MXPA99002108A - Homogeneously branched ethylene/alpha-olefin interpolymer compositions for use in gasket applications - Google Patents

Abstract

Flexible gaskets are formed from blends of ethylene/&agr;-olefin interpolymers which contain long chain branching and that possess improved processability as well as low temperature resistance and resistance to staining and attack by microbes. Such gaskets do not require formulation other than the addition of color, to produce a functional product. The gaskets of the present invention do not impact negatively on the environment and are also relatively inexpensive to produce.

Description

COMPOSITIONS OF I NTERPOLI ERO OF ETI LE N Q / a-OLE F I N A BRANCHED HOMOGENEOUSLY. TO BE USED IN APPLICATIONS FOR PACKAGING This invention relates to packages made from certain polymer compositions. In particular, this application relates to flexible packages formed from homogeneously branched ethylene / α-olefin interpolymer mixtures, preferably those interpolymers containing long chain branching. Such packages have improved processability, as well as improved low temperature flexibility and resistance to microbial attack and spotting. The packages are used in a variety of applications, for example in household appliances such as refrigerators and freezers that require a flexible packing to seal the area between the door and the body of the appliance. One of the most commonly used materials for the production of packaging is polyvinyl chloride (PVC). However, polyvinyl chloride composite packaging suffers from many inconveniences. Polyvinyl chloride requires combination and formulation in order to incorporate the different additives necessary to impart the desirable properties to the packaging. Apart from the additional time and money required for the additional mixing steps, additives such as plasticizers can absorb splashes and become discolored. Plasticizer additives are also susceptible to attack by microbes, which can also lead to discoloration of the packaging, for example, with black spots. On the other hand, polyvinyl chloride gaskets become brittle at low temperatures and cracking becomes a problem. Therefore, polyvinyl chloride packaging is difficult to install at low temperatures. The polyvinyl chloride packaging is also warned as having a negative impact on the environment. Thermoplastic polyolefins (TPOs) are also used in the production of flexible packaging. Thermoplastic polyolefins are not based on polyvinyl chloride (thus eliminating the negative effects of polyvinyl chloride), but are typically mixtures of polypropylene and low modulus elastomers, but while these thermoplastic poiiolefins are effective in packaging applications, they require a step of mixed extra "offline" that contributes negatively to the cost of the formulation. For thermoplastic polyolefins, oils are sometimes added that can also contribute to discoloration. WO 95/05427 describes compositions for packaging useful for sealing beverage containers, which comprise at least one homogeneous ethylene polymer having a narrow molecular weight distribution. Both substantially linear ethylene polymers (SLEPS), such as those taught in U.S. Patent No. 5,272,236 and U.S. Patent No. 5,278,272, as well as linearly branched ethylene linear polymers. , have been proposed for flexible packaging, especially when using flat plate dies that are notorious for inducing melt fracture. Although the substantially linear ethylene polymers have a reduced melt fracture, relative to the comparative linear ethylene polymers, due to the presence of long chain branching, the demands of the flat plate dies still create a need for high molecular weight polymers. ethylene that retains flexibility while simultaneously having a smooth packing surface (ie, little or no melt fracture). Although it has been found that the increase in the melt index remedies the melt fracture in substantially linear ethylene polymers, such polymers with increased melt index suffer problems with melt strength, ie, the low melting resistance resins simply slide off the die without any profile definition. Thus, in the design of resins for packaging applications, it is desirable to maximize the low shear viscosity, and minimize the high shear viscosity. A flexible packaging material is needed that does not require formulation (apart from color) to produce a functional product. This material must be resistant to stains and not be susceptible to attack by microbes. Other desirable characteristics of such packaging are that it has improved flexibility at low temperature and that it has no negative impact on the environment. This packaging must also retain the properties over time, since the current polyvinyl chloride technology, using plasticizer, often has problems of migration of the plasticizer, creating embrittlement. Finally, a packaging material is needed that incorporates all the above characteristics and that is also relatively inexpensive to produce. These and other advantages are taught by the present invention. This invention relates to a packaging composition comprising: (A) At least one homogenously branched ethylene / α-olefin interpolymer, comprising from about 10 to about 90 percent by weight of the packaging composition, the interpolymer homogeneously branched having a melt index of from about 0.001 decigram / minute to about 50 decigram / minute; (B) At least one second homogeneously branched ethylene / α-olefin interpolymer, having a melt index greater than (A) and a melt index of from about 20 decigram / minute to about 5000 decigram / minute; wherein (A) and (B) have a density difference of 0.002 grams / cubic centimeter, and greater up to about 0.11 grams / cubic centimeter; and wherein the resulting packaging composition has an overall melt index of from about 0.5 to about 50 decigrams / minute, an Mw / Mn, from 2 to about 14, and a density of 0.857 grams / cubic centimeter to about 0.91 grams / cubic centimeter. Yet another embodiment of the present invention involves a composition as described above, which also contains a lubricant. Yet another aspect of the present invention includes packages made from the compositions as described above. An example of such a package comprises an ethylene interpolymer composition, wherein the composition has: (1) at least two perceptible melting peaks, as determined using differential scanning calorimetry, or (2) at least two molecular weight peaks. perceptible, as determined using gel permeation chromatography, and (3) a melt flow rate, l? 0 l2, from 6 to about 51, and (4) a Shore A hardness << b0 + ^ (density) + b2 (density) 2 where b0 = -9.679, b?, = 21.360 and b2 = -11.668, where the density is units of grams / cubic centimeter, (5) a tangential flexural modulus (Flex Mod) (psi) > b0 + ^ (density) + b2 (density) where -b0 = 5,795,477, h, = -13,399,463 and b2 = 7,747,721, and where the density is units of grams / cubic centimeter. Figure 1 illustrates the viscosity against the shear rate of a comparative substantially linear ethylene / 1-ketene copolymer, having an I2 of 10.57 decigram / minute (dg / min), an I? O / I2 of about 8, a Mw / Mn, of about 2, and a density of 0.8747 grams / cubic centimeter, compared to Mix B, a substantially linear ethylene / 1-octene interpolymer composition of the invention, having an I2 of 10.57, an I ? 0 / I2 of 27, one Mw / Mn, of about 8.9, and a density of 0.8747 grams / cubic centimeter. Figure 2 illustrates the gel permeation chromatogram for Mixture A, a substantially linear ethylene / 1-octene interpolymer composition of the present invention, having a melt index of 10.81 decigram / minute, one I10 / I2 = 19.8 , a density of 0.8704 grams / cubic centimeter, an Mw = 71800, an Mn = 12400, and an Mw / Mn = 5.79. Figure 3 illustrates the gel permeation chromatogram for Mixture B, a substantially linear ethylene / 1-octene interpolymer composition of the present invention, having a melt index of 10.57 decigram / minute, an I10 / I2 = 27 , a density of 0.8747 grams / cubic centimeter, an Mw = 77500, an Mn = 8700, and an Mw / Mn 8.9.

