# Patent

## Title
Polyethylene compositions, process and closures

## Abstract

A dual reactor solution process gives high density polyethylene compositions containing a first ethylene copolymer and a second ethylene copolymer and which have good processability and ESCR properties. The polyethylene compositions are suitable for compression molding or injection molding applications and are particularly useful in the manufacture of caps and closures for bottles or containers.

## Background
The present disclosure relates to polyethylene compositions that are useful in the manufacture of molded articles such as for example closures for containers or bottles.
Polymer compositions useful for molding applications, such as caps and closures for bottles are known. One-piece closures, such as screw caps have been made from high density polyethylene resins. The use of high density resin polyethylene is required to impart sufficient stiffness to the closures, while broader molecular weight distributions are also desirable in order to provide good flow properties and to improve environmental stress crack resistance (ESCR).
Polyethylene blends produced with conventional Ziegler-Natta or Phillips type catalysts systems can be made having suitably high density and ESCR properties, see for example, WO 00/71615 and U.S. Pat. No. 5,981,664. However, the use of conventional catalyst systems typically produces significant amounts of low molecular weight polymer chains having high comonomer contents, which results in resins having non-ideal organoleptic properties.
Examples of high density multimodal polyethylene blends made using conventional catalyst systems for the manufacture of caps or closures are taught in U.S. Patent Nos 2005/0004315A1; 2005/0267249A1; as well as WO 2006/048253, WO 2006/048254, WO 2007/060007; and EP 2,017,302A1. Further high density, multimodal polyethylene blends made by employing conventional Ziegler-Natta catalysts are disclosed in U.S. Patent Nos. 2009/0062463A1; 2009/0198018; 2009/0203848 and in WO 2007/130515, WO 2008/136849 and WO 2010/088265.
In contrast to traditional catalysts, the use of so called single site catalysts (such as “metallocene” and “constrained geometry” catalysts) provides resin having lower catalyst residues and improved organoleptic properties as taught by U.S. Pat. No. 6,806,338. The disclosed resins are suitable for use in molded articles. Further resins comprising metallocene catalyzed components and which are useful for molding applications are described in U.S. Pat. Nos. 7,022,770; 7,307,126; 7,396,878 and 7,396,881 and 7,700,708.
U.S. Patent Application Publication No. 2011/0165357A1 discloses a blend of metallocene catalyzed resins which is suitable for use in pressure resistant pipe applications.
U.S. Patent Application Publication No. 2006/0241256A1 teaches blends formulated from polyethylenes made using a hafnocene catalyst in the slurry phase.
A bimodal resin having a relatively narrow molecular weight distribution and long chain branching is described in U.S. Pat. No. 7,868,106. The resin is made using a bis-indenyl type metallocene catalyst in a dual slurry loop polymerization process and can be used to manufacture caps and closures.
U.S. Pat. No. 6,642,313 discloses multimodal polyethylene resins which are suitable for use in the manufacture of pipes. A dual reactor solution process is used to prepare the resins in the presence of a phosphinimine catalyst.
Narrow molecular weight polyethylene blends comprising a metallocene produced polyethylene component and a Ziegler-Natta or metallocene produced polyethylene component are reported in U.S. Pat. No. 7,250,474. The blends can be used in blow molding and injection molding applications such as for example, milk bottles and bottle caps respectively.
In U.S. Pat. No. 8,022,143 we disclosed a resin composition having a good balance of toughness, ESCR, processability, and organoleptic properties for use in the manufacture of caps and closures. The resins were made using a single site catalyst system in a dual reactor solution process, to provide bimodal polyethylene compositions in which comonomer was present in both a high and a low molecular weight component. The disclosed resins had a normal comonomer distribution in that the low molecular weight component had a larger amount of comonomer than did the high molecular weight component. In U.S. Pat. No. 8,962,755 we disclosed that by adding more comonomer to the high molecular weight component of these resins, we can improve the ESCR properties.
We now report a new polyethylene composition which is suitable for molding applications, with a good balance of ESCR and processability and which has improved melt strength.
The present disclosure provides a polyethylene composition that can be used in the manufacture of caps and closures.
Provided in one embodiment of the disclosure is a closure, the closure comprising a bimodal polyethylene composition comprising: (1) 10 to 70 wt % of a first ethylene copolymer having a melt index I2, of less than 0.4 g/10 min; a molecular weight distribution Mw/Mn, of less than 2.7; and a density of from 0.920 to 0.955 g/cm3; and (2) 90 to 30 wt % of a second ethylene copolymer having a melt index I2, of from 250 to 20,000 g/10 min; a molecular weight distribution Mw/Mn, of less than 2.7; and a density higher than the density of the first ethylene copolymer, but less than 0.965 g/cm3; wherein the density of the second ethylene copolymer is less than 0.035 g/cm3 higher than the density of the first ethylene copolymer; the ratio (SCB1/SCB2) of the number of short chain branches per thousand carbon atoms in the first ethylene copolymer (SCB1) to the number of short chain branches per thousand carbon atoms in the second ethylene copolymer (SCB2) is greater than 1.0; and wherein the bimodal polyethylene composition has a molecular weight distribution Mw/Mn, of from 5.0 to 13.0, a density of from 0.949 to 0.958 g/cm3, a stress exponent of less than 1.53, a melt index (I2) of from 0.3 to 3.0 g/10 min, and which satisfies the following: 400,000≦Mz≦500,000.
Provided in one embodiment of the disclosure is a process to prepare a polyethylene composition, the polyethylene composition comprising: (1) 10 to 70 wt % of a first ethylene copolymer having a melt index I2, of less than 0.4 g/10 min; a molecular weight distribution Mw/Mn, of less than 2.7; and a density of from 0.920 to 0.955 g/cm3; and (2) 90 to 30 wt % of a second ethylene copolymer having a melt index I2, of from 250 to 20,000 g/10 min; a molecular weight distribution Mw/Mn, of less than 2.7; and a density higher than the density of the first ethylene copolymer, but less than 0.965 g/cm3; wherein the density of the second ethylene copolymer is less than 0.035 g/cm3 higher than the density of the first ethylene copolymer; the ratio (SCB1/SCB2) of the number of short chain branches per thousand carbon atoms in the first ethylene copolymer (SCB1) to the number of short chain branches per thousand carbon atoms in the second ethylene copolymer (SCB2) is greater than 1.0; and wherein the bimodal polyethylene composition has a molecular weight distribution Mw/Mn, of from 5.0 to 13.0, a density of from 0.949 to 0.958 g/cm3, a stress exponent of less than 1.53, a melt index (I2) of from 0.3 to 3.0 g/10 min, a broadness factor defined as (Mw/Mn)/(Mz/Mw) of ≦2.75, and which satisfies the following: 400,000≦Mz≦500,000; the process comprising contacting at least one single site polymerization catalyst system with ethylene and at least one alpha-olefin under solution polymerization conditions in at least two polymerization reactors.
Provided in one embodiment of the disclosure is a bimodal polyethylene composition comprising: (1) 10 to 70 wt % of a first ethylene copolymer having a melt index I2, of less than 0.4 g/10 min; a molecular weight distribution Mw/Mn, of less than 2.7; and a density of from 0.920 to 0.955 g/cm3; and (2) 90 to 30 wt % of a second ethylene copolymer having a melt index I2, of from 250 to 20,000 g/10 min; a molecular weight distribution Mw/Mn, of less than 2.7; and a density higher than the density of the first ethylene copolymer, but less than 0.965 g/cm3; wherein the density of the second ethylene copolymer is less than 0.035 g/cm3 higher than the density of the first ethylene copolymer; the ratio (SCB1/SCB2) of the number of short chain branches per thousand carbon atoms in said first ethylene copolymer (SCB1) to the number of short chain branches per thousand carbon atoms in the second ethylene copolymer (SCB2) is greater than 1.0; and wherein the bimodal polyethylene composition has a molecular weight distribution Mw/Mn, of from 5.0 to 13.0, a density of from 0.949 to 0.958 g/cm3, a stress exponent of less than 1.53, a melt index (I2) of from 0.3 to 3.0 g/10 min, and which satisfies the following: 400,000≦Mz≦500,000.
Provided in one embodiment of the disclosure is a bimodal polyethylene composition comprising: (1) 10 to 70 wt % of a first ethylene copolymer having a melt index I2, of less than 0.4 g/10 min; a molecular weight distribution Mw/Mn, of less than 2.7; and a density of from 0.920 to 0.940 g/cm3; and (2) 90 to 30 wt % of a second ethylene copolymer having a melt index I2, of from 1000 to 20,000 g/10 min; a molecular weight distribution Mw/Mn, of less than 2.7; and a density higher than the density of the first ethylene copolymer, but less than 0.965 g/cm3; wherein the density of the second ethylene copolymer is less than 0.035 g/cm3 higher than the density of the first ethylene copolymer; the ratio (SCB1/SCB2) of the number of short chain branches per thousand carbon atoms in the first ethylene copolymer (SCB1) to the number of short chain branches per thousand carbon atoms in the second ethylene copolymer (SCB2) is greater than 1.0; and wherein the bimodal polyethylene composition has a molecular weight distribution Mw/Mn, of from 6.0 to 12.0, a density of from 0.949 to 0.957 g/cm3, a stress exponent of less than 1.50, a melt index (I2) of from 0.3 to 2.0 g/10 min, a Rosand melt strength of at least 3.0 cN, and which satisfies the following: 400,000≦Mz≦500,000.
In an embodiment of the disclosure, the bimodal polyethylene composition has an ESCR Condition B (10% IGEPAL) of at least 150 hrs.
In an embodiment of the disclosure, the bimodal polyethylene composition has a molecular weight distribution, Mw/Mn, of from 6.0 to 11.0.
In an embodiment of the disclosure, the bimodal polyethylene composition has melt index I2, of from 0.3 to less than 1.0 g/10 min.
In an embodiment of the disclosure, the bimodal polyethylene composition has a density of from 0.951 to 0.955 g/cm3.
In an embodiment of the disclosure, the bimodal polyethylene composition has a composition distribution breadth index (CDBI25) of greater than 55% by weight.
In an embodiment of the disclosure, the bimodal polyethylene composition comprises: from 30 to 60 wt % of the first ethylene copolymer; and from 70 to 40 wt % of the second ethylene copolymer.
In an embodiment of the disclosure, the bimodal polyethylene composition has a Rosand melt strength of at least 3.0 cN.
In an embodiment of the disclosure, the bimodal polyethylene composition has a broadness factor defined as (Mw/Mn)/(Mz/Mw) of ≦2.75.
In an embodiment of the disclosure, the bimodal polyethylene composition has a shear viscosity ratio of ≧15.
In an embodiment of the disclosure, the bimodal polyethylene composition further comprises a nucleating agent or a mixture of nucleating agents.
In an embodiment of the disclosure, the closure is made by compression molding or injection molding.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a plot of the ESCR in hours (the ESCR B10 for a molded plaque) against the 2% secant flexural modulus (MPa) for selected inventive and comparative polyethylene example compositions.
FIG. 2 shows a plot of the “the shear viscosity ratio” (η10/η1000 at 240° C.) against the ESCR in hours (the ESCR B10 for a molded plaque) for selected inventive and comparative polyethylene examples.
FIG. 3 shows a plot of the “the shear viscosity ratio” (η10/η1000 at 240° C.) against the Rosand melt strength (cN) for selected inventive and comparative polyethylene examples.
FIG. 4 shows a gel permeation chromatograph for inventive polyethylene examples Nos 1, 2 and 3.
FIG. 5 shows the relationship between the shear thinning index SHI(1,100) and the melt index, I2 of polyethylene compositions of the current disclosure.



