FIELD OF THE INVENTION

[0001] The present invention relates to a novel polyethylene of Raised Temperature Resistance (PE-RT) for use in hot water piping systems.

BACKGROUND OF THE INVENTION

[0002] As explained in WO03033586, PE-RT materials are required to have a pressure test resistance, as determined according to DIN 16 833, of at least 165 h at 3.6 MPa and 95°C.

[0003] Moreover they should be preferably flexible, which translates into having an E- modulus of less than about 900 MPa.

[0004] According to WO03033586, such requirements are met by providing a multimodal polyethylene composition having a density of 0.921-0.950 and comprising a

HMW fraction having a density of at least 0.920.

SUMMARY OF THE INVENTION

[0005] It has now been found that a particularly high balance of the said mechanical properties and resistance to oxidation and crosslinking is achieved by properly selecting specific rheological and molecular parameters.

[0006] Thus the present invention provides a polyethylene composition having the following features:

1) density from 0.935 to 0.945 g/cm ³ , preferably from 0.936 to 0.943 g/cm ³ , determined according to ISO 1183 at 23°C;

2) melt flow index MIF at 190°C with a load of 21.60 kg, determined according to ISO 113, from 10 to 18 g/10 min., preferably from 12 to 18 g/10 min;

3) melt flow index MIP at 190°C with a load of 5 kg, determined according to ISO 113, from 1 to 2.5 g/10 min;

4) ratio MIF/MIP from 5 to 10, in particular from 6 to 9. [0007] Preferably, in addition to said features 1) to 4), the polyethylene composition of the inventions also has one or more of the following features:

5) a ratio M _w /M _n , where M _w is the weight average molar mass and M _n is the number average molar mass, both measured by GPC (Gel Permeation Chromatography) of 4 or more, in particular of 5 or more, preferred ranges being from 4 to 10, more preferably from 5 to 8, in particular from 5.5 to 8;

6) intrinsic viscosity [η], determined according to ISO 1628-1 and -3 in decalin at 135°C by capillary viscosity measurement, from 1.8 to 2.8 dl/g;

7) a substantially linear chain structure;

8) a content of vinyl groups, determined by means of infrared (IR) analysis in accordance with ASTM D 6248-98, of from 0.3 to 0.7 vinyl groups/1000 carbon atoms;

9) a content of vinyl groups in the polymer fraction having intrinsic viscosity [η] of less than 0.5 dl/g, of more than 0.3 vinyl groups/1000 carbon atoms, in particular from 0.4 to 0.9 vinyl groups/1000 carbon atoms.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] These and other features, aspects, and advantages of the present invention will become better understood with reference to the following description and appended claims, and accompanying drawings where:

[0009] Figure 1 shows the percentage of MIF decrease (Y axis) with ageing time (in minutes, X axis) for the polymer of Example 1 (upper line) and the polymer of

Comparative Example 1 (lower line).

[0010] It should be understood that the various embodiments are not limited to the arrangements and instrumentality shown in the drawings.

DETAILED DESCRIPTION OF THE INVENTION

[0011] The expression "polyethylene composition" is intended to embrace, as alternatives, both a single ethylene polymer and an ethylene polymer composition, in particular a composition of two or more ethylene polymer components, preferably with different molecular weights.

[0012] Typically the polyethylene composition of the present invention consists of or comprises copolymers of ethylene with 1-alkenes, or mixtures of ethylene homopolymers and said copolymers of ethylene with 1-alkenes.

[0013] Examples of suitable 1-alkenes in the copolymers according to present invention are C3-C2o-alpha-olefins such as propene, 1-butene, 1-pentene, 1-hexene, 4-methyl-l- pentene, 1-heptene or 1-octene.

[0014] Particularly preferred are 1-butene, 1-hexene or 1-octene.

[0015] Preferred amounts of 1-hexene in the copolymers are from 1.5-3.5% preferably 2.0 to 3.0% by weight.

[0016] In one preferred embodiment, the polyethylene composition of the present invention has a substantially monomodal molecular mass distribution curve as determined by GPC, hence is monomodal in GPC, because the individual molecular weight distributions of polymer sub-fractions overlap and do not resolve as to display two distinct maxima any more.

