Thermoplastic polymer composition and method for preparing a film therefrom

Abstract

A thermoplastic polymer composition includes a polyethylene polymer composition and a bicyclo[2.2.1]heptane-2,3-dicarboxylate. The polyethylene polymer composition can have a melt relaxation index of 2 or greater. A method for molding a thermoplastic polymer composition includes the steps of: (a) providing an apparatus including a die having an annular die orifice, means for blowing a pressurized fluid into a tubular exiting the orifice, and means for stretching and collecting the tubular; (b) providing the above-described thermoplastic polymer composition; (c) heating the thermoplastic polymer composition to melt the thermoplastic polymer composition; (d) extruding the molten thermoplastic polymer composition through the die to form a tubular; (e) blowing a pressurized fluid into the tubular to expand the tubular while simultaneously stretching it; (f) allowing the film to cool; and (g) collecting the film.

Description

Technical Field

[0001] This invention relates to thermoplastic polymer compositions and methods for preparing films (e.g., blown films) therefrom. Background Technology

[0002] Several nucleating agents for thermoplastic polymers are known in the art. These nucleating agents typically function by forming crystal nuclei or providing sites for crystal formation and / or growth in the thermoplastic polymer as it solidifies from a molten state. The nuclei or sites provided by the nucleating agent allow crystal formation in the cooled polymer at higher temperatures and / or at a faster rate compared to crystal formation in the original, unnucleated thermoplastic polymer. These effects can then allow for the processing of nucleated thermoplastic polymer compositions at shorter cycle times than in the original, unnucleated thermoplastic polymer. Nucleating agents can also induce the orientation of crystalline lamellae in the polymer, which does not lead to self-nucleation crystallization. Depending on the orientation of the lamellae produced by the nucleating agent, the physical properties of articles made from the polymer can be improved relative to polymers undergoing self-nucleation crystallization.

[0003] Furthermore, the effectiveness of a nucleating agent can depend on certain physical properties of the polymer being nucleated. In other words, a given nucleating agent can nucleate a polyethylene polymer with a set of physical properties more effectively than another polyethylene polymer with a different set of physical properties. The effectiveness of a nucleating agent typically depends on several physical properties of the polymer. The interrelationships between these various physical properties and their effects on the nucleating agent make it difficult to easily determine the pairing of the nucleating agent and the polymer that will produce a polymer composition with the desired properties.

[0004] Therefore, there remains a need for combinations of polymers and nucleating agents that exhibit favorable nucleation effects and produce polymer compositions with desired physical properties, such as low water vapor and oxygen permeability. Methods utilizing such advantageous combinations of polymers and nucleating agents, such as blown film and blown film processes, are also needed. The polymer compositions and methods described in this application seek to meet these needs. Summary of the Invention

[0005] In a first embodiment, the present invention provides a thermoplastic polymer composition comprising:

[0006] (a) A polyethylene polymer composition having a melt relaxation index of 2 or greater; and

[0007] (b) Bicyclic [2.2.1]heptane-2,3-dicarboxylate.

[0008] In a second embodiment, the present invention provides a method for preparing a film from a thermoplastic polymer composition. The method includes the following steps:

[0009] (a) Provides an apparatus comprising:

[0010] (i) A die head having an annular die orifice suitable for extruding tubular materials;

[0011] (ii) A device for blowing pressurized fluid into a tubular structure exiting the annular orifice; and

[0012] (iii) A device for stretching and collecting the tubular object;

[0013] (b) Provides a thermoplastic polymer composition comprising (i) a polyethylene polymer composition having a melt relaxation index of 2 or greater; and (ii) a bicyclo[2.2.1]heptane-2,3-dicarboxylate;

[0014] (c) Heating the thermoplastic polymer composition to a temperature sufficient to melt it, so that it can be extruded through the die;

[0015] (d) Extruding a molten thermoplastic polymer composition through the annular die to form a tubular object exiting the annular die in a first direction, the tubular object having a diameter and a length;

[0016] (e) Pressurized fluid is blown into the tubular material under sufficient pressure to expand the tubular material and increase its diameter, while the tubular material is stretched in a first direction to increase its length, thereby producing a thin film;

[0017] (f) Cooling the film to the temperature at which the thermoplastic polymer composition cures; and

[0018] (g) Collect the film. Detailed Implementation

[0019] In a first embodiment, the present invention provides a thermoplastic polymer composition comprising a polyethylene polymer composition and a bicyclo[2.2.1]heptane-2,3-dicarboxylate.

[0020] The polyethylene polymer composition used in the composition may include any suitable polyethylene polymer or mixture of polyethylene polymers. However, it is believed that bicyclo[2.2.1]heptane-2,3-dicarboxylate can more effectively nucleate polyethylene polymer compositions exhibiting a greater degree of melt relaxation. During certain melt processing of polymers (e.g., blown film manufacturing), the polymer melt undergoes stretching or strain as it is extruded through a die. When the extruded polymer melt is further processed, such as stretched and / or blown, the polymer melt may undergo further stretching or strain. The strain applied to the polymer melt causes the flow direction orientation of the extended polymer chains in the polymer melt. When the processed polymer melt cools, these oriented extended polymer chains may return to a less ordered state before the polymer melt crystallizes. This process is referred to herein as “melt relaxation”. Alternatively, the oriented extended polymer chains may remain oriented in the melt and crystallize to form fibrils. These fibrils provide sites that can initiate polymer self-nucleation. If sufficient fibrils are formed in the polymer as it solidifies from the melt, the resulting strain-induced self-nucleation can become the dominant nucleation mode in the polymer. While self-nucleation in polymers may seem beneficial, the polymer structures resulting from such self-nucleation are often less advantageous for certain desired physical properties. For example, self-nucleated polyethylene typically exhibits higher water vapor and oxygen permeability than polyethylene that has been heterogeneously nucleated with bicyclo[2.2.1]heptane-2,3-dicarboxylate. Therefore, to maximize the degree of nucleation induced by bicyclo[2.2.1]heptane-2,3-dicarboxylate, thermoplastic polymer compositions preferably contain polyethylene polymers that exhibit sufficient melt relaxation to ensure that strain-induced self-nucleation does not become dominant.

