MXPA98002079A - Compositions of high barrier polypropylene and its use in empa applications - Google Patents

Abstract

The present invention relates to film wherein at least one layer comprises polymer, a molecular majority of which is propylene derivative, having a water vapor transmission rate less than or equal to about (-7.4428g xæm / m2day polymer crystallinity) (percentage crystallinity of the polymer) + 627.32 gxæmxday, or (-0.0189xmil / 100 in2xday percent crystallinity of the polymer) (percent crystallinity of the polymer) + 1,593 gxmilx100 in2xd

Description

COMPOSITIONS OF HIGH BARRIER POLYPROPYLENE AND YOUR USE IN PACKAGING APPLICATIONS Field of the Invention This invention relates to polypropylene films of low water vapor transmission rate, or high barrier. The films have remarkably better barrier properties than would be expected in light of their polymer crystallinity levels. BACKGROUND OF THE INVENTION A variety of plastic films are used in packaging applications such as bags, cavities, tubes, trays, bubble packings, metal sheet composite materials, composite materials with cellulosic material such as paper, and combinations thereof. In many of these applications, it is important that the plastic film possess good physical and mechanical properties such as tear strength, high tensile strength, and high-speed equipment processing capability. In many applications for packaging of items in the food and medical industries, it may also be desirable to have films with high barrier characteristics.

This is particularly true for water vapor or moisture. Films that have low water vapor or moisture transmission rates (WVTR or VTR) will be particularly useful in food packaging to prevent dehydration of packaged foods and / or to prevent re-hydration of dry foods. Similar needs arise in packaging of medical, chemical and electronic articles for which it is desired to retain high levels of moisture inside the packaging or prevent the transport of water, or other moisture, through the film barrier. It is generally believed that random polypropylene homopolymers and copolymers, having high strength and the ability to be manufactured in films, such as by film forging, with or without post-extrusion orientation, generally have a WVTR that is a directly related function of the crystallinity. of the polypropylene polymer. It is thought that at higher levels of polymer crystallinity, the lower the WVTR; in this way, imparting better barrier properties to more highly crystalline polypropylene films. Accordingly, copolymeric polypropylenes, because of their relatively low crystallinity, will show a higher WVTR when compared to homopolypropylene films. It is also known that the melting point of polypropylene can be reduced by the inclusion of co-monomer during the polymerization reaction; the co-monomer within the polymeric backbone appears to break up the crystallization of the polymer. This phenomenon seems to be independent of the polymerization catalyst. This behavior is exhibited when the polypropylene is catalyzed with either the traditional Ziegler-Natta catalyst or with a metallocene type catalyst. Therefore, random copolymer polypropylenes exhibit lower melting points and levels of crystallinity. These properties are beneficial during the process of thermo-sealing the films. Thus, random copolymer polypropylenes, currently being typically copolymers of propylene and ethylene, are useful and widely accepted in the industry for packaging films. This arises due to its good thermal sealing ability, good mechanical film properties and good optical film properties. However, such copolymer films do not have a particularly low WVTR. EP-A-318 049 discloses crystalline copolymers of propylene with ethylene and / or alpha-olefins. These copolymers have melting points within the range of about 110-140 ° C and low solubility in xylene. EP A 495 099 describes random copolymers of propylene and alpha-olefin having 1 to 10 mol% alpha-olefin. Ziegler-Natta and metallocene catalyzed polypropylene copolymers were compared and evaluated for melting point reduction. Figure 2 illustrates that the melting point is reduced linearly by increasing the content of co-monomer, which is ethylene in both cases. The slope of the line shown for metallocene-catalyzed polypropylene is substantially identical to that of polypropylene catalyzed by Ziegler-Natta catalyst; however, it is shown that the metallocene line is about 10-20 ° C lower than the polypropylene line catalyzed by Ziegler-Natta catalyst. This behavior for metallocene-catalyzed polypropylene is also documented in the technical literature, including Antberg et al., Makromolecular Chemistry, Macromolecular Symposium, 