Bimodal medium density polyethylene composition suitable for use as micro-irrigation driptape

Abstract

This invention provides a bimodal medium-density polyethylene (MDPE) composition and a micro-irrigation drip tape comprising the MDPE composition. The MDPE composition can be extruded at high linear velocity while maintaining other desired properties. The MDPE composition comprises a high molecular weight (HMW) polyethylene component and a low molecular weight (LMW) polyethylene component. The MDPE composition has a molecular weight of 0.937 g / cm³. 3 Up to 0.946 g / cm 3 Density; high-load melt index (I21) of 7 g / 10 min to 20 g / 10 min; cross G' = G” of 30 kPa to 50 kPa; notched constant tensile load failure time greater than 700 hours at 30% yield stress as measured according to ASTM D5397; and strain hardening modulus greater than 65 MPa.

Description

Technical Field

[0001] The embodiments disclosed herein generally relate to bimodal medium-density polyethylene compositions and micro-irrigation drip tapes comprising the bimodal medium-density polyethylene compositions. Background Technology

[0002] Micro-irrigation drip tape is a type of tubing used in irrigation systems to deliver and drip water, fertilizer, and / or nutrients. The US micro-irrigation drip tape market consumes over 120 mm pounds of polyethylene resin annually. Currently, micro-irrigation drip tape is primarily made of materials with a density of 0.939 g / cm³. 3 Up to 0.944 g / cm 3 The process involves forming unimodal polyethylene resins with a melt index (I2) of 0.2 g / 10 min to 0.3 g / 10 min and a molecular weight distribution greater than 15. However, existing polyethylene resins have limited processability because they lack properties that prevent processors from producing micro-irrigation drip tapes with suitable wall thicknesses while maintaining tensile strength, strain hardening modulus, and service life. Therefore, there remains a need for polyethylene compositions suitable for micro-irrigation drip tapes that possess the desired processability and maintain or improve storage hardening modulus, tensile strength, and service life as indicated by notched constant tensile load failure time. Summary of the Invention

[0003] Embodiments of this disclosure satisfy one or more of the aforementioned needs by providing bimodal medium-density polyethylene compositions that can be processed at high extrusion rates and exhibit improved or maintained tensile strength, storage hardening modulus, and notched constant tensile load failure time. Without being bound by any theory, in some embodiments, the bimodal medium-density polyethylene compositions possess specific properties, including cross-G'=G (which indicates melt elasticity) and average short-chain branching in the low molecular weight polyethylene components, which allow the compositions to be extruded at high speeds and exhibit maintained or improved storage hardening modulus and notched constant tensile load failure time.

[0004] This document discloses a bimodal medium-density polyethylene composition. In one or more embodiments, the bimodal medium-density polyethylene composition comprises (i) a high molecular weight (HMW) polyethylene component comprising an ethylene / α-olefin copolymer and (ii) a low molecular weight (LMW) polyethylene component comprising an ethylene / α-olefin copolymer; the bimodal medium-density polyethylene composition has the following characteristics: (a) 0.937 g / cm³ 3 Up to 0.946 g / cm 3(a) density; (b) high-load melt index (I21) of 7 g / 10 min to 20 g / 10 min; (c) cross G' = G” of 30 kPa to 50 kPa; (d) notched constant tensile load failure time greater than 700 hours at 30% yield stress as measured according to ASTM D5397; (e) strain hardening modulus greater than 65 MPa; wherein the LMW polyethylene component has an average short-chain branching frequency greater than 0.9 SCB / 1000 carbons; wherein the HMW polyethylene component has a weight-average molecular weight Mw of 300,000 g / mol to 600,000 g / mol; and wherein the Mw polyethylene component is present in an amount of 45 wt% to 60 wt% based on the total weight of the bimodal medium-density polyethylene composition.

[0005] This article discloses a micro-irrigation drip tape. The micro-irrigation drip tape comprises the bimodal medium-density polyethylene composition disclosed herein.

[0006] These and other implementation schemes are described in more detail in the specific embodiments. Attached Figure Description

[0007] Figure 1 This is a perspective view of a micro-irrigation drip tape with a circular cross-section.

[0008] Figure 2 These are absolute GPC chromatograms of certain embodiments and comparative examples of the present invention, showing the local maximum values ​​of the LMW and HMW polyethylene component peaks and the local minimum values ​​between the LMW and HMW polyethylene component peaks. Detailed Implementation

[0009] The disclosed bimodal medium-density polyethylene composition is described in more detail below. The bimodal medium-density polyethylene composition is suitable for use as a micro-irrigation drip tape and has a wide range of applications, including, for example, pipes, fittings, hoses, tapes, etc. However, this disclosure should not be construed as limiting the embodiments set forth below, as this disclosure is an illustrative description of the embodiments described herein.

[0010] As used herein, the term "polymer" refers to a polymeric compound prepared by polymerizing monomers of the same or different types. Therefore, the general term polymer encompasses the term homopolymer (used to refer to a polymer prepared from only one type of monomer) and the term copolymer or interpolymer. Trace impurities (e.g., catalyst residues) may be incorporated into and / or within a polymer. A polymer can be a single polymer, a polymer blend, or a mixture of polymers comprising a mixture of polymers formed in situ during polymerization.

[0011] As used herein, the term "copolymer" refers to a polymer formed by the polymerization of at least two monomers with different structures. The term "copolymer" includes terpolymers.

[0012] As used herein, the terms "polyethylene" or "ethylene-based polymer" should mean a polymer comprising a majority (>50 mol%) unit derived from ethylene monomers. This includes polyethylene homopolymers and copolymers (meaning units derived from two or more comonomers). The terms "ethylene-based polymer" and "polyethylene" are used interchangeably. Generally, polyethylene can be produced in gas-phase fluidized bed reactors, liquid-phase slurry reactors, or liquid-phase solution reactors using heterogeneous catalyst systems (such as Ziegler-Natta catalysts) and homogeneous catalyst systems containing Group 4 transition metals and ligand structures (such as metallocenes, non-metallocene metal centers, heteroaryl groups, isovalent aryloxy ethers, phosphine imides, etc.). Combinations of heterogeneous and / or homogeneous catalysts can also be used in single-reactor or dual-reactor configurations.

[0013] As used herein, the term "composition" means a mixture of materials comprising the composition, as well as reaction products and decomposition products formed from the materials of the composition.

[0014] As used herein, the term "bimodal catalyst" refers to a catalyst system containing two different catalysts used to catalyze the polymerization of ethylene copolymers to produce bimodal copolymer compositions. These two catalysts typically differ from each other in at least one of the following properties: (a) their catalytic metals are different (e.g., Ti vs. Zr, Zr vs. Hf, Ti vs. Hf; non-activating metals such as Al); (b) one catalyst has a functional ligand bonded to its catalytic metal, while the other catalyst does not; (c) both catalysts have functional ligands bonded to their catalytic metals, and the structure of at least one functional ligand of one catalyst differs from the structure of a functional ligand of the other catalyst; and (d) for catalysts disposed on support materials, the compositions of these support materials are different. The two catalysts in a bimodal catalyst system may be disposed on the same support material, on the same particles of the same support material, or each on different particles of the same support material. When the catalyst system contains the same catalyst with respect to the catalytic metal and ligands, wherein a portion of it is disposed on the support material and its different portions are dissolved in an inert solvent, these different portions do not themselves constitute a bimodal catalyst system.

[0015] As used herein, the term "main chain" refers to the longest continuous polymer chain. All other polymer chains are referred to as side chains, branches, or graft polymer chains. As used herein, the term "short chain" or "short-chain branching" (SCB) refers to a branch derived from the main chain resulting from the polymerization of monomers containing three or more carbon atoms.

[0016] The terms “comprising,” “including,” “having,” and their derivatives are not intended to exclude the presence of any additional components, steps, or procedures, whether or not such components, steps, or procedures are specifically disclosed. For the avoidance of any doubt, unless stated to the contrary, all compositions claimed using the term “comprising” may include any additional additives, adjuvants, or compounds, whether polymerized or otherwise. In contrast, the term “consistently composed of” excludes any other components, steps, or procedures from any subsequently listed scope, except those that are not essential for operability. The term “composed of” excludes any ingredients, steps, or procedures not specifically described or listed.

[0017] This document discloses a bimodal medium-density polyethylene composition. As used herein, the medium-density polyethylene composition has a content of 0.937 g / cm³. 3 Up to 0.946 g / cm 3 A medium-density polyethylene composition of a specific density. The bimodal medium-density polyethylene composition according to the embodiments disclosed herein comprises a high molecular weight (HMW) polyethylene component and a low molecular weight (LMW) polyethylene component. The HMW polyethylene component has a higher molecular weight than the LMW polyethylene component.