Figure 4 illustrates the gel permeation chromatogram for Mixture C, a substantially linear ethylene / 1-octene interpolymer composition of the present invention, having a melt index of 9.03 decigram / minute, an I? 0 / I2 = 19.19, a density of 0.8821 grams / cubic centimeter, an Mw = 75900, an Mn = 12400, and an Mw / Mn = 6.12. Figure 5 compares the storage modulus, G ', (dynes / square centimeter) against the temperature (° C) for Mixture B, a substantially linear ethylene / 1-octene interpolymer composition of the present invention, which has a melting index of 10.57 decigrams / minute, an I? 0 I2 = 27, a density of 0.8747 grams / cubic centimeter, an Mw = 77500, an Mn = 8700, and an Mw / Mn = 8.9, and a comparative chloride composition of polyvinyl which has a melt index of 2.75 decigrams / minute, and a density of 1. 39 grams / cubic centimeter. Figure 6 compares Shore A hardness versus density for conventional narrow molecular weight distribution polyethylene (solid line), against the broader molecular weight distribution polyethylene compositions (dashed line) of the present invention. The term "linear ethylene polymers" used in the present invention means that the ethylene polymer has no long chain branching. That is, the linear ethylene polymer has an absence of long chain branching, such as for example the traditional heterogeneous linear low density polyethylene polymers, or the linear high density polyethylene polymers, using Ziegler polymerization processes (e.g. , U.S. Patent Number 4,076,698 (Anderson et al.), sometimes called heterogeneous polymers The Ziegler polymerization process, by its catalytic nature, makes polymers that are heterogeneous, i.e., the polymer has many types Different branching within the same polymer composition as a result of numerous metal atom catalytic sites In addition, the heterogeneous polymers produced in the Ziegler process also have broad molecular weight distributions (Mw / Mn); When the Mw / Mn is increased, the I10 I2 ratio increases concurrently. The term "linear ethylene polymers" does not refer to polyethylene (LDPE), ethylene / vinyl acetate (EVA) copolymers, or ethylene / vinyl alcohol copolymers (EVOH) branched at high pressure, which are known to those skilled in the art. the technique as having numerous long chain branches. The term "linear ethylene polymers" may refer to polymers made using polymerization processes of uniform branching distribution, sometimes called homogeneous polymers. These uniformly or homogeneously branched polymers include those made as described in U.S. Patent No. 3,645,992 (Elston), and those made using so-called site catalysts in a batch reactor, which have relatively high concentrations of olefin (as described in U.S. Patent No. 5,026,798 (Canich), or in U.S. Patent Number 5,055,438 (Canich) or those made using constrained geometry catalysts in a batch reactor, which also have relatively high concentrations of olefin (as described in U.S. Patent No. 5,064,802 (Stevens et al.), or EPA 0 416 815 A2 (Stevens et al.). / homogeneous are those polymers in which the comonomer is distributed randomly within a molecule given interpolymer molecule, and wherein substantially all of the interpolymer molecules have the same proportion of ethylene / comonomer within that interpolymer, but the linear version of these polymers has an absence of long chain branching, as, for example, Exxon Chemical has taught in its Tappi Journal newspaper of February 1992. The term "substantially linear" means that the polymer has long chain branching, and that the base structure of the polymer is replaced with 0.01 branching. long chain / 1000 carbons to 3 long chain branches / 1000 carbons, more preferably 0.01 long chain branches / 1000 carbons to 1 long chain branch / 1000 carbons, and especially 0.05 long chain branches / 1000 carbons to one long chain branch / 1000 carbons. Like traditional linear homogeneous polymers, the substantially linear ethylene / α-olefin interpolymers used in this invention also have a homogeneous branching distribution, and only a single melting peak (determined using differential scanning calorimetry (DSC)), using a second heating and a scanning rate of 10C / minute from -40 ° C to 160 ° C), as opposed to the traditional Ziegler polymerized linear heterogeneous ethylene / α-olefin copolymers, which have two or more melting peaks ( determined using differential scanning calorimetry (DSC), US Patent No. 5,272,236 and US Patent No. 5,278,272 discloses substantially linear ethylene polymers and interpolymers. the substantially linear ethylene polymers is defined herein as a at chain length of at least 6 carbons, over which the length can not be distinguished using 13C nuclear magnetic resonance spectroscopy. The long chain branching of substantially linear ethylene polymers is, of course, at least one longer carbon that two