DETAILED DESCRIPTION
The present disclosure is related to molded parts, such as closures for bottles/containers and the polyethylene compositions used to manufacture them. The polyethylene compositions are composed of at least two ethylene copolymer components: a first ethylene copolymer and a second ethylene copolymer.
By the term “ethylene copolymer” it is meant that the copolymer comprises both ethylene and at least one alpha-olefin comonomer.
The terms “cap” and “closure” are used interchangeably in the current disclosure, and both connote any suitably shaped molded article for enclosing, sealing, closing or covering etc., a suitably shaped opening, a suitably molded aperture, an open necked structure or the like used in combination with a container, a bottle, a jar and the like.
The terms “homogeneous” or “homogeneously branched polymer” as used herein define homogeneously branched polyethylene which has a relatively narrow composition distribution, as indicated by a relatively high composition distribution breadth index (CDBI50). That is, the comonomer is randomly distributed within a given polymer chain and a substantial portion of the polymer chains have same ethylene/comonomer ratio. It is well known that metallocene catalysts and other so called “single site catalysts” incorporate comonomer more evenly than traditional Ziegler-Natta catalysts when used for catalytic ethylene copolymerization with alpha olefins. This fact is often demonstrated by measuring the composition distribution breadth index (CDBI50) for corresponding ethylene copolymers. The composition distribution of a polymer can be characterized by the short chain distribution index (SCDI) or composition distribution breadth index (CDBI50). The definition of composition distribution breadth index (CDBI50) can be found in PCT publication WO 93/03093 and U.S. Pat. No. 5,206,075. The CDBI50 is conveniently determined using techniques which isolate polymer fractions based on their solubility (and hence their comonomer content). For example, temperature rising elution fractionation (TREF) as described by Wild et al. J. Poly. Sci., Poly. Phys. Ed. Vol. 20, p 441, 1982 or in U.S. Pat. No. 4,798,081 can be employed. From the weight fraction versus composition distribution curve, the CDBI50 is determined by establishing the weight percentage of a copolymer sample that has a comonomer content within 50% of the median comonomer content on each side of the median. Generally, Ziegler-Natta catalysts produce ethylene copolymers with a CDBI50 of less than about 50 weight %, or less than about 55 weight %, consistent with a heterogeneously branched copolymer. In contrast, metallocenes and other single site catalysts will most often produce ethylene copolymers having a CDBI50 of greater than about 55 weight %, or greater than about 60 weight %, consistent with a homogeneously branched copolymer.
The First Ethylene Copolymer
In an embodiment of the disclosure, the first ethylene copolymer of the polyethylene composition has a density of from about 0.920 g/cm3 to about 0.955 g/cm3; a melt index, I2, of less than about 0.4 g/10 min; a molecular weight distribution, Mw/Mn, of below about 2.7 and a weight average molecular weight, Mw, that is greater than the Mw of the second ethylene copolymer.
In an embodiment of the disclosure the first ethylene copolymer is a homogeneously branched copolymer.
In an embodiment of the disclosure, the first ethylene copolymer is made with a single site catalyst, such as for example a phosphinimine catalyst.
In an embodiment of the disclosure, the comonomer (i.e., alpha-olefin) content in the first ethylene copolymer can be from about 0.05 to about 3.0 mol %. The comonomer content of the first ethylene copolymer may be determined by mathematical deconvolution methods as applied to a bimodal polyethylene composition (see the Examples section).
In embodiments of the disclosure, the comonomer in the first ethylene copolymer is one or more alpha olefin such as but not limited to 1-butene, 1-hexene, 1-octene and the like.
In an embodiment of the disclosure, the first ethylene copolymer is a copolymer of ethylene and 1-octene.
In an embodiment of the disclosure, the short chain branching in the first ethylene copolymer can be from about 0.25 to about 15 short chain branches per thousand carbon atoms (SCB1/1000Cs). In further embodiments of the disclosure, the short chain branching in the first ethylene copolymer can be from 0.5 to 15, or from 0.5 to 12, or from 0.5 to 10, or from 0.75 to 15, or from 0.75 to 12, or from 0.75 to 10, or from 1.0 to 10, or from 1.0 to 8.0, or from 1.0 to 5, or from 1.0 to 3 branches per thousand carbon atoms (SCB1/1000Cs). The short chain branching is the branching due to the presence of alpha-olefin comonomer in the ethylene copolymer and will for example have two carbon atoms for a 1-butene comonomer, or four carbon atoms for a 1-hexene comonomer, or six carbon atoms for a 1-octene comonomer, etc. The number of short chain branches in the first ethylene copolymer may be determined by mathematical deconvolution methods as applied to a bimodal polyethylene composition (see the Examples section).
In an embodiment of the disclosure, the comonomer content in the first ethylene copolymer is greater than comonomer content of the second ethylene copolymer (as reported for example in mol %).
In an embodiment of the disclosure, the amount of short chain branching in the first ethylene copolymer is greater than the amount of short chain branching in the second ethylene copolymer (as reported in short chain branches, SCB per thousand carbons in the polymer backbone, 1000Cs).
The melt index, I2 of the first ethylene copolymer can in an embodiment of the disclosure be above 0.01, but below 0.4 g/10 min. In further embodiments of the disclosure, the melt index, I2 of the first ethylene copolymer will be from 0.01 to 0.40 g/10 min, or from 0.01 to 0.30 g/10 min, or from 0.01 to 0.25 g/10 min, or from 0.01 to 0.20 g/10 min, or from 0.01 to 0.10 g/10 min.
In an embodiment of the disclosure, the first ethylene copolymer has a weight average molecular weight Mw of from about 110,000 to about 300,000 (g/mol). In another embodiment of the disclosure, the first ethylene copolymer has a weight average molecular weight Mw of from about 110,000 to about 275,000. In embodiments of the disclosure, the first ethylene copolymer has a weight average molecular weight Mw of from about 125,000 to about 275,000, or from about 125,000 to about 250,000, or from 125,000 to about 230,000, or from about 150,000 to about 275,000, or from about 150,000 to about 250,000, or from about 175,000 to about 250,000, or from about 180,000 to about 230,000. In embodiments of the disclosure, the first ethylene copolymer has a Mw of greater than 150,000, or greater than 175,000, or greater than 180,000, or greater than 190,000, or greater than 200,000. In embodiments of the disclosure the first ethylene copolymer has a Mw of greater than 150,000, or greater than 175,000, or greater than 180,000, or greater than 190,000, or greater than 200,000 while at the same time being lower than 275,000, or 250,000.
In an embodiment of the disclosure, the density of the first ethylene copolymer is from 0.920 to 0.955 g/cm3, including narrower ranges within this range and all the numbers encompassed by this range. For example, in further embodiments of the disclosure, the density of the first ethylene copolymer can be from 0.925 to 0.955 g/cm3, or from 0.925 to 0.950 g/cm3, or from 0.925 to 0.945 g/cm3, or from 0.925 to 0.940 g/cm3, or from 0.920 to 0.940 g/cm3, or from 0.922 to 0.948 g/cm3, or from 0.925 to 0.935 g/cm3, or from 0.927 to 0.945 g/cm3, or from 0.927 to 0.940 g/cm3, or from 0.927 to 0.935 g/cm3.
In an embodiments of the disclosure, the first ethylene copolymer has a molecular weight distribution (Mw/Mn) of <3.0, or ≦2.7, or <2.7, or ≦2.5, or <2.5, or ≦2.3, or from 1.8 to 2.3.
The Mw/Mn value of the first ethylene copolymer can in an embodiment of the disclosure be estimated by a de-covolution of a GPC profile obtained for a bimodal polyethylene composition of which the first ethylene copolymer is a component.
The density and the melt index, I2, of the first ethylene copolymer can be estimated from GPC (gel permeation chromatography) and GPC-FTIR (gel permeation chromatography with Fourier transform infra-red detection) experiments and deconvolutions carried out on the bimodal polyethylene composition (see the Examples section).
In an embodiment of the disclosure, the first ethylene copolymer of the polyethylene composition is a homogeneously branched ethylene copolymer having a weight average molecular weight, Mw, of at least 175,000; a molecular weight distribution, Mw/Mn, of less than 2.7 and a density of from 0.922 to 0.948 g/cm3.
In an embodiment of the present disclosure, the first ethylene copolymer is homogeneously branched ethylene copolymer and has a CDBI50 of greater than about 60 weight %. In further embodiments of the disclosure, the first ethylene copolymer has a CDBI50 of greater than about 65 weight %, or greater than about 70 weight %, or greater than about 75 weight %, or greater than about 80 weight %.
In an embodiment of the disclosure, the first ethylene copolymer comprises from 10 to 70 weight percent (wt %) of the total weight of the first and second ethylene copolymers. In an embodiment of the disclosure, the first ethylene copolymer comprises from 20 to 60 weight percent (wt %) of the total weight of the first and second ethylene copolymers. In an embodiment of the disclosure, the first ethylene copolymer comprises from 30 to 60 weight percent (wt %) of the total weight of the first and second ethylene copolymers. In an embodiment of the disclosure, the first ethylene copolymer comprises from 40 to 50 weight percent (wt %) of the total weight of the first and second ethylene copolymers.
The Second Ethylene Copolymer
In an embodiment of the disclosure, the second ethylene copolymer of the polyethylene composition has a density below 0.965 g/cm3 but which is higher than the density of the first ethylene copolymer; a melt index, I2, of from about 250 to 20,000 g/10 min; a molecular weight distribution, Mw/Mn, of below about 2.7 and a weight average molecular weight Mw that is less than the Mw of the first ethylene copolymer.
In an embodiment of the disclosure, the second ethylene copolymer is homogeneously branched copolymer.
In an embodiment of the disclosure, the second ethylene copolymer is made with a single site catalyst, such as for example a phosphinimine catalyst.
In an embodiment of the disclosure, the comonomer content in the second ethylene copolymer can be from about 0.01 to about 3 mol % or from about 0.03 to about 3 mol %, or from about 0.05 to about 3 mol % as measured by 13C NMR, or FTIR or GPC-FTIR methods. The comonomer content of the second ethylene polymer may be determined by mathematical deconvolution methods applied to a bimodal polyethylene composition (see the Examples section).
In an embodiment of the disclosure, the comonomer in the second ethylene copolymer is one or more alpha olefin such as but not limited to 1-butene, 1-hexene, 1-octene and the like.
In an embodiment of the disclosure, the second ethylene copolymer is a copolymer of ethylene and 1-octene.
In an embodiment of the disclosure, the short chain branching in the second ethylene copolymer can be from about 0.15 to about 15 short chain branches per thousand carbon atoms (SCB2/1000Cs). In further embodiments of the disclosure, the short chain branching in the second ethylene copolymer can be from 0.15 to 12, or from 0.15 to 8, or from 0.15 to 5, or from 0.15 to 3, or from 0.15 to 2 branches per thousand carbon atoms (SCB2/1000Cs). The short chain branching is the branching due to the presence of alpha-olefin comonomer in the ethylene copolymer and will for example have two carbon atoms for a 1-butene comonomer, or four carbon atoms for a 1-hexene comonomer, or six carbon atoms for a 1-octene comonomer, etc.
The number of short chain branches in the second ethylene copolymer may be determined by mathematical deconvolution methods applied to a bimodal polyethylene composition (see the Examples section).
In an embodiment of the disclosure, the short chain branching in the second ethylene copolymer can be from about 0.05 to about 10 short chain branches per thousand carbon atoms (SCB1/1000Cs). In further embodiments of the disclosure, the short chain branching in the second copolymer can be from 0.05 to 7.5, or from 0.05 to 5.0, or from 0.05 to 2.5, or from 0.05 to 1.5, or from 0.1 to 12, or from 0.1 to 10, or from 0.1 to 7.5, or from 0.1 to 5.0, or from 0.1 to 2.5, or from 0.1 to 2.0, or from 0.1 to 1.0 branches per thousand carbon atoms (SCB1/1000Cs).
In an embodiment of the disclosure, the comonomer content in the second ethylene copolymer is less than the comonomer content of the first ethylene copolymer (as reported for example in mol %).
In an embodiment of the disclosure, the amount of short chain branching in the second ethylene copolymer is less than the amount of short chain branching in the first ethylene copolymer (as reported in short chain branches, SCB per thousand carbons in the polymer backbone, 1000Cs).
In an embodiment of the present disclosure, the density of the second ethylene copolymer is less than 0.967 g/cm3. The density of the second ethylene copolymer in another embodiment of the disclosure is less than 0.966 g/cm3. In another embodiment of the disclosure, the density of the second ethylene copolymer is less than 0.965 g/cm3. In another embodiment of the disclosure, the density of the second ethylene copolymer is less than 0.964 g/cm3. In another embodiment of the disclosure, the density of the second ethylene copolymer is less than 0.963 g/cm3. In another embodiment of the disclosure, the density of the second ethylene copolymer is less than 0.962 g/cm3.
In an embodiment of the present disclosure, the density of the second ethylene copolymer is higher than the density of the first ethylene copolymer, but is less than 0.967 g/cm3. The density of the second ethylene copolymer in another embodiment of the disclosure is higher than the density of the first ethylene copolymer, but is less than 0.966 g/cm3. In another embodiment of the disclosure, the density of the second ethylene copolymer is higher than the density of the first ethylene copolymer, but is less than 0.965 g/cm3. In another embodiment of the disclosure, the density of the second ethylene copolymer is higher than the density of the first ethylene copolymer, but is less than 0.964 g/cm3. In another embodiment of the disclosure, the density of the second ethylene copolymer is higher than the density of the first ethylene copolymer, but is less than 0.963 g/cm3. In another embodiment of the disclosure, the density of the second ethylene copolymer is higher than the density of the first ethylene copolymer, but is less than 0.962 g/cm3.
In embodiments of the disclosure, the density of the second ethylene copolymer is from 0.952 to 0.966 g/cm3 including narrower ranges within this range and all the numbers within this range, such as, for example, from 0.952 to 0.965 g/cm3, or from 0.952 to 0.964 g/cm3, or from 0.952 to 0.963 g/cm3, or from 0.954 to 0.963 g/cm3, or from 0.954 to 0.964 g/cm3, or from 0.956 to 0.963 g/cm3.
In embodiments of the disclosure, the second ethylene copolymer has a weight average molecular weight Mw of less than about 45,000, or less than about 40,000 or less than about 35,000. In another embodiment of the disclosure, the second ethylene copolymer has a weight average molecular weight Mw of from about 7,500 to about 35,000. In further embodiments of the disclosure, the second ethylene copolymer has a weight average molecular weight Mw of from about 9,000 to about 35,000, or from about 10,000 to about 35,000, or from about 12,500 to about 30,000, or from about 10,000 to about 25,000, or from about 10,000 to about 20,000.
In some embodiments of the disclosure, the second ethylene copolymer has a molecular weight distribution (Mw/Mn) of <3.0, or ≦2.7, or <2.7, or ≦2.5, or <2.5, or ≦2.3, or from 1.8 to 2.3.
The Mw/Mn value of the second ethylene copolymer can in an embodiment of the disclosure be estimated by a de-covolution of a GPC profile obtained for a bimodal polyethylene composition of which the first ethylene copolymer is a component.
