 105 ° C in hot oil against the polymer composition density for Examples 10-12 and Comparative Examples 13 and 14. FIGURE 4 is a graph of a 1 percent secant module (MPa) ) against the density of the polymer composition (in grams / cubic centimeter) for Examples 10-12, comparative examples 13-18. The term "polymer" as used herein refers to a polymeric compound prepared by polymerizing monomers, either the same or a different time. The term "polymer" is used generically herein to encompass the terms "homopolymer", "copolymer", "terpolymer" and "interpolymer". The term "interpolymer" as used herein refers to polymers prepared by the polymerization of at least two different types of monomers. The generic term "interpolymer", therefore, includes the term "copolymers" (which is usually used to refer to polymers prepared from two different monomers) as well as the term "terpolymers" (which is usually used to refer to polymers prepared from three different types of monomers, e.g., an ethylene / butene / hexene polymer). "Stretched" and "oriented" are used interchangeably in the art and in the present, although the orientation is actually the consequence of a film being stretched, for example, for pushing of internal air pressure on the tube or for a push of tension frame on the edges of the film. The term "lower stretch temperature", as used herein, means the temperature below which the film tears and / or stretches non-uniformly at a rate of stretch and stretch ratio (extraction) during operation. of stretching or the passage of an orientation technique. The lowermost stretching temperature is (1) below the melting point of the film, (2) at a temperature below which the film can not be stretched uniformly (i.e. without the formation of bands or rings or that the sample is discharged from the restoring fasteners at set pressures of approximately 3.5 MPa, (3) a temperature below which the film is torn during a particular stretch regime and stretch ratio. maximum the imparted stretch and therefore the shrinkage response, the objective is to operate as close as possible to the lower stretch temperature as your equipment and capabilities can allow either a significant stretch or orientation to be achieved or not. a single step or a combination of the sequential steps.In addition, practitioners will appreciate that the stretching temperature or almost optimal for the shrinkage response maximally increased at a given shrinkage temperature are inter-related to the rate and stretch ratio. That is, as long as it is optimum or near optimum at a particular stretch temperature in a combination of rate and stretch ratio, the same stretch temperature will not be optimal or nearly optimal at a different combination of rate and stretch ratio. Practitioners will also appreciate that to obtain the maximum stretch response from the orientation frozen in the film, the shrinkage temperature will be equal to or exceed the stretch temperature. That is, reduced shrinkage temperatures will not allow full relaxation or shrinkage of the film. However, excessive shrinkage temperatures can decrease the integrity of the film. Practitioners will also appreciate that for a given combination of stretching temperatureStretching rate and stretch ratio, increases in the shrinkage temperature to a temperature immediately below the temperature at which the integrity of the film fails produces superior shrinkage responses and higher levels of shrinkage stress. Shrinkage temperatures in the range of 70 to 140 ° C, especially 80 to 125 ° C, and more especially 85 to 1 1 0 ° C are suitable in the present invention. The term "residual crystallinity" is used in the present to refer to the crystallinity of a polymeric film at a particular stretch temperature. Residual crystallinity was determined using a Perkin-Elmer CBD 7 assembly for a first heat at 10 ° C / min. of a sample of compression molded film, cooled with polymer water. The residual crystallinity for a polymer at a particular temperature is determined by measuring the heat of fusion between the temperature and the melting temperature completed using a partial area technique and dividing the heat of fusion by 292 Joules / gram. The heat of fusion is determined by integration of the partial area computer using PC series of Software Version 3. 1 of Perkin-Elmer. An example of the determination of residual crystallinity and calculation is shown in FI G U RA 1. The term "shrinkage control layer" is used herein to refer to the film layer that provides or controls the response to shrinkage. Said layer is inherent in all heat shrink films. In a heat shrink film of a layer, the shrinkage control layer will be the film itself. In the multilayer heat shrink film, the shrinkage control layer is usually the core or an inner film layer and usually the thicker film layer. See, for example WO 95/08441. The term "substantially unoriented form" is used herein with reference to the fact that an amount of orientation is usually imparted to a film during ordinary manufacturing. As such, it is understood that the manufacturing step, by itself, is not used to impart the degree of orientation required for the desired or required shrinkage response. It is thought that the present invention can generally be applied to operations where manufacturing and orientation steps (eg, tension frame) are separated as well as operations where manufacturing and orientation are presented simultaneously or sequentially as part of the process. own operation (eg, a double bubble technique). By "a single FEETA peak" is meant that the purge portion or the non-crystallizable polymer fraction observed in a FEETA curve is not considered to be a FEETA peak. For example, FIGURE 2, the elution at the elution temperature of about 20 ° C is a purge portion and not a FEETA peak. As such, the polymer is characterized by having a single FEETA peak whose peaks are an elution temperature of approximately 57.5 ° C. Elevation temperature elution fractionation (FEET) techniques such as those described, for example, by Wild et al., Can be used to "signal" or identify the composition of the polymer of the invention and the oriented shrink film. By "independently characterized" it is understood that the melt index of ASTM D-1238 of the polymer components need not be the same, although they may be the same. The term "linear" as used to describe ethylene polymers is used herein as well as in the conventional sense to mean the polymer base structure of the ethylene polymer that lacks measurable or demonstrable long chain branches, i.e. , the polymer is characterized by having branches of less than 0.01 long / 1000 carbons. The term "homogeneous ethylene polymer" as used to describe ethylene polymers is used in the conventional sense in accordance with the original description by Elston in the U.A. Number 3, 645,992, the description of which is incorporated herein by reference. The term "homogeneous ethylene polymer" refers to an ethylene polymer in which the comonomer is randomly distributed within a given polymer molecule and wherein substantially all of the polymer molecules have substantially the same molar ratio of ethylene to comonomer.

As defined herein, both the substantially linear ethylene polymers and the ethylene polymers homogeneously branched lines are homogeneous ethylene polymers.

Homogeneously branched ethylene polymers are homogeneous ethylene polymers having short chain branches and characterized by a relatively high short chain branching distribution index (I DRCC) or relatively high composition distribution branching index (IRDC). . That is, the ethylene polymer has an IRDC greater than or equal to 50%, preferably greater than or equal to 70 percent, more preferably, greater than or equal to 90 percent. Also, the ethylene polymer is typically characterized by having a measurable high density polymer fraction (ie, a crystalline polymer fraction that has no short chain branching or zero methyl / 1000 carbons on the scale of 86 ° C to 98 ° C. ° C as determined by FEETA) on a scale of 0 to 0.5 weight percent, based on the total weight of the entire polymer, and preferably, there is no measurable high density fraction. The IRDC is defined as the percentage by weight of the polymer molecules having a comonomer content within 50 percent of the average total molar comonomer content and represents a comparison of the comonomer distribution in the polymer to the expected comonomer distribution for the Bernoullian distribution. The I RDC of polyolefins can be conveniently calculated from the data obtained from techniques known in the art, such as, for example, elution fractionation of temperature rise (here abbreviated as "FEET") as described, for example , by Wild and others, Journal of Polvmer Science. Polv. Phvs. Ed .. Vol. 20, p. 441 (1982), L. D. Cady, "The Role of Comonomer Type and Distribution in LLDPE Product Performance," SPE Regional Technical Conference, Quaker Square Hilton, Akron, Ohio, October 1-2, pgs. 107-1 19 (1985), or in the Patents of E. U.A. Nos. 4,798,081; 5,008,204 and 5,322, 728; the descriptions of all of which are incorporated herein by reference. However, the preferred FEET technique does not include purge amounts in I RDC calculations. More preferably, the polymer comonomer distribution of I CDR is determined using 13 C NMR analysis according to the techniques described, for example, in the U.S. Patent. Number 5,292,845 and by J .C. Randall in Rev. Macromol. Chem. Phys. C29, pgs. 201-317.