48/49, 333 (1991). It is well known in the field of polymeric films that high density polyethylene (HDPE) is useful for its moisture barrier properties due to its high crystallinity; see, for example, W.E. Hamilton, "Food Packaging -An Opportunity for Barrier Coextrusions", 1985, Polymers, Laminations & Coatings Conference, pp. 417-440, on page 419. Although HDPE is used in food packaging applications, its use is accompanied by some disadvantages, including its brittle and hazy nature, or at best translucent. Currently known polypropylene compositions, although they have a slightly lower moisture barrier performance than HDPE, have some potential benefits, including clarity, and resistance to deformation and other undesirable effects at elevated temperatures. The aforementioned balance of properties makes polypropylene the material currently chosen in various food and medicine packaging applications. There is a need for a greater variety of useful films for packaging, particularly flexible packaging. It would be particularly useful to have oriented and non-oriented films with the benefits of thermal sealing capability, moderate stiffness and high optical clarity, coupled with a low WVTR. The present invention provides films with these qualities. Benefits of WVTR similar to or better than those of HDPE are provided while also providing other useful, beneficial properties of polypropylene. Barriers with improved WVTR are also provided over the polypropylene materials currently used. It has been found that homopolypropylene that is polymerized by catalysts that introduce minimal defects in stereo-regularity and regio-regularity also shows these beneficial effects. This is particularly true with metallocene-based catalysts with which the works herein were made. SUMMARY OF THE INVENTION Random copolymer polypropylene films offering low WVTR are provided despite having lower levels of polymeric crystallinity. This can be achieved by the use of polypropylene copolymers derived from propylene and ethylene co-monomers, higher alpha-olefins or their co-bininations, which are formed by catalysis in a single site. Homopolymeric polypropylene films are also provided, showing similar characteristics; These are produced from homopolypropylene that is generated by propylene catalysis in the presence of catalysts that introduce minimum stereo and regio defects within the polymer molecule. Useful catalysts for producing such polymers are those that introduce less than about 2.0 mol% of total defects, preferably less than about 1.5 mol%, more preferably less than about 1 mol%. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 provides a graphic representation of WVTR against percent crystallinity for various polypropylene films, including those of this invention and those representing the prior art. Figure 2 provides a graphical comparison of the primary melting temperature versus the amount of ethylene in the polymer backbone for traditionally polymerized copolymer polypropylenes and those produced by a family of catalysts at a single site.

Detailed Description The present invention provides films comprising a co-polymer, a molecular majority of whose backbone is derived from propylene, having a water vapor transmission rate that is equal to or less than about (-7.4428gxμm / m2xdayxcrystallinity of the polymer) (percent crystallinity of the polymer) + 627.32 gxμmxday, or (-0.0189xm.il/l00 in2xday percent crystallinity of the polymer) (percent polymer crystallinity) + 1,593 gxmilxlOO in2xday. Figure 1 illustrates the invention. A film is also provided, especially a single layer film, having a water vapor transmission rate that is equal to or less than about (-7.4428gxμm- / m2xday polymer crystallinity) (percent crystallinity of the polymer) + 627.32 gxμm day , or (-0.0189xmil / 100 in2xday x percent polymer percentage) (percent polymer crystallinity) + 1,593 gxmilxlOO in2xday, within the range of about 10 to about 70% crystallinity, comprising a polymer that is derived from a majority of propylene with at least one other monomer having at least one polymerizable Ziegler bond. Preferably, the polymer comprises at least about 80% by weight of propylene (based on the total weight of the polymer), more preferably at least about 85% by weight of propylene, even more preferably at least about of 90% by weight of propylene. Films having similar film characteristics are also provided which are obtainable by the production of homopolypropylene films derived from catalysis in a single propylene site with a catalyst introducing stereo minimums and royal defects, such as rac-dimethylsilylbis dichloride ( Activated 2-methyl-4-phenylindenyl) zirconium. The homopolymer film derived from