[0021] The degree of melt relaxation exhibited by polymers is not easily quantified directly. Furthermore, melt relaxation is believed to be influenced by numerous factors, such as molecular weight, the width of the molecular weight distribution, the relative amount of the high molecular weight fraction within the distribution, and branched or nonlinear chains in the polymer. The number of factors involved and the complex relationships between them make it difficult to determine a range for each factor sufficient to define a polyethylene polymer exhibiting adequate melt relaxation. In other words, one might attempt to define a molecular weight distribution for a polymer exhibiting sufficient melt relaxation, but the appropriate range would vary with the “shape” of the distribution (i.e., the relative amount of the high molecular weight fraction). Therefore, while these factors can be considered when attempting to determine a polyethylene polymer exhibiting sufficient melt relaxation, more direct and precise melt relaxation measurements are needed.

[0022] The shear storage modulus (G′) of a viscoelastic material (e.g., a polymer melt) is related to stored energy (stress), such as the stored energy (stress) in the aforementioned oriented, extended polymer chains. The shear loss modulus (G″) of a viscoelastic material is related to energy loss or dissipation, such as the energy loss or dissipation released through relaxation of the oriented, extended polymer chains in the polymer melt. The ratio of the shear loss modulus to the shear storage modulus (G″ / G′), defined as tanδ, is proportional to the energy loss to stored energy at a given strain rate. In materials with tanδ less than 1, energy storage dominates at the measured strain rate. In materials with tanδ greater than 1, energy loss (dissipation) dominates at the measured strain rate. Furthermore, comparing tanδ measured at different strain rates (e.g., the ratio of tanδ) can be used to quantify the extent to which the dominance of energy loss and energy storage in a material changes with strain rate.

[0023] Shear storage modulus and shear loss modulus can be measured using various techniques and at various strain rates. However, if the modulus is to be used for accurate measurement of melt relaxation in polymers, both moduli should be measured at or near the strain rate that the polymer melt will experience during melt processing. To this end, the inventors believe that measuring the shear storage modulus and shear loss modulus by parallel plate rheometer at angular frequencies of approximately 0.1 rad / s and approximately 10 rad / s provides a reasonable approximation of the strain rate that the polyethylene polymer composition melt will experience during processing. As previously mentioned, the ratio of tanδ at these two strain rates can be used to show the changes in energy loss and energy storage as the strain rate changes. After extensive experiments with various polymers and polymer compositions, polyethylene polymers in which energy loss increases significantly with decreasing strain rate (i.e., decreasing angular frequency) (i.e., significantly increasing tanδ) are considered to exhibit sufficient melt relaxation for heterogeneous nucleation with bicyclo[2.2.1]heptane-2,3-dicarboxylate. Specifically, the ratio of tanδ at about 0.1 rad / s to tanδ at about 10 rad / s is believed to be particularly useful for determining polymers exhibiting the desired level of melt relaxation. However, the tanδ ratio for sufficient melt relaxation has also been determined to be influenced by the polymer molecular weight; polymers with higher molecular weights require a higher ratio to achieve sufficient melt relaxation. Therefore, the ratio of tanδ values ​​needs to be accounted for by additional factors to explain the effect of polymer molecular weight. The molecular weight of a polymer is generally inversely proportional to its melt flow index. Furthermore, the relationship between molecular weight and melt flow index is not linear, but more typically logarithmic. Therefore, the ratio of tanδ values ​​can be increased to account for the molecular weight effect by multiplying the ratio of tanδ values ​​by 1 and the sum of the natural logarithms of the polymer melt flow index. The resulting parameter, hereinafter referred to as the "melt relaxation index," should be 2 or greater. In other words, polyethylene polymer compositions preferably have a melt relaxation index of 2 or greater, more preferably 2.1 or greater.

[0024] As described above, the melt relaxation index (MRI) is defined as the product of (i) the sum of 1 and the natural logarithm of the polymer melt flow index and (ii) the ratio of tanδ at approximately 0.1 rad / s to tanδ at approximately 10 rad / s:

[0025]

[0026] In this definition, two angular frequencies are defined as approximately equal to a given value. Therefore, tanδ at approximately 0.1 rad / s can be measured at any angular frequency between 0.095 and 0.105 rad / s, and tanδ at approximately 10 rad / s can be measured at any angular frequency between 9.5 and 10.5 rad / s. While the precise angular frequency used to determine the MRR can vary within the above range, the ratio of the two angular frequencies must be 0.01 (i.e., there must be a difference of 100 times between the two angular frequencies). The melt flow index of the polymer can be reported in decigrams per minute (dg / min) or grams per ten minutes (g / 10min), measured at 190°C using a 2.16 kg load according to ASTM standard D1238.

[0027] Melt relaxation index can be measured by any suitable technique. Preferably, shear loss modulus (G″), shear storage modulus (G′), and tanδ are determined by a rotational rheometer equipped with 25 mm parallel plates set at a 1.1 mm gap at a temperature of 190 °C using a parallel plate rheometer. The polymer sample used for measurement is provided in the form of a compression molding disc. During the measurement, the angular distance or strain is preferably kept low to remain in the non-hysteresis region, preferably with a nominal strain of about 1%. Since these parameters are determined by the polymer melt, the presence of a nucleating agent will not have any significant effect on the shear loss modulus (G″), shear storage modulus (G′), tanδ, or melt flow index measured by the polyethylene polymer composition. Therefore, these parameters (and melt relaxation index) can be measured by the polyethylene polymer composition before being combined with bicyclo[2.2.1]heptane-2,3-dicarboxylate, or these parameters can be measured by a thermoplastic polymer composition comprising the polyethylene polymer composition and bicyclo[2.2.1]heptane-2,3-dicarboxylate.