[0018] The bimodal medium-density polyethylene composition according to the embodiments disclosed herein is bimodal. The “bimodal” polyethylene composition contains two polyethylene fractions (e.g., an HMW polyethylene component and an LMW polyethylene component), which are generated in a polymerization reactor under copolymerization conditions by contacting a mixture of ethylene (monomer) and α-olefin (comonomer) with a bimodal catalyst system and a trimming solution in the presence of molecular hydrogen (H2) and an inducing condensation agent (ICA), thereby obtaining fractions with different molecular weights and / or different comonomer contents, as demonstrated by the bimodality test method described below. For the avoidance of any doubt, the bimodal medium-density polyethylene compositions disclosed herein do not include and are not unimodal polyethylene having a single polyethylene fraction.

[0019] HMW polyethylene component

[0020] This bimodal medium-density polyethylene composition comprises an HMW polyethylene component. In some embodiments, the HMW polyethylene component comprises an ethylene / α-olefin copolymer.

[0021] In some embodiments, the ethylene / α-olefin copolymer of the HMW polyethylene component comprises ethylene and α-olefin comonomers. Non-limiting examples of suitable α-olefins include C3-C20 α-olefins, or C4-C20 α-olefins, or C3-C10 α-olefins, or C4-C10 α-olefins, or C4-C8 α-olefins. Representative α-olefins include propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, and 1-octene. In one embodiment, the ethylene / α-olefin copolymer does not contain aromatic comonomers polymerized therein. In another embodiment, the ethylene / α-olefin copolymer is an ethylene / 1-hexene copolymer. In one embodiment, the ethylene / α-olefin copolymer consists of ethylene, C4-C8 α-olefin comonomers, and optional additives.

[0022] In one embodiment, based on the weight of the ethylene / α-olefin copolymer, the ethylene / α-olefin copolymer contains more than 50% by weight of ethylene-derived units, or 51% by weight, or 55% by weight, or 60% to 70% by weight, or 80% by weight, or 90% by weight, or 95% by weight, or 99% by weight of ethylene-derived units. In one embodiment, based on the weight of the ethylene / α-olefin copolymer, the ethylene / α-olefin copolymer contains complementary numbers of units derived from α-olefin comonomers, or less than 50% by weight, or 49% by weight, or 45% by weight, or 40% to 30% by weight, or 20% by weight, or 10% by weight, or 5% by weight, or 1% by weight of units derived from α-olefin comonomers. The content of comonomers can be measured using any suitable technique, such as techniques based on nuclear magnetic resonance (“NMR”) spectroscopy, for example, by 13C NMR analysis as described in U.S. Patent No. 7,498,282 (which is incorporated herein by reference).

[0023] In some embodiments, the HMW polyethylene component has an average short-chain branching frequency greater than 1.4 SCB / 1000 carbons. This document includes and discloses all individual values ​​and subranges greater than 1.4 SCB / 1000 carbons. For example, the HMW polyethylene component may have an average short-chain branching frequency greater than 1.5 SCB / 1000 carbon, or greater than 1.6 SCB / 1000 carbon, or greater than 1.7 SCB / 1000 carbon, or greater than 1.8 SCB / 1000 carbon; or within the range of 1.4 SCB / 1000 carbon to 4.0 SCB / 1000 carbon, or 1.5 SCB / 1000 carbon to 3.9 SCB / 1000 carbon, or 1.6 SCB / 1000 carbon to 3.8 SCB / 1000 carbon, or 1.7 SCB / 1000 carbon to 3.7 SCB / 1000 carbon, or 1.8 SCB / 1000 carbon to 3.6 SCB / 1000 carbon. The average short-chain branching frequency of the HMW polyethylene component can be measured according to the test methods described below.

[0024] In some embodiments, the HMW polyethylene component is present in an amount of 45 wt% to 60 wt% based on the total weight of the bimodal medium-density polyethylene composition. This document includes and discloses all individual values ​​and sub-ranges of 45 wt% to 60 wt%. For example, the HMW polyethylene component may be present in amounts of 45 wt% to 60 wt%, 50 wt% to 60 wt%, 53 wt% to 60 wt%, 50 wt% to 58 wt%, 50 wt% to 56 wt%, 52 wt% to 58 wt%, 53 wt% to 57 wt%, or 52 wt% to 56 wt% based on the total weight of the bimodal medium-density polyethylene composition. The presence of the HMW polyethylene component may also be expressed as a weight fraction relative to a weight percentage. For example, 50 wt% may be expressed as 0.50 weight fraction, 60 wt% may be expressed as 0.60 weight fraction, etc.

[0025] In some embodiments, the HMW polyethylene component has a weight-average molecular weight (Mw) of 300,000 g / mol to 600,000 g / mol. This document discloses and includes all individual values ​​and sub-ranges of 300,000 g / mol to 600,000 g / mol. For example, the HMW polyethylene component may have a weight-average molecular weight (Mw) of 325,000 g / mol to 575,000 g / mol, 350,000 g / mol to 550,000 g / mol, 375,000 g / mol to 525,000 g / mol, 375,000 g / mol to 500,000 g / mol, 375,000 g / mol to 475,000 g / mol, or 375,000 g / mol to 450,000 g / mol. The weight-average molecular weight (Mw) can be measured according to the GPC test method described below.

[0026] LMW polyethylene component

[0027] This bimodal medium-density polyethylene composition comprises an LMW polyethylene component. In some embodiments, the LMW polyethylene component comprises an ethylene / α-olefin copolymer.

[0028] In some embodiments, the ethylene / α-olefin copolymer of the LMW polyethylene component comprises ethylene and α-olefin comonomers. Non-limiting examples of suitable α-olefins include C3-C20 α-olefins, or C4-C20 α-olefins, or C3-C10 α-olefins, or C4-C10 α-olefins, or C4-C8 α-olefins. Representative α-olefins include propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, and 1-octene. In one embodiment, the ethylene / α-olefin copolymer does not contain aromatic comonomers polymerized therein. In another embodiment, the ethylene / α-olefin copolymer is an ethylene / 1-hexene copolymer. In one embodiment, the ethylene / α-olefin copolymer consists of ethylene, C4–C8 α-olefin comonomers, and optional additives.

[0029] In one embodiment, based on the weight of the ethylene / α-olefin copolymer, the ethylene / α-olefin copolymer of the LMW polyethylene component contains more than 50% by weight of ethylene-derived units, or 51% by weight, or 55% by weight, or 60% to 70% by weight, or 80% by weight, or 90% by weight, or 95% by weight, or 99% by weight of ethylene-derived units. In one embodiment, based on the weight of the ethylene / α-olefin copolymer, the ethylene / α-olefin copolymer contains complementary numbers of units derived from α-olefin comonomers, or less than 50% by weight, or 49% by weight, or 45% by weight, or 40% to 30% by weight, or 20% by weight, or 10% by weight, or 5% by weight, or 1% by weight of units derived from α-olefin comonomers.

[0030] In some embodiments, the LMW polyethylene component has an average short-chain branching frequency greater than 0.9 SCB / 1000 carbon. This document includes and discloses all individual values ​​and sub-ranges greater than 0.9 SCB / 1000 carbon. For example, the LMW polyethylene component may have an average short-chain branching frequency greater than 0.9 SCB / 1000 carbon, or greater than 1.0 SCB / 1000 carbon, or greater than 1.1 SCB / 1000 carbon, or in the range of 1.0 SCB / 1000 to 2.5 SCB / 1000 carbon, 1.0 SCB / 1000 to 2.2 SCB / 1000 carbon, or 1.0 SCB / 1000 to 2.0 SCB / 1000 carbon. The average short-chain branching frequency of the LMW polyethylene component can be measured according to the test methods described below.

[0031] The ethylene / α-olefin copolymers of the LMW polyethylene component and the HMW polyethylene component differ at least in terms of the molecular weights of their respective components. In one embodiment, the weight-average molecular weight (Mw) of the LMW polyethylene component is less than that of the HMW polyethylene component, and the density of the LMW polyethylene component is greater than that of the HMW polyethylene component. In some embodiments, the ratio of the weight-average molecular weight (Mw) of the HMW polyethylene component to that of the LMW polyethylene component is 16 to 27. This document includes and discloses all individual values ​​and sub-ranges of 16 to 27. For example, the ratio of the weight-average molecular weight (Mw) of the HMW polyethylene component to that of the LMW polyethylene component can be 17 to 26, 18 to 25, or 20 to 25. The weight-average molecular weight (Mw) can be measured according to the GPC test method described below.

[0032] Characteristics of medium-density polyethylene compositions

[0033] In some embodiments, the bimodal medium-density polyethylene composition has a content of 0.937 g / cm³. 3 Up to 0.946 g / cm 3 Density, high-load melt index (I21) of 7 g / 10 min to 20 g / 10 min, notched constant tensile load (NCTL) failure time of more than 700 hours at 30% yield stress as measured by ASTM D5397, and strain hardening modulus of more than 65 MPa.