this catalyst will have less than about 2.0 mol% of total defects in the homopolymer product, preferably less than about 1.5 mol% of total defects in the homopolymer product. Most preferred polymers will have less than about 1 mol% of total defects in the homopolymer. Many defects can be tolerated insofar as the films produced from such catalysts have these characteristics. Of course, even fewer defects are desirable, and polymers produced with minor defects, by any of such known or evolving catalysts, will produce finished films with similar characteristics, i.e. with fewer defects. ("Defects refer to the total molar percentage of bad monomer inserts, as well as misalignments in stereo-regularity.) Although the films of the present invention have been described as single-ply films, multi-layer films or co-films. Extruded films comprising a layer that satisfies the description of the film of the invention will fall within the scope of the invention, of course, as well as oriented films having these important characteristics of the films of the present invention. The layer satisfying the description of the film of the present invention will, of course, fall within the scope of the invention, these will include polymer / aluminum films, polymer / paper films, films that are oriented uniaxially, films that are biaxial oriented -Well, their combinations, or other similar movies. It includes modifiers of film properties such as hydrocarbon resins, the most suitable of which are the hydrogenated aliphatic resins prepared from petroleum distillates and having softening points that are greater than about 115 ° C. The area of the present invention, particularly that which uses copolymer film or homopolymer with minimal defects, is easily visualized by reference to Figure 1, which graphic WVTR of films against the percentage crystallinity of propylene copolymer or homopropylene. The line that includes the points of the comparative examples, Examples 1-4, represents the film capabilities of the previously known technique that are produced by traditional Ziegler-Natta (Z-N) catalysis. These samples are commercial products available from Exxon Chemical Company, of Houston, Texas, United States. They are, respectively, PP 1042 and PP 4722, both homopolypropylene and PD 9302 and PD 9272, both propylene / ethylene copolymers. The dots representing the films of Examples 5 and 6-12 illustrate the films of the invention, which combine low crystallinity and low WVTR. The present invention falls within the area below the prior art line. The WVTR for all the materials identified in Figure 1 was measured in the same way, according to the method ASTM-F-372. Each of the aspects of the invention encompasses preferred features, including a water vapor transmission rate equal to or less than about (-7,797 g xμm / mx-day x crystallinity of the polymer) (percent crystallinity of the polymer) + 622.2 gxμmxday, or ( -0.0198xmil / 100 in2xday x polymer percentage) (percent polymer crystallinity) + 1.58 gxmilxlOO in2xday; packaging for perishable items, medical devices, other items that must retain specified levels of moisture, or combinations thereof, comprising the films of the invention; packaging of dehydrated articles, or instruments sensitive to moisture, in which the acceptable level of humidity is specified to less than around 60%, 40%, 30%, 20% or 10% to prevent re-hydration, for example of food or chemical products or damage to various equipment, including electronics and articles susceptible to corrosion, by high humidity; packaging in which perishable items are foods, medicines or combinations thereof; and combinations of the above. Lower, preferred, lower limits of polypropylene crystallinity will be 10, 20 and 30%. At lower crystallinity ranges, various properties, including modulus or rigidity, high temperature resistance, and tensile strength, will begin to decrease below about 30% crystallinity, will be markedly below about 20%, and will suffer substantially below about 10%. This means that the films, although possibly useful for barrier properties at lower levels of polymer crystallinity, will need to be carefully selected for specific applications in light of the reduction of other properties to lower levels of crystallinity. Higher, preferred limits of crystallinity will be around 70%, 60%, and 50%. At higher levels of crystallinity, the film can be quite brittle, and insufficiently layered and operable for use in flexible packaging applications. Also, the impact resistance and the shear strength will probably be lower. Furthermore, the seal start temperature will probably be greater than desired. Film processing capacity is also a challenge at more than 