The terms "homogenously branched linear ethylene polymer" and "homogenously branched linear ethylene / α-olefin polymer" mean that the olefin polymer has a short, homogeneous or narrow branching distribution (i.e., that the polymer has an I RDC). relatively high) but that has no long chain branching. That is, the linear ethylene polymer is a homogeneous ethylene polymer characterized by an absence of long chain branching. Homogeneously branched linear ethylene polymers can be made using the polymerization process (eg, as described by Elston in U.S. Patent Number 3,645,992) which provides a uniform (ie, homogeneously branched) short chain branching distribution. In its polymerization process, Elston uses soluble vanadium catalyst systems to form such polymers, however, others, such as Mitsui Petrochemical Industries and Exxon Chemical Company, have used, as a report, the single-site catalyst systems as well. Lamados, to form polymers that have a homogeneous structure similar to the polymer described by Elston. The Patent of E. U.A. 4, 937, 299 of Ewen et al. And the Patent of E. U.A. 5,21 8, 071 of Tsotsui et al., Describes the use of metallocene catalysts, such as hafnium-based catalyst systems, for the preparation of homogeneously branched linear ethylene polymers. Homogeneously branched linear ethylene polymers are usually characterized by having a molecular weight distribution of Mp / Mn, of about 2. The terms "homogeneously linear branched ethylene polymer" or "homogenously branched linear ethylene / α-olefin polymer" do not refer to branched high-pressure polyethylene which is known to those skilled in the art to have numerous long chain branches. A homogenously branched linear ethylene / α-olefin interpolymer has short chain branching and the α-olefin normally at least is C3-C2o α-olefin (eg, propylene, 1-butene, 1-pentene) , 4-methyl-1-pentene, 1-hexen and 1-ketene). When used herein with reference to even ethylene homopolymer (ie, a high density ethylene polymer that does not contain any comonomer and therefore does not have short chain branches), the term "homogeneous ethylene polymer" or "homogeneous linear ethylene polymer" means that the polymers were formed using a so-called homogeneous catalyst system, such as, for example, the system described by Elston or Ewen or described by Canich in US Patents. Numbers 5,026, 798 and 5,055,438 or by Stevens et al., In the Patent of E. U.A. Number 5,064,802. The term "substantially linear ethylene polymer" is used herein to refer especially to homogeneously branched ethylene polymers having long chain branching. The term does not refer to heterogeneously or homogeneously branched ethylene polymers having a polymer base structure. For substantially linear ethylene polymers, the long chain branches have the same comonomer distribution as the polymer base structure and the long chain branches can be as long as about the same length as the length of the structure of the polymer. base of the polymer to which they are attached. The substantially linear ethylene polymers used in the present invention have 0.01 long chain branches / 1000 carbons to 3 long chain branches / 1000 carbons, more preferably 0.01 long chain branches / 1000 carbons to about 1 long chain branch / 1000 carbons and especially of 0.05 long chain branches / 1000 carbons to 1 long chain branch / 1000 carbons. The long chain branching is defined herein as a chain length of at least 6 carbons, above which the length can not be distinguished using C13 nuclear magnetic resonance spectroscopy. The long chain branches are obviously longer than the short chain branches that result from the incorporation of the comonomer. The presence of long chain branching can be determined in ethylene homopolymers using C13 nuclear magnetic resonance (NMR) spectroscopy and quantified using the method described by Randall (Rev. Macromol. Chem. Phys., C29, V. 2 &; 3, p. 285-297), the description of which is incorporated herein by reference. Although conventional C13 nuclear magnetic resonance spectroscopy can not determine the length of a long chain branch in excess of six carbon atoms, there are other known techniques useful for determining the presence of long chain branches in excess of six carbon atoms. , there are other known techniques useful for determining the presence of long chain branches in ethylene polymers, including ethylene / 1-ketene interpolymers. Two such methods are gel permeation chromatography coupled with a low angle laser light scanner (CPG-BLLAB) and gel permeation chromatography coupled with a differential viscometer detector (CPG-VD). The use of these techniques for the detection of long chain branches and the underlying theories have been well documented in the literature. See for example Zimm, G. H. and Stockmayer, W. H., J. Chem. Phys., 17, 1301 (1949) and Rudin, A., Modern Methods of Polvmer Characterization, John Wiley & Sons, New York (1991) p. 103-1 12. A. Willem deGroot and P. Steve Chum, both of The Dow Chemical Company, at the October 4, 1994 conference of the Federation of Analytical Chemistry and Spectroscopy Society (FACSS) in St. Louis, Missouri, presented data demonstrating that CPG-VD is a useful technique for quantifying the presence of long chain branches in substantially linear ethylene polymers. In particular, deGroot and Chum found that the level of long chain branches in samples of substantially linear ethylene homopolymers measured using the Zimm-Stockmayer equation correlated well with the level of long chain branches using C13 NMR. In addition, deGroot and Chum found that the presence of octene does not change the hydrodynamic volume of the polyethylene samples in solution and, as such, can be taken into account for the molecular weight increase attributable to short chain octene branches knowing the percentage mole of the octene in the sample. Regardless of the contribution to the molecular weight increase attributable to the short chain branches of 1-octene, deGroot and Chum showed that CPG-VD can be used to quantify the level of long chain branches in ethylene / octene copolymers substantially linear DeGroot and Chum also showed that a Log graphic (melting index of 12) as a function of LOG (Molecular Weight Weight Average CPG) as determined by CPG-VD illustrate that the long chain branching aspects (but not the extension of long chain branching) of substantially linear ethylene polymers are compared to that of highly branched low density polyethylene high pressure (PEDB) and are clearly different from ethylene polymers produced using Ziegler type catalysts such as titanium complexes and ordinary homogeneous catalysts such as hafnium and vanadium complexes. For substantially linear ethylene polymers, the long chain branching is larger than the short chain branching resulting from the incorporation of α-olefins into the polymer base structure. The empirical effect of the presence of long chain branching in the substantially linear ethylene polymers used in the invention manifests as improved rheological properties. The improved rheological properties of substantially linear ethylene polymers can be quantified and expressed herein in gas extrusion rheometry (REG) results and / or melt flow increments, 11 or I 2 - The substantially linear ethylene polymers are homogeneously branched ethylene polymers and are described in the patent of E.U.A. 5,272,236 and Patent of E. U.A. 5,278,272. Homogeneously branched substantially linear ethylene polymers can be prepared via the continuous solution, slurry or gas phase polymerization of ethylene and at least one optional α-olefin comonomer in the presence of a catalyst of restricted geometry, such as the method described in European Patent Application 416, 815-A, which is incorporated herein by reference. Polymerization can generally be carried out in a reactor system known in the art including, but not limited to tank reactors, a sphere reactor, a recycling cycle reactor or combinations thereof and the like, any reactor or all Reactors operated partially or completely adiabatically, not adiabatically or a combination of both and the like. Preferably, a continuous solution polymerization process is used to manufacture the substantially linear ethylene polymer used in the present invention. The terms "heterogeneous" and "heterogeneously branched" mean that the ethylene polymer is characterized as a mixture of interpolymer molecules having various molar ratios of ethylene to comonomer. As used herein, the terms "heterogeneous" and "heterogeneously branched" belong to a polymer of a single component or a polymer component of a polymeric composition, as such, the terms "heterogeneous" and "heterogeneously branched" are not significant with respect to a polymer composition comprised of polymers of multiple components.

The heterogeneously branched ethylene polymers are characterized by having a short chain branching distribution index (IDRCC) or branching index of IRDC composition distribution of less than 50 percent. The heterogeneously branched ethylene polymers are typically characterized by having molecular weight distributions, Mp / Mn, in the range of 3.5 to 4.1 and, as such, are different from substantially linear ethylene polymers and homogeneously branched linear ethylene polymers with respect to to the compositional composition of short chain branching and molecular weight distribution. For the broad aspect of the present invention, that is to say that it pertains to the provision of improved properties and rigidity, the density differential between at least two components of ethylene polymer, is generally in the range of 0 to 0.05 g / cc., preferably from 0 to 0.02 g / cc and even more preferably from 0 to 0.015 g / cc, measured in accordance with ASTM D-792. Also, for the broad aspect of the present invention, preferably at least one first component of ethylene polymer is a homogeneously branched ethylene polymer and more preferably a substantially linear ethylene / α-olefin interpolymer and at least one second component of The ethylene polymer is a heterogeneously branched ethylene polymer and more preferably a heterogeneously branched ethylene / α-olefin interpolymer.

For the aspect of the invention which provides balanced properties, the density differential between at least one first component of ethylene polymer (A) and at least one second component of ethylene polymer (B) is generally in the scale of 0. at 0.03 g / cc, preferably in the range of 0.01 to 0.03 g / cc, more preferably in the range of 0.015 to 0.025 g / cc, measured in accordance with ASTM D-792. A percent CBD crystallinity can also be used to characterize at least a first component of ethylene polymer (A) and at least a second component of ethylene polymer (B). That is, the percent CBD crystallinity differential between at least one first component of ethylene polymer (A) and at least one second component of ethylene polymer (B) is generally in the range of 0 to 23%, preferably on the scale of 7 to 20%, even more preferably on the scale of 10 to 18%. The first ethylene polymer component (A) has a density on the scale of 0.87 to 0.93 g / cc, preferably 0.88 to 0.92% g / cc (measured according to ASTM D-792). The second ethylene polymer component (B) has a density on the scale of 0.89 to 0.96 g / cc, preferably 0.90 to 0.94 g / cc (measured according to ASTM D-792). Additionally, it is preferred that the density of at least one component of ethylene polymer (A) is lower than the density of at least one second component of ethylene polymer (B).