carbons less than the total length of the comonomer copolymerized with ethylene. For example, in a substantially linear polymer of ethylene / 1-octene, the long chain branch will have at least seven carbons in length; however, as a practical matter, the long chain branching has to be longer than the side chain resulting from the incorporation of the comonomer. For the substantially linear ethylene / α-olefin copolymers, the long chain branch is itself branched homogeneously, since it is the base structure to which the branch is attached. For the ethylene homopolymers and certain ethylene / α-olefin copolymers, the long chain branching is determined by the use of 13C nuclear magnetic resonance spectroscopy, and quantified using the method of Randall (Rev. Macromol. Chem. Phvs. C29 (2 and 3), pages 285-297). The CDBI (abbreviation for Composition Distribution Branch Index) is defined as the percentage by weight of the polymer molecules having a comonomer content within 50 percent of the total average molar content of comonomer. The composition distribution branching index of a polymer is quickly calculated from the data obtained from techniques known in the art, such as, for example, leaching fractionation of temperature rise (abbreviated in the present high "TREF" ), as described, for example, in Wild et al., Journal of Polvmer Science. Polv. Phvs. Ed .. Volume 20, page 441 (1982), or as described in U.S. Patent No. 4,798,081, or as described in U.S. Patent No. 5,008,204 (Stehiing). The technique for calculating the Composition Distribution Branching Index is described in U.S. Patent Number 5,322,728 (Davey et al.), And in U.S. Patent Number 5,246,783, (Spenadel et al.) . The Composition Distribution Branching Index for homogeneously branched linear, or substantially linear, branched linear olefin polymers of the present invention is greater than about 30 percent, preferably greater than about 50 percent, and especially greater than about 90 percent. A unique feature of the substantially linear olefin polymers used in the present invention is a highly unexpected flow property, wherein the value I 0 / I 2 is essentially independent of the polydispersity index (ie, M w / M n). This is in contrast to the conventional Ziegler polymerized heterogeneous polyethylene resins, and with homogeneous linear polyethylene resins polymerized by conventional single site catalyst, which have rheological properties, so that as the rate polydispersity (or the MWD), the value is also increased The density of homogeneously branched, linearly branched, homogeneously branched, or linear ethylene / α-olefin interpolymers, and for the interpolymer compositions used in the present invention, is measured according to ASTM D-792, and for individual components is generally from about 0.85 grams / cubic centimeter to about 0.96 grams / cubic centimeter, with the proviso that other conditions specified herein are met (eg, the density difference of more than 0.002 grams / cubic centimeter and less than, or equal to, approximately 0.11 grams / cubic centimeter, between each component). The densities of the individual components of the mixture were determined by the overall composition of the mixture and the overall density of the mixture. The overall density of the mixture for the mixture of homogeneous ethylene interpolymer / homogeneous ethylene interpolymer is from about 0.857 to about 0.91 grams / cubic centimeter, preferably from about 0.86 to about 0.9 grams / cubic centimeter, more preferably from about 0.87 to approximately 0.895 grams / cubic centimeter. The most preferred density was determined, by the specific application. More specifically, the most preferred density was determined by the modulus or flexibility required in the final part. Recent studies suggest that a density of 0.87 to 0.88 grams / cubic centimeter is most preferred for a refrigerator package, while the most preferred density for a door package is 0.88 to 0.895 grams / cubic centimeter. Table 1 illustrates the density ranges of the individual components giving the most preferred blend composition (24 to 40 weight percent of the composition comprising the highest molecular weight component), and the most preferred overall density range of . 0.87 to 0.895 grams / cubic centimeter. Table 1 assumes that the difference in density between the high and low molecular weight fractions is 0.02 grams / cubic centimeter. The operational difference in density between the two components of the mixture is equal to, or greater than 0.002 grams / cubic centimeter, and equal to or less than 0.11 grams / cubic centimeter, the preferred being equal to or greater than 0.002 grams / cubic centimeter and less that or equal to 0.05 grams / cubic centimeter, and most preferred equal to or greater than 0.002 grams / cubic centimeter and less than or equal to 0.03 grams / cubic centimeter.