[0034] In some embodiments, the bimodal medium-density polyethylene composition has a content of 0.937 g / cm³. 3 Up to 0.946 g / cm 3 The density is disclosed and included in this document as 0.937 g / cm³. 3 Up to 0.946 g / cm 3 All individual values ​​and sub-ranges. For example, a bimodal medium-density polyethylene composition can have 0.938 g / cm³. 3 Up to 0.946 g / cm 3 0.939 g / cm 3 Up to 0.946 g / cm 3 0.940 g / cm 3 Up to 0.946 g / cm 3 0.941 g / cm 3 Up to 0.946 g / cm 3 0.938g / cm 3 Up to 0.946 g / cm 3 0.938g / cm 3 Up to 0.945 g / cm 3 0.940 g / cm3 Up to 0.943 g / cm 3 Or 0.940 g / cm 3 Up to 0.942 g / cm 3 The density, where the density is measured according to ASTM D792.

[0035] In some embodiments, the bimodal medium-density polyethylene composition has a high-load melt index (I21) of 7 g / 10 min to 20 g / 10 min. All individual values ​​and sub-ranges of 7 g / 10 min to 20 g / 10 min are disclosed and included herein. For example, the bimodal medium-density polyethylene composition may have a total high-load melt index (I21) of 8 g / 10 min to 20 g / 10 min, 9 g / 10 min to 20 g / 10 min, 8 g / 10 min to 19 g / 10 min, 9 g / 10 min to 19 g / 10 min, 10 g / 10 min to 20 g / 10 min, 10 g / 10 min to 19 g / 10 min, or 10 g / 10 min to 18 g / 10 min, wherein the high-load melt index (I21) of the bimodal medium-density polyethylene composition is measured according to ASTM D1238 (190°C / 21.6 kg).

[0036] In some embodiments, the bimodal medium-density polyethylene composition has a cross G' = G" at 30 kPa to 50 kPa. This document discloses and includes all individual values ​​and sub-ranges of 30 kPa to 50 kPa. For example, the bimodal medium-density polyethylene composition may have a cross G' = G" at 32 kPa to 48 kPa, 33 kPa to 48 kPa, 34 kPa to 48 kPa, or 34 kPa to 47 kPa, wherein the cross G' = G" is measured according to the test methods described below.

[0037] In some embodiments, the HMW polyethylene component has an average short-chain branching frequency (HMW SCB / 1000C) and satisfies the following equation:

[0038] 3094·HMW weight% – 30.52·cross G'=G” – 160.1·(LMW SCB / 1000C / HMW SCB / 1000C) – 211.7≥0 (Equation A)

[0039] Wherein, "HMW wt%" is the weight percentage of HWM polyethylene present in the bimodal medium-density polyethylene composition based on the total weight of the bimodal medium-density polyethylene composition, "cross G' = G" is the cross G' = G of the bimodal medium-density polyethylene composition, "LMW SCB / 1000C" is the average short-chain branching frequency of the LMW polyethylene component, and "HMW SCB / 1000C" is the average short-chain branching frequency of the HMW polyethylene component. In some embodiments, the left side of the above equation A is equal to or greater than 5, equal to or greater than 10, or equal to or greater than 15.

[0040] In some embodiments, the bimodal medium-density polyethylene composition has a molecular weight distribution (Mw / Mn) of 12 to 30. This document includes all individual values ​​and sub-ranges of 12 to 30. For example, the bimodal medium-density polyethylene composition may have a molecular weight distribution (Mw / Mn) of 12 to 28, 12 to 26, 12 to 24, 12 to 22, 12 to 20, 14 to 28, 14 to 26, 14 to 24, 14 to 22, or 14 to 20, wherein the molecular weight distribution (Mw / Mn) can be measured according to the test methods described below.

[0041] In some embodiments, the bimodal medium-density polyethylene composition has a notched constant tensile load (NCTL) failure time greater than 700 hours at 30% yield stress. In some embodiments, the bimodal medium-density polyethylene composition has an NCTL failure time greater than 750 hours, or 800 hours, or 850 hours, or 900 hours, or 950 hours at 30% yield stress, wherein the NCTL failure time at 30% yield stress is measured according to the test methods described below.

[0042] In some embodiments, the bimodal medium-density polyethylene composition has a strain hardening modulus greater than 65 MPa. This document discloses and includes all individual values ​​and sub-ranges greater than 65 MPa. For example, the bimodal medium-density polyethylene composition may have a strain hardening modulus greater than 68 MPa, or greater than 70 MPa, or in the ranges of 65 MPa to 100 MPa, 70 MPa to 95 MPa, and 70 MPa to 90 MPa. The strain hardening modulus can be measured according to the test methods described below.

[0043] In some embodiments, the bimodal medium-density polyethylene composition has a yield tensile stress of 19 MPa to 30 MPa. All individual values ​​and sub-ranges of 19 MPa to 30 MPa are disclosed and included herein. For example, the bimodal medium-density polyethylene composition may have a yield tensile stress of 19 MPa to 27 MPa, 19 MPa to 26 MPa, 19 MPa to 25 MPa, 19 MPa to 24 MPa, 20 MPa to 27 MPa, 20 MPa to 26 MPa, 20 MPa to 25 MPa, or 20 MPa to 24 MPa, wherein the yield tensile stress is measured according to the test methods described below.

[0044] In some embodiments, the bimodal medium-density polyethylene composition has an elucidated bimodality (elucidated molecular weight distribution) as shown in a gel permeation chromatography (GPC) chromatogram of the bimodal medium-density polyethylene composition, wherein the chromatogram shows a peak representing the HMW polyethylene component, a peak representing the LMW polyethylene component, and a local minimum between the peak representing the HMW polyethylene component and the peak representing the LMW polyethylene component in the range of Log(molecular weight) (“Log(MW)”) 3.0 to 7.0, measured according to the bimodality test method described below.

[0045] In some embodiments, the bimodal medium-density polyethylene composition can be extruded at a processing speed greater than 300 m / min. In some embodiments, the bimodal medium-density polyethylene composition can be extruded at a processing speed greater than 325 m / min, or greater than 350 m / min, or greater than 375 m / min. The extrusion linear speed can be measured according to the test methods described below.

[0046] Bimodal medium-density polyethylene compositions can be prepared by polymerizing ethylene monomers and α-olefin comonomers in a reactor with a catalyst and optional other reagents and diluents. The polymerization can be carried out in the liquid phase, slurry phase, or gas phase, but is preferably carried out in the gas phase.

[0047] To produce a bimodal molecular weight distribution, the copolymer can be generated in a two-stage polymerization or a one-stage polymerization, but is preferably produced in a one-stage polymerization.

[0048] In a two-stage polymerization, a higher molecular weight polyethylene component is polymerized in a first reactor under a first set of process conditions using a first catalyst, and a lower molecular weight polyethylene component is produced in a second reactor under a second set of process conditions using a second catalyst. Examples of such production are described in the following patent disclosures, which are incorporated herein by reference: US 5,627,242; US 5,665,818; US 5,677,375; US2007 / 0043177 A1; EP-A-0 794 200; EP-B1-0 649992; EP-A-0 802 202; EP-B-634421 and WO 2009 / 148,487A1.

[0049] In one-stage polymerization, both the higher molecular weight polyethylene component and the lower molecular weight polyethylene component are polymerized in a single reactor using a bimodal catalyst. One-stage polymerization is preferably carried out in a fluidized bed gas-phase polymerization reactor (FB-GPP reactor) using a bimodal catalyst. Such reactors and methods are well known in the art. For example, FB-GPP reactors and methods are described in the following patent publications, which are incorporated herein by reference: US 3,709,853; US 4,003,712; US 4,011,382; US 4,302,566; US 4,543,399; US 4,882,400; US 5,352,749; US 5,541,270; US 2020 / 0024376A1, US2020 / 024376 A1, US2018 / 0155473 A1, and WO 2016 / 172279A1.

[0050] The optimal operating conditions for producing the polymers of this invention vary depending on the reactor used, the catalyst system used, and the specific properties required of the copolymer. The following discussion describes the general conditions for a typical FB-GPP reactor using the following bimodal catalyst:

[0051] The molar ratio of comonomer to ethylene fed into the reactor (C) x The molar ratio of comonomer to ethylene fed into the reactor (C2) is preferably at least 0.0001, more preferably at least 0.0002, and most preferably at least 0.0004. x / C2) is preferably at most 0.1, more preferably at most 0.05, and most preferably at most 0.02.

[0052] The partial pressure of ethylene in the reactor is preferably at least 690 kPa (100 psia), more preferably at least 830 kPa (120 psia), and most preferably at least 1300 kPa (190 psia). The partial pressure of ethylene in the reactor is preferably at most 2070 kPa (300 psia), more preferably at most 1720 kPa (250 psia), and most preferably at most 1590 kPa (230 psia).

[0053] The molar ratio of hydrogen to ethylene (H2 / C2) in the reactor varies depending on the molecular weight of the polymer produced. The hydrogen to ethylene (H2 / C2) molar ratio is preferably at least 0.0003, and more preferably at least 0.001. The hydrogen to ethylene (H2 / C2) molar ratio is preferably at most 0.01, and more preferably at most about 0.006.

[0054] The catalyst system (described below) can be fed into the polymerization reactor in either a "dry mode" or a "wet mode". The dry mode involves drying the powder or granules. The wet mode involves a suspension in an inert liquid (such as mineral oil). Preferably, the catalyst system is fed in a wet mode.