60% crystallinity. For all these reasons, the utility amplitude of such films can be limited although the WVTR barrier performance can be excellent. Again, the barrier properties at these higher levels of crystallinity will be beneficial but other properties of the films may limit the breadth of their utility. For broad, general applications, the range of between about 25 and about 60% crystallinity will be preferred. Polypropylene polymer films with crystallinity in this range will find wide application useful in a variety of end uses, including for packaging and medical purposes. BACKGROUND FOR EXAMPLES Polypropylene materials used in the practice of this invention can be produced by polymerization in the presence of single-site catalysts, particularly metallocene-based catalysts. Such catalysts can be activated with any of various bulky, labile alumoxane materials or with ionic activators. The catalyst system or its components can be supported on inert material or can be used without a support. The following examples demonstrate that the propylene polymers used for polymerization experiments that provide the polymer used in the tests were made with the use of an activated catalyst with alumoxane, the catalyst system being usually supported on silica. The following examples are intended to provide an increased understanding of the invention and should not be seen as limiting the full scope of the invention. In recent years, various catalyst systems based on metallocene-type chemistry have been developed. These include Welborn, EP A 129 368, or US Pat. No. 5,055,438, which are incorporated herein by reference and which describe the use of cyclopentadienyl transition metal compounds for olefin catalysis. Turner and Hlatky, EP A 277 003, EP A 277 004, and US 5 patent, 153,157, which are incorporated herein by reference, disclose discrete catalyst systems based on metallocene type chemistry but employing anionic activators. Canich, US Pat. No. 5,057,475, incorporated by reference, discloses olefin polymerization catalysis using modified metallocene-type catalysts where a heteroatom / monocyclopentadienyl transition metal compound is replaced by the earliest generations of metallocene compounds. Canich, Hlatky and Turner describe, in WO 92/00333, also incorporated by reference, the use of ionic activators with heteroatom / monocyclopentadienyl transition metal compounds for polymerization of olefins. Descriptions of the use of catalyst compounds with ionic activators in US Patents 5,198,401 and 5,278,119 are also incorporated by reference. Specific metallocene type catalysts for producing isotactic olefin polymers can be found in EP A 485 820, EP A 485 821, EP A 485 822 and EP A 485 823, to Winter et al., And US Pat. Nos. 5,017,714 and 5,120,867, to Welborn. , each incorporated herein by reference. Other useful metallocene-type catalyst compounds can be found in EP A 518 092 and EP A 519 237, as well as US Patent 5,145,819, each incorporated herein by reference. Some of the syntheses can be found in Orcranometallics 13 (3), pp. 954-963 (1994) and EP A 320 762 (incorporated herein by reference). Various publications describe the placement of catalyst systems on a support medium and the use of the resulting supported catalysts. These include United States patents 5,006,500; 4,925,821; 4,937,217; 4,953,397; 5,086,025; 4,912,075; and 4,937,301, Chang, and U.S. Patents 4,808,561; 4,897,455; 5,077,255; 5,124,418; and 4,701,432, Welborn, all of which are incorporated herein by reference. The following examples demonstrate the use of supported metallocene-type catalysts for preparation of isotactic poly-alpha-olefin. Additional information regarding the support and use techniques of the supported catalysts can be found in US Pat. No. 5,240,894, to Burkhardt (incorporated herein by reference). Although the catalysts used for the examples included herein were employed in a liquid phase polymerization process, in bulk, the concepts relating to the use of the catalyst presented herein may be applied to other polymerization processes, including, for example, in gaseous phase, in the grout phase, and other processes. Molecular Weight Determination and MWD Gel permeation chromatography (GPC) is a liquid chromatography technique widely used to measure molecular weight (MW) and molecular weight distributions (MWD) or polydispersity of the polymers. This is a common and well-known technique. Such features, as described herein, have been measured using widely practiced techniques involving the conditions described below. Equipment and reagents used: Waters chromatograph model 15OC Three columns Shodex AT-80M (mixed bed) 1, 2,4-trichlorobenzene (HPLC grade) as solvent Sample polymer to