[0028] As described above, a polyethylene polymer composition may comprise any suitable polyethylene polymer or mixture of polyethylene polymers exhibiting the desired melt relaxation index. Therefore, a polyethylene polymer composition may comprise a single polyethylene polymer exhibiting the desired melt relaxation index. Alternatively, a polyethylene polymer composition may comprise a mixture of two or more polyethylene polymers exhibiting the desired melt relaxation index. In such a mixture, each polyethylene polymer may exhibit a melt relaxation index falling within the desired range, but this is not required. For example, a polyethylene polymer exhibiting a relatively low melt relaxation index (e.g., less than 2) may be mixed with an appropriate amount of another polyethylene polymer having a higher melt relaxation index (e.g., 2.1 or higher) to produce a polyethylene polymer composition exhibiting the desired melt relaxation index.

[0029] Polyethylene polymers suitable for polyethylene polymer compositions include polyethylene homopolymers and polyethylene copolymers. Suitable polyethylene copolymers include copolymers of ethylene with one or more α-olefins. Suitable α-olefins include, but are not limited to, 1-butene, 1-hexene, 1-octene, 1-decene, and 4-methyl-1-pentene. Comonomers may be present in the copolymer in any suitable amount, such as about 8% by weight (e.g., less than about 5 mol%) or more preferably about 5% by weight or less (e.g., about 3 mol%) or less. Those skilled in the art will understand that the amount of comonomer suitable for polyethylene copolymers depends largely on the end use of the copolymer and the polymer properties required or desired by that end use.

[0030] Polyethylene polymers suitable for thermoplastic polymer compositions can be prepared by any suitable method. For example, polymers can be prepared by free radical methods using very high pressures, such as those described in U.S. Patent No. 2,816,883 (Larchar et al.), but polymers are generally prepared in “low-pressure” catalytic methods. In this document, the term “low-pressure” is used to refer to methods carried out at pressures less than 6.9 MPa (e.g., 1000 psig), such as 1.4–6.9 MPa (200–1000 psig). Examples of suitable low-pressure catalytic methods include, but are not limited to, solution polymerization methods (i.e., methods in which polymerization is carried out using a solvent for the polymer), slurry polymerization methods (i.e., methods in which polymerization is carried out using a liquid hydrocarbon in which the polymer does not dissolve or swell), gas-phase polymerization methods (e.g., methods in which polymerization is carried out without the use of a liquid medium or diluent), or staged reactor polymerization methods. Suitable gas-phase polymerization methods also include so-called “condensation mode” or “ultra-condensation mode” methods, in which liquid hydrocarbons are introduced into a fluidized bed to increase the absorption of heat generated during polymerization. In these condensation and supercondensation methods, liquid hydrocarbons are typically condensed in a circulating stream and reused in the reactor. Staged reactor methods can utilize combinations of slurry reactors (tanks or loops) connected in series, parallel, or a combination of series and parallel connections, exposing the catalyst (e.g., a chromium catalyst) to more than one set of reaction conditions. Staged reactor methods can also be carried out using multiple series gas-phase reactors, or loop-gas-phase arrangements, by combining two loops in series, combining one or more tanks and loops in series, or combining them in series. Due to their ability to expose the catalyst to different sets of reactor conditions, staged reactor methods are frequently used for the production of multi-peak polymers, such as those discussed below. Suitable methods also include those in which a prepolymerization step is carried out. In this prepolymerization step, the catalyst is typically exposed to a co-catalyst and ethylene under mild conditions in a smaller, separate reactor, and the polymerization reaction is allowed to proceed until the catalyst constitutes a relatively small amount of the resulting composition (e.g., about 5% to about 30% of the total weight). This prepolymerized catalyst is then introduced into the large-scale reactor in which polymerization is to be carried out.

[0031] Polyethylene polymers suitable for thermoplastic polymer compositions can be prepared using any suitable catalyst or combination of catalysts. Suitable catalysts include transition metal catalysts, such as supported reduced molybdenum oxide, cobalt molybdate supported on alumina, chromium oxide, and transition metal halides. Chromium oxide catalysts are typically prepared by impregnating a chromium compound onto a porous, high-surface-area oxide support, such as silica, followed by calcination in dry air at 500–900°C. This converts chromium to hexavalent surface chromates or dichromates. Chromium oxide catalysts can be used in combination with metal alkyl co-catalysts such as alkylboron, alkylaluminum, alkylzinc, and alkyllithium. Supports for chromium oxide include silica, silica-titanium dioxide, silica-alumina, alumina, and aluminum phosphate. Other examples of chromium oxide catalysts include those using lower-valence organochromium compounds such as bis(aromatic)Cr 0 Allyl Cr 2+ and Cr 3+ Cr 2+ and Cr 4+ β-stabilized alkyl groups, and bis(cyclopentadienyl)Cr 2+ Catalysts prepared by deposition onto chromium oxide catalysts, as described above. Suitable transition metal catalysts also include supported chromium catalysts, such as those based on chromium diacene or silyl chromates (e.g., bis(triphenylsilyl) chromate). These chromium catalysts can be supported on any suitable high surface area support, such as those described above for chromium oxide catalysts, typically silica. Supported chromium catalysts can also be used in combination with co-catalysts, such as the metal alkyl co-catalysts listed above for chromium oxide catalysts. Suitable transition metal halide catalysts include titanium(III) halides (e.g., titanium(II) chloride), titanium(IV) halides (e.g., titanium(IV) chloride), vanadium halides, zirconium halides, and combinations thereof. These transition metal halides are typically supported on high surface area solids such as magnesium chloride. Transition metal halide catalysts are typically used in combination with alkyl aluminum co-catalysts such as trimethylaluminum (i.e., Al(CH3)3) or triethylaluminum (i.e., Al(C2H5)3). These transition metal halides can also be used in staged reactor processes. Suitable catalysts also include metallocene catalysts, such as cyclopentadienyl titanium halides (e.g., cyclopentadienyl titanium chloride), cyclopentadienyl zirconium halides (e.g., cyclopentadienyl zirconium chloride), cyclopentadienyl hafnium halides (e.g., cyclopentadienyl hafnium chloride), and combinations thereof. Metallocene catalysts based on transition metals complexed with indenyl or fluorene ligands are also known and can be used to produce high-density polyethylene polymers suitable for the present invention. The catalysts typically contain multiple ligands, and the ligands can be substituted with various groups (e.g., n-butyl) or linked to bridging groups (e.g., -CH2CH2- or >SiPh2). Metallocene catalysts are typically used with co-catalysts such as methylaluminoxane (i.e., Al(CH3)). x Oy ) n Other cocatalysts include those described in U.S. Patent Nos. 5,919,983 (Rosen et al.), 6,107,230 (McDaniel et al.), 6,632,894 (McDaniel et al.), and 6,300,271 (McDaniel et al.). Other “unit-site” catalysts suitable for the preparation of polyethylene polymers include diimine complexes, such as those described in U.S. Patent No. 5,891,963 (Brookhart et al.).