In an embodiment of the disclosure, the melt index I2 of the second ethylene copolymer can be from 50 to 20,000 g/10 min. In another embodiment of the disclosure, the melt index I2 of the second ethylene copolymer can be from 250 to 20,000 g/10 min. In another embodiment of the disclosure, the melt index I2 of the second ethylene copolymer can be from 500 to 20,000 g/10 min. In another embodiment of the disclosure, the melt index I2 of the second ethylene copolymer can be from 1000 to 20,000 g/10 min. In yet another embodiment of the disclosure, the melt index I2 of the second ethylene copolymer can be from 1500 to 20,000 g/10 min. In yet another embodiment of the disclosure, the melt index I2 of the second ethylene copolymer can be from 1500 to 10,000 g/10 min. In yet another embodiment of the disclosure, the melt index I2 of the second ethylene copolymer can be from 1500 to 7,000 g/10 min. In yet another embodiment of the disclosure, the melt index I2 of the second ethylene copolymer can be greater than 1500, but less than 7000 g/10 min. In yet another embodiment of the disclosure, the melt index I2 of the second ethylene copolymer can be greater than 1500, but less than 5000 g/10 min. In yet another embodiment of the disclosure, the melt index I2 of the second ethylene copolymer can be greater than 1000, but less than 3500 g/10 min.
In an embodiment of the disclosure, the melt index I2 of the second ethylene copolymer is greater than 200 g/10 min. In an embodiment of the disclosure, the melt index I2 of the second ethylene copolymer is greater than 500 g/10 min. In an embodiment of the disclosure, the melt index I2 of the second ethylene copolymer is greater than 1000 g/10 min. In an embodiment of the disclosure, the melt index I2 of the second ethylene copolymer is greater than 1500 g/10 min. In an embodiment of the disclosure, the melt index I2 of the second ethylene copolymer is greater than 1750 g/10 min.
The density and the melt index, I2, of the second ethylene copolymer can be estimated from GPC and GPC-FTIR experiments and deconvolutions carried out on a bimodal polyethylene composition (see the below Examples section).
In an embodiment of the disclosure, the second ethylene copolymer of the polyethylene composition is a homogeneous ethylene copolymer having a weight average molecular weight, Mw, of at most 45,000; a molecular weight distribution, Mw/Mn, of less than 2.7 and a density higher than the density of the first ethylene copolymer, but less than 0.965 g/cm3.
In an embodiment of the present disclosure, the second ethylene copolymer is homogeneously branched ethylene copolymer and has a CDBI50 of greater than about 60 weight %. In further embodiments of the disclosure, the second ethylene copolymer has a CDBI50 of greater than about 65 weight %, or greater than about 70 weight %, or greater than about 75 weight %, or greater than about 80 weight %.
In an embodiment of the disclosure, the second ethylene copolymer comprises from 90 to 30 wt % of the total weight of the first and second ethylene copolymers. In an embodiment of the disclosure, the second ethylene copolymer comprises from 80 to 40 wt % of the total weight of the first and second ethylene copolymers. In an embodiment of the disclosure, the second ethylene copolymer comprises from 70 to 40 wt % of the total weight of the first and second ethylene copolymers. In an embodiment of the disclosure, the second ethylene copolymer comprises from 60 to 50 wt % of the total weight of the first and second ethylene copolymers.
In the present disclosure, the second ethylene copolymer has a density which is higher than the density of the first ethylene copolymer, but less than about 0.037 g/cm3 higher than the density of the first ethylene copolymer. In an embodiment of the disclosure, the second ethylene copolymer has a density which is higher than the density of the first ethylene copolymer, but less than about 0.035 g/cm3 higher than the density of the first ethylene copolymer. In another embodiment of the disclosure, the second ethylene copolymer has a density which is higher than the density of the first ethylene copolymer, but less than about 0.033 g/cm3 higher than the density of the first ethylene copolymer. In another embodiment of the disclosure, the second ethylene copolymer has a density which is higher than the density of the first ethylene copolymer, but less than about 0.032 g/cm3 higher than the density of the first ethylene copolymer. In still another embodiment of the disclosure, the second ethylene copolymer has a density which is higher than the density of the first ethylene copolymer, but less than about 0.031 g/cm3 higher than the density of the first ethylene copolymer. In still another embodiment of the disclosure, the second ethylene copolymer has a density which is higher than the density of the first ethylene copolymer, but less than about 0.030 g/cm3 higher than the density of the first ethylene copolymer.
In embodiments of the disclosure, the I2 of the second ethylene copolymer is at least 100 times, or at least 1000 times, or at least 10,000 times, or at least 50,000 times the I2 of the first ethylene copolymer.
The Polyethylene Composition
Minimally, the polyethylene composition will contain a first ethylene copolymer (as defined above) and a second ethylene copolymer (as defined above) which are of different weight average molecular weight (Mw) and/or melt index, I2.
In embodiments of the disclosure, the polyethylene composition has a broad, bimodal or multimodal molecular weight distribution.
In an embodiment of the disclosure, the polyethylene composition will minimally comprise a first ethylene copolymer (as defined above) and a second ethylene copolymer (as defined above) and the ratio (SCB1/SCB2) of the number of short chain branches per thousand carbon atoms in the first ethylene copolymer (i.e., SCB1) to the number of short chain branches per thousand carbon atoms in the second ethylene copolymer (i.e., SCB2) will be greater than 1.0 (i.e., SCB1/SCB2>1.0).
In an embodiment of the disclosure, the ratio of the short chain branching in the first ethylene copolymer (SCB1) to the short chain branching in the second ethylene copolymer (SCB2) is at least 1.0. In yet another embodiment of the disclosure, the ratio of the short chain branching in the first ethylene copolymer (SCB1) to the short chain branching in the second ethylene copolymer (SCB2) is at least 1.25. In another embodiment of the disclosure, the ratio of the short chain branching in the first ethylene copolymer (SCB1) to the short chain branching in the second ethylene copolymer (SCB2) is at least 1.5. In another embodiment of the disclosure, the ratio of the short chain branching in the first ethylene copolymer (SCB1) to the short chain branching in the second ethylene copolymer (SCB2) is at least 1.75 or 2.0 or 2.5.
In an embodiment of the disclosure, the ratio of the short chain branching in the first ethylene copolymer (SCB1) to the short chain branching in the second ethylene copolymer (SCB2) will be from greater than 1.0 to about 5.0, or from greater than 1.0 to about 4.0, or from greater than 1.0 to about 3.5.
In embodiments of the disclosure, the ratio (SCB1/SCB2) of the short chain branching in the first ethylene copolymer (SCB1) to the short chain branching in the second ethylene copolymer (SCB2) will be from 1.0 to 12.0, or from 1.0 to 10, or from 1.0 to 7.0, or from 1.0 to 5.0, or from 1.0 to 3.0.
In an embodiment of the disclosure, the polyethylene composition has a bimodal molecular weight distribution. In the current disclosure, the term “bimodal” means that the polyethylene composition comprises at least two components, one of which has a lower weight average molecular weight and a higher density and another of which has a higher weight average molecular weight and a lower density. A bimodal or multimodal polyethylene composition may be identified by using gel permeation chromatography (GPC). Generally, the GPC chromatograph will exhibit two or more component ethylene copolymers, where the number of component ethylene copolymers corresponds to the number of discernible peaks. One or more component ethylene copolymers may also exist as a hump, shoulder or tail relative to the molecular weight distribution of the other ethylene copolymer component.
In an embodiment of the disclosure, the polyethylene composition has a density of greater than or equal to 0.949 g/cm3, as measured according to ASTM D792; a melt index, I2, of from about 0.3 to about 4.0 g/10 min, as measured according to ASTM D1238 (when conducted at 190° C., using a 2.16 kg weight); a molecular weight distribution, Mw/Mn, of from about 5.0 to about 13.0, a Z-average molecular weight, Mz of from 400,000 to 520,000, a stress exponent of less than 1.53 and an environmental stress crack resistance, ESCR Condition B at 10% of at least 120 hours.
In embodiments of the disclosure, the polyethylene composition has a comonomer content of less than 0.75 mol %, or less than 0.70 mol %, or less than 0.65 mol %, or less than 0.60 mol %, or less than 0.55 mol % as measured by FTIR or 13C NMR methods, where the comonomer is one or more alpha olefins such as but not limited to 1-butene, 1-hexene, 1-octene and the like. In an embodiment of the disclosure, the polyethylene composition has a comonomer content of from 0.1 to 0.75 mol %, or from 0.20 to 0.55 mol %, or from 0.25 to 0.50 mol %.
In embodiment of the present disclosure, the polyethylene composition has a density of at least 0.949 g/cm3. In further embodiments of the disclosure, the polyethylene composition has a density of >0.949 g/cm3, or ≧0.950 g/cm3, or >0.950 g/cm3.
In an embodiment of the current disclosure, the polyethylene composition has a density in the range of from 0.949 to 0.960 g/cm3.
In an embodiment of the current disclosure, the polyethylene composition has a density in the range of from 0.949 to 0.959 g/cm3.
In an embodiment of the current disclosure, the polyethylene composition has a density in the range of from 0.949 to 0.958 g/cm3.
In an embodiment of the current disclosure, the polyethylene composition has a density in the range of from 0.949 to 0.957 g/cm3.
In an embodiment of the current disclosure, the polyethylene composition has a density in the range of from 0.949 to 0.956 g/cm3.
In an embodiment of the current disclosure, the polyethylene composition has a density in the range of from 0.949 to 0.955 g/cm3.
In an embodiment of the current disclosure, the polyethylene composition has a density in the range of from 0.950 to 0.955 g/cm3.
In an embodiment of the current disclosure, the polyethylene composition has a density in the range of from 0.951 to 0.957 g/cm3.
In an embodiment of the current disclosure, the polyethylene composition has a density in the range of from 0.951 to 0.955 g/cm3.
In an embodiment of the disclosure, the polyethylene composition has a melt index, I2, of from 0.1 to 5.0 g/10 min according to ASTM D1238 (when conducted at 190° C., using a 2.16 kg weight) including narrower ranges within this range and all the numbers within this range. For example, in further embodiments of the disclosure, the polyethylene composition has a melt index, I2, of from 0.3 to 4.0 g/10 min, or from 0.4 to 3.5 g/10 min, or from 0.4 to 3.0 g/10 min, or from 0.3 to 3.5 g/10 min, or from 0.3 to 3.0 g/10 min, or from 0.3 to 2.5 g/10 min, or from 0.1 to 4.0 g/10 min, or from 0.1 to 3.5 g/10 min, or from 0.1 to 3.0 g/10 min, or from 0.1 to 2.5 g/10 min, or from 0.1 to 2.0 g/10 min, or from 0.1 to 1.5 g/10 min, or from 0.25 to 1.5 g/10 min, or from 0.3 to 2.0 g/10 min, or from 0.3 to 1.5 g/10 min, or less than 1.0 g/10 min, or from greater than 0.1 to less than 1.0 g/10 min, or from greater than 0.2 to less than 1.0 g/10 min, or from greater than 0.3 to less than 1.0 g/10 min.
In an embodiment of the disclosure, the polyethylene composition has a melt index I5 of at least 1.0 g/10 min according to ASTM D1238 (when conducted at 190° C., using a 5 kg weight). In another embodiment of the disclosure, the polyethylene composition has a melt index, I5, of greater than about 1.1 g/10 min, as measured according to ASTM D1238 (when conducted at 190° C., using a 5 kg weight). In still further embodiments of the disclosure, the polyethylene composition has a melt index I5 of from about 1.0 to about 5.0 g/10 min, or from about 1.5 to about 5.0 g/10 min, or from about 2.0 to about 5.0 g/10 min, or from about 2.0 to about 4.5 g/10 min.
In an embodiment of the disclosure, the polyethylene composition has a high load melt index, I21 of at least 25 g/10 min according to ASTM D1238 (when conducted at 190° C., using a 21 kg weight). In another embodiment of the disclosure, the polyethylene composition has a high load melt index, I21, of greater than about 50 g/10 min. In yet another embodiment of the disclosure, the polyethylene composition has a high load melt index, I21, of greater than about 65 g/10 min.
In an embodiment of the disclosure, the ratio of the melt index, I2, of the second ethylene copolymer to the melt index, I5, of the polyethylene composition is from 200 to 2000. In another embodiment of the disclosure, the ratio of the melt index, I2, of the second ethylene copolymer to the melt index, I5, of the polyethylene composition is from 400 to 1300. In yet another embodiment of the disclosure, the ratio of the melt index, I2, of the second ethylene copolymer to the melt index, I5, of the polyethylene composition is from 600 to 1200.
In an embodiment of the disclosure, the polyethylene composition has a complex viscosity, η* at a shear stress (G*) anywhere between from about 1 to about 10 kPa which is between 1,000 to 25,000 Pa·s. In an embodiment of the disclosure, the polyethylene composition has a complex viscosity, η* at a shear stress (G*) anywhere from about 1 to about 10 kPa which is between 1,000 and 15,000, or from 5000 to 15,000.
In an embodiment of the disclosure, the polyethylene composition has a number average molecular weight, Mn, of below about 30,000. In further embodiments of the disclosure, the polyethylene composition has a number average molecular weight, Mn, of below about 20,000 or below about 17,500. In further embodiments of the disclosure, the polyethylene composition has a number average molecular weight, Mn, of from about 9,000 to 28,000, or from about 10,000 to 25,000, or from about 10,000 to about 20,000.
In embodiments of the disclosure, the polyethylene composition has a weight average molecular weight, Mw, of from about 65,000 to about 200,000 including narrower ranges within this range and the numbers within this range. For example, in further embodiments of the disclosure, the polyethylene composition has a weight average molecular weight, Mw, of from about 75,000 to about 175,000, or from about 90,000 to about 150,000, or from about 100,000 to about 140,000.
In embodiments of the disclosure, the polyethylene composition has a z-average molecular weight, Mz, of from 400,000 to 520,000 including narrower ranges within this range and the numbers within this range. For example, in further embodiments of the disclosure, the polyethylene composition has a z-average molecular weight, Mz, of from 400,000 to 510,000, or from 400,000 to 500,000, or from 400,000 to 490,000, or from 410,000 to 480,000.
In embodiments of the disclosure, the polyethylene composition has a z-average molecular weight, Mz which satisfies: 400,000<Mz<500,000 or 400,000≦Mz≦500,000.
In embodiments of the present disclosure, the polyethylene composition has a molecular weight distribution Mw/Mn of from 3.0 to 13.0, including narrower ranges within this range and all the numbers within this range. For example, in further embodiments of the disclosure, the polyethylene composition has a Mw/Mn of from 5.0 to 13.0, or from 4.0 to 12.0, or from 5.0 to 12.0 or from 6.0 to 12.0, or from 6.0 to 11.0, or from 5.0 to 12.0, or from 5.0 to 10.0, or from 6.0 to 10.0, or from 6.0 to 11.0, or from 7.0 to 11.0, or from greater than 7.0 to 11.0, or from 7.0 to 10.0, or from greater than 7.0 to 12.0.
In embodiments of the disclosure, the polyethylene composition has a ratio of Z-average molecular weight to weight average molecular weight (Mz/Mw) of from 2.25 to 5.0, or from 2.5 to 4.5, or from 2.75 to 5.0, or from 2.75 to 4.25, or from 3.0 to 4.0.
In an embodiment of the disclosure, the polyethylene composition has a broadness factor defined as (Mw/Mn)/(Mz/Mw) of less than 3.00, or less than 2.95, or less than 2.90, or less than 2.85, or less than 2.80, or less than 2.75, or less than 2.70, or less than 2.65, or less than 2.60, or less than 2.55, or less than 2.50, or less than 2.45, or less than 2.40, or less than 2.35, or ≦2.75, or ≦2.70, or ≦2.65, or ≦2.60, or ≦2.55, or ≦2.50, or ≦2.45, or ≦2.40, or ≦2.35.
In embodiments of the disclosure, the polyethylene composition has a melt flow ratio defined as I21/I12 of >40, or ≧45, or ≧50, or ≧55, or ≧60, or ≧65, or ≧70. In a further embodiment of the disclosure, the polyethylene composition has a melt flow ratio I21/I2 of from about 40 to about 120, including narrower ranges within this range and all the numbers within this range. For example, the polyethylene composition may have a melt flow ratio I21/I2 of from about 50 to about 120, or from about 40 to about 110, or from about 45 to about 100, or from about 50 to about 110, or from about 55 to about 95.