Table 1 Density of the Components of the Mixture, Using the Most Preferred Weight Fraction and the Global Density.

The packages of the present invention also retain the low temperature flexibility, as evident from Figure 5, which compares a composition of the invention (Mixture B) with a conventional polyvinyl chloride packaging formulation. The values of G '(the storage modulus, which is an indication of stiffness) of Mixture B are consistently lower than those for polyvinyl chloride, at the same temperatures in the range of about -60 ° C to about 0 ° C (the effective operating temperature of a refrigerator or freezer). In this manner, the packages of the present invention have improved flexibility relative to polyvinyl chloride at lower temperatures. Figure 5 also shows that the packages of the present invention also have a lower heat resistance relative to polyvinyl chloride. The lowest heat resistance becomes a concern when the manufactured packaging is shipped to the original equipment manufacturer (OEM) for installation. The packages made from the compositions of the invention also have higher temperature stability than the conventional narrow molecular weight distribution polyethylene, which is especially useful during shipping. The molecular weight of linear branched olefin polymer compositions homogeneously or substantially linearly branched homogeneously, used in the present invention, is conveniently indicated using a melt index measurement, in accordance with ASTM D-1238, Condition of 190 ° C / 2.16 kilograms (formerly known as "Condition (E)" and also known as I2) . The melt index is inversely proportional to the molecular weight of the polymer. In this way, the higher the molecular weight, the lower the melting index, although the relationship is not linear. The melt index for the high molecular weight component of the compositions, an ethylene interpolymer either linearly branched homogeneously, or substantially linearly branched homogeneously, used herein, is generally from about 0.001 decigram / minute to about 50 decigram / minute, preferably from approximately 0.01 decigram / minute to approximately 30 decigram / minute, and especially from approximately 0.02 decigram / minute to approximately 10 decigram / minute. The melt index of the low molecular weight fraction is from about 20 to about 5000, preferably from about 100 to about 4000, most preferably from about 200 to about 3000 decigrams / minute. The range of the melt index of the final blend or composition is from about 0.5 to about 50 decigrams / minute, preferably from about 1 to about 25 decigrams / minute, most preferably from about 4 to about 15 decigram / minute. Another useful measurement in characterizing the molecular weight of linear branched olefin polymers homogeneously, or substantially linearly branched in a homogeneous manner is conveniently indicated using a melt index measurement, in accordance with ASTM D-1238, 190 ° Condition C / 10 kilograms (formerly known as "Condition- (N)" and also known as I10). The ratio of these two melt index terms is the melt flow ratio and is designated I10 / I2, which also indicates the processability of that polymer. For the substantially linear ethylene / α-olefin polymers of the single component used in the present invention, the ratio I 0 / I 2 indicates the degree of long chain branching, especially for polymers having a relatively low I 2 (e.g. , an I2 from about 0.01 to about 50 decigrams / minute), that is, the higher the ratio of I? 0 / I2, the more long-chain branching in the polymer. Generally, the I? 0 / I2 ratio of the substantially linear ethylene / α-olefin polymers of the individual component is at least about 5.63, preferably at least about 7, especially at least about 8 or more. The upper limit of the ratio I 0 0 I2 for the individual components may be about 50, preferably about 20, and especially about 15. For the novel substantially linear ethylene interpolymer compositions used in the invention, it may be increased the proportion of melt flow (I10 / I2) through mixing, either discrete mixtures of interpolymer or mixtures polymerized by in-situ reactor. The I10 / I2 indicates the degree of fluidity and / or processability, therefore, the higher the I10 /? 2, the more likely the interpolymer composition can be formed in a desired package, without surface abnormalities. For the novel substantially linear ethylene interpolymer compositions used in the invention, the melt flow index (I? 0 / I2) is from 6 to 51, preferably from 10 to 42, most preferably from 15 to 33.

Packings made from novel substantially linear ethylene interpolymers should be flexible enough to form an adequate seal. The flexibility can be indicated by the module, or for the polyolefins, this can be indicated by the Shore A hardness. The hardness is measured herein as "Shore A" hardness (as determined using ASTM D-2240). For the substantially linear ethylene interpolymer compositions comprising the packages, the Shore A hardness ranges from about 50 to about 98, even without the use of petroleum oils or plasticizers, commonly included to reduce the hardness of the polymer and the resulting packing. Table 3 summarizes Shore A data against polymer density for three interpolymer compositions useful in the present invention, while Figure 6 graphically shows the reduction in Shore A for the novel compositions of the invention, as compared to polyethylene. Conventional narrow MWD.