[0032] The polyethylene polymer composition (and the polyethylene polymer present in such composition) can have any suitable density. A suitable density is about 880 kg / m³. 3 Approximately 970 kg / m 3 Preferably, the polyethylene polymer composition has a content of about 940 kg / m³. 3 Or larger (e.g., approximately 940 kg / m²) 3 Approximately 970 kg / m 3 The density of the polyethylene polymer composition is approximately 945 kg / m³. More preferably, the polyethylene polymer composition has a density of approximately 945 kg / m³. 3 Approximately 967 kg / m 3 The density. In another preferred embodiment, the polyethylene polymer composition has a density of about 955 kg / m³. 3 Approximately 965 kg / m 3 The density.

[0033] The polyethylene polymer composition (and the polyethylene polymer present in such composition) can have any suitable melt flow index (MFI). Preferably, the polyethylene polymer composition has an MFI of about 2 dg / min or less. In another preferred embodiment, the polyethylene polymer composition has an MFI of about 1.8 dg / min or less. In yet another preferred embodiment, the polyethylene polymer composition has an MFI of about 1.7 dg / min or less. Preferably, the polyethylene polymer composition has an MFI of about 0.1 dg / min or greater. In another preferred embodiment, the polyethylene polymer composition has an MFI of about 0.2 dg / min or greater. In yet another preferred embodiment, the polyethylene polymer composition has an MFI of about 0.3 dg / min or greater. Therefore, in a series of preferred embodiments, the polyethylene polymer composition has an MFI of about 0.1 dg / min to about 2 dg / min (e.g., about 0.1 dg / min to about 1.8 dg / min or about 0.1 dg / min to about 1.7 dg / min), about 0.2 dg / min to about 2 dg / min (e.g., about 0.2 dg / min to about 1.8 dg / min or about 0.2 dg / min to about 1.7 dg / min), or about 0.3 dg / min to about 2 dg / min (e.g., about 0.3 dg / min to about 1.8 dg / min or about 0.3 dg / min to about 1.7 dg / min). The melt flow index of the polyethylene polymer composition is preferably measured according to ASTM standard D1238 at 190°C using a 2.16 kg load.

[0034] The thermoplastic polymer composition comprises a salt of bicyclic [2.2.1]heptane-2,3-dicarboxylic acid. The two carboxylic acid moieties of the bicyclic [2.2.1]heptane-2,3-dicarboxylic acid anion are preferably located in the cis position relative to each other. Furthermore, the two carboxylic acid moieties of the bicyclic [2.2.1]heptane-2,3-dicarboxylic acid anion are preferably located inside the longest bridge relative to the anion. Therefore, in a preferred embodiment, the thermoplastic polymer composition comprises a salt of cis-endo-bicyclic [2.2.1]heptane-2,3-dicarboxylic acid (i.e., (1R,2R,3S,4S)-bicyclic [2.2.1]heptane-2,3-dicarboxylic acid). The salt of bicyclic [2.2.1]heptane-2,3-dicarboxylic acid may contain any suitable counterion for the bicyclic [2.2.1]heptane-2,3-dicarboxylic acid anion. Preferably, the counterion is selected from alkali metal cations and alkaline earth metal cations. In another preferred embodiment, the counter ion is selected from alkaline earth metal cations. Most preferably, the counter ion is a calcium cation (i.e., Ca). 2+(Cation). Therefore, in a particularly preferred embodiment, the salt is bicyclic [2.2.1]heptane-2,3-dicarboxylic acid calcium, especially cis-endo-bicyclic [2.2.1]heptane-2,3-dicarboxylic acid calcium (i.e., (1R,2R,3S,4S)-bicyclic [2.2.1]heptane-2,3-dicarboxylic acid calcium).

[0035] The bicyclic [2.2.1]heptane-2,3-dicarboxylate can be a hydrate (i.e., a crystalline solid with water of crystallization) or a dehydrate (i.e., a crystalline solid without water of crystallization). Those skilled in the art will understand that the bicyclic [2.2.1]heptane-2,3-dicarboxylate can also be a physical mixture of hydrate and dehydrate. In a preferred embodiment, the bicyclic [2.2.1]heptane-2,3-dicarboxylate is a dehydrate. In another preferred embodiment, the bicyclic [2.2.1]heptane-2,3-dicarboxylate is a hydrate, more preferably a monohydrate. Those skilled in the art will recognize that melt treatment of the polymer composition will remove any water of crystallization from the bicyclic [2.2.1]heptane-2,3-dicarboxylate. Therefore, in one of the preferred embodiments described above, the bicyclic [2.2.1]heptane-2,3-dicarboxylate is a dehydrate prior to melt treatment of the thermoplastic polymer composition. Therefore, the corresponding thermoplastic polymer composition is prepared by adding the desired amount of the dehydrated bicyclo[2.2.1]heptane-2,3-dicarboxylate to the above-described polyethylene polymer composition. In another preferred embodiment, the bicyclo[2.2.1]heptane-2,3-dicarboxylate is a hydrate (preferably a monohydrate) before the thermoplastic polymer composition is melt-processed. Therefore, the corresponding thermoplastic polymer composition is prepared by adding the desired amount of the hydrated bicyclo[2.2.1]heptane-2,3-dicarboxylate to the above-described polyethylene polymer composition. The addition of the bicyclo[2.2.1]heptane-2,3-dicarboxylate can be carried out by dry mixing the salt and the polyethylene polymer composition before melt mixing, or the salt can be added to the polyethylene polymer composition during melt processing, for example, by a side feeder connected to an extruder.