In an embodiment of the disclosure, the polyethylene composition has a melt flow rate defined as I21/I5 of less than 35. In another embodiment of the disclosure, the polyethylene composition has a melt flow rate defined as I21/I5 of less than 30.
In an embodiment of the disclosure, the polyethylene composition has a shear viscosity at about 105s−1 (240° C.) of less than about 10 (Pa·s). In further embodiments of the disclosure, the polyethylene composition has a shear viscosity at about 105s−1 (240° C.) of less than 7.5 Pa·s, or less than 7.0 Pa·s, or less than 6.5 Pa·s.
In an embodiment of the disclosure, the polyethylene composition has a hexane extractables level of below 0.55 wt %.
In an embodiment of the disclosure, the polyethylene composition has at least one type of alpha-olefin that has at least 4 carbon atoms and its content is less than 0.75 mol % as determined by 13C NMR. In an embodiment of the disclosure, the polyethylene composition has at least one type of alpha-olefin that has at least 4 carbon atoms and its content is less than 0.65 mol % as determined by 13C NMR. In an embodiment of the disclosure, the polyethylene composition has at least one type of alpha-olefin that has at least 4 carbon atoms and its content is less than 0.55 mol % as determined by 13C NMR.
In an embodiment of the disclosure, the shear viscosity ratio, SVR(10,1000) at 240° C. of the polyethylene composition can be from about 10 to 30, or from 12 to 27, or from 12.5 to 25, or from 15 to 25, or from 17.5 to 23.0. The shear viscosity ratio SVR(10,1000) is determined by taking the ratio of shear viscosity at shear rate of 10 s−1 and shear viscosity at shear rate of 1000 s−1 as measured with a capillary rheometer at a constant temperature (e.g., 240° C.), and a die with L/D ratio of 20 and diameter of 0.06′′. Without wishing to be bound by theory, the higher the value for the shear viscosity ratio, the easier the polyethylene composition is to be processed on converting equipment for caps and closures. The “shear viscosity ratio” is used herein as a means to describe the relative processability of a polyethylene composition.
In an embodiment of the disclosure, the polyethylene composition has a shear viscosity ratio (η10/η1000 at 240° C.) of ≧12.0, ≧12.5, or ≧13.0, or ≧13.5, or ≧14.0, or ≧14.5, or ≧15.0, or ≧17.5, or ≧20.0.
In an embodiment of the disclosure, the shear thinning index, SHI(1,100) of the polyethylene composition is less than about 10. The shear thinning index (SHI), was calculated using dynamic mechanical analysis (DMA) frequency sweep methods as disclosed in PCT applications WO 2006/048253 and WO 2006/048254. The SHI value is obtained by calculating the complex viscosities η*(1) and η*(100) at a constant shear stress of 1 kPa (G*) and 100 kPa (G*), respectively.
In an embodiment of the disclosure, the SHI(1,100) of the polyethylene composition satisfies the equation: SHI(1,100)<−10.58 (log I2 of polyethylene composition in g/10 min)/(g/10 min)+12.94. In another embodiment of the disclosure, the SHI(1,100) of the polyethylene composition satisfies the equation: SHI(1,100)<−5.5 (log I2 of the polyethylene composition in g/10 min)/(g/10 min)+9.66.
In an embodiment of the disclosure, the polyethylene composition has a Rosand melt strength in centiNewtons (cN) of at least 2.0, or at least 2.25, or at least 2.5, or at least 2.75, or at least 3.0, or at least 3.25, or at least 3.5, or at least 3.75, or from 2.5 to 6.0, or from 2.75 to 6.0, or from 2.75 to 5.5, or from 3.0 to 6.0, or from 3.0 to 5.5, or from 3.25 to 6.0, or from 3.5 to 6.0, or from 3.25 to 5.5.
In an embodiment of the disclosure, the polyethylene composition or a molded article (or plaque) made from the polyethylene composition, has an environment stress crack resistance ESCR Condition B at 10% of at least 50 hrs, as measured according to ASTM D1693 (at 10% Igepal and 50° C. under condition B).
In an embodiment of the disclosure, the polyethylene composition or a molded article (or plaque) made from the polyethylene composition, has an environment stress crack resistance ESCR Condition B at 10% of at least 100 hrs, as measured according to ASTM D1693 (at 10% Igepal and 50° C. under condition B).
In an embodiment of the disclosure, the polyethylene composition or a molded article (or plaque) made from the polyethylene composition, has an environment stress crack resistance ESCR Condition B at 10% of at least 150 hrs, as measured according to ASTM D1693 (at 10% Igepal and 50° C. under condition B).
In an embodiment of the disclosure, the polyethylene composition or a molded article (or plaque) made from the polyethylene composition, has an environment stress crack resistance ESCR Condition B at 10% of at least 200 hrs, as measured according to ASTM D1693 (at 10% Igepal and 50° C. under condition B).
In an embodiment of the disclosure, the polyethylene composition or a molded article (or plaque) made from the polyethylene composition, has an environment stress crack resistance ESCR Condition B at 10% of from 50 to 600 hrs, as measured according to ASTM D1693 (at 10% Igepal and 50° C. under condition B).
In an embodiment of the disclosure, the polyethylene composition or a molded article (or plaque) made from the polyethylene composition, has an environment stress crack resistance ESCR Condition B at 10% of from 100 to 500 hrs, as measured according to ASTM D1693 (at 10% Igepal and 50° C. under condition B).
In an embodiment of the disclosure, the polyethylene composition or a molded article (or plaque) made from the polyethylene composition, has an environment stress crack resistance ESCR Condition B at 10% of from 150 to 500 hrs, as measured according to ASTM D1693 (at 10% Igepal and 50° C. under condition B).
In an embodiment of the disclosure, the polyethylene composition or a molded article (or plaque) made from the polyethylene composition has a notched Izod impact strength of at least 60 J/m, or at least 80 J/m as measured according to ASTM D256.
In an embodiment of the disclosure the polyethylene composition of the current disclosure has a density of from 0.949 to 0.957 g/cm3; a melt index, I2, of from 0.3 to 2.0 g/10 min; a molecular weight distribution of from 6.0 to 12.0; a number average molecular weight, Mn, of below 30,000; a shear viscosity at 105s−1 (240° C.) of less than 10 (Pa·s), a hexane extractables of less than 0.55%, a notched Izod impact strength of more than 60 J/m, and an ESCR B at 10% of at least 150 hrs.
In embodiments of the disclosure, the polyethylene composition has a 2% secant flexural modulus in megapascals (MPa) of greater than about 750, or greater than about 850, or greater than about 1000, or from about 750 to about 1600, or from about 750 to about 1250, or from about 850 to about 1150. In some embodiments, the polyethylene composition further comprises a nucleating agent which increases the 2% secant flexural modulus in megapascals (MPa) to above these ranges to for example from more than about 1000 and up to about 1600. Without wishing to be bound by theory, the 2% secant flexural modulus is a measure of polymer stiffness. The higher the 2% secant flexural modulus, the higher the polymer stiffness.
In an embodiment of the disclosure, the polyethylene composition has a stress exponent, defined as Log10[I6/I2]/Log10[6.48/2.16], which is ≦1.53. In further embodiments of the disclosure the polyethylene composition has a stress exponent, Log10[I6/I2]/Log10[6.48/2.16] of less than 1.50, or less than 1.48, or less than 1.45.
In an embodiment of the disclosure, the polyethylene composition has a composition distribution breadth index (CDBI50), as determined by temperature elution fractionation (TREF), of ≧60 weight %. In further embodiments of the disclosure, the polyethylene composition will have a CDBI50 of greater than 65 weight %, or greater than 70 weight %, or greater than 75 weight %, or greater than 80 weight %.
In an embodiment of the disclosure, the polyethylene composition has a composition distribution breadth index (CDBI25), as determined by temperature elution fractionation (TREF), of ≧50 weight %. In further embodiments of the disclosure, the polyethylene composition will have a CDBI25 of greater than 55 weight %, or greater than 60 weight %, or greater than 65 weight %, or greater than 70 weight %.
The polyethylene composition of this disclosure can be made using any conventional blending method such as but not limited to physical blending and in-situ blending by polymerization in multi reactor systems. For example, it is possible to perform the mixing of the first ethylene copolymer with the second ethylene copolymer by molten mixing of the two preformed polymers. In some embodiments, preferred are processes in which the first and second ethylene copolymers are prepared in at least two sequential polymerization stages, however, both in-series, or an in-parallel dual reactor process are contemplated for use in the current disclosure. If the at least two reactors are configured in parallel, comonomer addition to each reactor makes an ethylene copolymer in each reactor. If the at least two reactors are configured in series, comonomer may be added to at least the first reactor, and unreacted comonomer can flow into later reactors to make an ethylene copolymer in each reactor. Alternatively, if the at least two reactors are configured in series, comonomer may be added to each reactor, to make an ethylene copolymer in each reactor. Gas phase, slurry phase or solution phase reactor systems may be used, with solution phase reactor systems being preferred in some embodiments.
In an embodiment of the current disclosure, a dual reactor solution process is used as has been described in for example U.S. Pat. No. 6,372,864 and U.S. Patent Application Publication No. 20060247373A1 which are incorporated herein by reference.
Homogeneously branched ethylene copolymers can be prepared using any catalyst capable of producing homogeneous branching. Generally, the catalysts will be based on a group 4 metal having at least one cyclopentadienyl ligand that is well known in the art. Examples of such catalysts, which include metallocenes, constrained geometry catalysts and phosphinimine catalysts are typically used in combination with activators selected from methylaluminoxanes, boranes or ionic borate salts and are further described in U.S. Pat. Nos. 3,645,992; 5,324,800; 5,064,802; 5,055,438; 6,689,847; 6,114,481 and 6,063,879. Such catalysts may also be referred to as “single site catalysts” to distinguish them from traditional Ziegler-Natta or Phillips catalysts which are also well known in the art. In general, single site catalysts produce ethylene copolymers having a molecular weight distribution (Mw/Mn) of less than about 3.0 and a composition distribution breadth index (CDBI50) of greater than about 50% by weight.
In an embodiment of the current disclosure, homogeneously branched ethylene polymers are prepared using an organometallic complex of a group 3, 4 or 5 metal that is further characterized as having a phosphinimine ligand. Such catalysts are known generally as phosphinimine catalysts. Some non-limiting examples of phosphinimine catalysts can be found in U.S. Pat. Nos. 6,342,463; 6,235,672; 6,372,864; 6,984,695; 6,063,879; 6,777,509 and 6,277,931 all of which are incorporated by reference herein.
Some non-limiting examples of metallocene catalysts can be found in U.S. Pat. Nos. 4,808,561; 4,701,432; 4,937,301; 5,324,800; 5,633,394; 4,935,397; 6,002,033 and 6,489,413, which are incorporated herein by reference. Some non-limiting examples of constrained geometry catalysts can be found in U.S. Pat. Nos. 5,057,475; 5,096,867; 5,064,802; 5,132,380; 5,703,187 and 6,034,021, all of which are incorporated by reference herein in their entirety.
In an embodiment of the disclosure, use of a single site catalyst that does not produce long chain branching (LCB) is preferred. Without wishing to be bound by any single theory, long chain branching can increase viscosity at low shear rates, thereby negatively impacting cycle times during the manufacture of caps and closures, such as during the process of compression molding. Long chain branching may be determined using 13C NMR methods and may be quantitatively assessed using the method disclosed by Randall in Rev. Macromol. Chem. Phys. C29 (2 and 3), p. 285.
In an embodiment of the disclosure, the polyethylene composition will contain fewer than 0.3 long chain branches per 1000 carbon atoms. In another embodiment of the disclosure, the polyethylene composition will contain fewer than 0.01 long chain branches per 1000 carbon atoms.
In an embodiment of the disclosure, the polyethylene composition (defined as above) is prepared by contacting ethylene and at least one alpha-olefin with a polymerization catalyst under solution phase polymerization conditions in at least two polymerization reactors (for an example of solution phase polymerization conditions see for example U.S. Pat. Nos. 6,372,864; 6,984,695 and U.S. Patent Application Publication No. 20060247373A1 which are incorporated herein by reference).
In an embodiment of the disclosure, the polyethylene composition is prepared by contacting at least one single site polymerization catalyst system (comprising at least one single site catalyst and at least one activator) with ethylene and a least one comonomer (e.g., a C3-C8 alpha-olefin) under solution polymerization conditions in at least two polymerization reactors.
In an embodiment of the disclosure, a group 4 single site catalyst system, comprising a single site catalyst and an activator, is used in a solution phase dual reactor system to prepare a bimodal polyethylene composition by polymerization of ethylene in the presence of an alpha-olefin comonomer.
In an embodiment of the disclosure, a group 4 single site catalyst system, comprising a single site catalyst and an activator, is used in a solution phase dual reactor system to prepare a bimodal polyethylene composition by polymerization of ethylene in the presence of 1-octene.
In an embodiment of the disclosure, a group 4 phosphinimine catalyst system, comprising a phosphinimine catalyst and an activator, is used in a solution phase dual reactor system to prepare a bimodal polyethylene composition by polymerization of ethylene in the presence of an alpha-olefin comonomer.
In an embodiment of the disclosure, a group 4 phosphinimine catalyst system, comprising a phosphinimine catalyst and an activator, is used in a solution phase dual reactor system to prepare a bimodal polyethylene composition by polymerization of ethylene in the presence of 1-octene.
In an embodiment of the disclosure, a solution phase dual reactor system comprises two solution phase reactors connected in series.
In an embodiment of the disclosure, a polymerization process to prepare the polyethylene composition comprises contacting at least one single site polymerization catalyst system with ethylene and at least one alpha-olefin comonomer under solution polymerization conditions in at least two polymerization reactors.
In an embodiment of the disclosure, a polymerization process to prepare the polyethylene composition comprises contacting at least one single site polymerization catalyst system with ethylene and at least one alpha-olefin comonomer under solution polymerization conditions in at least a first reactor and a second reactor configured in series.
In an embodiment of the disclosure, a polymerization process to prepare the polyethylene composition comprises contacting at least one single site polymerization catalyst system with ethylene and at least one alpha-olefin comonomer under solution polymerization conditions in at least a first reactor and a second reactor configured in series, with the at least one alpha-olefin comonomer being fed exclusively to the first reactor.
The production of the polyethylene composition of the present disclosure will typically include an extrusion or compounding step. Such steps are well known in the art.
The polyethylene composition can comprise further polymer components in addition to the first and second ethylene polymers. Such polymer components include polymers made in situ or polymers added to the polymer composition during an extrusion or compounding step.