[0055] Optionally, the catalyst system may comprise a main catalyst plus a "trimming catalyst" that provides additional control over the ratio of higher molecular weight polyethylene components to lower molecular weight polyethylene components in the final copolymer. For example, the trimming catalyst may contain a catalytic material that increases the formation of either the higher or lower molecular weight polyethylene components in the composition. The use of trimming catalysts is described in more detail in PCT patent publications WO 2015 / 123172A1 and WO2015 / 123179A1, which are incorporated herein by reference.

[0056] The bed temperature in the reactor is preferably at least 70°C, more preferably at least 80°C, and most preferably at least 85°C. The bed temperature in the reactor is preferably at most 110°C, more preferably at most 100°C, and most preferably at most 95°C.

[0057] The reactants preferably flow through the reactor at a rate sufficient to maintain the reactor bed in a fluidized state.

[0058] Optionally, an inert liquid (referred to as an induced condensate (ICA)) can be added to the reactor to help cool it. The ICA is preferably (C5 to C6). 20 Alkanes, more preferably (C5 to C6) 10Alkanes, and most preferably pentane or 2-methylbutane (i.e., isopentane). Use of ICA is described in the following patent disclosures, which are incorporated herein by reference: US 4,453,399; US 4,588,790; US 4,994,534; US 5,352,749; US 5,462,999; and US 6,489,408. The concentration of ICA is preferably at least 1 mol%, and more preferably at least 3 mol%. The concentration of ICA is preferably at most 20 mol%, and more preferably at most 8 mol%.

[0059] Optionally, a continuous additive may be added to the reactor to control sheeting. Suitable continuous additives are commercially available as CA-200 and CA-300 from Univation Technologies LLC. The concentration of the continuous additive is preferably at least 0.5 ppmw, and more preferably at least 30 ppmw. The concentration of the continuous additive is preferably at most 200 ppmw, and more preferably at most 80 ppmw.

[0060] Polymerization conditions may also include one or more additives, such as chain transfer agents or accelerators. Chain transfer agents are well known and may be alkyl metals, such as diethylzinc. Accelerators are known as in US 4,988,783 and may include chloroform, CFC13, trichloroethane, and difluorotetrachloroethane. A scavenger may be used to react with moisture before reactor start-up and during reactor transition, a scavenger may be used to react with excess activator. The scavenger may be trialkylaluminum. Gas-phase polymerization can be operated without (unintentionally added) scavengers. Polymerization conditions for gas-phase polymerization reactors / methods may also include a certain amount (e.g., 0.5 ppm to 200 ppm based on all feed entering the reactor) of electrostatic control agents and / or continuous additives, such as aluminum stearate or polyethyleneimine. Electrostatic control agents may be added to the FB-GPP reactor to suppress the formation or accumulation of static charge therein.

[0061] Start-up (cold start) of a reactivated FB-GPP reactor or restart of an FB-GPP reactor during transition (hot start) includes the time period prior to reaching steady-state polymerization conditions. Start-up or restart may include the use of a polymer seed bed pre-loaded into the fluidized bed reactor. The polymer seed bed may consist of polyethylene powder; preferably, it is a bimodal copolymer similar to the bimodal medium-density polyethylene composition to be produced.

[0062] Start-up or restart of an FB-GPP reactor may also include a gas atmosphere transition, which involves purging the reactor's air or other unwanted gases with a dry (anhydrous) inert purge gas, followed by purging the FB-GPP reactor's dry inert purge gas with dry ethylene gas. The dry inert purge gas may consist essentially of molecular nitrogen (N2), argon, helium, or any mixture of two or more of these. When not in operation, the FB-GPP reactor contains an air atmosphere prior to start-up (cold start). The dry inert purge gas can be used to purge the air from a restarted FB-GPP reactor during the early stages of start-up to obtain an FB-GPP reactor with an atmosphere consisting of the dry inert purge gas. Before restart (e.g., after a seed bed change), the FB-GPP reactor in transition may contain an atmosphere of unwanted ICA or other unwanted gases or vapors. The dry inert purge gas can be used to purge unwanted vapors or gases from the FB-GPP reactor in transition during the early stages of restart to give the FB-GPP reactor an atmosphere consisting of the dry inert purge gas. Any dry, inert purge gas can be purged from the FB-GPP reactor by dry ethylene gas. The dry ethylene gas can be further contaminated with molecular hydrogen so that it is fed into the fluidized bed reactor as a mixture. Alternatively, dry molecular hydrogen can be introduced separately and after the atmosphere in the fluidized bed reactor has been converted to ethylene. The gas atmosphere conversion can occur before, during, or after heating the FB-GPP reactor to the reaction temperature for polymerization conditions.

[0063] Start-up or restart of an FB-GPP reactor also involves introducing reactants and reagents into it. Reactants include ethylene and α-olefins (e.g., 1-hexene). Reagents fed into the fluidized bed reactor include molecular hydrogen and induced condenser (ICA), as well as a bimodal catalyst system and trimmed catalyst.

[0064] Two-reactor polymerization of bimodal copolymers can be carried out using conventional catalyst systems. Single-reactor polymerization of bimodal copolymers is typically carried out using bimodal catalysts having one catalyst component particularly suitable for preparing the higher molecular weight (HMW) polyethylene fraction of the composition and another catalyst component particularly suitable for preparing the lower molecular weight (LMW) polyethylene fraction of the composition. Preferred bimodal catalyst systems preferentially direct a larger portion of the α-olefin comonomer into the higher molecular weight fraction; such bimodal catalysts (and methods for their preparation) are described in the following patent disclosures incorporated herein by reference: US2020 / 048379 A1, US2020 / 024376 A1, US 2018 / 0155473A1, WO 2016 / 172279 A1.

[0065] The following describes bimodal catalyst systems particularly suitable for generating copolymers: U.S. Patent Application 62 / 880,826, entitled "Bimodal Poly(Ethylene-Co-1-Alkene) Copolymer," filed July 31, 2019; U.S. Patent Application 62 / 990,549, entitled "Metal-Ligand Complexes," filed March 17, 2020; and PCT Application PCT / US20 / 30033, entitled "Metal-Ligand Complexes," filed April 27, 2020, all of which are incorporated herein by reference.

[0066] The preferred catalyst system comprises a bis(2-(pentamethylphenylamino)ethyl)amine dibenzylzirconium component and a (cyclopentadienyl)(1,5-dimethylindene)zirconium (X)2 component, wherein X is the fraction that achieves the valence of zirconium. X is preferably a halide ion or an alkyl group containing one to four carbon atoms, and more preferably a methyl group. Without being bound by theory, it is believed that bis(2-(pentamethylphenylamino)ethyl)amine dibenzylzirconium can efficiently prepare HMW polyethylene components of bimodal copolymers, and (cyclopentadienyl)(1,5-dimethylindene)dimethylzirconium can efficiently prepare LMW polyethylene components of bimodal copolymers.

[0067] In a bimodal catalyst system, the HMW and LMW catalysts can be kept separate until they are added to the reactor, in which case each catalyst can be unloaded or deposited on its own support. Preferably, the HMW and LMW catalysts in the bimodal catalyst system are deposited together on a single support.

[0068] Preferably, the catalyst of the bimodal catalyst system is applied to a solid support material, such as by spray drying. The support material preferably comprises a porous inorganic or organic material. More preferably, the support material comprises Group 2, 3, 4, 5, 13, or 14 metal oxides, and more preferably Group 13 or 14 metal oxides. Examples of inorganic oxide-type support materials are silica, alumina, titanium dioxide, zirconium oxide, thorium oxide, and mixtures of any two or more of these inorganic oxides. The solid support material is most preferably hydrophobic fumed silica (such as fumed silica treated with dimethyldichlorosilane).

[0069] Inorganic oxide support materials are porous and have variable surface area, pore volume, and average particle size. In some embodiments, the surface area is 50 to 1000 square meters per gram (m²). 2 The particles are 20 to 300 micrometers (μm) in size and have an average particle size of 20 to 300 micrometers (μm). Alternatively, the pore volume is 0.5 to 6.0 cubic centimeters per gram (cm³). 3 / g), and the surface area is 200m². 2 / g to 600m 2 / g. Alternatively, the pore volume is 1.1cm³. 3 / g to 1.8cm 3 / g, and the surface area is 245m² 2 / g to 375m 2 / g. Alternatively, the pore volume is 2.4 cm³. 3 / g to 3.7cm 3 / g, and the surface area is 410m² 2 / g to 620m 2 / g. Alternatively, the pore volume is 0.9 cm³. 3 / g to 1.4cm 3 / g, and the surface area is 390m² 2 / g to 590m 2 / g. Each of the above properties is measured using conventional techniques known in the art.

[0070] The support material can be pretreated by heating it in air before contacting the catalyst to obtain a calcined support material. The pretreatment involves heating the support material at a peak temperature of 350°C to 850°C, alternatively 400°C to 800°C, alternatively 400°C to 700°C, or alternatively 500°C to 650°C, for a period of 2 hours to 24 hours, alternatively 4 hours to 16 hours, alternatively 8 hours to 12 hours, or alternatively 1 hour to 4 hours, thereby preparing the calcined support material. In some aspects, the support material is a calcined support material.