Determination of Molecular Weight Distribution All samples of interpolymer product and individual interpolymer components were analyzed by gel permeation chromatography (GPC) in a Waters 150C high temperature chromatographic unit, equipped with three columns of mixed porosity (Polymer Laboratories 103, 104, 105 and 106) operating at a system temperature of 140 ° C. The solvent is 1, 2,4-trichlorobenzene, from which the solutions were prepared at 0.3 percent by weight of the samples for injection. The flow rate is 1.0 milliliters / minute and the injection size is 100 microliters. Molecular weight determination is deduced by using narrow molecular weight distribution polystyrene standards (from Polymer Laboratories) along with their leach volumes. The molecular weights of the equivalent polyethylene were determined by using the appropriate Mark-Houwink coefficients for polyethylene and polystyrene (as described by Williams and Ward in Journal of Polymer Science, Polvmer Letters, Volume 6, (621) 1968) to derive the following equation: "Ipolietlleno - ß (Mp0 | est Treno) In this equation, a = 0.4316 and b 1.0. The weight average molecular weight, Mw, and the number average molecular weight, Mn, are calculated in the usual manner, according to the following formula: Mj = (Sw¡ (M1i)) i where wj is the fraction of weight of molecules with molecular weight Ml leaching from the column of gel permeation chromatography in the fraction i and j = 1 when calculating Mw, and j = -1 when calculating Mn. The molecular weight distribution (Mw / Mn) for the substantially linear ethylene interpolymers or homogeneous linear ethylene interpolymers of the individual component, used in the invention is generally from about 1.8 to about 2.8. The molecular weight distribution (Mw / Mn) for the compositions comprising the substantially linear ethylene interpolymers or homogeneous linear ethylene interpolymers used in the invention, is generally from about 2 to about 14, preferably from about 3 to about 10, especially from about 4 to about 8.

Generally, a graph of apparent shear stress versus apparent shear stress index is used to identify melt fracture phenomena. According to Ramamurthy in Journal of Rheoloav 30 (2), 337-357, 1986, on a certain index of critical flow, the irregularities of the extrudate observed can be broadly classified into two main types: fracture by superficial fusion and fracture by total merger. Surface fusion fracture occurs under seemingly stable flow conditions, and varies in detail from loss of specular brightness to the more severe form of "shark skin". In this description, the beginning of the superficial fusion fracture is characterized as the point where the extruded profile loses the surface brightness (the surface quality was evaluated using a 10x magnification lens). As shown in Table 4, packages produced from substantially linear ethylene / α-olefin interpolymers develop surface imperfections at a shear stress of approximately 0.20 ± 0.03 MPa (2.0 x 106 0.3 x 106 dynes / square centimeter) . However, as shown in Table 5, a door package produced by extrusion of Polymer Blends B and C, did not develop surface imperfections. The packing profile produced from Polymer Blend A contained smaller strips of melt fracture along the length of the part, these melt fracture strips were the result of imperfections in the die, ie lines of die, as shown in Table 5. The fact that the melt fracture was not observed while Polymer Blends B and C were being extruded was surprising, given the very high levels of shear stress, for example, 0.651 and 0.850 MPa, respectively, as shown in Table 5. For example, it is generally presumed that the development of surface defects is determined by the shear stress level. The melt fracture of the ethylene interpolymer compositions also depends very much on the design of the die, for example, the inlet geometry, the length to width ratio of the surface region between die ridges and the construction material (see J). Dealy, "Melt Technology, and its Role in Plastics Processing", Van Nostrand Reinhold, New York, 1990, Chapter 8, pages 336-341). It is common practice to tune the die to maintain a constant face velocity across the entire profile of the package. Generally, this tuning process leads to a die which is more likely to produce melt fracture profiles, since the surface region between die ridges is shortened. Of course, the melt fracture also depends on the extrusion temperature and the flow rate. The substantially linear and linear ethylene polymers useful in the present invention are interpolymers of ethylene with at least one α-olefin of 3 to 20 carbon atoms and / or acetylenically unsaturated monomer of 2 to 20, carbon atoms and / or diolefins of 4 to 18 carbon atoms. The substantially linear polymers used in the present invention may also be interpolymers of ethylene with at least one comonomer selected from the group consisting of α-olefins of 3 to 20 carbon atoms, conjugated dienes, and non-conjugated dienes and mixtures thereof. Ethylene / alpha-olefin / diene (EPDM) are also suitable for this invention and can include the α-olefins of 3 to 20 carbon atoms above and at least one non-conjugated diene (eg, 5-ethylidene-2-norbornene ) or a conjugated diene (eg, 1,3-pentadiene (commonly called piperylene)). The term "interpolymer" means that the polymer has at least two comonomers (e.g., a copolymer) and also includes more than two comonomers (e.g., terpolymers). Preferred are substantially linear ethylene / alpha-olefin copolymers, however, ethylene / α-olefin copolymers of 3 to 20 carbon atoms are especially preferred.