[0036] The thermoplastic polymer composition may contain any suitable amount of bicyclic [2.2.1]heptane-2,3-dicarboxylate. In a preferred embodiment, the thermoplastic polymer composition contains about 50 ppm or more of bicyclic [2.2.1]heptane-2,3-dicarboxylate. In another preferred embodiment, the thermoplastic polymer composition contains about 100 ppm or more of bicyclic [2.2.1]heptane-2,3-dicarboxylate. In yet another preferred embodiment, the thermoplastic polymer composition contains about 200 ppm or more of bicyclic [2.2.1]heptane-2,3-dicarboxylate. In a preferred embodiment, the thermoplastic polymer composition contains about 5000 ppm or less of bicyclic [2.2.1]heptane-2,3-dicarboxylate. In yet another preferred embodiment, the thermoplastic polymer composition contains about 3000 ppm or less of a salt of bicyclic [2.2.1]heptane-2,3-dicarboxylate. In yet another preferred embodiment, the thermoplastic polymer composition comprises about 2500 ppm or less of bicyclic [2.2.1]heptane-2,3-dicarboxylate. Thus, in a range of preferred embodiments, the thermoplastic polymer composition comprises about 50 ppm to about 5000 ppm (e.g., about 50 ppm to about 3000 ppm, about 50 ppm to about 2500 ppm, or about 50 to about 2000 ppm), about 100 ppm to about 5000 ppm (e.g., about 100 ppm to about 3000 ppm, about 100 ppm to about 2500 ppm, or about 100 to about 2000 ppm), or about 200 to about 5000 ppm (e.g., about 200 ppm to about 3000 ppm, about 200 ppm to about 2500 ppm, or about 200 to about 2000 ppm) of bicyclic [2.2.1]heptane-2,3-dicarboxylate.

[0037] In a preferred embodiment, in addition to the polyethylene polymer composition and the bicyclo[2.2.1]heptane-2,3-dicarboxylate, the thermoplastic polymer composition also contains an acid scavenger. Suitable acid scavengers include, but are not limited to, fatty acid salts, hydrotalcite compounds, and mixtures thereof.

[0038] Therefore, in a preferred embodiment, in addition to the polyethylene polymer composition and the bicyclo[2.2.1]heptane-2,3-dicarboxylate, the thermoplastic polymer composition also comprises a fatty acid salt. In a preferred embodiment, the fatty acid salt is C 12 -C 22 Fatty acid salts, preferably C 14 -C 20 Fatty acid salts or C 16 -C 18 Fatty acid salts. In another preferred embodiment, the fatty acid is a saturated fatty acid (e.g., saturated C450). 12 -C22 Fatty acids, saturated C 14 -C 20 Fatty acids or saturated C 16 -C 18 (Fatty acids). In a particularly preferred embodiment, the fatty acid salt is a stearate. The fatty acid salt may include any suitable counterion of the fatty acid anion. Preferably, the counterion is selected from the group consisting of alkali metal cations (e.g., sodium or potassium cations), alkaline earth metal cations (e.g., magnesium or calcium cations), and Group 12 cations (e.g., zinc cations). In a preferred embodiment, the counterion of the fatty acid salt is a zinc cation. Therefore, in a particularly preferred embodiment, the fatty acid salt is zinc stearate (i.e., the polymer composition further comprises zinc stearate).

[0039] When present in a thermoplastic polymer composition, fatty acid salts can be present in any suitable amount. In one preferred embodiment, the thermoplastic polymer composition contains about 50 ppm or more of fatty acid salts. In another preferred embodiment, the thermoplastic polymer composition contains about 100 ppm or more of fatty acid salts. In yet another preferred embodiment, the thermoplastic polymer composition contains about 200 ppm or more of fatty acid salts. In one preferred embodiment, the thermoplastic polymer composition contains about 5000 ppm or less of fatty acid salts. In another preferred embodiment, the thermoplastic polymer composition contains about 3000 ppm or less of fatty acid salts. In yet another preferred embodiment, the thermoplastic polymer composition contains about 2500 ppm or less of fatty acid salts. Therefore, in a series of preferred embodiments, the thermoplastic polymer composition comprises about 50 ppm to about 5000 ppm (e.g., about 50 ppm to about 3000 ppm, about 50 ppm to about 2500 ppm, or about 50 to about 2000 ppm), about 100 ppm to about 5000 ppm (e.g., about 100 ppm to about 3000 ppm, about 100 ppm to about 2500 ppm, or about 100 to about 2000 ppm), or about 200 to about 5000 ppm (e.g., about 200 ppm to about 3000 ppm, about 200 ppm to about 2500 ppm, or about 200 to about 2000 ppm) of fatty acid salts.

[0040] When present in the thermoplastic polymer composition, the fatty acid salt may be present in any suitable relative amount to the amount of the bicyclo[2.2.1]heptane-2,3-dicarboxylate. In a preferred embodiment, the fatty acid salt is present in the thermoplastic polymer composition in a mass ratio of about 5:1 to about 1:5 based on the mass of the bicyclo[2.2.1]heptane-2,3-dicarboxylate to the mass of the fatty acid salt. In another preferred embodiment, the fatty acid salt is present in the thermoplastic polymer composition in a mass ratio of about 3:1 to about 1:3 based on the mass of the bicyclo[2.2.1]heptane-2,3-dicarboxylate to the mass of the fatty acid salt. In yet another preferred embodiment, the fatty acid salt is present in the thermoplastic polymer composition in a mass ratio of about 2:1 to about 1:2 based on the mass of the bicyclo[2.2.1]heptane-2,3-dicarboxylate to the mass of the fatty acid salt. More preferably, the fatty acid salt is present in the thermoplastic polymer composition in a mass ratio of about 2:1 to about 1:1 based on the mass of the bicyclo[2.2.1]heptane-2,3-dicarboxylate to the mass of the fatty acid salt. Most preferably, the bicyclo[2.2.1]heptane-2,3-dicarboxylate salt and the fatty acid salt are present in the thermoplastic polymer composition in a mass ratio of about 2:1.