[0071] Most preferably, the bimodal catalyst system comprises 1.0 wt% to 5.0 wt% of bis(2-(pentamethylphenylamino)ethyl)amine dibenzylzirconium and 0.1 wt% to 2.0 wt% of (cyclopentadienyl)(1,5-dimethylindene)dimethylzirconium or (1,3-dimethyl-4,5,6,7-tetrahydroindene)(methylcyclopentadienyl)dimethylzirconium applied to a fumed silica support.

[0072] The trimming catalyst can be any HMW or LMW catalyst. Preferably, the trimming catalyst is the same as the HMW or LMW catalyst in the bimodal catalyst system. For the most preferred catalytic system, the trimming catalyst is preferably (cyclopentadienyl)(1,5-dimethylindenyl)dimethylzirconium or (1,3-dimethyl4,5,6,7-tetrahydroindenyl)(methylcyclopentadienyl)dimethylzirconium bis(positive apical cyclopentadienyl)dimethylzirconium.

[0073] For convenience, the trimming catalyst is preferably fed into the reactor in the form of a solution in a hydrocarbon solvent. The hydrocarbon solvent can be an alkane or a mixture of alkanes, wherein each alkane independently has 5 to 20 carbon atoms, or 5 to 12 carbon atoms, or 5 to 10 carbon atoms. Each alkane can be independently acyclic or cyclic. Each acyclic alkane can be independently straight-chain or branched. Examples of acyclic alkanes include pentane, 1-methylbutane (isopentane), hexane, 1-methylpentane (isohexane), heptane, 1-methylhexane (isoheptane), octane, nonane, decane, or any two or more mixtures thereof. Examples of cyclic alkanes include cyclopentane, cyclohexane, cycloheptane, cyclooctane, cyclononane, cyclodecane, methylcyclopentane, methylcyclohexane, dimethylcyclopentane, or any two or more mixtures thereof.

[0074] Each catalyst in the bimodal catalyst system and the trimmed catalyst is preferably activated by contacting it with at least one activator. The activator is preferably a Lewis acid, a noncoordinate ion activator, an ionizing activator, a Lewis base, an alkylaluminoxane, or an alkylaluminoxane. The alkylaluminoxane can be a trialkylaluminum, an alkylaluminum halide, or an alkylaluminum alkoxide (diethylethoxyaluminum). The trialkylaluminum can be trimethylaluminum, triethylaluminum (“TEAL”), tripropylaluminum, or tri(2-methylpropyl)aluminum. The alkylaluminum halide can be diethylaluminum chloride. The alkylaluminum alkoxide can be diethylethoxyaluminum. The alkylaluminoxane can be methylaluminoxane (MAO), ethylaluminoxane, 2-methylpropylaluminoxane, or modified methylaluminoxane (MMAO). Each alkyl group in the alkylaluminum or alkylaluminoxane can be independently (C1 to C7) alkyl, alternatively (C1 to C6) alkyl, or alternatively (C1 to C4) alkyl. The molar ratio of the activator's metal (Al) to the metal (catalytic metal, such as Zr) of the specific catalyst compound can be from 1000:1 to 0.5:1, alternatively from 300:1 to 1:1, or alternatively from 150:1 to 1:1. Suitable activators are commercially available.

[0075] Each contact step between the activator and the catalyst can be carried out independently (a) in a separate vessel outside the GPP reactor (e.g., outside the FB-GPP reactor), (b) in the feed line to the GPP reactor, and / or (c) inside the GPP reactor (in situ). In option (a), once the catalyst of the bimodal catalyst system is activated, the bimodal catalyst system can be fed into the GPP reactor in the form of a dry powder, or alternatively in the form of a slurry in a nonpolar, aprotic (hydrocarbon) solvent. In option (c), the bimodal catalyst system can be fed into the reactor through a first feed line before activation, the first activator can be fed into the reactor through a second feed line, the trimmed catalyst can be fed into the reactor through a third feed line, and the second activator can be fed into the reactor through a fourth feed line. Any two of the first to fourth feed lines can be the same or different. One or more activators can be fed into the reactor in a "wet mode" as a solution in an inert liquid such as mineral oil or toluene, in a slurry mode as a suspension, or in a dry mode as a powder. Each contact step can be carried out at the same or different times in a separate vessel, feed line, or reactor, or at different times in the same vessel, feed line, or reactor, to obtain a bimodal catalyst system and a trimmed catalyst, respectively. Alternatively, the contact steps can be carried out simultaneously in the same vessel, feed line, or reactor to obtain a mixture of the bimodal catalyst system and the trimmed catalyst in situ.

[0076] The bimodal medium-density polyethylene composition may include two or more embodiments discussed herein.

[0077] This document also discloses a micro-irrigation drip tape. The micro-irrigation drip tape comprises the bimodal medium-density polyethylene composition described herein. A “micro-irrigation drip tape” is an extruded structure having an annular wall composed of a bimodal medium-density polyethylene composition, which defines an annular channel. In other words, a micro-irrigation drip tape is a pipe through which water or another liquid can pass. Figure 1 A micro-irrigation drip tape 10 is depicted having an annular wall 12 defining an annular channel 14. The annular wall 12 has an outer surface 16 and an inner surface 18. In an embodiment, the annular wall 12 of the micro-irrigation drip tape 10 is composed solely of a bimodal medium-density polyethylene composition.

[0078] The emitters 20 are arranged at intervals along the inner surface 18 of the annular wall 12. An "emitter" is an insert that controls the rate at which water or another liquid passes through an opening 22 (e.g., a hole, slit, or perforation), which is formed in the annular wall by mechanical drilling, cutting, or laser cutting. After the micro-irrigation drip tape 10 exits the extruder, the emitters 20 are placed on the inner surface 18 of the annular wall 12 while the formulation is transitioning from a molten state to a rigid state, allowing the emitters 20 to adhere to the micro-irrigation drip tape 10 via welding. The adhesion of the emitters 20 to the annular wall 12 is sufficient to hold the emitters 20 in place and maintain a leak-proof seal between the annular wall 12 and the emitters 20.

[0079] Micro-irrigation drip tape has a cross-sectional shape. Non-limiting examples of suitable cross-sectional shapes for micro-irrigation drip tape include ellipses, polygons, and combinations thereof. A "polygon" is a closed planar figure defined by at least three boundaries. A polygon can be a regular polygon or an irregular polygon with three, four, five, six, seven, eight, nine, ten, or more sides. Non-limiting examples of suitable polygonal shapes include triangles, squares, rectangles, rhombuses, trapezoids, parallelograms, hexagons, and octagons. An "ellipse" is a plane curve such that the sum of the distances from each point on its perimeter to two fixed points (foci) is equal. The center of the ellipse is the midpoint of the line segment connecting the two foci. An ellipse has a major axis (the longest diameter passing through the center). The minor axis is the shortest line passing through the center. The center of the ellipse is the intersection of the major and minor axes. A "circle" is a specific form of ellipse in which the two foci are located in the same position (at the center of the circle). Non-limiting examples of elliptical shapes include circles, ovals, and oval shapes. Figure 1 Depict a micro-irrigation drip tape 10 with a circular cross-sectional shape.

[0080] Test methods

[0081] density

[0082] Density was measured according to ASTM D792 and expressed in grams per cubic centimeter. 3 (g / cm 3 (or g / cc) indicates.

[0083] Melt flow rates (I2, I5, and I21)

[0084] Melt flow rate was determined according to the procedure described in ASTM D1238. This test method involves determining the extrusion rate of molten thermoplastic resin using an extruder. After a specific preheating time of 7 (+ / - 0.5) minutes, the resin was extruded through a die with a specific length and orifice diameter under specified temperature, load, and piston position in the barrel. Method B of ASTM D1238 was used. Method B is an automated timing method. Here, the sample is extruded from a melt indexer, and the piston stroke is timed over a predetermined distance, automatically controlled by the position of a movable arm located below the load frame. For I2 up to 10 g / 10 min, the predetermined distance is 6.35 mm; for I2 > 10 g / 10 min, the predetermined distance is 25.4 mm. The weight of the extrudate was determined by volume (distance × orifice area) and melt density. The melt density of polyethylene was taken as 0.7636 g / cm³. 3 Data are reported as MFR in g / 10min or dg / min. Samples can be run at loads of 21.6 kg, 5.0 kg, or 2.16 kg (i.e., I21, I5, or I2, respectively).

[0085] Notched Constant Tensile Load (NCTL)

[0086] According to ASTM D5397, the notched constant tensile load (NCTL) failure time is measured in hours at 30% yield stress. The test is performed at 50°C using a 10% Igepal aqueous solution. The sample thickness is 0.075" and the notch is extended to a depth of 20% of the thickness. The applied stress is equal to 30% of the resin yield stress measured at room temperature.

[0087] Tensile yield strength

[0088] The tensile yield strength (in MPa) of bimodal medium-density polyethylene compositions was measured using samples prepared from compression-molded pellets, according to ASTM D638 (crosshead speed of 2 inches / min, crosshead speed of 5.08 cm / min).