[0017] The mass distribution curve is not required to be perfectly bell-shaped; therefore it is merely "substantially" monomodal. Most preferably, such monomodal distribution is obtained in situ in a one-pot reaction with a mixed or hybrid catalyst system, preferably with mixed single-site catalysts, giving rise to a particularly homogenous, in-situ mixture of different catalyst's products which homogeneity is generally not obtainable by conventional blending techniques.

[0018] For "substantially linear chain structure" (feature (7) above) it is meant that the polyethylene composition of the invention has degree of long chain branching λ (lambda) of from 0 to 2 long chain branches/10 000 carbon atoms and particularly preferably from 0.1 to 1.5 long chain branches/10 000 carbon atoms. The degree of long chain branching λ (lambda) is measured by light scattering as described, for example, in ACS Series 521, 1993, Chromatography of Polymers, Ed. Theodore Provder; Simon Pang and Alfred Rudin: Size-Exclusion Chromatographic Assessment of Long-Chain Branch (LCB) Frequency in Polyethylenes, page 254-269. The presence of LCB can further be inferred from rheological data, see Trinkle et al. (Rheol. Acta 2002, 41: 103-113; van Gurp-Palmen Plot - classification of long chain branched polymers by their topology).

[0019] The polyethylene composition of the invention is obtainable using the catalyst system described below and in particular its preferred embodiments. Preferably, a single site catalyst or catalyst system is employed for providing said polyethylene according to the present invention. More preferably, the present invention employs a catalyst composition comprising at least two different single-site polymerization catalysts A) and B), of which A) is at least one metallocene polymerization catalyst and B) is at least one polymerization catalyst based on a non-metallocene transition metal complex, preferably wherein B) is an iron complex component which iron complex more preferably has a tridentate ligand.

[0020] Preferably, the metallocene catalyst A) is at least one zirconocene catalyst or catalyst system, zirconocene catalyst according to the present invention are, for example, cyclopentadienyl complexes. The cyclopentadienyl complexes can be, for example, bridged or unbridged biscyclopentadienyl complexes as described, for example, in EP129368, EP561479, EP545304 and EP576970, bridged or unbridged monocyclopentadienyl T alf- sandwich' complexes such as e.g. bridged amidocyclopentadienyl complexes described in EP416815 or half-sandwich complexes described in US6,069,213, US5,026,798. Further they can be multinuclear cyclopentadienyl complexes as described in EP 632 063, pi- ligand-substituted tetrahydropentalenes as described in EP659758 or pi-ligand-substituted tetrahydroindenes as described in EP 661 300.

[0021] Other suitable metallocene catalysts A) are hafnocenes, in particular the hafnocene catalysts wherein the hafnium atom forms a complex with two cyclopentadienyl, indenyl or fluorenyl ligands, each ligand being optionally substituted with one or more C - Cg-alkyl and/or C6-Cg aryl groups, the free valencies of the hafnium atom being saturated with halogen, preferably chlorine, or CrC ₄ alkyl or benzyl groups, or a combination of them.

[0022] Non-limiting examples of metallocene catalyst components consistent with the description herein include, for example: bis(cyclopentadienyl)zirconiumdichloride; bis(indenyl)zirconiumdichloride; bis(l-methylindenyl)zirconiumdichloride;

bis(2-methylindenyl)zirconiumdichloride;

bis(l-propylindenyl)zirconiumdichloride;

bis(2-propylindenyl)zirconiumdichloride;

bis(l-butylindenyl)zirconiumdichloride;

bis(2-butylindenyl)zirconiumdichloride;

bis(methylcyclopentadienyl)zirconiumdichloride;

bis(tetrahydroindenyl)zirconiumdichloride;

bis(pentamethylcyclopentadienyl)zirconiumdichloride,

bis(l,2,4-trimethylcyclopentadienyl)zirconiumdichloride;

bis(l-n-butyl-3-methyl-cyclopentadienyl) zirconiumdichloride;

bis(dimethylsilylcyclopentadienylindenyl)zirconium dichloride;

bis (n-butylcyclopentadienyl) hafnium dichloride;

bis (indenyl) hafnium dichloride;

bis (trimethysilylcyclopentadienyl) hafnium dichloride.