The overall density of the polymer mixture (ie, the combination of component (A) and component (B) is generally in the range of 0.88 to 0.94 g / cc, preferably in the range of 0.89 to 0.93 g / cc, more preferably in the range of 0.90 to 0.93 g / cc and even more preferably in the range of 0.90 to 0.92 g / cc (measured in accordance with ASTM D-792) The first ethylene polymer component of the polymer composition used in the invention, Component (A), at least one ethylene polymer having a single melting peak of CBD, or alternatively a single peak of FEETA The second component polymer (B) of the polymer composition is at least one polymer having one or more melting peaks of CBD Polymers suitable for use as at least one second ethylene polymer include heterogeneously branched linear low density polyethylene (e.g., linear low density polyethylene and ultra density polyethylene). low or very low), substantially linear ethylene polymers, homogeneously branched linear ethylene polymers, high pressure ethylene polymers (e.g. , low density polyethylene, ethylene vinyl acetate copolymer (EVA), ethylene acrylic acid copolymer (EAA) or ethylene methacrylic acid ionomer (EMAA) and combinations or mixtures thereof. However, preferably the first ethylene polymer component (A) is at least one substantially linear ethylene polymer and the second polymer component (B) is a heterogeneously branched linear ethylene polymer. Substantially linear ethylene polymers are preferred as the first ethylene polymer (A) due to their melt extrusion processability and unique rheological properties as described by Lai et al. In U.S.A. Patents. Numbers 5,272,236 and 5,278,272. The molecular weight of the polyolefin polymers are conventionally indicated using a melt index measurement according to ASTM D-1238, Condition 190 ° C / 2.16 kg. (formerly known as "Condition E" and also known as I). The melt index is inversely proportional to the molecular weight of the polymer. The higher the molecular weight, the lower the melting index, although the relationship is not linear. The component (A) and component (B) are independently characterized by the melt index I2 and preferably at least one first ethylene polymer (A) will have a higher molecular weight (or lower l2) than at least one second polymer of ethylene (B). By "independently characterized" as used in the reference in polymer components (A) and (B), it is understood that the melt index l2 of the polymer component (A) is not necessarily the same as the melt index l2 of the polymer component (B), although it can be. The first ethylene polymer component (A) has a melt index l2 in the scale of more than or equal to 0.01 g / 10 minutes to less than or equal to 50 g / 10 minutes, preferably more than or equal to 0.05 g / 10 minutes less than or equal to 20 g / 10 minutes, even more preferably more than or equal to 0.5 g / 10 minutes less than or equal to 10 g / 10 minutes. The second ethylene polymer component (B) can have a melt index l2 in the range of 0.01 g / 10 minutes to 100 g / 10 minutes, preferably 0.05 g / 10 minutes to 50 g / 10 minutes, more preferably 0.1 g / 10 minutes at 20 g / 10 minutes, and even more preferably from 0.5 g / 10 minutes to 10 g / 10 minutes. The overall melt index of the polymer composition based on the components (A) and (B) is preferably in the range of 0.1 to 5 g / 10 minutes, more preferably 0.5 to 4 g / 10 minutes. Other useful measurements for characterizing the molecular weight of substantially linear ethylene interpolymers and homopolymers involve melt index determinations with higher weights, such as, as a common example, ASTM D-1238, Condition 190 ° C / 10 kg. (formerly known as "Condition N" and also known as l 0). The ratio of a higher melting index determination to a lower weight determination is known as a melt flow ratio and for melting index values o and l2 the melting flow ratio is conveniently designated as o / l ? - For the substantially linear ethylene polymers used to prepare the films of the present invention, the melt flow ratio indicates the degree of long chain branching, ie, the higher the melt flow ratio of I10 / l2 , the longer the long chain branching in the polymer will be. In addition to indicating the longer chain branching, higher I10 I2 ratios also indicate lower viscosity at higher shear rates (easier processing) and higher extensional viscosity. In general, at least one first ethylene polymer component (A) has a melt flow ratio of I10 / I2 greater than 6, preferably greater than 7, more preferably greater than 8, and even more preferably in the 8.5 scale. 20. The embodiments that comply with the specified density differential and which have a melt flow ratio of I10 / I2 greater than 8 in particular, is a preferred embodiment of the present invention. The first ethylene polymer component (A) generally constitutes from 20 to 80 weight percent of the polymer composition, based on the total weight of the polymer composition and preferably from 30 to 70 weight percent of the composition of the polymer composition. polymers, based on the total weight of the polymer composition. Conversely, the polymer composition used in the present invention comprises from 20 to 80 weight percent and preferably from 30 to 70 weight percent of at least one second component of ethylene polymer (B), based on the total weight of the polymer composition. Ethylene polymers suitable for use as the second component polymer (B) include substantially linear ethylene ether polymers, homogeneously branched linear ethylene interpolymers, heterogeneously branched linear ethylene interpolymers (e.g., linear low density polyethylene (PLBDL). ), measured density polyethylene (PEDM), high density polyethylene (PEDA) and ultra low or very low density polyethylene (PEDU B or PEDMB) and combinations or mixtures thereof For the aspect of the invention that provides improved rigidity , at least one second polymer component (D) has a higher density than at least one first polymer component (C) The density differential between at least one first ethylene polymer component (c) and therefore less a second component of ethylene polymer (D) is generally in the range of 0.001 to 0.05 g / cc, preferably in the range of 0.01 to 0.05 g / cc, even more preferably in the range of 0.01 to 0.03 g / cc, measured in accordance with ASTM D-792. As the aspect described above, a percent CBD crystallinity can be used to characterize at least a first component of ethylene polymer (C) and at least a second component of ethylene polymer (D). That is, the percent CBD crystallinity differential between at least one first component of ethylene polymer (C) and at least one second component of ethylene polymer (D) is generally in the range of 1 to 23%, preferably on the scale of 7 to 20% and even more preferably on the scale of 10 to 18%. The first ethylene polymer component (C) has a density on the scale of 0.87 to 0.93 g / cc, preferably 0.88 to 0.92 g / cc (measured in accordance with ASTM D-792). The second ethylene polymer component (D) has a density on the scale of 0.89 to 0.96 g / cc, preferably 0.90 to 0.94 g / cc (measured according to ASTM D-792). Additionally, the density of at least one first component of ethylene polymer (C) is lower than the density of at least one second component of ethylene (D). The density of the polymer composition of the invention (ie, the combination of component (C) and component (D)) is generally in the range of 0.88 to 0.94 g / cc, preferably in the range of 0.89 to 0.93 g / cc, more preferably in the range of 0.90 to 0.93 g / cc, and even more preferably in the range of 0.90 to 0.92 g / cc (measured in accordance with ASTM D-792). The first ethylene polymer component of the polymer composition of the invention, Component (C), is at least one ethylene polymer having one or more fusion peaks of CBD. However, preferably, at least one ethylene polymer will have a single melting peak of CBD or a single peak of FEETA and more preferably, at least one ethylene polymer (C) will have both a single melting peak of CBD. as a single FEETA peak. The second polymer of the polymer composition component is at least one ethylene polymer having one or more fusion peaks of CBD. The polymer component (C) and the polymer component (D) will be independently characterized by a melt index of ASTM D-1238 with at least one second ethylene polymer (D) having a molecular weight equal to or greater than at least one first ethylene polymer (C). The first ethylene polymer component (C) may have a melt index l2 on the scale greater than or equal to 0.01 g / 10 minutes or less than or equal to 100 g / 10 minutes, preferably greater than or equal to 0.05 g / minutes to less than or equal to 50 g / 10 minutes, more preferably greater than or equal to 0.1 g / 10 minutes unless or equal to 10 g / 10 minutes and even more preferably from 0.5 g / 10 minutes to 5 g /10 minutes. The second ethylene polymer component (D) can have a melt index l2 in the range from 0.01 g / 10 minutes to 10 g / 10 minutes, preferably from 0.05 g / 10 minutes to 5 g / 10 minutes, more preferably from 0.05 g / 10 minutes at 10 g / 10 minutes, and even more preferably 0.01 g / 10 minutes at 1 g / 10 minutes. The melt index of the polymer composition of the invention which is based on the polymer components (C) and (D) preferably is in the range of 0.01 to 10 g / 10 minutes, more preferably 0.1 to 4 g / 10. minutes, even more preferably 0.2 to 1.2 grams / 10 minutes. In general, at least one first component of ethylene polymer (C) has a melt flow ratio of I10 / I2 greater than 5, preferably greater than 7, more preferably greater than 8, and even more preferably in the scale of 8.5 to 20. For the polymer composition of the invention itself, the melt flow ratio of I10 / l2 preferably is greater than 7. The polymer composition used for the second aspect of the invention generally comprises or is made from 20 to 80 weight percent to at least one first component of ethylene polymer (C), based on the total weight of the polymer composition and preferably 30 to 70 weight percent of at least one polymer component (C) based on the total weight of the polymer composition. Conversely, the polymer composition of the invention comprises or is made from 20 to 80 percent by weight and preferably from 30 to 70 percent by weight of at least one second component of ethylene polymer (D), based on the total weight of the polymer composition. Broadly, polymers suitable for use as at least one first ethylene polymer (C), including homogeneously branched substantially linear ethylene polymers and homogeneously branched linear ethylene polymers. That is, ethylene polymers characterized by having I DRCC or IRDC greater than 50 percent are widely useful in the present invention as at least one first ethylene polymer. As described and incorporated herein, such polymers can be manufactured using a single catalyst system (e.g., metallocene catalyst system including a suitable catalyst); however, preferably such polymers are manufactured using a restricted geometry system including a suitable cocatalyst such as, for example, a boron compound. Ethylene polymers suitable for use as at least a second polymer component (D) include substantially linear ethylene interpolymers, homogeneously branched linear ethylene ether polymers, heterogeneously branched linear ethylene interpolymers (e.g. low linear density (PLBDL), medium density polyethylene (PEDM), high density polyethylene (PEDA) and ultra low or very low density polyethylene (PEBU D or PEDMB) and combinations or mixtures thereof. Linear resins are sold under the designation of AFFI N ITY ™ and ENGAGE ™ resins by The Dow Chemical Company and Dupont Dow Elastomers, respectively.The homogeneously branched linear ethylene polymers suitable for use in the invention are sold under the designation of EXACT ™ resins. and EXCEED ™ by Exxon Chemical Corporation, respectively, linear heterogeneous ethylene polymers Suitable for use in the invention are sold under the designations of ATTAN E ™ and DOWLEX ™ by The Dow Chemical Company and under the designation FLEXOMER by U nion Carbide Corporation. Preferably at least one first component of ethylene polymer (A) or (C) is a substantially linear ethylene polymer and at least one second polymer of component (B) or (D) is a heterogeneously branched ethylene polymer. As such, when the composition of the invention is manufactured using a multiple reactor polymerization system, preferably at least one first component of ethylene polymer (A) or (C) is made using a catalyst system, polymerization conditions and similar ones which will form a substantially linear ethylene polymer in at least one of the reactors and likewise, at least a second component of ethylene polymer (B) or (D) is made using a catalyst system, polymerization conditions and similar that will form a heterogeneously branched linear polymer in at least one other reactor of the multiple reactor system. Substantially linear ethylene polymers are preferred as the first ethylene polymer component (A), among others due to their improved melt extrusion processability and unique rheological properties as described by Lai et al., In U.S. Patents .TO. We 5,272,236 and 5,278,272. The substantially linear ethylene polymers used in the present invention are not in the same class as homogeneously branched linear ethylene polymers, nor are heterogeneously branched linear ethylene polymers, nor are they substantially linear ethylene polymers in the same class as polyethylene. density (PEDB) initiated by free radicals, highly branched, traditional high pressure. The substantially linear ethylene polymers useful in the present invention have excellent processability, although they have relatively narrow molecular weight distributions (DPM). Only, the melt flow ratio (I10 / I2) of the substantially linear ethylene polymers can vary essentially independently of the polydispersity index (ie, a molecular weight distribution (Mp / Mn)). This is in contrast to conventional heterogeneously branched linear polyethylene resins, increases in polydispersity index, the value of 110 I2 is also increased. The rheological properties of substantially linear ethylene polymers also differ from homogeneously branched linear ethylene polymers having I10 / I2 relations essentially fixed, relatively fixed. The single-site polymerization catalyst (e.g., monocyte-pentadienyl transition metal olefin polymerization catalysts described by Canich in U.S. Patent No. 5), 026,798 or by Canich in the Patent of E. U.A. Number 5, 055,438) or restricted geometry catalysts (e.g., as described by Stevens et al., In U.S. Patent Number 5,064,802) can be used to prepare substantially linear ethylene polymers, while the catalysts are used for according to the methods described in the Patents of E. U.A. Numbers 5,272,236 and 5,278,272. Such polymerization methods are also described in PCT / US92 / 08812 (filed October 15, 1992). However, substantially linear ethylene polymers suitable for use in the present invention are preferably made using catalysts of suitable restricted geometry, especially restricted geometry catalysts as described in the application of E.U.A. Series Numbers. 545: 403, presented on July 3, 1990; 758,654, filed September 12, 1991; 758,660, filed September 12, 1991; and 720,041 filed on June 24, 1991. Suitable cocatalysts for use herein include but are not limited to, for example, polymeric or oligomeric aluminoxanes, especially methyl aluminoxane or modified methyl aluminoxane (eg, eg, as described in U.S. Pat. .A. Numbers: 5, 041, 584; 4, 544,762; 5,015,749; and 5, 041, 585) as well as inert, compatible, non-coordinating, ion-forming compounds. Preferred cocatalysts are inert, noncoordinating, boron compounds. The polymerization conditions for manufacturing substantially linear ethylene interpolymers useful in the present invention are preferably those useful in a low pressure continuous solution polymerization process, although the application of the present invention is not limited thereto. Polymerization of continuous high pressure solution, continuous slurry polymerization and continuous gas phase polymerization processes can also be used, as long as the appropriate catalysts and polymerization conditions are also employed. To polymerize the substantially linear polymers useful in the present invention, the single-site restricted geometry catalysts mentioned above can be used; however, for substantially linear ethylene polymers, the polymerization process should be operated so that substantially linear ethylene polymers are formed as well. That is, not all inherent polymerization processes and conditions form substantially linear ethylene polymers even when appropriate catalysts are used. For example, in one embodiment of a polymerization process useful for manufacturing substantially linear ethylene polymers, a continuous solution process is used, as opposed to a batch solution process. Generally, the handling of 10/12 while maintaining relatively low M w / M n when manufacturing substantially linear ethylene polymers with restricted geometry catalysts is a function of the reactor temperature and / or ethylene concentration. Reduced ethylene concentrations and higher reactor temperatures generally produce higher I10 / I2 ratios as well as higher melt strength values. Generally, as the concentration of ethylene in the reactor decreases, the polymer concentration in the reactor increases. For the substantially linear ethylene polymers useful in the invention, the polymer concentration for continuous solution polymerization process is preferably present above 5 weight percent of the reactor content, especially above 6 weight percent of the content of the reactor. If desired a narrow molecular weight distribution polymer (Mp / Mn from 1.5 to 2.5) having a higher ratio of I10 I2 (e.g., I10 / L2 of 7 or more, preferably at least 8, especially by at least 9). The concentration of ethylene in the reactor is preferably not greater than 8 weight percent of the reactor content, especially not more than 6 weight percent of the reactor content and especially not more than 4 weight percent of the reactor content. . Generally, the temperature of the continuous process polymerization reactor, using constrained geometry catalyst, is from 20 ° C to 250 ° C. Single-site polymerization catalysts (e.g., monocycline-pentadienyl transition metal olefin polymerization catalysts described by Canich in U.S. Patent Number 5,026,798 or by Canich in the U.S. Patent. No. 5,055,438) can be used to prepare homogeneously branched linear ethylene polymers. As exemplified in the Patent of E. U.A. Number 3,645,992 of Elston, homogenously branched linear ethylene polymers can also be prepared in conventional polymerization processes using Ziegler type catalysts such as, for example, zirconium and vanadium catalyst systems. Another example is provided in the patent of E.U.A. Number 5,218, 071 of Tsutsui et al. Tsutsui et al., Describe the use of hafnium-based catalyst system with amounts of zirconium impurity for the manufacture of homogenously branched linear ethylene polymer blends. Homogeneously branched linear ethylene polymers can be prepared using any reactor system known in the art, including, but not limited to solution and gas phase polymerization using for example a tank reactor, a sphere reactor, a cycle reactor of recycling or combinations thereof and the like, any reactor or all reactors partially or completely operated in an adiabatic, non-adiabatic manner or a combination of both and the like. Homogeneously branched linear ethylene polymers can be prepared via the polymerization of solution, slurry or gaseous phase of ethylene and at least one optional alpha-olefin comonomer in the presence of a Ziegler Natta catalyst by processes such as those described in the Patent from E. U .A. Number 4, 076,698 of Anderson and others. The heterogeneously branched linear ethylene polymers can be manufactured by any known method and process, including continuous, batch or semi-batch polymerization of solution, slurry or gas phase of ethylene and at least one optional α-olefin comonomer in the presence of a Ziegler Natta catalyst, such as by the process described in the Patent of E. U.A. Number 4, 076,698 by Anderson and others. Linear heterogeneously branched ethylene polymers can be prepared using any reactor system known in the art including, but not limited to, a tank reactor, a sphere reactor, a recycle cycle reactor or a combination thereof and the like , any reactor or all reactors partially or completely operated adiabatically, not adiabatically, or a combination of both or similar. As described above, the preferred homogeneously branched ethylene polymer for use in the present invention is a substantially linear ethylene polymer characterized by having: (a) a melt flow ratio, I10 I2 >; 5.63, (b) a molecular weight distribution, Mp / Mn, as determined by gel permeation chromatography and defined by the equation: (Mp / Mn) < (l 10/12) -4.63, (c) a gas extrusion rheology such as the critical shear rate at the beginning of the surface melt fracture for the substantially linear ethylene polymer is at least 50 percent greater than the critical shear rate at the beginning of the surface melt fracture for a linear ethylene polymer, where the linear ethylene polymer has a homogeneously branched short chain branching index (RCC ID) greater than 50 percent, long chain branching and values of l2 and Mp / Mn with 1 0 percent of 12 and Mp / Mn of the substantially linear ethylene polymer where the respective critical shear rates of the substantially linear ethylene polymer and the linear ethylene polymer is measured at the same melting temperature and under the same scale of pressures using a gas extrusion rheometer, (d) a single lime melting peak differential scanning orimetry, CBD, between 30 and 140 ° C, and (e) a short chain branching distribution index (IDRCC) greater than 50 percent, determined using fractionation of the temperature rise elution. The above combination of properties characterizing the substantially linear ethylene polymer useful in the invention pertains to a single component polymer and not necessarily a polymer composition, mixture or combination comprising a substantially linear ethylene polymer as one of the component polymers. The determination of the critical shear rate with respect to the melt fracture as well as other rheological properties such as "rheological processing index" (IP) is carried out using a gas extrusion rheometer (REG). The gas extrusion meter is described by M. Shida, R. N.