be tested Operating conditions: Temperature: 145 ° C Flow rate: 1 ml / min Run time: 50 min Injection volume: 300 microliters (μl) Sample preparation: The samples are weighed directly into flasks of CPG and then trichlorobenzene (TCB) is added at a concentration of about 1 mg / ml. The solution is achieved in four hours in an oven maintained at around 160 ° C. Gentle, occasional agitation is applied to the samples to facilitate the solvation process. After dissolution, the samples are inserted into the injector compartment of a Waters 150C unit. The injector and column compartments are maintained at around 145 ° C. The instrument is calibrated using narrow MWD standards and adjusting the results to a third order calibration curve. The standards are polystyrene and the molecular weights shown are the equivalent weights obtained using the appropriate Mark-Houwink constants. Data acquisition and evaluation: Data are acquired and all calculations carried out using Waters Expert-Ease software, installed on a VAX 6410 computer. Determination of Transmission Rate Humidity or water vapor transmission rates (MVTR or WVTR) were determined according to the ASTM F-372 method using a Permatran W600 instrument available from Mocon, Modern Controls, Inc., of Minneapolis, Minnesota, United States. This instrument measures the rate of water vapor transmission through coated papers, flat films, and other flexible packaging materials. Briefly, the technique involves passing a known and constant flow of a dry carrier gas through a test chamber, which is isolated from a known humidity atmosphere by means of the film sample to be tested. The gas left by the test chamber, carrying what has passed through the barrier of the test sample, is then analyzed using an infrared source and a detector. Multiple measurements in different samples are averaged to obtain a value for each sample of film that was tested. Determination of Crystallinity Crystallinity levels were determined using fusion enthalpy from differential scanning calorimetry (DSC) measurements. The methodology is described in the book by B. Wunderlich, Macromolecular Physics, vol. 1, Academic Press (1973). Briefly, the crystallinity of the fraction by weight is derived from the relationship: Wc =? H'f /? Hf where W, the crystallinity of the weight fraction, is obtained by comparing the enthalpy of fusion of the particular sample (? H'f) with that of the completely crystalline isotactic polypropylene (? Hf). From Macromolecular Phvsics, vol. 3, Academic Press (1980), by B. Wunderlich, a literature value was obtained for? Hf of 164 J / g and was used in the determinations. The enthalpies of fusion for all the examples cited here were from measurements of DSC (DSC Perkin-Elmer 7), the instrument being operated at a heating rate of 10 ° C / min., After cooling / crystallization in the DSC, also at 10 ° C / min. The crystallinity was also determined from density measurements (described in B. Wunderlich, Macromolecular Phvsics, vol.1) to verify the trends of the WVTR vs. crystallinity, as shown in the examples. The same trends were observed regardless of whether the enthalpy or density was used to derive the crystallinity. Preparation of Polymerization Catalyst Preparation of Catalyst Supported by Rae-Dimethylsilanedilbis (2-Methyl-4,5-Benzo-Indenyl) Dichloride Zirconium with Alumoxane To an eight-liter vessel equipped with a cooling jacket and an efficient head agitator methylalumoxane in toluene was added, as obtained from Albermarle in Baton Rouge, Louisiana, United States (30 wt.%, 925 ml). With stirring, a catalyst suspension (5.0 g of rac-dimethylsilanedilbis (2-methyl-4,5-benzo-indenyl) zirconium dichloride) in toluene (700 ml) was added under N2 through a double-ended needle. . After stirring for 10 minutes, dehydrated silica (200 g, Davison 948, dried at 800 ° C) was added to the solution for 20 minutes. The slurry was stirred for 10 minutes and then, while vacuum was applied from the top of the vessel, a slight flow of N2 was added through the bottom. The mixture was heated to 70 ° C on evaporation of the solvent over a period of 9 hours. The dried solid was cooled to room temperature overnight. Isopentane (5 liters) was added to the slurry, and the mixture was cooled to 0 ° C. Ethylene was added to the stirred mixture by a drop tube at a rate of 0.85-1.7 1 / min. (0.03-0.06 SCF / min.) Until a total of 491 liters of ethylene had been added. Agitation stopped and the solids were allowed to settle. The liquid was decanted from the solids, which were washed twice, each with 1.5 liters of isopentane. The wet solids were transferred to a dry box under N2 and filtered through a No. 14 mesh screen. The fine particles were