[0089] strain hardening modulus

[0090] According to ISO 18488:2015 (sample thickness 0.3 mm, crosshead speed 20 mm / min, test temperature 80 °C), the strain hardening modulus (in MPa) of bimodal medium-density polyethylene compositions was measured using samples prepared by compression molding granules.

[0091] Dynamic mechanical spectrum (crossing G' = G”)

[0092] Each sample was compressed and molded into a disc for rheological measurements. Discs were prepared by pressing the sample into a 3.0 mm thick plate and then cutting it into 25 mm diameter discs. Resin rheology was measured on an ARES-G2 rheometer from TA Instruments. ARES is a strain-controlled rheometer. A rotary actuator (servo motor) applied shear deformation in the form of strain to the sample. In response, the sample generated torque, which was measured by a transducer. Strain and torque were used to calculate dynamic mechanical properties such as modulus and viscosity. Viscoelastic properties of the sample were measured in the melt using a 25 mm diameter parallel plate apparatus at 190 °C as a function of the frequency of change (range 0.01 s⁻¹ to 100 s⁻¹). A small, constant strain (5%) was applied to ensure the measurements were performed in the linear viscoelastic region. The storage modulus (G'), loss modulus (G”), tanδ (G” / G'), and complex viscosity (η) of the resin were determined. The cross G' = G” is recorded in kPa as a measure of melt elasticity, where the lower the value, the higher the melt elasticity.

[0093] Absolute GPC (molecular weight distribution)

[0094] The chromatographic system consisted of a PolymerChar GPC-IR (Valencia, Spain) high-temperature GPC chromatograph equipped with an internal IR5 infrared detector (IR5) connected to a Precision Detector (now an Agilent Technologies 2040 model 2-angle laser scattering (LS) detector. A 15-degree angle was used for all light scattering measurements. The autosampler oven chamber was set to 160 degrees Celsius, and the column and detector chambers were set to 150 degrees Celsius. The columns used were four Agilent "Mixed A" 30 cm 20 μm linear mixed-bed columns. The chromatographic solvent used was 1,2,4-trichlorobenzene containing 200 ppm of butylated hydroxytoluene (BHT). The solvent source was nitrogen injection. The injection volume used was 200 μL, and the flow rate was 1.0 mL / min.

[0095] The calibration of the GPC column assembly was performed using 21 narrow molecular weight distribution polystyrene standards ranging from 580 g / mol to 8,400,000 g / mol, arranged in six “mixture” formulations with individual molecular weights spaced at least tenfold apart. The standards were purchased from Agilent Technologies. For molecular weights equal to or greater than 1,000,000 g / mol, the polystyrene standards were prepared at a concentration of 0.025 g per 50 mL of solvent, and for molecular weights less than 1,000,000 g / mol, at a concentration of 0.05 g per 50 mL of solvent. The polystyrene standards were dissolved by gentle stirring at 80 °C for 30 minutes. The molecular weights of the polystyrene standard peaks were converted to those of vinyl polymers using Equation 2 (as described by Williams and Ward in J. Polym. Sci., Polym. Let., 6, 621 (1968)).

[0096] M 聚乙烯 =A×(M) 聚苯乙烯 ) B Equation 2

[0097] Where M is the molecular weight, A has a value of 0.4315, and B equals 1.0.

[0098] A fifth-order polynomial is used to fit the corresponding vinyl polymer—the equivalent calibration point.

[0099] Total plate counts were performed on the GPC column assembly using decane without further dilution. Plate counts and symmetry were measured at 200 μL injections according to the following equations (Equation 3 and Equation 4).

[0100]

[0101] Where RV is the retention volume in milliliters, peak width is in milliliters, peak maximum is the maximum height of the peak, and half height is half the height of the peak maximum.

[0102]

[0103] Where RV is the retention volume in milliliters, and peak width is in milliliters, peak maximum is the position of the peak maximum, one-tenth height is one-tenth of the peak maximum height, and a subsequent peak refers to the tail of a peak at a retention volume later than the peak maximum, while a preceding peak refers to the front of a peak at a retention volume earlier than the peak maximum. The plate count of the chromatographic system should be greater than 18,000, and the symmetry should be between 0.98 and 1.22.

[0104] Samples were prepared semi-automatically using PolymerChar "Instrument Control" software, with a target sample weight of 2 mg / ml. Solvent (containing 200 ppm BHT) was added to a pre-bubbled, diaphragm-capped vial using a PolymerChar high-temperature autosampler. The sample was dissolved at 160°C for 3 hours with "low-speed" oscillation.

[0105] To monitor deviations over time, a flow rate marker (decane) was introduced into each sample via a micropump controlled by a PolymerChar GPC-IR system. This flow rate marker (FM) was used to linearly correct the pump flow rate (nominal flow rate) for each sample by comparing the RV (RV(FM sample)) of the corresponding decane peak within the sample with the RV (RV(FM calibrated)) of the decane peak within the narrow standard calibration. It was then assumed that any variation in the decane marker peak time was linearly related to the flow rate (effective flow rate) throughout the run. To facilitate the highest accuracy in RV measurement of the flow marker peak, a least-squares fitting procedure was used to fit the peak values ​​of the flow marker concentration chromatogram to a quadratic equation. The first derivative of the quadratic equation was then used to solve for the true peak position. After calibration based on the flow marker peak, the effective flow rate (relative to the narrow standard calibration) was calculated according to Equation 5. (Seen using PolymerChar GPCOne) TM The software processes the flow marker peaks. Acceptable flow rate correction ensures that the effective flow rate is within 0.5% of the nominal flow rate.

[0106] Flow rate 有效 =flow rate 标称 ×(RV(FM 校准的 ) / RV(FM 样品 Equation 5

[0107] A systematic method for determining multi-detector offsets was developed in conjunction with Balke, Mourey et al. (Mourey and Balke, Chromatography Polym. Chapter 12, (1992)) (Balke, Thitiratsakul, Lew, Cheung, Mourey, Chromatography Polym. Chapter 13, (1992)), thereby utilizing PolymerChar GPCOne. TM The software optimizes the triple detector logarithmic (MW and IV) results from wide homopolymer polyethylene standards (Mw / Mn>3) with the narrow standard column calibration results from the narrow standard calibration curve.

[0108] Absolute molecular weight data were obtained using PolymerChar GPCOne. TM The software was obtained in a manner consistent with the following publications: Zimm (Zimm, BH, J. Chem. Phys., 16, 1099 (1948)) and Kratochvil (Kratochvil, P., Classical Light Scattering from Polymer Solutions, Elsevier, Oxford, NY (1987)). The total injection concentration used for determining the molecular weight was obtained from the mass detector area and the mass detector constant, which was derived from one of suitable linear polyethylene homopolymers or polyethylene standards with known weight-average molecular weights. The calculated molecular weight (using GPCOne) TM The light scattering constants and a refractive index concentration coefficient of dn / dc of 0.104 from one or more polyethylene standards mentioned below are typically obtained. The mass detector response (IR5) and light scattering constants (using GPCOne) are also used. TM The determination should be performed using linear standards with a molecular weight exceeding approximately 50,000 g / mol. Viscometer calibration (using GPCOne) TM The determination can be performed using the method described by the manufacturer, or alternatively, by using published values ​​of a suitable linear standard (such as Standard Reference Material (SRM) 1475a), which are available from the National Institute of Standards and Technology (NIST). The viscometer constant is calculated (using GPCOne). TM The specific viscosity area (DV) of the calibration standard and the injection mass are related to its intrinsic viscosity. It is assumed that the chromatographic concentration is low enough to eliminate the effect of the second viral coefficient (the effect of concentration on molecular weight).

[0109] Absolute weight-average molecular weight (MW) (Abs) (using GPCOne) TM The molecular weight and intrinsic viscosity responses are obtained by dividing the area of ​​the light scattering (LS) integral chromatogram (calculated from the light scattering constant) by the mass recovered from the mass constant and the area of ​​the mass detector (IR5). The molecular weight and intrinsic viscosity responses are obtained at the chromatographic ends where the signal-to-noise ratio decreases (using GPCOne). TM Linear extrapolation.

[0110] Absolute number average molecular weight (Mn) (Abs) ), weight average (Mw) (Abs) ) and absolute z-average molecular weight (Mz) (Abs) Calculate according to the following equation 6-8:

[0111]

[0112] Average short chain branching frequency

[0113] Calibration of the IR5 detector ratio method was performed using at least ten ethylene polymer standards (ethylene polymer homopolymers and ethylene / octene copolymers) with known short-chain branching (SCB) frequencies (the comonomer content of the reference materials was determined using 13C NMR analysis according to the techniques described in the following literature: e.g., U.S. Patent No. 5,292,845 (Kawasaki et al.) and J. Cranall, Rev. Macromol. Chem. Phys., C29, 201-317, which is incorporated herein by reference). These frequencies ranged from homopolymers (0 SCB / 1000 total C) to approximately 50 SCB / 1000 total C, where total C equals the carbon in the main chain plus the carbon in the branches. Each standard had a weight-average molecular weight of 36,000 g / mol to 126,000 g / mol and a molecular weight distribution of 2.0 to 2.5, as determined by GPC.