Shroff and L.V. Cancio in Polymer Engineering Science. Col. 17, No. 1 1, p. 770 (1977), and in "Rheometers for Molten Plastics" by John Dealy published by Van Nostrand Reinhold Co. (1982) on pgs. 97-99, both of which are hereby incorporated by reference in their entirety. The REG experiments are carried out at a temperature of 190 ° C, at nitrogen pressures between 1.7 to 37.9 MPa using a diameter of 0.0754, a die of 10: 1 L / D with an inlet of 180 °. For the substantially linear ethylene polymers used herein, I P is the apparent viscosity at (Kpoise) of a medium material per REG at an apparent shear rate of 2.15 x 106 dyne / cm2. The substantially linear ethylene polymer for use in the invention has an I P in the range of 0.01 kpoise to 50 kpoise, preferably 15 kpoise or less. The substantially linear ethylene polymers used herein also have an IP less than or equal to 70 percent of the IP of a linear ethylene polymer (either a Ziegler catalyzed polymer or a homogeneously branched polymer as described by Elston in the U.S. Patent Number 3,645,992) having one l2 and Mp / M "each within ten percent of the substantially linear ethylene polymer. A plot of apparent shear stress versus apparent shear rate is used to identify the melting fracture phenomenon and quantify the critical shear rate and critical shear stress of ethylene polymers. According to Ramamurthy in the Journal of Rheology, 30 (2), 337-357, 1986, above a certain critical flow regime, irregularities can be observed in rheometric extrudates that can be broadly classified into two main types: surface fusion fracture and thick fusion fracture. The surface fusion fracture occurs under seemingly stable extrusion flow conditions and varies in detail from loss of brightness of spectacular film to the more severe form of "shark skin". At present, as determined using the REG described above, at the onset of surface melt fracture (IFFS), it is characterized by an initial loss of extrudate gloss wherein the roughness of the extrudate surface can be conveniently detected under 40x magnification. . As described in the Patent of E. U.A. No. 5,278,272, the rate of critical shear stress at the beginning of the surface melt fracture for substantially linear ethylene interpolymers and homopolymers is at least 50 percent greater than the rate of critical shear stress at the beginning of the melt fracture of a linear comparative linear ethylene polymer surface having essentially the same l2 and Mp / Mn. The gloss fusion fracture occurs at unstable extrusion flow conditions and varies in detail from regular distortions (alternately rough and smooth, helical, etc.) to random. For commercial acceptability as well as to maximize shrinkage response and stiffness properties of shrink films, surface defects should be minimal, if not absent. The critical shear stress at the beginning of the gloss melt fracture for the substantially linear ethylene polymers used in the invention, especially those having a density greater than 0.910 g / cc, is greater than 4 x 10 dynes / cm2. The regime of critical shear stress at the beginning of the surface fusion fracture (I FFS) and at the beginning of the coarse melt fracture (I FFG) will be used in the present based on changes in surface roughness and configurations of extrudates extruded by REG. As mentioned before, the preferred homogeneous ethylene polymers used in the present invention are characterized by a single melting peak of CBD. The unique melting peak is determined using a differential scanning calorimeter (CBD) normalized with indium and deionized water. The method involves sample sizes of 5-7 mg, a "first heat" at 140 ° C which is maintained for 4 minutes, a cooling at 10 ° / min. At -30 ° C which is maintained for 3 minutes, and a heating up to 10 ° C / min. at 140 ° C for the "second heat". The unique melting peak is taken from the heat flow curve of the "second heat" against temperature. The total heat of the polymer melt is calculated from the area under the curve. For polymers having a density of 0.875 g / cc to 0.910 g / cc, the single melting peak can show, depending on the sensitivity of the equipment, a "shoulder" or a "hump" on the low melting side that constitutes less of 12 percent, normally, less than 9 percent, and more preferably less than 6 percent of the total heat of the polymer melt. Such an artifact can be observed by homogeneously branched polymers such as EXACT ™ resins and is discerned on the basis of the inclination of the single melting peak that varies monotonically through the melting region of the artifact. This artifact occurs within 34 ° C, normally within 27 ° C and more usually within 20 ° C of the melting point of the single melting peak. The heat of fusion attributable to an artifact can be determined separately by the specific integration of its associated area below the curve of heat flow versus temperature. The Vicat softening point of the compositions of the invention was determined in accordance with ASTM D-1525. The complete polymer product samples (eg, the polymer composition of the invention) and individual polymer components were analyzed by gel permeation chromatography (CPG) in a Waters 1 50 upper temperature chromatographic unit equipped with columns of mixed porosity operating at a system temperature of 140 ° C. The solvent is 1, 2, 4-trichlorobenzene, from which 0.3 percent by weight solutions of the polymer samples to be measured are prepared by injection. The flow rate is 1.0 milliliters / minute and the injection size is 1000 microliters. The molecule weight determination is deduced using narrow molecular weight distribution polystyrene normals (from Polymer Laboratories) along with their elution volumes. Molecular weights of polyethylene eq uivalents are determined using appropriate Mark-Houwink coefficients for polyethylene and polystyrene (described by Williams and Ward in Journal of Polymer Science, Polymer Letters, Vol 6, page 621, 1968) to derive the following equation M po l ßtilßno = a (M po | estárneo) • In this equation, a = 0.4316 and b = 1 .0. The weight average molecular weight, Mp, and the number average molecular weight, Mn, are calculated in the usual manner according to the following formula: Mj = (? P¡ (Mi ')) *, where pj is the fraction by weight of the molecules with M, eluting from the column of CPG in the fraction i and j = 1 when calculating Mp and j = -1 when calculating M ". The molecule weight distribution (Mp / Mn) for the substantially linear ethylene polymers and homogeneous linear ethylene polymers useful in the present invention is generally in the range of 1.2 to 2.8. the heterogeneously branched ethylene polymers useful in the invention typically have molecular weight distributions, Mp / Mn, on the scale of 3.5 to 4.1. Substantially linear ethylene polymers are known to have excellent processability, despite having a relatively narrow molecular weight distribution. Unlike homogeneously branched and heterogeneously branched linear ethylene polymers, the melt flow ratio (I10 / I2) of substantially linear ethylene polymers can vary essentially independently of their molecular weight distribution, Mp / Mn. Homogeneously branched ethylene polymers suitable for use in the present invention include ethylene homopolymers and interpolymers of ethylene and at least one α-olefin prepared by a low or high pressure solution process, a gas phase process or grout process or combinations thereof. Suitable α-olefins are represented by the following formula: CH 2 = CHR, wherein R is a hydrocarbyl radical. In addition, R may be a hydrocarbyl radical having from one to twenty carbon atoms and as such the formula includes C3-C2o α-olefins. The α-olefins suitable for use as comonomers include propylene, 1-butene, 1 -isobutylene. , 1-pentene, -hexene, 4-methyl-1-pentene, isopentene, 1-heptene and 1-ketene, as well as other types of comonomers such as styrene, halo or alkyl-substituted styrenes, tetrafluoroethylene, vinyl benzocyclobutane, 1,4-hexadiene, 1,7-octadiene and cycloalkenes, e.g. , cyclopentene, cyclohexene and cyclooctene. Preferably, at least the α-oieffine comonomer will be 1-butene, 1-pentene, 4-methyl-1-pentene, 1 -hexene, 1-heptene, 1-ketene or mixtures thereof, since the Contraction comprised of higher α-olefins will have especially improved stiffness properties. However, more preferably, at least one α-olefin comonomer will be 1-octene and the first and second ethylene polymer will be prepared in a continuous solution polymerization process.