Optionally, additives can be added to the polyethylene composition. Additives can be added to the polyethylene composition during an extrusion or compounding step, but other suitable known methods will be apparent to a person skilled in the art. The additives can be added as is or as part of a separate polymer component (i.e. not the first or second ethylene polymers described above) added during an extrusion or compounding step. Suitable additives are known in the art and include but are not-limited to antioxidants, phosphites and phosphonites, nitrones, antacids, UV light stabilizers, UV absorbers, metal deactivators, dyes, fillers and reinforcing agents, nano-scale organic or inorganic materials, antistatic agents, lubricating agents such as calcium stearates, slip additives such as erucimide, and nucleating agents (including nucleators, pigments or any other chemicals which may provide a nucleating effect to the polyethylene composition). The additives that can be optionally added are typically added in amount of up to 20 weight percent (wt %).
One or more nucleating agent(s) may be introduced into the polyethylene composition by kneading a mixture of the polymer, usually in powder or pellet form, with the nucleating agent, which may be utilized alone or in the form of a concentrate containing further additives such as stabilizers, pigments, antistatics, UV stabilizers and fillers. It should be a material which is wetted or absorbed by the polymer, which is insoluble in the polymer and of melting point higher than that of the polymer, and it should be homogeneously dispersible in the polymer melt in as fine a form as possible (1 to 10 μm). Compounds known to have a nucleating capacity for polyolefins include salts of aliphatic monobasic or dibasic acids or arylalkyl acids, such as sodium succinate, or aluminum phenylacetate; and alkali metal or aluminum salts of aromatic or alicyclic carboxylic acids such as sodium β-naphthoate, or sodium benzoate.
Examples of nucleating agents which are commercially available and which may be added to the polyethylene composition are dibenzylidene sorbital esters (such as the products sold under the trademark MilladTM 3988 by Milliken Chemical and Irgacleamm by Ciba Specialty Chemicals). Further examples of nucleating agents which may be added to the polyethylene composition include the cyclic organic structures disclosed in U.S. Pat. No. 5,981,636 (and salts thereof, such as disodium bicyclo [2.2.1] heptene dicarboxylate); the saturated versions of the structures disclosed in U.S. Pat. No. 5,981,636 (as disclosed in U.S. Pat. No. 6,465,551; Zhao et al., to Milliken); the salts of certain cyclic dicarboxylic acids having a hexahydrophthalic acid structure (or “HHPA” structure) as disclosed in U.S. Pat. No. 6,599,971 (Dotson et al., to Milliken); and phosphate esters, such as those disclosed in U.S. Pat. No. 5,342,868 and those sold under the trade names NA-11 and NA-21 by Asahi Denka Kogyo, cyclic dicarboxylates and the salts thereof, such as the divalent metal or metalloid salts, (particularly, calcium salts) of the HHPA structures disclosed in U.S. Pat. No. 6,599,971. For clarity, the HHPA structure generally comprises a ring structure with six carbon atoms in the ring and two carboxylic acid groups which are substituents on adjacent atoms of the ring structure. The other four carbon atoms in the ring may be substituted, as disclosed in U.S. Pat. No. 6,599,971. An example is 1,2-cyclohexanedicarboxylicacid, calcium salt (CAS registry number 491589-22-1). Still further examples of nucleating agents which may be added to the polyethylene composition include those disclosed in WO2015042561, WO2015042563, WO2015042562 and WO2011050042.
Many of the above described nucleating agents may be difficult to mix with the polyethylene composition that is being nucleated and it is known to use dispersion aids, such as, for example, zinc stearate, to mitigate this problem.
In an embodiment of the disclosure, the nucleating agents are well dispersed in the polyethylene composition.
In an embodiment of the disclosure, the amount of nucleating agent used is comparatively small—from 100 to 3000 parts by million per weight (based on the weight of the polyethylene composition) so it will be appreciated by those skilled in the art that some care must be taken to ensure that the nucleating agent is well dispersed. In an embodiment of the disclosure, the nucleating agent is added in finely divided form (less than 50 microns, especially less than 10 microns) to the polyethylene composition to facilitate mixing. This type of “physical blend” (i.e., a mixture of the nucleating agent and the resin in solid form) is generally preferable to the use of a “masterbatch” of the nucleator (where the term “masterbatch” refers to the practice of first melt mixing the additive—the nucleator, in this case—with a small amount of the polyethylene composition resin—then melt mixing the “masterbatch” with the remaining bulk of the polyethylene composition resin).
In an embodiment of the disclosure, an additive such as nucleating agent may be added to the polyethylene composition by way of a “masterbatch”, where the term “masterbatch” refers to the practice of first melt mixing the additive (e.g., a nucleator) with a small amount of the polyethylene composition, followed by melt mixing the “masterbatch” with the remaining bulk of the polyethylene composition.
In an embodiment of the disclosure, the polymer composition further comprises a nucleating agent or a mixture of nucleating agents.
In an embodiment of the disclosure, the polymer compositions described above are used in the formation of molded articles. For example, articles formed by compression molding and injection molding are contemplated. Such articles include, for example, caps, screw caps, and closures for bottles and/or containers. However, a person skilled in the art will readily appreciate that the compositions described above may also be used for other applications such as but not limited to film, injection blow molding, blow molding and sheet extrusion applications.
In an embodiment of the disclosure, the polyethylene compositions described above are used in the formation of a closure for bottles, containers, pouches and the like. For example, closures for bottles formed by compression molding or injection molding are contemplated. Such closures include, for example, hinged caps, hinged screw caps, hinged snap-top caps, and hinged closures for bottles, containers, pouches and the like.
In an embodiment of the disclosure, a closure (or cap) is a screw cap for a bottle, container, pouches and the like.
In an embodiment of the disclosure, a closure (or cap) is a snap closure for a bottle, container, pouches and the like.
In an embodiment of the disclosure, a closure (or cap) comprises a hinge made of the same material as the rest of the closure (or cap).
In an embodiment of the disclosure, a closure (or cap) is hinged closure.
In an embodiment of the disclosure, a closure (or cap) is a hinged closure for bottles, containers, pouches and the like.
In an embodiment of the disclosure, a closure (or cap) is a flip-top hinge closure, such as a flip-top hinge closure for use on a plastic ketchup bottle or similar containers containing foodstuffs.
When a closure is a hinged closure, it comprises a hinged component and generally consists of at least two bodies which are connected by a thinner section that acts as a hinge allowing the at least two bodies to bend from an initially molded position. The thinner section may be continuous or web-like, wide or narrow.
A useful closure (for bottles, containers and the like) is a hinged closure and may consist of two bodies joined to each other by at least one thinner bendable portion (e.g. the two bodies can be joined by a single bridging portion, or more than one bridging portion, or by a webbed portion, etc.). A first body may contain a dispensing hole and which may snap onto or screw onto a container to cover a container opening (e.g. a bottle opening) while a second body may serve as a snap on lid which may mate with the first body.
The caps and closures, of which hinged caps and closures and screw caps etc. are a subset, can be made according to any known method, including for example injection molding and compression molding techniques that are well known to persons skilled in the art. Hence, in an embodiment of the disclosure a closure (or cap) comprising the polyethylene composition (defined above) is prepared with a process comprising at least one compression molding step and/or at least one injection molding step.
In one embodiment, the caps and closures (including single piece or multi-piece variants or hinged variants) comprise the polyethylene composition described above and have good organoleptic properties, good toughness, as well as good ESCR values. Hence the closures and caps of this embodiment are well suited for sealing bottles, containers and the like, for examples bottles that may contain drinkable water, and other foodstuffs, including but not limited to liquids that are under an appropriate pressure (i.e., carbonated beverages or appropriately pressurized drinkable liquids).
The closures and caps may also be used for sealing bottles containing drinkable water or non-carbonated beverages (e.g., juice). Other applications, include caps and closures for bottles, containers and pouches containing foodstuffs, such as for example ketchup bottles and the like.
The disclosure is further illustrated by the following non-limiting examples.
EXAMPLES
Mn, Mw, and Mz (g/mol) were determined by high temperature Gel Permeation Chromatography (GPC) with differential refractive index (DRI) detection using universal calibration (e.g. ASTM 06474-99). GPC data was obtained using an instrument sold under the trade name “Waters 150c”, with 1,2,4-trichlorobenzene as the mobile phase at 140° C. The samples were prepared by dissolving the polymer in this solvent and were run without filtration. Molecular weights are expressed as polyethylene equivalents with a relative standard deviation of 2.9% for the number average molecular weight (“Mn”) and 5.0% for the weight average molecular weight (“Mw”). The molecular weight distribution (MWD) is the weight average molecular weight divided by the number average molecular weight, Mw/Mn. The z-average molecular weight distribution is Mz/Mn. Polymer sample solutions (1 to 2 mg/mL) were prepared by heating the polymer in 1,2,4-trichlorobenzene (TCB) and rotating on a wheel for 4 hours at 150° C. in an oven. The antioxidant 2,6-di-tert-butyl-4-methylphenol (BHT) was added to the mixture in order to stabilize the polymer against oxidative degradation. The BHT concentration was 250 ppm. Sample solutions were chromatographed at 140° C. on a PL 220 high-temperature chromatography unit equipped with four Shodex columns (HT803, HT804, HT805 and HT806) using TCB as the mobile phase with a flow rate of 1.0 mL/minute, with a differential refractive index (DRI) as the concentration detector. BHT was added to the mobile phase at a concentration of 250 ppm to protect the columns from oxidative degradation. The sample injection volume was 200 mL. The raw data were processed with Cirrus GPC software. The columns were calibrated with narrow distribution polystyrene standards. The polystyrene molecular weights were converted to polyethylene molecular weights using the Mark-Houwink equation, as described in the ASTM standard test method D6474.
Primary melting peak (° C.), heat of fusion (J/g) and crystallinity (%) was determined using differential scanning calorimetry (DSC) as follows: the instrument was first calibrated with indium; after the calibration, a polymer specimen is equilibrated at 0° C. and then the temperature was increased to 200° C. at a heating rate of 10° C./min; the melt was then kept isothermally at 200° C. for five minutes; the melt was then cooled to 0° C. at a cooling rate of 10° C./min and kept at 0° C. for five minutes; the specimen was then heated to 200° C. at a heating rate of 10° C./min. The DSC Tm, heat of fusion and crystallinity are reported from the 2nd heating cycle.
The short chain branch frequency (SCB per 1000 carbon atoms) of copolymer samples was determined by Fourier Transform Infrared Spectroscopy (FTIR) as per the ASTM D6645-01 method. A Thermo-Nicolet 750 Magna-IR Spectrophotometer equipped with OMNIC version 7.2a software was used for the measurements.
Comonomer content can also be measured using 13C NMR techniques as discussed in Randall, Rev. Macromol. Chem. Phys., C29 (2&3), p 285; U.S. Pat. No. 5,292,845 and WO 2005/121239.
Polyethylene composition density (g/cm3) was measured according to ASTM D792.
Hexane extractables were determined according to ASTM D5227.
Shear viscosity was measured by using a Kayeness WinKARS Capillary Rheometer (model # D5052M-115). For the shear viscosity at lower shear rates, a die having a die diameter of 0.06 inch and L/D ratio of 20 and an entrance angle of 180 degrees was used. For the shear viscosity at higher shear rates, a die having a die diameter of 0.012 inch and L/D ratio of 20 was used.
The Shear Viscosity Ratio as the term is used in the present disclosure is defined as: η10/η1000 at 240° C. The η10 is the melt shear viscosity at the shear rate of 10 s−1 and the η1000 is the melt shear viscosity at the shear rate of 1000 s−1 measured at 240° C.
Melt indexes, I2, I5, I6 and I21 for the polyethylene composition were measured according to ASTM D1238 (when conducted at 190° C., using a 2.16 kg, a 5 kg, a 6.48 kg and a 21 kg weight respectively).
The “Rosand” melt strength of the polyethylene composition was measured on Rosand RH-7 capillary rheometer (barrel diameter=15 mm) with a flat die of 2-mm Diameter, L/D ratio 10:1 at 190° C. Pressure Transducer: 10,000 psi (68.95 MPa). Piston Speed: 5.33 mm/min. Haul-off Angle: 52°. Haul-off incremental speed: 50-80 m/min2 or 65±15 m/min2. A polymer melt is extruded through a capillary die under a constant rate and then the polymer strand is drawn at an increasing haul-off speed until it ruptures. The maximum steady value of the force in the plateau region of a force versus time curve is defined as the melt strength for the polymer.
To determine CDBI50, a solubility distribution curve is first generated for the polyethylene composition. This is accomplished using data acquired from the TREF technique. This solubility distribution curve is a plot of the weight fraction of the copolymer that is solubilized as a function of temperature. This is converted to a cumulative distribution curve of weight fraction versus comonomer content, from which the CDBI50 is determined by establishing the weight percentage of a copolymer sample that has a comonomer content within 50% of the median comonomer content on each side of the median (See WO 93/03093 and U.S. Pat. No. 5,376,439). The CDBI25 is determined by establishing the weight percentage of a copolymer sample that has a comonomer content within 25% of the median comonomer content on each side of the median.
The specific temperature rising elution fractionation (TREF) method used herein was as follows. Polymer samples (50 to 150 mg) were introduced into the reactor vessel of a crystallization-TREF unit (Polymer ChARTM). The reactor vessel was filled with 20 to 40 ml 1,2,4-trichlorobenzene (TCB), and heated td the desired dissolution temperature (e.g., 150° C.) for 1 to 3 hours. The solution (0.5 to 1.5 ml) was then loaded into the TREF column filled with stainless steel beads. After equilibration at a given stabilization temperature (e.g., 110° C.) for 30 to 45 minutes, the polymer solution was allowed to crystallize with a temperature drop from the stabilization temperature to 30° C. (0.1 or 0.2° C./minute). After equilibrating at 30° C. for 30 minutes, the crystallized sample was eluted with TCB (0.5 or 0.75 mL/minute) with a temperature ramp from 30° C. to the stabilization temperature (0.25 or 1.0° C./minute). The TREF column was cleaned at the end of the run for 30 minutes at the dissolution temperature. The data were processed using Polymer ChAR software, Excel spreadsheet and TREF software developed in-house.
The melt index, I2 and density of the first and second ethylene copolymers were estimated by GPC and GPC-FTIR deconvolutions as discussed further below.
High temperature GPC equipped with an online FTIR detector (GPC-FTIR) was used to measure the comonomer content as the function of molecular weight. Mathematical deconvolutions are performed to determine the relative amount of polymer, molecular weight and comonomer content of the component made in each reactor, by assuming that each polymer component follows a Flory's molecular weight distribution function and it has a homogeneous comonomer distribution across the whole molecular weight range.
For these single site catalyzed resins, the GPC data from GPC chromatographs was fit based on Flory's molecular weight distribution function.
To improve the deconvolution accuracy and consistency, as a constraint, the melt index, I2, of the targeted resin was set and the following relationship was satisfied during the deconvolution:

Log10(I2)=22.326528+0.003467*[Log10(Mn)]3−4.322582*Log10(Mw)−0.180061*[Log10(Mz)]2+0.026478*[Log10(Mz)]3 

where the experimentally measured overall melt index, I2, was used on the left side of the equation, while Mn of each component (Mw=2×Mn and Mz=1.5×Mw for each component) was adjusted to change the calculated overall Mn, Mw and Mz of the composition until the fitting criteria were met. During the deconvolution, the overall Mn, Mw and Mz are calculated with the following relationships: Mn=1/SUM(wi/Mn(i)), Mw=SUM(wi×Mw(i)), Mz=SUM(wi×Mz(i)2), where i represents the i-th component and wi represents the relative weight fraction of the i-th component in the composition.
The uniform comonomer distribution (which results from the use of a single site catalyst) of the resin components (i.e., the first and second ethylene copolymers) allowed the estimation of the short chain branching content (SCB) from the GPC-FTIR data, in branches per 1000 carbon atoms and calculation of comonomer content (in mol %) and density (in g/cm3) for the first and second ethylene copolymers, based on the deconvoluted relative amounts of first and second ethylene copolymer components in the polyethylene composition, and their estimated resin molecular weight parameters from the above procedure.
A component (or composition) density model and a component (or composition) melt index, I2, model was used according to the following equations to calculate the density and melt index I2 of the first and second ethylene polymers:

density=0.979863−0.00594808*(FTIR SCB/1000C)0.65−0.000383133*[Log10(Mn)]30.00000577986*(Mw/Mn)3+0.00557395*(Mz/Mw)0.25;

Log10(melt index,I2)=22.326528+0.003467*[Log10(Mn)]3−4.322582*Log10(Mw)−0.180061*[Log10(Mz)]2+0.026478*[Log10(Mz)]3 

where the Mn, Mw and Mz were the deconvoluted values of the individual ethylene polymer components, as obtained from the results of the above GPC deconvolutions. Hence, these two models were used to estimate the melt indexes and the densities of the components (i.e., the first and second ethylene copolymers).
Plaques molded from the polyethylene compositions were tested according to the following ASTM methods: Bent Strip Environmental Stress Crack Resistance (ESCR) at Condition B at 10% IGEPAL at 50° C., ASTM D1693; notched Izod impact properties, ASTM 0256; Flexural Properties, ASTM D 790; Tensile properties, ASTM D 638; Vicat softening point, ASTM D 1525; Heat deflection temperature, ASTM D 648.
Dynamic mechanical analyses were carried out with a rheometer, namely Rheometrics Dynamic Spectrometer (RDS-II) or Rheometrics SR5 or ATS Stresstech, on compression molded samples under nitrogen atmosphere at 190° C., using 25 mm diameter cone and plate geometry. The oscillatory shear experiments were done within the linear viscoelastic range of strain (10% strain) at frequencies from 0.05 to 100 rad/s. The values of storage modulus (G′), loss modulus (G′′), complex modulus (G*) and complex viscosity (η*) were obtained as a function of frequency. The same rheological data can also be obtained by using a 25 mm diameter parallel plate geometry at 190° C. under nitrogen atmosphere. The SHI (1,100) value is calculated according to the methods described in WO 2006/048253 and WO 2006/048254.
Examples of the polyethylene compositions were produced in a dual reactor solution polymerization process in which the contents of the first reactor flow into the second reactor. This in-series “dual reactor” process produces an “in-situ” polyethylene blend (i.e. the polyethylene composition). Note, that when an in-series reactor configuration is used, un-reacted ethylene monomer, and un-reacted alpha-olefin comonomer present in the first reactor will flow into the downstream second reactor for further polymerization.
In the present inventive examples, although no co-monomer is fed directly to the downstream second reactor, an ethylene copolymer is nevertheless formed in the second reactor due to the significant presence of un-reacted 1-octene flowing from the first reactor to the second reactor where it is copolymerized with ethylene. Each reactor is sufficiently agitated to give conditions in which components are well mixed. The volume of the first reactor was 12 liters and the volume of the second reactor was 22 liters. Optionally, a tubular reactor section which receives the discharge from the second reactor may be also be present as described in U.S. Pat. No. 8,101,693. These are the pilot plant scales. The first reactor was operated at a pressure of 6000 to 35000 kPa and the second reactor was operated at a lower pressure to facilitate continuous flow from the first reactor to the second. The solvent employed was methylpentane. The process operates using continuous feed streams. The catalyst employed in the dual reactor solution process experiments was a titanium complex having a phosphinimine ligand, a cyclopentadienide ligand and two activatable ligands, such as but not limited to chloride ligands. A boron based co-catalyst was used in approximately stoichiometric amounts relative to the titanium complex. Commercially available methylaluminoxane (MAO) was included as a scavenger at an Al:Ti of about 40:1. In addition, 2,6-di-tert-butylhydroxy-4-ethylbenzene was added to scavenge free trimethylaluminum within the MAO in a ratio of Al:OH of about 0.5:1.
The polymerization conditions used to make the inventive compositions are provided in Table 1.
Inventive and comparative polyethylene composition properties are described in Table 2.
Calculated properties for the first ethylene copolymer and the second ethylene copolymer for inventive polyethylene compositions, as obtained from GPC-FTIR deconvolution studies, are provided in Table 3.
Comparative polyethylene composition 1 was made using a single site phosphinimine catalyst in a dual reactor solution process and has an ESCR at condition B10 (at 50° C., 10% IGEPAL) of less than 24 hours, a SCB1/SCB2 ratio of 0.50 or less, and a Mz of less than 400,000.
Comparative polyethylene compositions 2 and 3 were made using a single site phosphinimine catalyst in a dual reactor solution process and have an ESCR at condition B10 (at 50° C., 10% IGEPAL) of 309 hrs and 86 hrs respectively, a SCB1/SCB2 ratio of greater than 1.0, and a Mz of less than 400,000.
Comparative polyethylene composition 4 is a commercially available, high density, bimodal polyethylene resin from Dow Chemical, DMDA-1250 NT 7 which has an ESCR at condition B-10 (at 50° C., 10% IGEPAL) of more than 150 hours, a melt strength of less than 3.0 cN, and an Mz of greater than 500,000. It also has a stress exponent value of 1.58.
Comparative polyethylene composition 5 is a commercially available, high density polyethylene resin from Dow Chemical, DMDC-1270 NT 7 which has an ESCR at condition B-10 (at 50° C., 10% IGEPAL) of less than 100 hours, a Rosand melt strength of less than 2.0 cN, and an Mz of greater than 450,000. It also has a stress exponent value of 1.53.
Inventive polyethylene compositions (Inventive Examples 1-3) are made using a single site phosphinimine catalyst in a dual reactor solution process as described above and have an ESCR at condition B10 (at 50° C., 10% IGEPAL) of greater than 100 hours and a SCB1/SCB2 ratio of greater than 1.0. These inventive examples also each have a Mz value of between 400,000 and 500,000 and a stress exponent of less than 1.53.
As shown in FIG. 1, inventive polyethylene compositions 1-3 provide an improved balance of ESCR and stiffness (as indicated by 2% secant floral modulus) when compared to comparative polyethylene compositions 4 and 5.
As shown in FIG. 2, inventive polyethylene compositions 1-3 provide an improved balance of processability (as indicated by the “shear viscosity ratio”) and ESCR when compared to comparative polyethylene compositions 2, 4 and 5.
FIG. 3 shows that inventive polyethylene compositions 1-3 have an improved balance of processability (as indicated by the “shear viscosity ratio”) and melt strength (the Rosand melt strength) when compared to comparative polyethylene compositions 2, 4 and 5.
FIG. 4 shows the bimodal nature of the inventive polyethylene compositions 1-3. Each ethylene copolymer component has a Mw/Mn value of less than 2.5.
As shown in FIG. 5, the inventive polyethylene compositions 1-3 do not satisfy the equation SHI(1, 100)≧−10/58 (log I2 of the polyethylene composition in g/10 min)/(g/10 min)+12.94, which is a property of the blends taught in WO 2006/048253. As shown in FIG. 5, the inventive polyethylene compositions 1-3 do not satisfy the equation: SHI(1,100)≧−5.5 (log I2 of the polyethylene composition in g/10 min)/(g/10 min)+9.66, which is a property of the blends taught in and WO 2006/048254.







TABLE 1







Reactor Conditions for Inventive Examples










Example No.
Inventive 1
Inventive 2
Inventive 3













Reactor 1





Ethylene (kg/h)
35.4
34.9
36.4


1-Octene (kg/h)
3.4
4.5
3.6


Hydrogen (g/h)
0.3
0.4
0.5


Solvent (kg/h)
353.4
321.8
341


Reactor Feed Inlet
35
35.1
30


Temperature (° C.)





Reactor Temperature (° C.)
140
140.7
140


Titanium Catalyst to the
0.093
0.052
0.070


Reactor (ppm)





Reactor 2





Ethylene (kg/h)
43.3
42.7
44.5


1-Octene (kg/h)
0
0
0


Hydrogen (g/h)
15
17
16


Solvent (kg/h)
104.4
136.2
114.2


Reactor Feed Inlet
36.8
36.3
30.3


Temperature (° C.)





Reactor Temperature (° C.)
199.9
198.3
201


Titanium Catalyst to the
0.40
0.42
0.52


Reactor (ppm)



















TABLE 2





Resin Properties


















Example No.
Inventive 1
Inventive 2
Inventive 3





Density (g/cm3)
0.9523
0.953
0.9539







Rheology/Flow Properties










Melt Index I2 (g/10
0.73
0.77
0.75


min)





Melt Flow Ratio
66
85
80.4


(I21/I2)





I21
47.9
65
60


I5


2.46


I21/I5


24.39


Stress Exponent
1.41
1.46
1.46


Shear Viscosity at
6.1
5.6
5.2


105 s−1 (240° C., Pa-s)





Shear Viscosity
19.9
19.44
20.9


Ratio η(10s−1)/





η(1000 s−1) at





240° C.





Rosand Melt
3.77
3.32
3.32


Strength (190° C., cN)










GPC - conventional










Mn
15401
13272
13077


Mw
122538
122190
117899


Mz
419614
471630
439444


Polydispersity Index
7.96
9.21
9.02


(Mw/Mn)





Mz/Mw
3.42
3.86
3.73


Broadness Factor
2.33
2.39
2.42


(Mw/Mn)/(Mz/Mw)










Branch Frequency - FTIR (uncorrected for chain end —CH3)










Uncorrected
2.3
2.4
2.3


SCB/1000 C





Uncorrected
0.5
0.5
0.5


comonomer content





(mol %)





Internal unsaturation
0.05
0.04
0.05


(/1000 C)





Side chain
0
0
0


unsaturation





(/1000 C)





Terminal
0.10
0.09
0.14


unsaturation





(/1000 C)





Comonomer ID
1-octene
1-octene
1-octene







Comononner mol % measured by 13C-NMR










1-Octene or 1-hexene, mol %





CDBI50 (wt. %)
75.4
71.9
72.2


CDBI25 (wt. %)
65.4
61.8
61.8







DSC










Primary Melting
128.76
128.63
129.23


Peak (° C.)