filtered, washed with pentane (4 liters) and dried under vacuum. Yield: 326 grams. A useful synthesis of rac-dimethylsilane-dilbis (2-methyl-4,5-benzo-indenyl) zirconium dichloride can be found in EP A 549 900 and CA 2,084,017, which are incorporated by reference. This catalyst was used to make the polymer used for Examples 6-12. The catalyst used for Example 5 is described in EP A 576 970 and CA 2,099,214, which are also incorporated by reference. Other useful catalysts and their synthesis are described in EP A 600 461 and US 5,296,434, as well as US 5,328,969 and EP A 576 970 and CN 2,099,214. Polymerization Examples A summary of the polymerized product examples is shown in Table 1. Examples 1-4 are commercially available polypropylene polymers that are polymerized with traditional Ziegler-Natta catalysts. Examples 6-9 and 11-12 are polymers of this invention produced in a liquid phase reaction process, on a laboratory scale, using the supported metallocene catalyst whose preparation was described above. The polymer of Example 10 was produced with the same catalyst but the polymerization was conducted in a pilot phase liquid phase reactor. Finally, the polymer of Example 5 was polymerized by means of unsupported MAO activated catalyst, based on rae-dimethylsilylbis (2-methyl-4-phenylindenyl) zirconium dichloride, as described in EP A 576 970 and CA 2,099,214, in a pilot phase liquid phase reactor. Laboratory Scale Polymerizations (Examples 6-9 and 11-12) Triethyl Alumoxane is injected as a stripping agent with a total of 1,000 ml of dry propylene, with the desired amount of co-monomer, into a jacketed stainless steel reactor. The agitation of the reactor is initiated and the reactor is brought to the desired temperature by passing water vapor through the jacket. The catalyst system is loaded into the jacketed reactor with a flood of 250 ml of propylene. The reaction is then allowed to run for about an hour. The polymerization reaction is stopped by cooling the reactor to a temperature of less than about 40 ° C and the stirrer is stopped. The reactor is depressurized and purged with nitrogen for about 20 minutes. At this point, the reactor is opened and the polymer of interest is removed. The polymerization details for the different examples produced at the laboratory scale are included in Table 1. Pilot Scale Polymerization (Example 10) The polymerization of this propylene / he-xeno-1 copolymer was conducted in a phase polymerization process liquid, in bulk, in a single stirred tank reactor, conti-nuo. The reactor was equipped with a jacket to remove the heat generated by the polymerization reaction. The temperature of the reactor was set at 55 ° C. The catalyst, as described above, was fed at a rate of 18.2 g / hour. The catalyst was fed as a 15% slurry in mineral oil and was flooded in the reactor with propylene. The propylene monomer was fed at a rate of 63.5 kg / hour. Hexene-1 was delivered to a propylene feed ratio of 0.05. No hydrogen was added during the polymerization. Copolymer was produced at a rate of 9.1 kg / hour. The polymer was discharged from the reactor as a granular product having MFR of 4.3 and hexane incorporation of 2.8% by weight. Pilot Scale Polymerization (Example 5) The polymerization was conducted in a stirred tank reactor. The liquid propylene was introduced to the reactor at a temperature of about 30 ° C. The catalyst system comprised metallocene of rae dichloride dimethylsilylbis (2-methyl-4-phenylindenyl) zirconium and MAO (10% in toluene), for activation. 0.1 g of metallocene was used, the ratio of MAO to metallocene in the catalyst being 500: 1 on a molar basis. The catalyst solution was charged to the reactor and the temperature of the reactor taken at about 65 ° C. After a residence time of three hours, the reaction was stopped, residual monomer distilled, and the polymer recovered as a fine granular product. The productivity of the polymer was about 500 kg of polymer per gram of metallocene per hour. The MFR value of the homopolymer was measured at 5.5. Characteristics of the Polymer The weight percentage of co-monomer in the polymer was determined by 13 C NMR. A description of the general NMR technique can be found in The Encyclopedia of Polymer Science and Encrineering, 2a. edition, vol. 10, p. 254, Wiley-Interscience Publication (1987). A description of the methodology for propylene-ethylene polymers can be found in Carman, C.J., Harrington, R.A. and Wilkes, CE., Macromolecules 10 (3), p. 536, 1977. Table 1 Polymerization Process and Characteristics of Propylene-based Polymers Tested as Examples Co-Monomer Reactor Co-Monomer Example Type of TEAL (ral) (ml) Temp ° C% weight M "M" / M "ssu ..g Catalyst (quantity) 