A preferred shrink film of the present invention will further be characterized as having an extractable level of compositional hexane of less than 15 percent, preferably less than 10 percent, more preferably less than 6, more preferably less than 3 percent. based on the total weight of the composition. Another preferred shrink film of the present invention is characterized by a Vicat smoothing point of at least 75 ° C, preferably at least 85 ° C and still more preferably at least 90 ° C. Another embodiment of the present invention of a method for forming an improved shrinkage film either as a single layer film or as a shrinkage control layer in a multilayer structure. The method for forming a multilayer structure comprising the shrinkage control layer of the invention may include a lamination and coextrusion technique or combination thereof and may include the use of the polymer composition of the invention only for all layers or other polymeric layers and may also include blowing film, cast film, extrusion coating, injection molding, blow molding, thermoforming, profile extrusion, stretch extrusion, compression molding, rotomolding or molding injection blow or combinations thereof. The shrink film of the invention can be formed using simple bubble or cast extrusion techniques, however preferred film structures are prepared using more elaborate techniques such as "stress structuring" or a "double bubble" process, "bubble" of tape "," trapped bubble "or combinations thereof and the like, so that the surprising attributes of the invention can be realized. The double bubble technique is described by Pankle in the U.S. Patent. Number 3,456,044. The polymer composition of the invention used in the invention can be formed by any convenient method, including dry blending the individual components and subsequently melt mixing in a mixer or mixing the components together directly in a mixer (e.g. a Banbury mixer, a Haake mixer, an internal Brabender mixer, or a one or two screw extruder including a compounding extruder and a side arm extruder used directly downstream of an interpolymerization process. invention used in the invention (as well as at least one first polymer of ethylene and at least one second ethylene polymer) can be formed in situ via a multiple reactor polymerization of ethylene and at least one optional comonomer using a catalyst of a only site, preferably a restricted geometry catalyst, in so I We have a single-site reactor and catalyst, preferably a restricted geometry catalyst, or more preferably a Ziegler-Natta type catalyst in at least one other reactor. The reactors can be operated sequentially or in parallel. An illustrative in situ interpolymerization process is described in PCT Patent Application 94/01052. The polymer composition used in the invention (as well as at least one first polymer of ethylene (A) or (C) and at least one second polymer of ethylene (B) or (D) can be further formed by isolating the components ( A), (B), (C) and / or component (D) of a heterogeneously branched ethylene polymer by fractionating the heterogeneous ethylene polymer into specific polymer fractions (or isolating polymer components (A) or (C) from a homogeneously branched ethylene polymer fractionating the ethylene polymer homogeneously into polymer fractions), selecting the appropriate fractions to meet the specific limitations for the different polymer components and mixing the selected fractions in the appropriate amounts with at least one first component of ethylene polymer (A) or (C) or at least a second component of ethylene polymer (B) or (D) This method is obviously not as economical as a polymer in-situ ation such as, for example, as described above, but which can not be used to obtain the composition of the polymer as well as the polymer of the invention as well as at least one first polymer of ethylene and / or at least one second polymer of ethylene. Additives, such as antioxidants (e.g., hidden phenolics, such as I RGANOX ™ 1010 or I RGANOX ™ 1076 supplied by Ciba Geigy), phosphites (e.g., IRGAFOS ™ 168 also supplied by Ciba Geigy), additives of adhesion (e.g., PIB), SANDOSTAB PEPQ ™ (supplied by Sandoz), pigments, colorants, fillers and the like may also be included in the shrink film of the invention. Although not generally required, the shrink film of the invention may also comprise additives to improve the anti-blocking, mold release and coefficient of friction characteristics including, but not limited to, untreated and treated silicon dioxide, talc , calcium carbonate and clay, as well as primary, secondary and substituted fatty acid amides, release agents, silicone coatings, etc. Still other additives, such as quaternary ammonium compounds alone or in combination with ethylene-acrylic acid copolymers (EAA) or other functional polymers, can also be added to improve the anti-static characteristics of the shrink film of the invention and allow the use of the shrinkage film of the invention in, for example, the shrinkage packaging of electronically sensitive articles. The shrink film of the invention may further include recycled and waste materials and extender polymers to the extent that the improved properties discovered by the Applicants are not adversely affected. Exemplary thinner materials include, for example, polyethylenes modified by elastomers, rubbers, polypropylene, polysulfones, polycarbonates, polyamides, ABS, epoxies and anhydrides (e.g., PLBDL and PEDA grafted with maleic anhydride) as well as high pressure polyethylenes such such as, for example, low density polyethylene (LDPE) ethylene / acrylic acid (EAA) interpolymers, ethylene / vinyl acetate (EVA) interpolymers and ethylene / methacrylate (EMA) interpolymers and combinations thereof. The biaxially oriented film structures are used for their improved strength properties with the barrier and / or shrinkage. Biaxially oriented film structures find utility in various packaging and storage applications for non-food and food products such as primary and sub-primary cuts of meat, ham, poultry, bacon, cheese, etc. , the biaxially oriented film structures that use the polymer composition of the invention can be a two to seven layer structure. Said multi-layer structure can be of any suitable overall thickness and the shrink film layer of the invention of the multilayer structure can also have any suitable thickness. The shrink film layer of the invention (i.e., a biaxially oriented film layer comprising or made of the polymer composition of the invention) is usually the shrinkage control layer of the multilayer shrinkage film and it can comprise from 30 to 75 weight percent of the multilayer film, preferably from 50 to 70 percent of the multilayer film. The shrink film layer of the invention may be of any suitable thickness preferably and the film layer in the invention has a film thickness of about 2.5 to 51 microns), more preferably 7.6 to 45.7 microns). The multilayer structure comprised, made with or of the polymer composition of the invention, may also include a sealant layer composition (such as, for example, but not limited to, another polymer composition, or at least one polymer of substantially linear ethylene homogeneously branched, at least one homogenously branched linear ethylene polymer or at least one polyethylene of ultra low or very low heterogeneously branched density), an outer layer (such as, for example, another polymer blend or at least one density polyethylene) ultra low or linear heterogeneously branched low) and a core layer (such as a biaxially oriented polypropylene homopolymer or vinyloid chloride polymer) interposed therebetween. Adhesion that promotes bonding of layers (such as ethylene-acrylic acid copolymers (EAA) from PRIMACOR ™ available from The Dow Chemical Company and / or ethylene / vinyl acetate (EVA) copolymers), as well as additional structural layers (such as AFFI N ITY ™ polyolefin plastomers, ENGAGE ™ polyolefin elastomers, available from The Dow Chemical Company and Dupont Dow Elastomers, respectively, ultra low density polyethylene or mixtures of any of these polymers with one another or with one another polymers, such as EVA) can be optionally employed.

Other layers of a multilayer structure comprising, made with or of the polymer composition of the invention may include, but are not limited to, barrier layers and / or structural layers. Several materials can be used for these layers, with some of them used in more than one layer in the same multilayer structure. Some suitable materials include: foil, nylon, ethylene / vinyl alcohol copolymers (EVOH), polyvinylidene chloride (PVDC), polyethylene terephthalate (PET), oriented polypropylene (PPO), ethylene / vinyl acetate (EVA) copolymers, ethylene / acrylic acid (EAA) copolymers, ethylene / methacrylic acid (EMAA) copolymers, PEDUM, PLBDL, PEDA, PEDM, PEDML, LDPE, ionomers, graft-modified polymer (e.g., polyethylene grafted with maleic anhydride) and paper. Packed items for cooking are food that is pre-packaged and then cooked. The packaged and cooked foods go directly to the consumer, institution or the seller for consumption or sale. A cooking package must be structurally capable of withstanding exposure to cooking time and temperature conditions while containing a food product. Packed baking items are normally used to pack ham, turkey, vegetables, processed meats, etc. , due to the relatively high smoothing point for shrinkage response characteristics of the shrink film of the invention, the shrink film of the present invention is suitable for baking as well as for hot fill packaging applications. Biaxial double bubble and trapped bubble orientation methods can be similar to a laboratory scale using a T.M. Long stretcher which is analogous to a tension structure device. This device can guide polyolefin films in both monoaxial and biaxial modes at stretch ratios up to 5: 1. The device uses films that have an original dimension of 5.1 centimeters by 5.1 centimeters. Biaxial stretching is usually carried out by stretching in the machine direction and transverse direction of the film simultaneously, although the device can be operated to stretch sequentially. Residual crystallinity of polyolefin interpolymers (means using a partial area method with CBD) can be used to characterize the nature of the polyolefin film at the orientation temperature. In general, it is preferred to orient the polyolefin films to an orientation temperature wherein the residual crystallinity of the film is as high as possible. Such orientation will generally only be to a degree above the temperature where the film can no longer be oriented successfully. That is, 5 ° C above, preferably 3 ° C above, more preferably 2.5 ° C above the lower stretch temperature (defined above) is considered here to be the optimum or near optimal stretch temperature or orientation for a film composition. particular. Stretching temperatures less than 2.5 ° C above the lower stretch temperature are not preferred as they tend to produce inconsistent results due to the loss of film integrity, although such inconsistencies have to depend on the specific equipment and capabilities of the film. temperature control. However, for proper comparison of several films, an orientation temperature should be selected so that the residual crystallinity in the orientation is approximately equal for each film. That is, although wide orientation windows are desired, the selection of the current orientation temperature that will be used should never be arbitrary. However, for an appropriate comparison of several film compositions, an orientation temperature should be selected so that the residual crystallinity at the selected orientation temperature is approximately equal to that of each film or, alternatively, the orientation is carried out at the lower stretch temperature for each respective film composition. That is, the selection of the actual orientation temperature that will be employed should never be arbitrary and generally should not be maintained at a fixed temperature when evaluating various film compositions. Density densities and differentials are measured according to ASTM D-792 and reported as grams / cubic centimeter (g / cc). The measurements reported in the following Examples as overall densities were determined after the polymer samples were annealed for 24 hours at ambient conditions according to ASTM D-792. The density and percentage by weight of the first component of ethylene polymer (A) for example manufactured by in situ polymerization using two reactors can be determined by an Analytical Temperature Elevation Elution Fractionation (FEETA) technique. The accessories and procedures used for the FEET technique have been previously described, e.g. , Wild and others, Journal of Polvmer Science. Poly. Phys. Ed., 20.41 (1982), Hazlitt, et al., Patent of E. U.A. Number 4, 798,081 and Chum et al., Patent of E. U.A. Number 5,089,321. However, for the examples provided herein, the polymer compositions were all manufactured by melt extrusion in a twin screw extruder. Vicat softening temperatures were measured in accordance with ASTM D1525. The drying module was measured in accordance with ASTM D882 in slowly cooled compression molded samples. The impact of dart drop with total energy and dart was measured according to ASTM D-4272 and D-1709, respectively, on oriented film samples. The total energy test unit with a Kayeness Total Energy Impact Tester Model D-2090 where the total energy for a weight of 1.4 kilograms was >; / l .2 Kg. -metro.