Heat of Fusion (J/g)
215.3
217.8
220.4


Crystallinity (%)
74.23
75.11
76







Environmental Stress Crack Resistance (Plaques)










ESCR Cond. B at 10
365
310
227


% (hrs)










Flexural Properties (Plaques)










Flex Secant Mod.
1264
1281
1303


1% (MPa)





Flex Sec Mod 1%
20
12
32


(MPa) Dev.





Flex Secant Mod.
1054
1075
1090


2% (MPa)





Flex Sec Mod 2%
14
16
24


(MPa) Dev.





Flexural Strength
36.6
37.4
37.6


(MPa)





Flexural Strength
0.4
0.5
0.5


Dev. (MPa)










Tensile Properties (Plaques)










Elong. at Yield (%)
10
9
9


Elong. at Yield Dev.
1
1
0


(%)





Yield Strength (MPa)
26.1
26.9
26.9


Yield Strength Dev.
0.4
0.5
0.6


(MPa)





Ultimate Elong. (%)
781
710
877


Ultimate Elong. Dev.
77
45
106


(%)





Ultimate Strength
29.7
19.3
28.6


(MPa)





Ultimate Strength
7
3.8
5.6


Dev. (MPa)





Sec Mod 1% (MPa)
1380
1672
1470


Sec Mod 1% (MPa)
294
322
177


Dev.





Sec Mod 2% (MPa)
913
1034
978


Sec Mod 2% (MPa)
80
95
64


Dev.










Impact Properties (Plaques)










Izod Impact (J/m)
106.8
80.0
85.4


IZOD DV (J/m)
0.0
5.3
0.0







Other properties










Hexane Extractables
0.38
0.38
0.39


(%)





VICAT Soft. Pt. (° C.)-
126.2
126.5
126.5


Plaque





Heat Deflection
65.5
72.7
69.3


Temp. [° C.] @ 66





PSI



















Comparative
Comparative
Comparative
Comparative
Comparative


Example No.
1
2
3
4
5





Density (g/cm3)
0.9534
0.9529
0.9523
0.955
0.955







Rheology/Flow Properties












Melt Index I2 (g/10 min)
1.88
1.57
1.5
1.5
2.5


Melt Flow Ratio (I21/I2)
56.9
58
54.8
66
51


I21

90
82.3
99
113


I5

4.72
4.5
5.31
7.8


I21/I5

19.07
18.29
18.64
14.49


Stress Exponent
1.41
1.38
1.4
1.58
1.53


Shear Viscosity at 105 s−1

5.1

6.2
6.63


(240° C., Pa-s)







Shear Viscosity Ratio 

13.5

11.3
9.48


η(10 s−1)/η(1000 s−1) 







at 240° C.







Rosand Melt Strength 

2.12

2.56
1.79


(190° C., cN)












GPC - conventional












Mn
14393
10524
13309
10240
17100


Mw
91663
83712
88295
106992
102000


Mz
245479
256210
278141
533971
470400


Polydispersity Index 
6.37
7.95
6.63
10.45
5.96


(Mw/Mn)







Mz/Mw
2.68
3.06
3.15
4.99
4.61


Broadness Factor
2.8
2.60
2.11
2.09
1.20


(Mw/Mn)/(Mz/Mw)












Branch Frequency - FTIR (uncorrected for chain end —CH3)












Uncorrected SCB/1000 C
2.2
3
2.1
2.3
2.5


Uncorrected comonomer 
0.4
0.6
0.4
0.5
0.5


content (mol %)







Internal unsaturation 



0
0


(/1000 C)







Side chain unsaturation 



0.09
0


(/1000 C)







Terminal unsaturation 



0.13
0.17


(/1000 C)







Comonomer ID
1-octene
1-octene
1-octene
1-hexene
1-hexene







Comonomer mol % measured by 13C-NMR












1-Octene or 1-hexene, mol %


0.3

0.68


CDBI50 (wt. %)
36.7
81.8
76.5
63.4
67.3


CDBI25 (wt. %)
17.6


39
49.8







DSC












Primary Melting Peak (° C.)
128.3
127.3
129
130.06
131.24


Heat of Fusion (J/g)
204.7
203.8
209.00
217.4
217.6


Crystallinity (%)
70.58
70.27
72.08
74.98
75.04







Environmental Stress Crack Resistance (Plaque)












ESCR Cond. B at 10% (hrs)
<24
309
86
196
78







Flexural Properties (Plaques)












Flex Secant Mod. 1% (MPa)
1035
1274
1295
1372
1304


Flex Sec Mod 1% (MPa) Dev.
25
39
23
87
46


Flex Secant Mod. 2% (MPa)
877
1064
1085
1167
1102


Flex Sec Mod 2% (MPa) Dev.
19
29
21
45
41


Flexural Strength (MPa)
31.5
37.5
37.3
40.4
38.3


Flexural Strength Dev. (MPa)
0.6
0.8
0.4
1
0.6







Tensile Properties (Plaques)












Elong. at Yield (%)
10.2
9
10
9
9


Elong. at Yield Dev. (%)
0.8
1
0
1
1


Yield Strength (MPa)
26.6
26
26.3
28.5
26.4


Yield Strength Dev. (MPa)
0.3
0.2
0.3
0.3
0.3


Ultimate Elong. (%)
920
701
891
870
1055


Ultimate Elong. Dev. (%)
94.6
106
23
69
42


Ultimate Strength (MPa)
21.5
21.8
33.3
26.8
31.6


Ultimate Strength Dev. (MPa)
4.1
6.8
2
5.5
1


Sec Mod 1% (MPa)
1374
1483
1230
1696
1545


Sec Mod 1% (MPa) Dev.
276.4
121
90
279
231


Sec Mod 2% (MPa)
937
973
913
1118
993


Sec Mod 2% (MPa) Dev.
71
33
34
90
91







Impact Properties (Plaques)












lzod Impact (J/m)
76.0
74.7
80.1
80.1
80.0


IZOD DV (J/m)
7.0
0.0
2.7
5.3








Other properties












Hexane Extractables (%)
0.44
0.36
0.25
0.36
0.48


VICAT Soft. Pt. (° C.)-Plaque
126
125.2
126.4
126.8
126.6


Heat Deflection Temp. 
72
68
67.3
73
76.4


[° C.] @ 66 PSI





















TABLE 3







Polyethylene Component Properties












Example No.
Comparative 1
Comparative 3
Inventive 1
Inventive 2
Inventive 3















Density (g/cm3)
0.9534
0.9523
0.9523
0.953
0.9539


I2 (g/10 min.)
1.88
1.5
0.73
0.77
0.75


Stress Exponent
1.41
1.4
1.41
1.46
1.46


MFR (I21/I2)
56.9
54.8
66
85
80.4


Mn
14393
13309
15401
13272
13077


Mw
91663
88295
122538
122190
117899


Mz
245479
278141
419614
471630
439444


400000 < Mz <







520000
no
no
yes
yes
yes


Mw/Mn
6.37
6.63
7.96
9.21
9.02


Mz/Mw
2.68
3.15
3.42
3.86
3.73







First Ethylene Copolymer












weight %
0.43
0.454
0.447
0.419
0.421


Mw
162400
168100
209700
221100
221400


I2 (g/10 min.)
0.13
0.12
0.05
0.04
0.04


Density 1, d1 (g/cm3)
0.9389
0.9302
0.9332
0.9333
0.9339


SCB1 per 1000 Cs
0.15
2.24
0.6
0.45
0.34







Second Ethylene Copolymer












weight %
0.57
0.546
0.553
0.581
0.579 


Mw
18500
14900
14600
13600
13800


I2 (g/10 min.)
736
1817
1981
2696
2515


Density 2, d2 (g/cm3)
0.9559
0.9555
0.9618
0.9626
0.9622


SCB1 per 1000 Cs
1.06
1.64
0.2
0.17
0.2


Estimated (d2 − d1),
0.017
0.0253
0.0286
0.0293
0.0283


g/cm3







Estimated (SCB2 −
0.91
−0.6
−0.4
−0.28
−0.14 


SCB1)







SCB1/SCB2
0.16
1.37
3.00
2.65
1.70

## Claims

1. A closure, said closure comprising a bimodal polyethylene composition comprising:
(1) 10 to 70 wt % of a first ethylene copolymer having a melt index I2, of less than 0.4 g/10 min; a molecular weight distribution Mw/Mn, of less than 2.7; and a density of from 0.920 to 0.955 g/cm3; and
(2) 90 to 30 wt % of a second ethylene copolymer having a melt index I2, of from 250 to 20,000 g/10 min; a molecular weight distribution Mw/Mn, of less than 2.7; and a density higher than the density of said first ethylene copolymer, but less than 0.965 g/cm3;
wherein the density of said second ethylene copolymer is less than
0.035 g/cm3 higher than the density of said first ethylene copolymer; the ratio (SCB1/SCB2) of the number of short chain branches per thousand carbon atoms in said first ethylene copolymer (SCB1) to the number of short chain branches per thousand carbon atoms in said second ethylene copolymer (SCB2) is greater than 1.0; and
wherein said bimodal polyethylene composition has a molecular weight distribution Mw/Mn, of from 5.0 to 13.0, a density of from 0.949 to 0.958 g/cm3, a stress exponent of less than 1.53, a melt index (I2) of from 0.3 to 3.0 g/10 min, and which satisfies the following: 400,000≦Mz≦500,000.

2. The closure of claim 1 wherein said bimodal polyethylene composition comprises: from 30 to 60 wt % of said first ethylene copolymer; and from 70 to 40 wt % of said second ethylene copolymer.

3. The closure of claim 1 wherein said first and second ethylene copolymers are copolymers of ethylene and 1-octene.

4. The closure of claim 1 wherein said bimodal polyethylene composition has a density of from 0.951 to 0.957 g/cm3.

5. The closure of claim 1 wherein said bimodal polyethylene composition has melt index I2, of from about 0.3 to about 1.0 g/10 min.

6. The closure of claim 1 wherein said second ethylene copolymer has a melt index I2, of greater than 500 g/10 min.

7. The closure of claim 1 wherein said first and second ethylene copolymers have a Mw/Mn of less than 2.5.

8. The closure of claim 1 wherein said bimodal polyethylene composition has a molecular weight distribution, Mw/Mn, of from 6.0 to 12.0.

9. The closure of claim 1 wherein said bimodal polyethylene composition has a broadness factor defined as (Mw/Mn)/(Mz/Mw) of ≦2.75.

10. The closure of claim 1 wherein said bimodal polyethylene composition has a composition distribution breadth index (CDBI25) of greater than 55% by weight.

11. The closure of claim 1 wherein said bimodal polyethylene composition has a shear viscosity ratio of greater than or equal to 15.

12. The closure of claim 1 wherein said bimodal polyethylene composition has an ESCR Condition B (10% IGEPAL) of at least 150 hrs.

13. The closure of claim 12 wherein said bimodal polyethylene composition has a shear viscosity ratio of greater than or equal to 15.

14. The closure of claim 1 wherein said bimodal polyethylene composition has a Rosand melt strength of at least 3.0 cN.

15. The closure of claim 14 wherein said bimodal polyethylene composition has a shear viscosity ratio of greater than or equal to 15.

16. The closure of claim 1 wherein the bimodal polyethylene composition further comprises a nucleating agent or a mixture of nucleating agents.

17. The closure of claim 1 wherein said closure is made by compression molding or injection molding.