[0114] For each of the copolymer standards, calculate the "IR5 height ratio (or "IR5") of the "area response of the IR5 methyl channel sensor minus the baseline" to the "area response of the IR5 measurement channel sensor minus the baseline". 甲基通道高度 / IR5 测量通道高度 (Including standard filters and filter wheels supplied by PolymerChar: part number IR5_FWM01 as part of the GPC-IR instrument). The linear fit of the wt% comonomer frequency relative to the "IR5 height ratio" is constructed in the form of the following Equation 9:

[0115] % comonomer by weight = A0 + [A1(IR5)] 甲基通道面积 / IR5 测量通道面积 Equation 9

[0116] The coefficients are A0 = -47.94 and A1 = 239.0.

[0117] Therefore, a GPC-CC (GPC-comonomer content) plot (comonomer weight % vs. lgMW) can be obtained. If there is significant spectral overlap between the molecular weight determined at each chromatographic slice and the comonomer end-capping (methyl) group, then end-group correction of the % comonomer weight data can be performed by decapping the end-capping mechanism. The SCB frequency for each slice is lgMw. i SCB i It can be calculated using the following relationship:

[0118] SCBi =∑ i (0.8 * comonomer weight %) i Equation 10

[0119] For ethylene-octene copolymer

[0120] as well as

[0121]

[0122] For ethylene-hexene copolymers.

[0123] Then the average SCB frequency over the entire distribution can be calculated.

[0124] Average SCB = ∑ i (wtGPC i *SCB i Equation 12

[0125] Deconvolution of GPC chromatography

[0126] The chromatogram was fitted to high molecular weight (HMW) fractions and low molecular weight (LMW) fractions using a Flory distribution, which was broadened using the following normal distribution function:

[0127] For the log M axis, 501 equally spaced Log(M) points with a spacing of 0.01 are established between 2 and 7 to represent the molecular weight range between 100 and 10,000,000, where Log is a logarithmic function to the base 10.

[0128] For any given Log(M), the population of the Flory distribution takes the form of Equation 13:

[0129]

[0130] Where Mw is the weight-average molecular weight of the Flory distribution, and M is the molecular weight point on the x-axis (10^[Log(M)]).

[0131] The Flory distribution weighted score is widened at each equidistant Log(M) exponent based on the normal distribution function, with the width denoted by Log(M),σ; and the current M exponent is denoted as Log(M),μ.

[0132]

[0133] It should be noted that the area of ​​the distribution (dW) before and after applying the diffusion function differs. f / dLogM) is normalized to one as a function of Log(M).

[0134] The two weight fraction distributions of LMW and HMW components, or components 1 and 2, dW f 1 and dW f 2. Represented by two unique objective values ​​Mw1 and Mw2, and total components A1 and A2. Both distributions are broadened by the same width σ. The two distributions are summed as follows:

[0135] dW f =A1dW f1 +A2dW f2 Equation 15

[0136] Where: A1 + A2 = 1

[0137] The weighted fraction results of the measured GPC molecular weight distribution (from conventional GPC) were interpolated along 501 logM points using a second-order polynomial. Microsoft Excel was used. TM The 2010 Solver was used to minimize the sum of squares of the residuals of the equisional spatial ranges of the interpolated molecular weight distribution and the two broadened Flory distribution components (σ1 and σ2) at 501 LogM points, weighted by their respective components A1 and A2.

[0138] The initial values ​​for iteration of each component are as follows:

[0139] Component 1: Mw = 30,000, σ = 0.300, and A = 0.475

[0140] Component 2: Mw = 250,000, σ = 0.300, and A = 0.475

[0141] (Note that σ1 = σ2 and A1 + A2 = 1)

[0142] The boundaries between components 1 and 2 are: σ is restricted such that σ > 0.001 yields approximately 2.00 Mw / Mn, and σ < 0.450 yields approximately 5.71 Mw / Mn. Component A is restricted between 0.000 and 1.000. Mw is restricted between 2,500 and 2,000,000.

[0143] In Excel Solver TM Select the "GRG Nonlinear" engine, set the precision to 0.00001, and the convergence to 0.0001. Obtain the converged solution (in all cases shown, the solution converges within 60 iterations).

[0144] The average short-chain branching frequency distributions of the LMW and HMW components were obtained based on the dW values ​​of the two components.f1 and dW f2 The weight fraction distribution is estimated by taking the proportion of short chain branching, which is obtained from the above deconvolution and averaged for each component.

[0145] Bimodality test method

[0146] GPC chromatograms containing the local maximum log(MW) values ​​of the LMW and HMW polyethylene component peaks are obtained by plotting dWf / dLogM (mass detector response) on the y-axis and LogM on the x-axis. The presence or absence of local minimum values ​​between the LMW and HMW polyethylene component peaks is observed to determine the presence or absence of bimodality in the resolution. dWf is the change in weight fraction, dLogM is also called dLog(MW) and is the logarithmic change in molecular weight, and LogM is also called Log(MW) and is the logarithm of molecular weight. Figure 2 The absolute GPC chromatograms of certain embodiments and comparative examples of the present invention are shown, which display the local maxima of the LMW polyethylene component peak and the HMW polyethylene component peak, as well as the local minimum between the LMW polyethylene component peak and the HMW polyethylene component peak, to depict the points of the bimodality test method.

[0147] Extrusion line speed

[0148] Extrusion line speed is a critical parameter in drip micro-irrigation production as it determines the machine utilization rate per production unit. Therefore, high line speeds are beneficial for belt manufacturers. The line has been optimized in terms of die and pin geometry to allow for the highest possible line speed. To measure the maximum extrusion line speed, the line speed was incrementally increased from 200 m / min to 250 m / min, 300 m / min, 350 m / min, and 400 m / min. The line speed was recorded using extrusion parameters displayed by the control unit. The highest line speed recorded after the belt had been running stably for several minutes (e.g., 30 minutes) was considered the maximum extrusion line speed for this embodiment. Lower line speeds (where the product still runs stably) where extrudate breakage occurs at this speed are considered the maximum extrusion line speed.

[0149] Example

[0150] Materials used

[0151] The following materials are included in the embodiments discussed below.

[0152] FINGERPRINT TMDFDC 7525 (unimodal ethylene / 1-hexene copolymer medium-density polyethylene) was used as Comparative Example (CE) 1 and is commercially available from The Dow Chemical Company (Midland, MI) of Midland, Michigan.

[0153] Preparation of Comparative Examples 2 to 4 and Examples 5 to 7 of the present invention

[0154] Exemplary bimodal medium-density polyethylene compositions, named Comparative Examples (CE) 2, 3, and 4 and Examples (IE) 5, 6, and 7 of the present invention, were prepared in a single reactor via gas-phase polymerization. The main catalyst was fed via a 0.25-inch (") injection tube to a reactor suitable for use as a UNIPOL. TM The polyethylene reactor was purchased from Univation Technologies. The fine-tuning catalyst was also fed into the polyethylene reactor via the same 0.25" injection tube at a rate sufficient to provide the desired resin flow index. The reactor gas composition was controlled by metering the feed into the polyethylene reactor at a rate sufficient to maintain the desired ethylene partial pressure, the molar ratio of comonomer to ethylene (C2), the molar ratio of hydrogen (H2) to ethylene (C2), and the amount of isopentane. Based on the ethylene feed rate to the reactor, an additive, commercially available as CA-300 from Univation Technologies, was separately fed into the polyethylene reactor at a rate sufficient to maintain an additive concentration of approximately 35 to 55 parts by weight per million parts by weight (ppmw). The polyethylene reactor temperature was maintained at the desired temperature, and the reactor residence time was approximately 1.8 to 2.5 hours. The reactor bed weight was maintained by discharging the granular resin into a discharge tank, which was purged with nitrogen and then again with a mixture of nitrogen and steam before being poured into the fiber bundles. Table 1A lists the polymerization conditions for CE 2, CE 3, and CE 4. Table 1B lists the polymerization conditions for IE 5, IE... Aggregation conditions in IE 6 and IE 7.

[0155] The product was mixed with additives (500 ppm calcium stearate, 1300 ppm Irganox). TM 1010 and 1300ppm Irgafos TM 168) combined and fed into a continuous mixer (Kobe Steel, Ltd. LCM-100 continuous mixer), which is closely coupled to a gear pump and equipped with a melt filter and an underwater granulation system.

[0156] Comparative examples and characteristics of embodiments of the present invention are provided in Tables 2A and 2B below. In Tables 2A and 2B, "HMW" refers to the high molecular weight polyethylene component, and "LMW" refers to the low molecular weight polyethylene component.