[0041] In another preferred embodiment, in addition to the polyethylene polymer composition and the bicyclo[2.2.1]heptane-2,3-dicarboxylate, the thermoplastic polymer composition also comprises a hydrotalcite compound. Suitable hydrotalcite compounds can be naturally occurring or synthetically produced, although synthetically produced materials are generally preferred. Suitable synthetic hydrotalcite compounds include, but are not limited to, the series of materials sold by Kyowa Chemical Industry Co., Ltd. under the name "DHT," for example... Hydrotalcite-based materials. When present in a thermoplastic polymer composition, the hydrotalcite compound may be present in any suitable amount, including any amount and / or proportion described above for fatty acid salts. Furthermore, in some embodiments, the thermoplastic polymer composition may comprise both fatty acid salts and hydrotalcite compounds.

[0042] The thermoplastic polymer compositions described herein can be used to produce any suitable articles or products. Suitable products include, but are not limited to, medical devices (e.g., pre-filled syringes for distillation applications, intravenous supply containers, and blood collection devices), food packaging, liquid containers (e.g., containers for beverages, pharmaceuticals, personal care compositions, shampoos, etc.), garment boxes, microwaveable articles, shelves, cabinet doors, mechanical parts, automotive parts, sheets, pipes, tubes, rotationally molded parts, blow-molded parts, films, fibers, etc. The thermoplastic polymer compositions can be formed into the desired articles by any suitable technique, such as injection molding, injection rotational molding, blow molding (e.g., injection blow molding or injection stretch blow molding), extrusion (e.g., sheet extrusion, film extrusion, cast film extrusion, or foam extrusion), extrusion blow molding, thermoforming, rotational molding, film blow molding (blown film), film casting (cast film), etc. The thermoplastic polymer compositions disclosed herein are considered particularly suitable for extrusion blow molding and film blow molding methods, with film blow molding being particularly preferred.

[0043] The disclosed thermoplastic polymer compositions are considered highly suitable for use in extrusion blow molding and film blow molding methods because they exhibit significantly improved (i.e., lower) water vapor and oxygen permeability compared to unnucleated polymers and nucleated polymers that do not exhibit the aforementioned physical properties (e.g., density, melt relaxation index, melt flow index, etc.). For example, blown films made from the disclosed thermoplastic polymer compositions have been observed to exhibit significantly lower water vapor permeability compared to similar blown films made from nucleated polymers that do not exhibit the desired melt relaxation index. As stated above, this result is attributed to the selection of polyethylene polymer compositions exhibiting sufficient melt relaxation to maximize the nucleation effect of the bicyclo[2.2.1]heptane-2,3-dicarboxylate.

[0044] Therefore, in a second embodiment, the present invention provides a method for preparing a film from a thermoplastic polymer composition. The method includes the following steps:

[0045] (a) Provides an apparatus comprising:

[0046] (i) A die head having an annular die orifice suitable for extruding tubular materials;

[0047] (ii) A device for blowing pressurized fluid into a tubular structure exiting the annular orifice; and

[0048] (iii) A device for stretching and collecting tubular objects;

[0049] (b) Provides a thermoplastic polymer composition comprising (i) a polyethylene polymer composition having a melt relaxation index of 2 or greater; and (ii) a bicyclo[2.2.1]heptane-2,3-dicarboxylate;

[0050] (c) Heating the thermoplastic polymer composition to a temperature sufficient to melt it, so that it can be extruded through the die;

[0051] (d) Extruding molten thermoplastic polymer composition through the annular die to form a tube exiting the annular die in a first direction, the tube having a diameter and a length;

[0052] (e) Pressurized fluid is blown into the tubular material under sufficient pressure to expand the tubular material and increase its diameter, while the tubular material is stretched in a first direction to increase its length, thereby producing a thin film;

[0053] (f) Cooling the film to the temperature at which the thermoplastic polymer composition cures; and

[0054] (g) Collect the film.

[0055] The thermoplastic polymer composition used in the method of this second embodiment can be any of the thermoplastic polymer compositions described above. The equipment used to implement the method of the present invention can be any suitable blown film equipment. For example, a blown film machine can be equipped with a single extruder and an annular die to produce a single-layer film. Alternatively, a blown film machine can be equipped with multiple extruders and suitable dispensing dies adapted to combine multiple but separate layers in the melt. The film produced by such a blown film machine will be a multilayer film. When preparing a multilayer film, the thermoplastic polymer composition of the present invention can be used to prepare any one or more layers of the multilayer film. In other words, the above method includes a method for preparing a multilayer film, wherein all layers of the film are prepared using the thermoplastic polymer composition, and a method for preparing a multilayer film, wherein at least one layer of the multilayer film is prepared using the thermoplastic polymer composition, and the remaining layers of the multilayer film are prepared using one or more other polymer compositions.

[0056] In the above method, the thermoplastic polymer composition can be heated to any suitable temperature that melts the thermoplastic polymer composition and allows it to be extruded through a die. The temperature at which the thermoplastic polymer composition is heated has no significant effect on the nucleation properties of bicyclo[2.2.1]heptane-2,3-dicarboxylate, but higher temperatures can promote larger and faster melt relaxation, which in turn can improve the nucleation properties to some extent. However, the temperature at which the thermoplastic polymer composition is heated should not be too high, as this may reduce the viscosity of the molten polymer composition to the point that the tubular structure would break when it is expanded by a pressurized fluid. Preferably, the thermoplastic polymer composition is heated to a temperature of about 150°C to about 220°C. The thermoplastic polymer composition can be heated first in the feed inlet of the extruder to a temperature of about 150°C to about 170°C, and then in the final zone of the extruder to a temperature of about 180°C to about 220°C. Once heated to the desired temperature, the molten thermoplastic polymer composition is preferably held at the desired temperature until it is extruded through an annular die. Based on the polymer properties, ordinary technicians in the blown film production field will recognize the need for temperature regulation to maintain an appropriate trade-off between quality output, system back pressure, and bubble (pipe) stability.

[0057] The polymer tubule exiting the annular die can be expanded to the desired diameter using any suitable pressure. The pressure required to expand the tubule depends on several factors, such as the temperature of the molten thermoplastic polymer composition exiting the annular die, the extent to which the diameter of the tubule is to be increased, and the desired thickness of the resulting film. Therefore, in practice, the pressure is usually adjusted by the machine operator until a film with the desired properties is obtained.