1 Ziegler-Natta n / a -0- 391 K 5.26 2 Z-N n / a -0- 388 K 3.56 3 Z-N C2"4 290 K 3.74 4 Z-N C2"5 283 K 3.12 Metallocene n / a -0- 235 K 1.9 6 MCN (0.23 g) 0 .5 n / a 65 -0- 231 K 1.87 218 7 MCN (1.68 g) 1 .0 C "" (25) 60 1.6 201 K 1.7 89 8 MCN (1.8 g) 1 .0 C4 »(75) 60 4.2 227 K 1.71 117 9 MCN (0.203 g) 0. .5 C2"(50) 55 1.9 215 K 1.77 82 MCN C6 »2.8 248 K 1.77 11 MCN (0.209) 0. .5 C2"(150) 40 4.5 188 K 1.71 143 12 MCN (0.216) 0, .5 C2"(150) 40 4.8 185 K 1.86 148 Preparation of Film Samples Compression molded films were made from the polymerized examples and prepared as monolayer structures. The beads or granules of the polymers of the examples were compression molded using a laboratory-sized compression molding unit, Wabash Press model 30-1515-2T2WCMB, available from Wabash Metal Products, Inc., of Wabash, Indiana, United States. . The molding occurred with a maximum pressure of about 27,270 kg (30 tons) in a ram of approximately 12.7 cm (5 in) in diameter. The samples were subjected to a pressure of about 18,180 kg (20 tons) at around 220 ° C. Following the heating cycle of five minutes at around 220 ° C under this pressure, the molded films were immediately removed and cooled immediately in water at room temperature. The films were conditioned under ambient conditions for about 48 hours. The films were all about 0.13 mm (0.005 in) thick. The melting and crystallinity characteristics for the polymers and the barrier properties (WVTR) of the films produced therefrom are described in Table 2. The melting characteristics were determined using a differential scanning calorimeter (DSC), a a heating rate of around 10 ° C / min. The peak peak melting temperature data (second fusion in DSC) were noted and are reported in Table 2. This table also includes similar information relating to prior art films that were prepared and tested in the same way, and a value representative for the HDPE movie. Table 2 Characteristics of Fusion, Crystallinity and WVTR of Propylene-based Polymers Tested as Examples% by Weight of Example Type of Co-Monomer Co-Monomer Primary Tm CC)% Xtal WVTR Catalyst 1 Ziegler-Natta -0- -0- 160.5 57. .3 0. .6897 2 Z-N -0- -0- 161 55. .2 0., 7314 3 Z-N C2"4 138.5 36 .8 1 .048 4 Z-N C2"5 132 31. .9 1. .196 Metallocene -0- -0- 159 53. .4 0. .5325 6 MCN -0- -0- 144.5 46 .6 0. .7065 7 MCN C, "1.6 132.5 40. .5 0. .79 8 MCN C. "4.2 132.5 39. .3 0. .73 9 MCN c2"1.9 130 37. .4 0. .77 MCN c6"2.8 128 36 .8 0 .868 11 MCN c2 »4.5 111.5 26 .4 1 .0566 12 MCN C2"4.8 109.1 24 .5 1 .134 HDPE (reference) 0. .65 Notes:% crystallinity from melt enthalpy measurements. The WVTR units are gxmil / 100 in2xday. Representative value of 0.65 WVTR for HDPE of J.R. Newton, "High Barrier Materials", Future Trends in Vaccum Web Coating Seminar, Association of Industrial Metallizers, Coaters and Laminators, October 1983. Examples 1-4 represent the prior art; Examples 5-12 exemplify this invention. Although the tests were carried out with compression molded films, the data, the information derived from them, and the identified trends are applicable to the other films, such as extruded and forged films, including those that are oriented post-extrusion. Although co-extruded films or other multilayer films will benefit from the inclusion of the technology described by the present invention, the films of the invention will find particular beneficial use in monolayer film construction applications. In addition, the films of the present invention can usefully include various additives that can be added in the melted state prior to bead formation, added after the formation of beads or granules, added in the melt for the extruder, or combinations thereof. Any of the polyolefin additives typically used with traditionally catalysed polymers will serve for beneficial purposes. Such additives will include stabilizers and neutralizers, patinating agents including erucamide, anti-blocking agents including silica, and nucleating agents. It is common practice in the field of forming polypropylene composites to incorporate various types of nucleating agents to increase the rate of crystallization. An improvement of the barrier properties is expected by the use of such commercially available nucleating agents, including talc and sorbitol.

Claims (18)

1. CLAIMS 1. A film having one or more layers comprising polymer, a molecular majority of which is derived from propylene, said film having a water vapor transmission rate measured according to ASTM method F-372 less than or equal to ( -7.4428gxμm / m2xdayx polymer crystallinity) (percent polymer crystallinity) + 627.32 gxμmxdía, or (-0.0189 xmil / 100 in2xday percent polymer crystallinity) (percent polymer crystallinity) + 1,593 gxmilxlOO in2xdía.