The following examples are provided in order to explain and not to suggest any particular limitation of the present invention. EXAMPLES Examples 1-3 and Comparative Example 4 In an evaluation to discover the requirements for improved shrinkage properties, a single component ethylene polymer and three different ethylene polymer mixtures were evaluated. Table 1 lists several evaluated polymers and their properties (ie, melt index, density, Vicat smoothing point and description of the first and second polymer components and their density differential, where applicable). Table 1 Example Relationship First Second Differential Density Index Temp. of 1 ° / 2 ° Component Component Fusion Smoothing composition g / 10 min. of Polymer Density Vicat ° C g / cc (g / cc) 1 60/40 A B 0.82 0.9085 0.022 88.3 2 60/40 C D 0.94 0.9067 0.050 80.7 3 40/60 A B * 0.92 0.9075 0.014 87.1 Comp NA NA NA 0.81 0.9059 NA 84.4 .4 NA denotes not applicable Resin component A was XU-59220.4, a substantially linear experimental ethylene / 1-octene copolymer having an I2 melt index of 0.88 g / 10 minutes and a nominal density of 0.898 g / cc supplied by The Dow Chemical Company. Resin component B was 2045 of DOWLEX ™, a linear low density ethylene / 1-octene copolymer having a nominal l2 melt index of 1.0g / 10 minutes and a nominal density of approximately 0.920 g / cc supplied by The Dow Chemical Company. Component of Resin C was CL8003 from AFFIN ITY ™, an ethylene / 1-ketene copolymer having a nominal l2 melt index of 1.0 g / 10 minutes and a nominal density of 0.885 g / cc supplied by The Dow Chemical Company. Resin Component D was 2038.68 of DOWLEX ™, a linear low density ethylene / 1-octene copolymer having a nominal l2 melt index of 1.0 g / 10 minutes and a nominal density of 0.935 g / cc supplied by The Dow Chemical Company. Resin Component B * was 4201 of ATTANE ™, an ultra low density ethene / 1-octene copolymer having a nominal l2 melt index of 1.0 g / 10 minutes and a nominal density of 0.912 g / cc supplied by The Dow Chemical Company. Comparative Example 4 was 4213 of ATTANE ™, an ethylene / 1-octene copolymer of ultra low density having a nominal l2 melt index of 0.8 g / 10 minutes and a nominal density of 0.906 g / cc supplied by The Dow Chemical Company The melt characterization of water-cooled films of each Example was performed using a CBD-7 from Perkin-Elmer. The CBD was calibrated using indium and water as normal, the water-cooled films were placed on an aluminum tray and the samples were heated from -30 ° C to 140 ° C at 10 ° C / minute. The total heat of fusion for each resin was obtained from the area under the curve. The residual crystallinity at various temperatures was obtained using the partial area method by dropping the perpendicular to those temperatures where the crystallinity was taken by dividing the heat of fusion by 292 Joules / grams. The Examples were extruded into 0.8 mm cast sheets and quickly cooled using a cooling roll. The melting temperature in the die was approximately 249 ° C for each resin and the temperature of the quench roll was approximately 24 ° C. The castings were oriented at their respective lower orientation temperature using the Biaxial T.M. Long extruder (a tension structure extruder). The initial dimensions of the cast sheets were 5.1 cm x 5.1 cm and the draw ratio of the extruder was set at 4.5 x 4.5 and the draw rate was 12.7 cm / sec. The casting sheets were preheated in the drawer for 4 minutes before stretching and hot air was deflected so that it was not applied directly onto the casting sheets (ie to avoid hot spots in the casting sheets). In this evaluation, the lower orientation temperature was taken as the temperature which gives a residual residual crystallinity of about 20 percent which was about 5 ° C above the temperature where the casting sheet could tear, shows "banding" (i.e. non-uniform deformation) or could be repeatedly discharged by itself from the stretcher fasteners during stretching at a clamping pressure of approximately 3.4 MPa. The orientation window was taken as the temperature scale from the temperature scale of the orientation temperature lower than the peak peak temperature of CBD of the sample. The oriented casting sheets were tested for unrestrained (free) shrinkage at 90 ° C by measuring unrestricted shrinkage in a water bath at 90 ° C. The samples were cut in a 12 cm x 1.27 cm specimen. The specimens were marked with a marker exactly 10 cm from one end for identification. Each sample was completely submerged in the water bath for five seconds and then quickly removed. Film shrinkage was obtained from the calculations according to ASTM D-2732-83 and taken from the average of the four samples.

Table 2 summarizes the secant, shrinkage response and orientation temperature module for Examples 1 -3 and Comparative Example 4: Table 2 Example 2% Shrinkage Temperature Weight percent Window of Module of Percentual @ 90 ° C of Crystallinity ® and Temp. Orientation Drying (H20 hot) Orientation ° C Orientation ° C 1 17,023 34.5 87.8 20.8 33 Comp.2 17.218 25.0 93.3 19.6 29 3 15,327 30.8 87.8 21 .0 34 Comp.4 12,832 26.0 90.6 19.9 30 The data in Table 2 indicate that Examples 1 and 3 exhibit balanced shrinkage properties in relation to Example 2 and Comparative Example 4. Examples 1 and 3 exhibited lower shrinkage responses and wider orientation windows. Example 3 of the invention exhibited a shrinkage response of at least 18 percent higher than the linear heterogeneously branched ethylene polymer of a single component (comparative example 4) and Example 1 also exhibited a shrinkage response at least 32 percent higher than the heterogeneously branched linear ethylene polymer of a single component (comparative example 4). Additionally, Table 1 india that Examples 1 and 3 also exhibited the higher softening temperature in relation to Example 2 and Comparative Example 4. From the results in Table 1, it can be seen that Example 2 does not represent the preferred embodiment of the present invention that provides improved shrinkage properties. Examples 5-8 and Comparative Example 9 In another evaluation, another ethylene polymer of a single component and four different mixtures of different ethylene polymer were evaluated to discover the requirements for the improved shrinkage properties at higher polymer densities. The Table 3 lists the different polymers evaluated and their properties (ie, melt index, density, Vicat smoothing point and description of the first and secpolymer components and their density differential, where applicable). Table 3 Example Relationship First SecDifferential Density Index Temp. of 1 ° / 2 ° Component Component Fusion Smoothing composition g / 10 min. of Polymer Density Vicat ° C g / cc (g / cc) 5 40/60 A * B? TÓ 0.914 0.01 8 96 6 60/40 A ** B ** 1 .28 0.91 33 0.0385 91 .5 7 30/70 A B 0.86 0.9146 0.022 96 8 60/40 A B ** 0.85 0.91 41 0.037 94 Comp.9 NA NA NA 0.92 0.9128 NA 95.8 NA denotes not applicable Resin component A was XU-59220.4, a substantially linear experimental ethylene / 1-octene copolymer having an I2 melt index of 0.88 g / 10 minutes and a nominal density of 0.898 g / cc supplied by The Dow Chemical Company. Resin component A ** was PF 1 140 of AFFI N ITY ™, a substantially linear ethylene / 1-ketene copolymer having a nominal l2 melt index of 1.6 g / 10 minutes and a nominal density of about 0.8965 . The Resin B ** component was PL 1880 from AFFIN ITY ™, a substantially linear ethylene / 1-ketene copolymer having a nominal l2 melt index of 1.0 g / 10 minutes and a nominal density of 0.902 g / cc supplied by The Dow Chemical Company. Resin Component B ** was 2038.68 of DOWLEX ™, a linear low density ethylene / 1-octene copolymer having a nominal l2 melt index of 1.0 g / 10 minutes and a nominal density of 0.935 g / cc supplied by The Dow Chemical Company. Resin Component B was 2045A of DOWLEX ™, a linear low density ethylene / 1-octene copolymer having a nominal l2 melt index of 1.0 g / 10 minutes and a nominal density of 0.920 g / cc supplied by The Dow Chemical Company. Comparative Example 9 was 2256A of DOWLEX ™, a low density ethylene / 1-ketene copolymer having a nominal l2 melt index of 0.9 g / 10 minutes and a nominal density of 0.913 g / cc supplied by The Dow Chemical Company . The methods and procedures used for Examples 5 and 7 and Comparative Examples 6, 8 and 9 were the same for Example 1, except that instead of a water bath to induce shrinkage, hot oil was used at 105 ° C and the temperature orientation was taken to approximately 21% of the residual crystallinity instead of approximately 20%. Table 4 summarizes the different results.