[0058] The films produced by the above method can be collected in any suitable manner. For example, the expanded tubular material is typically flattened by two or more clamping rollers. The tubing or layflat can be collected in this flattened form, or the edges of the layflat can be cut to produce two separate films, which can then be collected.

[0059] The following examples further illustrate the above subject matter, but should not be construed as limiting its scope in any way.

[0060] Example 1

[0061] The following examples illustrate the production and properties of several thermoplastic polymer compositions according to the present invention.

[0062] Table 1 lists the density, melt flow index (MFI), tanδ, and melt relaxation index of several commercially available polyethylene polymers. The tanδ and melt relaxation index of 2908 were not reported because the viscosity of this polymer was too high for these two parameters to be measured at 190°C. The tanδ and melt relaxation index of ExxonMobil LL 1001X31 were not measured because this polymer was only used in blends under low loads to improve higher-speed extrusion. Seven polyethylene blends (blended 1-7) were prepared by mixing these polymers in the amounts shown in Table 1. Table 1 also lists the density, melt flow index (MFI), tanδ, and melt relaxation index of blends 1-7. To minimize melt fracture during processing, some blends also incorporated a small amount of commercially available polymer processing aid masterbatch containing 3% fluorinated polymer processing aid into the linear low-density polyethylene carrier polymer. These polyethylene polymers and polyethylene polymer blends were used to prepare several polymer compositions as described below.

[0063] Table 1. Density, melt flow index (MFI), tanδ, and melt relaxation index of several polyethylene polymers and polyethylene polymer blends

[0064]

[0065] To facilitate the mixing of bicyclic [2.2.1]heptane-2,3-dicarboxylate with the polymer to produce a thermoplastic polymer composition, five diluted granular masterbatch compositions were prepared using the formulations listed in Table 2 below. For each masterbatch composition, the amount of carrier polymer was the balance by weight of the masterbatch composition. The masterbatch compositions were prepared by grinding the carrier polymer in a mill at room temperature, adding the listed ingredients, and mixing for two minutes at 1200 rpm in a 30-liter Henschel high-intensity mixer. The resulting mixture was then mixed with a twin-screw extruder and extruded into granules. The “nucleating agent” in Table 2 was, in all cases, a dehydrated form of calcium cis-endo-bicyclic [2.2.1]heptane-2,3-dicarboxylate. Each masterbatch composition contained zinc stearate as a deacidifying agent.

[0066] Table 2 Formulation of Masterbatch Composition

[0067]

[0068] Blown films were prepared using the above-described polyethylene polymers, polymer blends, and / or masterbatch compositions. Blown films were prepared on a small-scale pilot-scale co-extrusion blown film production line equipped with a 5-layer flat die, a 100mm die lip assembly, a 1.8mm die gap, a 1.25-inch single-screw extruder (with a mixing section), and a double-lip air ring. The same dry blend was fed into all extruders to prepare substantially monolayer films, and the line was run at a feed rate of approximately 20-26 kg / hr, depending on the specific polymer or polymer blend used and the resulting back pressure. The resulting film thickness varied between 1.5 and 1.9 mils. The measured film thicknesses were used to normalize certain measurements, such as water vapor transmission rate, as described below. In Table 3, samples ending in “A” were prepared from polymers or polymer blends that did not contain any nucleating agents. Samples ending in “B” were prepared from polymer compositions containing cis-intra-bicyclic [2.2.1]heptane-2,3-dicarboxylate calcium as a nucleating agent. Samples with names ending in "B" were prepared by replacing a portion of the polymer or polymer blend with the stated amount of masterbatch composition. The final concentration of the nucleating agent in the polymer composition is listed in Table 3.

[0069] Water vapor transmission rate (WVTR) of each blown film was measured according to ASTM F 1249 (90% RH, 37.8°C). The resulting measured WVTR was then normalized relative to the film thickness to allow for more direct sample-to-sample comparisons. The normalized water vapor transmission rate is reported as “nWVTR” in Table 3 below.

[0070] Table 3. Formulation, melt relaxation index (MRI), nucleating agent concentration, and nWVTR of blown films.

[0071]

[0072] As can be seen from the data in Table 3, blown films made from thermoplastic polymer compositions containing bicyclic [2.2.1]heptane-2,3-dicarboxylate and polyethylene polymers or polymer blends with a melt relaxation index of 2 or greater (i.e., films made from samples 4B, 5B, 7B, 8B, 9B, 10B, and 11B) showed a significant improvement in nWVTR compared to their unnucleated counterparts (i.e., films made from samples 4A, 5A, 7A, 8A, 9A, 10A, and 11A, respectively). In contrast, the addition of the same bicyclic [2.2.1]heptane-2,3-dicarboxylate had no significant effect on those polymers with a melt relaxation index less than 2. In particular, blown films made from polymer compositions containing bicyclic [2.2.1]heptane-2,3-dicarboxylate and polyethylene polymers or polymer blends with a melt relaxation index less than 2 (i.e., films made from samples 1B, 2B, 3B, and 6B) exhibited substantially the same nWVTR as their unnucleated counterparts (i.e., films made from samples 1A, 2A, 3A, and 6A, respectively). The decrease in WVTR is directly related to the nucleation effect of bicyclic [2.2.1]heptane-2,3-dicarboxylate on the polyethylene polymer compositions. Therefore, the difference between these two sets of results suggests that bicyclic [2.2.1]heptane-2,3-dicarboxylate is more effective for nucleation of polymers and polymer blends with a melt relaxation index of 2 or greater. This is surprising, as there is no known evidence in the art that nucleation with bicyclic [2.2.1]heptane-2,3-dicarboxylate depends on these polymer properties. However, as stated above, the inventors believe that this difference is due to the lower degree of melt relaxation exhibited by polymers with a melt relaxation index of less than 2. In such polymers, the polymer melt relaxes slowly, resulting in a large amount of strain-induced self-nucleation rather than nucleation by the bicyclic [2.2.1]heptane-2,3-dicarboxylate.