2. 2. A film having one or more layers comprising propylene homopolymer, said film having a water vapor transmission rate measured according to ASTM F-372 method less than or equal to (-7.4428gxμm / m2xday polymer crystallinity) (crystallinity percent of the polymer) + 627.32 gxμmxday, or (-0.0189xmil / l00 in2xday percent crystallinity of the polymer) (percent crystallinity of the polymer) + 1,593 gxmil xlOO in2xday.
3. 3. A film having one or more layers comprising polymer, said polymer comprising at least 90% by weight of propylene based on the total weight of the polymer and at least one other monomer having at least one polymerizable Ziegler bond; said film having a water vapor transmission rate measured according to the ASTM F-372 method less than or equal to (-7.4428g xμm / m2xdayxcrystallinity of the polymer) (percent crystallinity of the polymer) + 627.32 gxμmxdía, or (-0.0189xmil / 100 in2xdayxcris-percentage percentage of the polymer) (percent crystallinity of the polymer) + 1,593 gxmil xlOO in2xday.
4. 4. The film of any one of the preceding claims, wherein the water vapor transmission rate is less than or equal to (-7.797g xμm / m2xdayxcrystallinity of the polymer) (percent polymer crystallinity) + 622.2 gxμmxday, or (-0.0198xm) .il / 100 in2xdayx percent crystallinity of the polymer) (percent polymer crystallinity) + 1.58 gxmil xlOO in2 xday.
5. 5. The film of any of the preceding claims, wherein the polymer crystallinity is in the range of 10 to 70%.
6. 6. The film of any of the preceding claims, wherein the polymer crystallinity is in the range of 20 to 60%.
7. The film of any of the preceding claims, wherein the polymer crystallinity is in the range of 30 to 50%.
8. 8. The film of claim 2, wherein the water vapor transmission rate is less than or equal to (-7.797g xμm / m2xday x crystallinity of the polymer) (percent polymer crystallinity) + 622.2 gxμmxday, or (-0.0198xmil / 100 in2xdayxcris-percentage percentage of the polymer) (percent crystallinity of the polymer) + 1.58 gxmil xlOO in2 xday.
9. 9. The film of claim 8, wherein the polymer crystallinity is in the range of 10 to 70%.
10. 10. The film of claim 8, wherein the polymer crystallinity is in the range of 20 to 60%.
11. 11. The film of claim 8, wherein the polymer crystallinity is in the range of 30 to 50%.
12. 12. The film of claim 3, wherein the water vapor transmission rate is less than or equal to (-7.797g xμm / m2xdayxcrystallinity of the polymer) (percent polymer crystallinity) + 622.2 gxμmxday, or (-0.0198xmil / 100 in2xdayxcris-percentage percentage of the polymer) (percent crystallinity of the polymer) + 1.58 gxmil xlOO in2 xday.
13. The film of claim 12, wherein the polymer crystallinity is in the range of 10 to 70%.
14. 14. The film of claim 12, wherein the polymer crystallinity is in the range of 20 to 60%.
15. 15. The film of claim 12, wherein the polymer crystallinity is in the range of 30 to 50%.
16. 16. Packaging for articles that must retain specified levels of moisture, said package comprising a film of claim 1.
17. 17. Composite film having one or more layers comprising polypropylene copolymer, a majority of whose backbone is derived from propylene, wherein said film has a water vapor transmission rate measured according to the ASTM F-372 method less than or equal to (-7.4428g xμm / m2xdayx-polymer crystallinity) (percent crystallinity of the polymer) + 627.32 gxμmx day , or (-0.0189xm.il/100 in2xdayx percent crystallinity of the polymer) (percentage crystallinity of the polymer) + 1.593 gxmil xlOO in2xdía.
18. 18. Oriented film having one or more layers comprising polypropylene copolymer, a majority of whose backbone is derived from propylene, wherein said film has a water vapor transmission rate measured according to ASTM F-372 method less than or equal to that (-7.4428g xμm / m2xdayx-crystallinity of the polymer) (percent crystallinity of the polymer) + 627.32 gxμmxdía, or (-0.0189xm.il/100 in2xdíaxcrystallinity percent of the polymer) (percent crystallinity of the polymer) + 1,593 gxmil xlOO in2xdía.