Table 4 Example 2% Shrinkage Temperature Percent by Weight of Window of Modules Percent @ 90 ° C of Crystallinity @ and Temp. Drying orientation (hot H20) Orientation ° C Orientation ° C (MPa) 5 149 44.85 96.1 20.6 25 6 149 35.8 97.8 21.8 23 7 163 41.3 96.1 22.5 25 8 167 37.8 98.3 21.9 23 Comp.9 129 38.5 98.3 21.0 23 The Data in Table 4 indicate that Examples 5 and 7 exhibit balanced contraction properties in relation to Examples 6 and 8 and Comparative Example 9. In this evaluation, Examples 5 and 7 exhibited the superior and equivalent shrinkage responses to the wider orientation windows. In addition, Table 3 indicates that Examples 5 and 7 also exhibited the upper softening temperature in relation to Examples 6 and 8. From the results in Tables 3 and 4, it can be seen that Examples 6 and 8 do not represent the preferred embodiment of the present invention that provides balanced contraction properties. Examples 10-12 and Comparative Example 13-18 In an evaluation to determine the heat shrinkage and stiffness response of various polymer compositions, new compositions were formed in rapidly cooled cast sheets with 0.8 mm thickness. In this evaluation, the fusion characterization of each Example was carried out as described above for Example 1 using a Perkin-Elmer CBD-7. The cast extrudate sheets were quickly cooled using a chill roll. The melt extrusion melting temperature in the die was 249 ° C and the temperature of the cooling roll was 24 ° C. The cast sheets were oriented at their respective lowermost orientation temperature using a Biaxial T.M. Long Extruder as described above for Example 1. The descriptions of component polymer (where applicable) and the orientation temperatures for all samples as well as their respective peak CBD melting temperatures, the residual crystallinity at the orientation temperature of the water cooled films and the Vicat softened are shown in Table 5. Samples consisted of Examples 10-12 and Comparative Examples 13-18. Examples 10-12, as well as comparative examples 13 and 14 were prepared by melt blending the polymers of respective components together in a compound extruder at a melting temperature of 177 ° C. Comparative example 15 was an EXCEED ™ plastomer supplied by Exxon Chemical Company. Comparative examples 16.18 were 2045 DOWLEX ™, 2256A DOWLEX ™ and 4213 ATTANE ™, respectively, all supplied by The Dow Chemical Company. Both 2045 and 2256A of DOWLEX ™ are linear low density ethylene / 1-ketene copolymers and 4213 of ATTANE ™ is an ultra low density ethylene / 1-ketene copolymer. Shrinkage values were obtained by measuring unrestricted shrinkage after separate exposures to a hot water bath maintained at about 90 ° C and a hot oil bath maintained at about 105 ° C. Before exposure to the baths, the different samples were cut into 12 cm x 1 .27 cm specimens and marked with a marker exactly 10 cm from one end for identification. After marking each sample, each sample was completely immersed in the water bath or hot oil bath for about five seconds and then removed. Film shrinkage (as the average of four determinations for each sample) was obtained from the calculations according to ASTM D2732-83 for each contracted specimen. Table 6 supports the contraction data of the different samples as well as the film stiffness on the oriented film samples determined by a total energy dart method using a 1.35 kg dart. in accordance with ASTM D4272. Because the samples were oriented equi-biaxially (4.5 x 4.5) the contraction in the machine direction (DM contraction) and the cross direction (DC contraction) were equal. Table 6 indicates that Examples 10 and 11 have excellent rigidity properties. The stiffness properties of Examples 10 and 11 were determined to be superior to those of Example 12 as well as comparative examples 13 and 14, three of which comprise or are made of two-component polymers. However, unlike Examples 10 and 11, for Example 12 and comparative examples 13 and 14, their first respective polymer component had a higher molecular weight (determined by measurements of melt index l2 according to ASTM D- 1238 Condition at 190 ° C / 2.16 kg.) Than its second respective polymer component. The difference in molecular weight between the component polymers of Example 12 and comparative examples 13 and 14 is a contradiction of Examples 10 and 1 1. That is, in contrast to Example 12 and Comparative Examples 13 and 14, Examples 10 and 12 comprise and are made of a second polymer component having a higher molecular weight and higher density than its first polymer component. Therefore, from the results in Tables 5 and 6, it can be seen that Example 12 does not represent the embodiment of the present invention that provides improved shrinkage film stiffness. Table 6 also indicates that the oriented film stiffness of Examples 10 and 11 can be compared to the homogeneously branched EXCEED ™ resin available from Exxon Chemical Company as well as the heterogeneously branched ATTANE ™ resin 4213 and DOWLEX ™ 2246A resin. PLBDL heterogeneously branched, both available from The Dow Chemical Company. FIGURE 3 is a graph of the contraction response to 90 ° C in water and 105 ° C in hot oil versus density of polymer composition for examples 10-12 and comparative examples 13 and 14. The data for FIGURE 3 are taken from Tables 5 and 6. FIGU RA indicates that Examples 10 and 11 also have a relatively high shrinkage response. That is, the shrinkage responses of Examples 10 and 11 were at least equivalent to (if not greater than) those of Example 12 and comparative examples 13 and 14 when measured in density is of equivalent polymer composition.

Table 5 Example% Density 12 of the Percentage Density 12 of the Differential Density I10 / I2 of Peak Vicat by weight of the First First by weight of the Second Comp. of Comp. of Comp. Comp. Fusion of Polymer, Polymer, Second Polymer, Polymer, Polymer Density Polymers, Comp. of First g / cc g / 10 min. Second Polymer g / 10 min. g / 10 min. polymers g / cc ° C polymers Polymer Polymer g / cc g / cc ° C 72 0.915 1.0 28 0.926 1.0 0.86 0.9193 0.011 10.3 105.7 114.9 11 60 0.885 1.0 40 0.935 1.0 0.94 0.9067 0.050 8.2 80.7 121.8 12 38 0.906 0.3 62 0.929 1.6 0.87 0.9205 0.023 7.4 107.3 123.1 13 * 26 0.883 1.2 74 0.923 1.7 1.55 0.9116 0.040 7.7 89.8 123.2 14 * 38 0.882 0.3 62 0.936 1.8 0.84 0.9208 0.044 7.3 106.9 122.5 * 0.96 0.920 NA 6.1 105.3 116.8 00 16 * 0.96 0.9202 NA 7.9 105.2 120.9 17 * 0.92 0.9128 NA 8.1 95.8 121.1 18 * 0.81 0.9059 NA 8.2 84.4 121.4 * Denotes that the example is not an example of the present invention; the examples are provided for comparative purposes only. Examples 10 and 11 were prepared by extruding the fusion compound at about 177 ° C. Example 12 and comparative examples 13 and 14 were manufactured using a multiple reactor polymerization system.

Table 6 Example Temperature Percentage Percentage of Thickness Film Energy of 1% of Module Orientation ° C Crystallinity @ shrinkage contraction in (miera) Total Dart of Dryer and Temp. of hot water @ hot oil / kg. (MPa) Orientation 90 ° C @ 105 ° C 10 106 21.5 6.5 16.5 48 without rupture 202 11 93 19.6 25.0 45.0 56 without rupture 134 12 112 21.4 7.0 15.0 36 4.288 221 13 * 102 22.6 13.3 30.8 43 3.417 170 14 * 112 21.1 7.0 15.5 36 3.752 237 15 * 107 18.1 8.7 20.8 36 without rupture 217 16 * 107 21.1 8.5 18.3 37 without rupture 207 17 * 98 21.0 15.8 38.5 46 without rupture 152 18 * 93 17.9 23.8 52.8 50 without rupture 101 00 * Denotes that the example is not an example of the present invention; the examples are provided for comparative purposes only. Examples 10 and 11 were prepared by extruding the fusion compound at about 177 ° C. Example 12 and comparative examples 13 and 14 were manufactured using a multiple reactor polymerization system In another evaluation, several comparative polymer compositions were oriented using a hot blow guidance technique. In this evaluation, the same polymer compositions are shown in Table 1 for Example 1 and Comparative Examples 14-18 were manufactured in a high blow ratio (ie 2.5: 1) in samples of heat blown (tubular) films single layer with 0.051 mm thickness at approximately 200 ° C melting temperature using a Goucester film line of 30: 1 L / D with 6.4 diameters equipped with a 15.2 cm annular die. The following Table 7 provides some of the manufacturing details for the evaluation as well as the dart impact properties of the different heat-blow shrink films.

Example Output Amps Temperature Pressure Impact thickness of given hr (MPa) of Fusion (° C) Film (microns) dart *** in grams Ex. 12HB * 36 83 37.4 232 51 > 850 Ex. Comp. 36 70 29.2 232 51 > 850 14H B * Ex. Comp. 36 95 33.7 234 51 > 850 15HB * Ex. Comp. 36 80 N D 232 51 331 16HB * Ex. Comp. 36 77.5 34.1 232 51 780 17H B * Ex. Comp. 36 N D 42.5 N D 51 > 850 18H B * * Denotes that the example is not an example of the present invention, the example is provided only for comparative purposes ** dart lmpact measured according to method B of ASTM-1709 where more 850 grams corresponds to "without rupture " N D denotes not determined.

Unlike Table 6 above, Table 7 indicates that the polymer compositions of Example 12 and Comparative Example 14 (see Examples 12 HB and Comparative Example 14HB) provide excellent stiffness properties when orientation is achieved by a simple blowing technique by heat. While Table 7 indicates that, ordinarily, excellent rigidity should be expected for the polymer compositions comprising and being made of at least two polymer components, Table 6 indicates that the case of two-polymer compositions is not necessary. components where the orientation is achieved by an elaborate orientation technique. From these results, we believe that the present invention allows the preparation of oriented shrink film with rigidity and bubble stability (including a more efficient irradiation interlacing response before substantial stretching) superior to polymer compositions such as EXCEED ™ resins, EXACT ™ resins, DOWLEX ™ PLBDL resins and PEDU B resins from ATTAN E ™. In the present invention the shrink film stiffness can be achieved where the molecular weight of the second polymer component is not only higher than the first polymer component of the polymer composition of the invention, but is also substantially higher than the molecular weight of the single-component polymer composition, although the final compositions have essentially the same overall molecular weight (determined by their respective melting index measured according to ASTM D-1238 Condition at 190 ° C / 2.15 kg .). We also think that the teaching herein is applied to the composition of polymers that comprise and are made of at least one first polymer component and at least one second polymer component wherein at least one first polymer component is a ethylene polymer heterogeneously branched (and as such both polymer components are heterogeneously branched ethylene polymers). However, the combination of at least one first polymer component which is homogeneously branched ethylene polymer with at least one second polymer component which is a homogeneous or heterogeneously branched ethylene polymer has the advantage of allowing more precise control in the design of the product This advantage is of particular commercial importance when it is necessary to choose more precisely the melting point or density of the polymer composition to ensure a desired level of shrinkage at the shrinkage temperature required or dedicated by a particular application. FIGURE 4 is a graph of the 1 percent secant modulus (in PMa) versus the polymer composition density (in g / cc) for Examples 10-12 and Comparative Examples 13-18. The data for FIGURE 4 was taken from Tables 5 and 6. FIGURE 4 indicates that Examples 10 and 11 are characterized by a relatively high modulus at low polymer composition densities of 0.919 g / cc and equivalent modules. polymer composition densities above 0.919 g / cc. That is, the 1 percent secant module of the examples of the invention was superior to that of the comparative examples 15-18 when measured at equivalent densities below 0.919. The relatively high module at lower densities provides the commercial advantage of improved craftsmanship and handling in automatic packaging operations along with superior shrinkage responses.