Polymerization of the Ethylene Interpolymer Branched Homogeneously Substantially Linear The substantially linear ethylene / α-olefin interpolymers are made by the use of restricted geometry catalysts, preferably the restricted geometry catalysts as described in the United States of America Patent Application Serial Numbers: 545,403, filed on July 3, 1990; U.S. Patent Number 5,132,380; U.S. Patent Number 5,064,802; U.S. Patent Number 5,153,157; U.S. Patent Number 5,470,993; U.S. Patent Number 5,453,410; U.S. Patent Number 5,374,696; U.S. Patent Number 5,532,394; U.S. Patent Number 5,494,874; U.S. Patent Number 5,189,192. The olefin polymerization, transition metal monocyclopentadienyl catalysts taught in U.S. Patent Number 5, 026, 798, are also suitable for use in the preparation of the polymers of the present invention, while that the conditions of the reaction are as specified below. Suitable cocatalysts for use herein include but are not limited to, for example, polymeric or oligomeric aluminoxanes, especially methyl aluminoxane or modified methyl aluminoxane (made, for example, as described in the US Pat. Number 5,041,584, U.S. Patent Number 4,544,762, U.S. Patent Number 5,015,749, and / or U.S. Patent Number 5,041,585, as well as inert, compatible, noncoordinating, forming compounds. The preferred cocatalysts are inert, noncoordinating boron compounds.The substantially linear ethylene polymers can be produced by a continuous controlled polymerization process (as opposed to a batch or semi-batch operation) using at least one reactor, but They can also be produced using multiple reactors (for example, using a multiple reactor configuration as described in U.S. Patent Number 3,914,342, pending application with serial number 208,068 filed March 8, 1994, pending application with serial number 433,785 filed on May 3, 1995, and pending application serial number 452,472 filed May 26, 1995) at a polymerization temperature and pressure sufficient to produce the interpolymer having the desired properties. The polymer compositions of the invention can be formed by any convenient method, including dry blending the individual components and subsequently melt mixing in a mixer, or by mixing the components together directly in a mixer (e.g., a Banbury mixer). , a Haake mixer, an internal Brabender mixer, or a single or twin screw extruder including a combination extruder and a side arm extruder directly downstream of an interpolymerization process Preferably, the mixtures are made by polymerization. direct, without the isolation of the components of the mixture. Preferably, the packaging compositions of the invention are formed in-situ by the interpolymerization of different combinations of substantially linear or linear elastic olefin polymers in multiple reactors using either single or multiple catalysts. The reactors can be operated sequentially or in parallel. In PCT Patent Publication WO 94/17112 an exemplary in-situ interpolymerization process is described. An alternative approach would be to produce the mixture in a reactor using multiple catalysts. The weight fraction of the high molecular weight component is from about 90 to about 10 weight percent (by weight of the packaging composition), with the remnant (10 to 90 percent) of lower molecular weight. Preferably, the weight fraction of the high molecular weight component is from about 15 to about 60 weight percent, with from about 20 to about 40 weight percent being most preferred. Other polymers can also be combined with effective amounts of substantially linear or linear ethylene polymer blends to make the packages as well, depending on the end-use properties required. These other polymers are thermoplastic (ie processable, melt) polymers and include polymers such as highly branched low density polyethylene, ethylene / vinyl acetate copolymers, and ionomers such as ionomers made from ethylene / acrylic acid copolymers (for example, PRIMACORMR Adhesive Polymers made by The Dow Chemical Company). Additives, such as antioxidants (for example, hindered phenolics, such as lrganoxMR 1010 or lrganoxMR 1076 supplied by Ciba Geigy), phosphates (for example, lrgafosMR 1.68 also supplied by Ciba Geigy), Standostab PEPQMR (supplied by Sandoz) , pigments, dyes, fillers, at least one processing aid selected from the group consisting of organo-silicones, fluoropolymers, and fluoro (co) polymers, and the like, may also be included in the polymer blend of the present invention. The packages formed from the polymer blend of the present invention may also contain additives to increase antiblocking, mold release and coefficient of friction characteristics including, but not limited to, untreated and treated silicone dioxides, talc, calcium carbonate, and clay, as well as acid amides, primary, secondary, and substituted fats, release agents, silicone coatings, and the like. Preferably, at least one lubricant is included in the packaging compositions. Lubricants such as erucamide are especially useful in the compositions at levels from about 500 ppm to about 10,000 ppm (1 percent), preferably about 2700 ppm. For example, the addition of ten percent (by weight of the composition) of an erucamide concentrate to 2.7 percent (in a similar substantially linear ethylene polymer) improves the extrusion of the package. The use of a mold release agent based on Teflon® (made by E.l. duPont de Nemours, Inc.) or permanent Teflon® coating of the forming blocks to reduce the coefficient of friction during extrusion is also recommended. The addition of 5000 ppm of the Ucarsil PA-1 processing aid has been found useful (Ucarsil PA-1 is an organically modified polydimethylsiloxane manufactured by Union Carbide (US Pat. No. 4,535,113)), to avoid surface imperfections in branched ethylene polymers in a homogeneous manner. The polymer blend of the invention may additionally include recycled and waste materials and diluting polymers (eg, defective packaging made from similar virgin compositions), to the extent that the desired performance properties are maintained. In addition to forming packaging for household appliances and outdoor demolding, the packaging compositions described in the present invention are also useful for irradiated or cured applications such as for medical and automotive applications, for example, medical tubing and automotive weathering.