[0157] Micro-irrigation drip tapes were formed from a bimodal medium-density polyethylene composition using a Mailefer International Oy Extruder MXC 60-36D with a diameter of 60 mm and a length / diameter (L / D) ratio of 36. The extruder employed a suitable temperature distribution to achieve a melt temperature of 240°C. The extruder was equipped with a 34.5 mm diameter annular die and 32.5 mm diameter pins (1 mm gap). The inner diameter of each micro-irrigation drip tape was 16 mm. The thickness of the annular wall was adjusted by varying the extruder's rotational speed (rpm) and linear speed. Each micro-irrigation drip tape was then calibrated and water-cooled. During tape cooling, just after exiting the extruder, the emitter was placed on the inner surface of the annular wall. A perforation was made in-line along this line at the emitter in the annular wall before passing through a mechanical drilling device or laser-cutting the wound tape. Extrusion linear speeds are provided in Tables 2A and 2B.

[0158] High-speed tape processing is a key characteristic and requirement for the efficient production of drip irrigation tape. Processing tests were conducted on the Merafell test line PIL032-miniFT. This line reflects an entry-level model for the drip irrigation market that is readily available from Merafell upon ordering. The line has been modified with an RCI 32 type tape traction device, enabling higher line speeds of 300 m / min to 400 m / min for development purposes. For calibration, a BRI 32-16m type Merafell vacuum chamber with a dryer was used.

[0159] Examples 5, 6, and 7 of the present invention were processed at linear speeds up to 400 m / min and according to the process settings in the table below: For Examples 5 and 6, 8-mil tapes were prepared. Example 7 prepared two different thicknesses, 8 mil (0.20 mm) (designated IE 7A) and 6 mil (0.15 mm) (designated IE 7B). The process parameters for the embodiments of the present invention are shown in Table A.

[0160] Table A - Process parameters of the micro-irrigation tape in the embodiments of the present invention

[0161]

[0162] Table 1A - Polymerization conditions of Comparative Examples 2 to 4

[0163]

[0164]

[0165] a Contains bis(2-pentamethylphenylamide)ethyl)amine dibenzylzirconium, (1,3-dimethyl-4,5,6,7-tetrahydroindene)(methylcyclopentadienyl)dimethylzirconium, methylaluminoxane (MAO), and pyrolytic silica (which can be used as...). TS-610 is a spray-dried mixture of mineral oil slurry (obtained commercially from Cabot Corporation).

[0166] b Contains bis(2-pentamethylphenylamino)ethyl)amine dibenzylzirconium, (cyclopentadienyl)(1,5-dimethylindenyl)dimethylzirconium, methylaluminoxane (MAO), and pyrolytic silica (which can be used as...). TS-610 is a spray-dried mixture of mineral oil slurry (obtained commercially from Cabot Corporation).

[0167] c 0.04 wt% (1,3-dimethyl-4,5,6,7-tetrahydroindene)(methylcyclopentadienyl)dimethylzirconium bis(n-butylcyclopentadienyl)dimethylzirconium in isopentane

[0168] d 0.04 wt% (cyclopentadienyl)(1,5-dimethylindenyl)dimethylzirconium in isopentane

[0169] Table 1B - Polymerization conditions of Examples 5 to 7 of the present invention

[0170]

[0171]

[0172] a Contains bis(2-pentamethylphenylamide)ethyl)amine dibenzylzirconium, (1,3-dimethyl-4,5,6,7-tetrahydroindene)(methylcyclopentadienyl)dimethylzirconium, methylaluminoxane (MAO), and pyrolytic silica (which can be used as...). TS-610 is a spray-dried mixture of mineral oil slurry (obtained commercially from Cabot Corporation).

[0173] b Contains bis(2-pentamethylphenylamino)ethyl)amine dibenzylzirconium, (cyclopentadienyl)(1,5-dimethylindenyl)dimethylzirconium, methylaluminoxane (MAO), and pyrolytic silica (which can be used as...). TS-610 is a spray-dried mixture of mineral oil slurry (obtained commercially from Cabot Corporation).

[0174] c 0.04 wt% (1,3-dimethyl-4,5,6,7-tetrahydroindene)(methylcyclopentadienyl)dimethylzirconium bis(n-butylcyclopentadienyl)dimethylzirconium in isopentane

[0175] d 0.04 wt% (cyclopentadienyl)(1,5-dimethylindenyl)dimethylzirconium in isopentane

[0176] Table 2A - Characteristics of Comparative Examples 1 to 4

[0177]

[0178]

[0179] 1 NM = Not measured.

[0180] 2 SCB / 1000C = Average short-chain branching frequency per 1000 carbons

[0181] 3 Comparative Example 1 is a single-peak resin, so these parameters are not applicable.

[0182] Table 2B - Characteristics of Embodiments 5 to 7 of the present invention

[0183]

[0184]

[0185] 1 NM = Not measured.

[0186] 2 SCB / 1000C = Average short-chain branching frequency per 1000 carbons

[0187] 3 Maximum extrusion line speed of Embodiment 7A (8 mils) and Embodiment 7B (6 mils) of the present invention

[0188] As can be seen from Tables 2A and 2B, the embodiments of the present invention have an NCTL failure time of >1000 hours, a strain hardening modulus of >65 MPa, and a maximum extrusion line speed of 400 m / min. No comparative examples have a combination of these parameters.

[0189] Unless expressly excluded or otherwise limited, every document cited herein (if any), including any cross-referenced or related patent or application and any patent application or patent claiming priority or benefit thereof, is incorporated herein by reference in its entirety. No reference to any document acknowledges it as prior art to any invention disclosed or claimed herein, or as teaching, indicating, or disclosing any such invention, alone or in combination with any other referenced document. Furthermore, in the event of any conflict between the meaning or definition of any term in this document and the meaning or definition of the same term in any document incorporated by reference, the meaning or definition given to the term in this document shall prevail.

[0190] While specific embodiments of the invention have been described and illustrated, it will be apparent to those skilled in the art that many other changes and modifications can be made without departing from the spirit and scope of the invention. Therefore, it is intended that all such changes and modifications falling within the scope of the invention be covered in the appended claims.

Claims

1. A bimodal medium density polyethylene composition comprising (i) a high molecular weight (HMW) polyethylene component comprising an ethylene / alpha-olefin copolymer and (ii) a low molecular weight (LMW) polyethylene component comprising an ethylene / alpha-olefin copolymer; the bimodal medium density polyethylene composition having: (a) a density of 0.937 g / cm 3 to 0.946 g / cm 3 to 0.946 g / cm (b) a high load melt index (I21) of from 7 g / 10 min to 20 g / 10 min; (c) a cross-over G’ = G” of from 30 kPa to 50 kPa; (d) a notched constant tensile load failure time of greater than 700 hours at 30% yield stress as measured according to ASTM D5397; and (e) a strain hardening modulus greater than 65 MPa; and wherein the LMW polyethylene component has an average short chain branching frequency of greater than 0.9 SCB / 1000 carbons; wherein the HMW polyethylene component has a weight average molecular weight Mw of from 300,000 g / mol to 600,000 g / mol; and wherein the HMW polyethylene component is present in an amount of from 45 wt% to 60 wt% based on the total weight of the bimodal medium density polyethylene composition.

2. The bimodal medium density polyethylene composition of claim 1, wherein the HMW polyethylene component has an average short chain branching frequency (HMW SCB / 1000C) and satisfies the following equation: 3094 · HMW wt% - 30.52 · cross-over G’ = G” - 160.1 · (LMW SCB / 1000C / HMW SCB / 1000C) - 211.7 > 0 wherein “HMW wt%” is the weight percent of the HWM polyethylene present in the bimodal medium density polyethylene composition based on the total weight of the bimodal medium density polyethylene composition, “cross-over G’ = G” is the cross-over G’ = G” of the bimodal medium density polyethylene composition, “LMW SCB / 1000C” is the average short chain branching frequency of the LMW polyethylene component, and “HMW SCB / 1000C” is the average short chain branching frequency of the HMW polyethylene component.

3. The bimodal medium density polyethylene composition of any preceding claim, wherein the bimodal medium density polyethylene composition has a resolved bimodality (resolved molecular weight distribution) shown in a chromatogram of a gel permeation chromatography (GPC) of the bimodal medium density polyethylene composition, wherein the chromatogram shows a peak representing the HMW polyethylene component, a peak representing the LMW polyethylene component, and a local minimum in the Log(molecular weight) (“Log(MW)”) range of from 3.0 to 7.0 between the peak representing the HMW polyethylene component and the peak representing the LMW polyethylene component, measured according to the Bimodality Test Method described in the disclosure above.

4. The bimodal medium density polyethylene composition of any preceding claim, wherein the HMW polyethylene component has an average short chain branching frequency of greater than 1.4 SCB / 1000 carbons. ​ 5. The bimodal medium density polyethylene composition of any preceding claim, wherein the ratio of the weight average molecular weight Mw of the HMW polyethylene component to the weight average molecular weight Mw of the LMW polyethylene component is from 16 to 27.

6. The bimodal medium density polyethylene composition of any preceding claim, wherein the bimodal medium density polyethylene composition is capable of being extruded at a processing speed of greater than 350 m / min.

7. A micro-irrigation drip tape comprising the bimodal medium density polyethylene composition of claim 1.

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