Claims (18)

1. CLAIMS 1. A contraction film comprising a polymer composition, the composition of polymers characterized by having a density on the scale of 0.88 g bouquets / centimeter (g / cc) to 0.94 g / cc, determined in accordance with ASTM D-792 and understood and is made of: 20 to 80 weight percent, based on the total weight of the polymer composition, of at least one first ethylene polymer characterized by having (i) one or more melting peaks as determined using the scanning calorimetry differential (CBD), and (ii) a density on the scale of 0.87 (g / cc) to 0.93 g / cc, as determined in accordance with ASTM D-792, and 20 to 80 weight percent, based on the total weight of the polymer composition, of at least one first ethylene polymer characterized as having (i) one or more melting peaks as determined using differential scanning calorimetry (CBD), and (ii) a density in the scale of 0.89 (g / cc) to 0.96 g / cc, as determined in accordance with ASTM D-792, wherein the density differential between the first and second ethylene polymer components, determined in accordance with ASTM D-792, is on a scale of 0 to 0.05 g / cc.
2. 2. A shrink film comprising a polymer composition, the polymer composition characterized by having a density on the scale of 0.88 grams / centimeter (g / cc) to 0.94 g / cc, determined in accordance with ASTM D- 792 and comprised and made of (A) from 20 to 80 weight percent, based on the total weight of the polymer composition, of at least one first polymer characterized by having (i) a single melting peak, determined using Differential Scanning Calorimetry (CBD), or a single Peak Fractionation of Analytical Temperature Elevation Elution (FEETA), and (ii) a density on the scale of 0.87 (g / cc) to 0.93 g / cc, determined in accordance with with ASTM D-792, and (B) from 20 to 80 weight percent, based on the total weight of the polymer composition, of at least one second polymer characterized by having (i) one or more melting peaks, determined using differential scanning calorimetry (CBD), and (ii) a density in the scale from 0.89 (g / cc) to 0.96 g / cc, determined in accordance with ASTM D-792, and wherein the density differential between the first ethylene polymer component (A) and the second polymer component of Ethylene (B), determined in accordance with ASTM D-792, is on a scale of 0 to 0.03 g / cc.
3. 3. A shrink film comprising a polymer composition, the polymer composition characterized by having a density on the scale of 0.88 g branches / centimeter (g / cc) to 0.94 g / cc, determined in accordance with ASTM D-792 and comprised and made of (C) from 20 to 80 weight percent, based on the total weight of the polymer composition, of at least one first ethylene polymer, wherein at least one first polymer of ethylene was manufactured using a single metallocene site or restricted geometry catalyst system and is characterized by having: (i) one or more melting peaks, as determined using differential scanning calorimetry (CB D), (ii) a short chain branching index (I RCC) or branching index of composition distribution (IR DC) greater than 50%, determined using an elevation elution fractionation of temperature, (iii) a molecular weight, as indicated by the value a melt index value determined in accordance with ASTM D-1238, and (iv) a density on the scale of 0.87 (g / cc) to 0.93 g / cc, and (D) from 20 to 80 percent in weight, based on the total weight of the polymer composition, of at least a second ethylene polymer characterized by having (i) one or more melting peaks, determined using differential scanning calorimetry (CBD), (ii) a molecular weight equal to or greater than the molecular weight of the first ethylene polymer (C) ) as indicated by the melt index values determined in accordance with ASTM B-1238, and (iii) a density on the scale of 0.89 (g / cc) to 0.96 g / cc, where the differential between the first and second components of ethylene polymers (C) and (D) is on the scale of 0.001 at 0.05 g / cc, the density of at least one first ethylene polymer (C) is lower than the density of at least one second ethylene polymer (D) and where the density of the polymer components (C) and (D) and for the polymer composition is determined in accordance with ASTM D-792.
4. 4. The shrink film of any of claims 1, 2 or 3, wherein at least one first ethylene polymer is a substantially linear ethylene polymer that is characterized by having: (a) a melt flow ratio, I10 / I2 >; 5.63, (b) a molecular weight distribution, Mp / Mn, as determined by gel permeation chromatography and defined by the equation: (Mp / Mn) < (10/2) -4.63, (c) a gas extrusion rheology such as the critical shear rate at the beginning of the surface melt fracture for the substantially linear ethylene polymer is at least 50 percent greater than the critical shear rate at the start of the surface melt fracture for a linear ethylene polymer, wherein the linear ethylene polymer has a homogeneously branched short chain branching distribution index (I DRCC) greater than 50 percent, long chain branching and values of L and Mp / Mn with 10 percent of 12 and Mp / M "of the substantially linear ethylene polymer where the respective critical shear rates of the substantially linear ethylene polymer and the linear ethylene polymer are measured at the same melting temperature and under the same pressure scale using a gas extrusion rheometer, (d) a single melting peak of heat. differential scanning rimetry, CBD, between 30 and 140 ° C, and
5. 5. The shrink film of any of claims 1, 2 or 3, wherein the density differential is in the range of 0 to 0.02 g / cc.
6. 6. The shrink film of any of claims 1, 2 or 3, wherein the density differential is in the range of 0 to 0.015 g / cc
7. 7. The shrink film of any of claims 2 or 3, wherein the film is a one layer film structure.
8. 8. The shrink film of claim 2 or 3, wherein the film is a multilayer film structure.
9. The shrink film of claim 2, wherein the molecular weight of at least one first polymer component (A) is greater than the molecular weight than the molecular weight of at least one second ethylene polymer component ( B) indicated by its respective melting index determined in accordance with ASTM D1238.
10. 10. The shrink film of claim 4, wherein the substantially linear ethylene polymer is a copolymer of ethylene and at least one C3-C20 α-olefin. 1.
11. The shrink film of claim 4, wherein the substantially linear ethylene polymer is a copolymer of ethylene and 1-ketene.
12. The shrink film of claim 4, wherein the substantially linear ethylene polymer has from about 0.01 to about 3 long chain branches / 1000 carbons.
13. 13. The shrink film of claim 1, wherein the film is a biaxially oriented shrink film having free shrinkage in the machine direction and transverse directions. The shrink film of claim 8, wherein the multilayer film structure includes a sealant layer comprising at least one homogeneously branched ethylene polymer. 5. The shrink film of claim 8, wherein the multilayer film structure includes a sealant layer comprising at least one homogeneously branched ethylene polymer or a mixture of at least one ethylene polymer homogeneously. branched and at least one ethylene polymer initiated from high pressure free radicals selected from the group consisting of a low density polyethylene, an ethylene / acrylic acid interpolymer, an ionomer of an ethylene / acrylic acid interpolymer, an interpolymer of ethylene / vinyl acetan, an ethylene / methacrylic acid interpolymer, an ionomer of an ethylene / methacrylic acid interpolymer and an ethylene / methacrylate ether. 16. A method for forming a shrink film having the balanced properties comprising: (a) providing a composition of polymers having a density on the scale of about 0.88 grams / centimeter (g / cc) to about 0.94 g / cc determined in accordance with ASTM D-792 and which comprises and is composed of i. from about 20 to about 80 weight percent, based on the total weight of the polymer composition, of at least one first ethylene polymer characterized by having a single melting peak determined using differential scanning calorimetry (C BD) only a peak of Analytical Temperature Elevation Elution Fractionation (FEETA) and a scale density of approximately 0.87 (g / cc) to about 0.93 g / cc determined in accordance with ASTM D-792, and ii. from about 20 to about 80 weight percent, based on the total weight of the polymer composition, of at least one second ethylene polymer characterized by having one or more melting peaks determined using differential scanning calorimetry (CBD) ) and a density on the scale of about 0.89 (g / cc) to about 0.96 g / cc determined according to ASTM D-79, where the density differential between the first and second ethylene polymer components, determined in accordance with ASTM D-792, is on the scale from about 0 to about 0.03 g / cc, (b) making the polymer composition into a substantially unoriented film, (c) further stretching the structure of the polymer. film made substantially non-oriented in a selected stretch, stretch ratio, and stretch temperature; and (d) collecting the oriented film. 1 7. A method for forming a shrink film having improved stiffness comprising: a. providing a polymer composition having a density on the scale of about 0.88 grams / centimeters (g / cc) to about 0.94 g / cc and which comprises and is formed of i. from about 20 to about 80 weight percent, based on the total weight of the polymer composition, of at least one first ethylene polymer, wherein at least one first ethylene polymer is manufactured using a single site of metallocene or restricted geometry catalyst system and is characterized by having: (a) one or more melting peaks, determined using differential scanning calorimetry (CBD), (b) a short chain branching index (IRCC) or branching ratio of composition distribution (IRDC) greater than about 50 percent, (c) a molecular weight, indicated by a melt index value in accordance with ASTM D-1238, (d) a density on the scale of about 0.87 (g / cc) to about

    0. 93 g / cc, and ii. from about 20 to about 80 weight percent, based on the total weight of the polymer composition, of at least one second ethylene polymer characterized by having: (a) one or more melting peaks, determined using calorimetry differential sweep (CBD), (b) a molecular weight equal to or greater than the molecular weight of the first ethylene polymer, indicated by melt index values determined in accordance with ASTM B-1238, and (c) a density on the scale of about 0.89 (g / cc) to about 0.96 g / cc, wherein the density differential between the first and second ethylene polymer components is on the scale of about 0.001 to about 0.05 g / cc and the density of at least one first ethylene polymer is lower than the density of at least one second ethylene polymer, and wherein the density of at least one first ethylene polymer, at least one second ethylene polymer and the polymer composition is determined in accordance with ASTM D-792; b. making the polymer composition in a substantially unoriented film; c. further stretching the manufactured film structure substantially not oriented to a rate of stretch, stretch ratio and stretch temperature; and d. compile the film oriented. The method of any of claims 16 or 17, wherein the film is oriented using an elaborate orientation technique selected from the group consisting of tension structure, double bubble orientation, trapped bubble orientation and ribbon orientation.