[0073] All references cited in this article, including publications, patent applications and patents, are incorporated herein by reference to the same extent that each reference individually and specifically represents it as it is incorporated herein by reference and is presented in its entirety.

[0074] The terms “a,” “an,” and “the,” and similar indicators used in the context of describing the subject matter of this application (particularly in the context of the appended claims) should be interpreted as encompassing both singular and plural forms, unless otherwise stated herein or clearly contradicted by the context. Unless otherwise specified, the terms “comprising,” “having,” “including,” and “containing” should be interpreted as open-ended terms (i.e., meaning “including, but not limited to”). Unless otherwise stated herein, the descriptions of numerical ranges herein are intended only as a shorthand method for individually referring to each individual value falling within that range, and each individual value is incorporated into the specification as if it were individually described herein. All methods described herein may be performed in any suitable order, unless otherwise stated herein or clearly contradicted by the context. The use of any and all embodiments or exemplary language (e.g., “for example”) provided herein is intended only to better illustrate the subject matter of this application and does not constitute a limitation on the scope of the subject matter, unless otherwise stated. No language in the specification should be construed as indicating that any unclaimed element is essential to the practice of the subject matter described herein.

[0075] This document describes preferred embodiments of the subject matter of this application, including the best modes known to the inventors for implementing the claimed subject matter. Variations of these preferred embodiments will become apparent to those skilled in the art upon reading the foregoing description. The inventors expect those skilled in the art to appropriately employ such variations, and the inventors intend that the subject matter described herein be practiced in ways different from those specifically described herein. Therefore, this disclosure includes all modifications and equivalents of the subject matter described in the appended claims as permitted by applicable law. Furthermore, unless otherwise stated herein or clearly contradicted by the context, this disclosure covers any combination of the foregoing elements in all possible variations.

Claims

1. A thermoplastic polymer composition comprising: (a) A polyethylene polymer composition having a melt relaxation index of 2 or greater, wherein the melt relaxation index is defined as the product of (i) the sum of 1 and the natural logarithm of the polymer melt flow index and (ii) the ratio of tanδ at 0.1 rad / s to tanδ at 10 rad / s, where tanδ is the ratio of shear loss modulus G″ to shear storage modulus G′, G″ / G′: and (b) Bicyclic [2.2.1]heptane-2,3-dicarboxylate.

2. The thermoplastic polymer composition of claim 1, wherein the polyethylene polymer composition has a melt relaxation index of 2.1 or greater.

3. The thermoplastic polymer composition of claim 1 or 2, wherein the polyethylene polymer composition has a melt flow index of 2 dg / min or less at 190°C.

4. The thermoplastic polymer composition of claim 1 or 2, wherein the thermoplastic polymer composition comprises cis-endo-bicyclo[2.2.1]heptane-2,3-dicarboxylate.

5. The thermoplastic polymer composition of claim 1 or 2, wherein the bicyclo[2.2.1]heptane-2,3-dicarboxylate is calcium bicyclo[2.2.1]heptane-2,3-dicarboxylate.

6. The thermoplastic polymer composition of claim 1 or 2, wherein the thermoplastic polymer composition comprises 100 ppm to 3000 ppm of the bicyclo[2.2.1]heptane-2,3-dicarboxylate.

7. The thermoplastic polymer composition of claim 1 or 2, wherein the thermoplastic polymer composition further comprises a component selected from C. 12 -C 22 Acid removers of fatty acid salts, hydrotalcite compounds and mixtures thereof.

8. The thermoplastic polymer composition of claim 7, wherein the thermoplastic polymer composition comprises 100 ppm to 3000 ppm of the C 12 -C 22 Fatty acid salts are used as the deacidifying agents.

9. A method for producing a thin film, the method comprising the following steps: (a) Provides an apparatus comprising: (i) A die head having an annular die orifice suitable for extruding tubular materials; (ii) A device for blowing pressurized fluid into the tubular material exiting the annular orifice; as well as (iii) A device for stretching and collecting the tubular object; (b) Providing a thermoplastic polymer composition comprising (i) a polyethylene polymer composition having a melt relaxation index of 2 or greater; and (ii) a bicyclo[2.2.1]heptane-2,3-dicarboxylate, wherein the melt relaxation index is defined as the product of (i) the sum of 1 and the natural logarithm of the polymer melt flow index and (ii) the ratio of tanδ at 0.1 rad / s to tanδ at 10 rad / s, where tanδ is the ratio of shear loss modulus G″ to shear storage modulus G′: G″ / G′ (c) Heating the thermoplastic polymer composition to a temperature sufficient to melt it, so that it can be extruded through the die; (d) Extruding a molten thermoplastic polymer composition through the annular die to form a tube exiting the annular die in a first direction, the tube having a diameter and a length; (e) Pressurized fluid is blown into the tubular material under sufficient pressure to expand the tubular material and increase its diameter, while the tubular material is stretched in the first direction to increase its length, thereby producing a thin film. (f) Cooling the film to the temperature at which the thermoplastic polymer composition cures; and (g) Collect the film.

10. The method of claim 9, wherein the polyethylene polymer composition has a melt relaxation index of 2.1 or greater.

11. The method of claim 9 or 10, wherein the polyethylene polymer composition has a melt flow index of 2 dg / min or less at 190°C.

12. The method of claim 9 or 10, wherein the thermoplastic polymer composition comprises cis-endo-bicyclo[2.2.1]heptane-2,3-dicarboxylate.

13. The method of claim 9 or 10, wherein the bicyclic [2.2.1]heptane-2,3-dicarboxylate is calcium bicyclic [2.2.1]heptane-2,3-dicarboxylate.

14. The method of claim 9 or 10, wherein the thermoplastic polymer composition comprises 100 ppm to 3000 ppm of the bicyclo[2.2.1]heptane-2,3-dicarboxylate.

15. The method of claim 9 or 10, wherein the thermoplastic polymer composition further comprises a material selected from C 12 -C 22 Acid removers of fatty acid salts, hydrotalcite compounds and mixtures thereof.

16. The method of claim 15, wherein the polymer composition comprises 100 ppm to 3000 ppm of the C 12 -C 22 Fatty acid salts are used as the deacidifying agents.

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