EXAMPLES Polymerization Materials and Conditions The homogeneously branched substantially linear ethylene / 1-octene interpolymers used in the examples herein are produced in accordance with the pending application serial number 208,068 filed on March 8, 1994, the pending application with serial number 433,785 filed on May 3, 1995 and the pending application with serial number 452,472 filed on May 26, 1995, with the exception that the percentage of the high molecular weight component changes from the percentages described in those applications. Additionally, each component is made using the same catalyst, but each component is polymerized at different temperatures. Table 2 lists in detail the specifications of the packaging compositions of the substantially linear ethylene / alpha-olefin interpolymer.

Table 2 Calculated using the density mixing rule (1 / pt = w, / Pi + (IW / P2), where Pf PT and P2 represent the high molecular weight, total the densities of the low molecular weight components, respectively, and w (is the weight fraction of the high molecular weight component.) mf was measured using ASTM D792 and P2 was measured by DSC. ** Calculated by means of tailoring experimental gel permeation chromatography to a more likely distribution. Calculated from the DSC thermogram. **** The melt index (I2) was calculated using: In (I2) = 62.781735 - 3.861973 * In (Mw) - 1.7909488 * In (I10 / I2) - 16.309713 (assuming that I10 / I2 = 8.0) METHODS Door gaskets are produced using an 88.9 millimeter extruder, L / D = 24, with a single flown screw. A flat plate profile die with a cross-sectional area of 48.90 square millimeters and having a minimum die gap of 0.381 millimeters is used to produce packages of Polymer B and C Mixtures. A flat plate die with a cross-sectional area of 56.06 square millimeters and having a minimum die gap of 0.254 millimeters is used to produce packages of Polymer Blend A. Once extruded, the profile is passed through three forming blocks and inside a cooling trough at 18 ° C.

The presence of the fusion fracture is visually determined using a 10X magnifying eye piece. The melting strength of the definition of the part and the ease to guide the profile through the three forming blocks were evaluated. Door gaskets are produced by extruding Polymer Blend A at 142 ° C at 47.2 kilograms / hour or 18.5 meters / minute, as shown in Table 5. Given the low density of Mixture A, and the high extrusion temperature, the forming blocks were not used since the mixture A did not adhere to the forming blocks. As a result, the definition of the profile was very poor. Door gaskets are produced by extruding Polymer Blend B, at 91.7 ° C at 14 - 0 kilograms / hour or 6.4 meters / minute, and by extruding Polymer Blend C at 98.9 ° C, at 20.6 ° C. kilograms / hour or 9.1 meters / minute, as shown in Table 5. The packages produced using Polymer B and C Mixtures are free of surface flow defects (melt fracture) even at these very low extrusion temperatures and very high stresses of shear stress. The definition of the profile is also acceptable (three forming blocks are used) which indicates that the fusion resistance was acceptable.

DISCUSSION Table 3 compares the physical properties of the substantially linear ethylene / alpha-olefin interpolymer packing compositions with a conventional linear single-component ethylene / alpha-olefin interpolymer packing. Note the broader molecular weight distribution (Mw / Mn) of the substantially linear linear ethylene / alpha-olefin interpolymer packing compositions, as indicated by the I / I2 and the polydispersity (Mw / Mn). Although we do not want to be, linked to no particular theory, we believe that it is the Mw / Mn, wider which produces the desired rheological changes, for example, lower shear viscosity higher with lower high shear viscosity, as shown in the Figure 1. These are the key rheological changes that are critical to this invention. More specifically, the low shear viscosity or melt strength of the substantially linear ethylene / alpha-olefin interpolymers should be increased to improve part definition while the high shear viscosity should remain low to avoid fusion fracture. The melt strength of the substantially linear ethylene / alpha-olefin interpolymer packing compositions could be improved by decreasing the melt index, eg, 6.0 decigram / minute, to increase the melt strength. As the difference in density between the two components of the mixture increases, one can increase the proportion at which the package sits (solidifies) and improve the higher service temperature. Although the maximum difference in density between the components of the mixture listed in Table 2 is 0. 022 grams / cubic centimeter (Mix b), a density difference of 0.072 grams / cubic centimeter has also been achieved.

Table 3 Comparison of the physical properties of each composition.

Affinity ™ HM1100 is a substantially linear ethylene / 1-octene copolymer of registered trademark produced by The Dow Chemical Company. * Resistance to fusion at 120 ° C. ** Flexible PVC = compound fully formulated for packaging (ie, includes plasticizers, stabilizers, color, etc.). By way of comparison, door packages using a commercially available substantially linear polyethylene having an Mw / Mn of about 2 are produced using an 88.9 millimeter extruder having an L / D = 24 with a single fly screw with a section of deep Maddox mixing at the tip. A flat plate profile die with a cross sectional area of 56.06 square millimeters is used to produce the door package. The determinations of the fusion fracture and the fusion resistance are of a qualitative nature. The presence of the fusion fracture is visually determined using a 10X magnifying eye piece. The melting strength of the definition of the part and the ease to guide the profile through the forming blocks are evaluated. Initial Table 4 results in where the substantially linear ethylene / alpha-olefin interpolymers of the single component (i.e., Mw / Mn of about 2) having melt indexes of 1, 5, 13 and 30 are converted into door gaskets. . All substantially linear ethylene / alpha-olefin interpolymers exhibit melt fracture (loss of surface brightness) at exit velocities below commercial targets of 27.22 kilograms / hour and 10,668 meters / minute. Although the output of 26.31 kilograms / hour of the 30 milliliter resin is close to the commercial target, this resin does not have enough melt strength to become a package, for example, the resin simply slips off the die without any definition of profile. In fact, the resin at 13 milliliters does not have the required melting strength. Table 4 also shows that the addition of the processing aid (Ucarsil PA-1) from 5000 ppm to 1.0 milliliter of the substantially linear ethylene / alpha-olefin interpolymer does not increase the exit velocity to the commercial target, although the exit velocity is of about double. Although the output speed is doubled, this is still a factor of three commercial speeds lower than the acceptable ones.

Table 4 Comparative Examples Extrusion of packaging profile for doors using interpolymers to the resin contains 500 ppm Ucarsil PA-1 processing aid (Ucarsil PA-1 is an organically modified polydimethylsiloxane manufactured by Union Carbide (U.S. Patent Number 4,535,113)) * Shear rate values and of the shear stress are at the beginning of the surface melt fracture, eg, loss of surface brightness, die cross-sectional area = 56. 06 square millimeters, narrowest die gap = 0 254 millimeters.

Table 5 The extrusion of packaging profile for doors using Mixtures A, B and C of the unique substantially linear ethylene interpolymers. a Mixture A packaging contained small surface melt fracture strips along the length of the packing profile, due to die lines or die imperfections. No fracture due to surface melting was observed in the packages produced from Mixture B and Mixture C, hence the greater than symbol. 1 Transverse area of the die = 56.06 square millimeters, narrowest die interval = 0.254 millimeters. 2 Transverse area of the die = 48.90 square millimeters, narrowest die interval = 0.381 millimeters. Although the invention has been described in considerable detail through the foregoing specific embodiments, it should be understood that these embodiments are for illustrative purposes only. One of skill in the art can make many variations and modifications without departing from the spirit and scope of the invention.

Claims (10)

1. A packaging composition comprising: (A) At least one homogenously branched ethylene / α-olefin interpolymer, comprising from 10 to 90 weight percent of the packaging composition, the branched interpolymer homogeneously having an index fusion, l2, from 0.001 decigram / minute to 50 decigram / minute; (B) At least one second homogeneously branched ethylene / α-olefin interpolymer, having a melt index, 12, greater than (A) and a melt index, 12, from 20 decigram / minute to 5000 decigram / minute; where (A) and (B) have a density difference of 0.002 grams / cubic centimeter, and higher up to 0.11 grams / cubic centimeter; and wherein the resulting packaging composition has a global melt index, 12, of 0.5 to 50 decigrams / minute, an Mw / Mn of 2 to 14, and a density of 0.857 grams / cubic centimeter to 0.91 grams / cubic centimeter.

2. The packaging composition of claim 1, wherein (A) has a melt index, 12, of 0.01 to 30 decigram / minute.

3. The packaging composition of claim 1, wherein (B) has a melt index, 12, of from about 100 to about 4,000 decigrams / minute.

4. The packaging composition of claim 1, wherein the packaging composition has a melt index, 12, of 1 to 25 decigrams / min. The packaging composition of claim 1, wherein each of (A) and (B) comprises a substantially linear ethylene / alpha-olefin interpolymer. The packaging composition of claim 1, wherein each of (A) and (B) comprises a linear ethylene / alpha-olefin interpolymer. The packaging composition of claim 1, wherein the alpha-olefin is at least one selected from the group consisting of alpha-olefins of 3 to 20 carbon atoms, conjugated dienes, non-conjugated dienes, and mixtures thereof . 8. The packaging composition of claim 1, wherein it also contains at least one lubricant. 9. The packaging composition of claim 1, wherein it also contains at least one polymer processing aid. 10. A package made from the packaging composition, according to claim 1.