[0023] As for preferred embodiments of afore said iron complexes B), reference is made to the respective disclosure in WO 2005/103096, incorporated herewith by reference.

[0024] Particularly suited tridentate ligands are 2,6-Bis[l-(phenylimino)ethyl] pyridine and preferably the corresponding compounds wherein both the two phenyl groups are substituted in the ortho-position with a halogen or tert. alkyl substituent, particularly with a chlorine or tert. butyl group, the free valencies of the iron atom being saturated with halogen, preferably chlorine, or Ci-Cw alkyl, or C ₂ -C ₁₀ alkenyl, or C6-C20 aryl groups, or a combination of them.

[0025] The preparation of the compounds B) is described, for example, in J. Am. Chem.

Soc. 120, p.4049 ff. (1998), J. Chem. Soc, Chem. Commun. 1998, 849, and WO 98/27124. Preferred examples of complexes B) are:

2,6-Bis[l-(2-tert.butylphenylimino)ethyl]pyridine iron(II) dichloride; 2,6-Bis[l-(2-tert.butyl-6-chlorophenylimino)ethyl]pyridine iron(II) dichloride; 2,6-Bis[l-(2-chloro-6-methylphenylimino)ethyl]pyridine iron(II) dichloride;

2,6-Bis[l-(2-chloro-4,6-dimethylphenylimino)ethyl]pyridine iron(II) dichloride;

2,6-Bis[l-(2,4-dichlorophenylimino)ethyl]pyridine iron(II) dichloride;

2,6-Bis[l-(2,6-dimethylphenylimino)ethyl]pyridine iron(II) dichloride;

2,6-Bis[l-(2,6-dichlorophenylimino)ethyl]pyridine iron(II) dichloride;

2,6-Bis[l-(2,4-dichlorophenylimino)methyl]pyridine iron(II) dichloride;

2,6-Bis[l-(2,4-dichloro-6-methylphenylimino)ethyl]pyridine iron(II) dichloride;

2,6-Bis[l-(2,4-difluorophenylimino)ethyl]pyridine iron(II) dichloride;

2,6-Bis[l-(2,4-dibromophenylimino)ethyl]pyridine iron(II) dichloride.

[0026] Most preferably, one sole zirconocene A) is used as catalyst under the same reaction conditions in the homopolymerization or copolymerization of ethylene in a single reactor along with one sole complex B), and wherein A) preferably produces a higher M _w than does the complex B). In an even more preferred embodiment, both the components A) and B) are supported. The two components A) and B) can in this case be applied to different supports or together on a joint support. Most preferably, they are applied to a joint support in order to ensure a relatively close spatial proximity of the various catalyst centers and thus to ensure good mixing of the different polymers formed. As for the preferred types and specification of support materials, as well as for the use of activator components in addition to the catalyst, otherwise called co-catalysts, reference is made to the respective disclosure in WO 2005/103096, incorporated herewith by reference.

[0027] The use of co-catalyst components is well known in the art of ethylene polymerization, as are the polymerization processes, for which further reference is made to WO 2005/103096.

[0028] As support materials, preference is given to using silica gel, magnesium chloride, aluminum oxide, mesoporous materials, aluminosilicates, hydrotalcites and organic polymers such as polyethylene, polypropylene, polystyrene, polytetrafluoroethylene or polymers bearing polar functional groups, for example copolymers of ethene and acrylic esters, acrolein or vinyl acetate. [0029] The inorganic supports, like silica, can be subjected to a thermal treatment, e. g. to remove adsorbed water.

[0030] Such a drying treatment is generally carried out at temperatures in the range from 50 to 1000 °C, preferably from 100 to 600 °C, with drying at from 100 to 200 °C preferably being carried out under reduced pressure and/or under a blanket of inert gas (e. g. nitrogen), or the inorganic support can be calcined at temperatures of from 200 to 1000 °C to produce the desired structure of the solid and/or set the desired OH concentration on the surface. The support can also be treated chemically using customary dessicants such as metal alkyls, preferably aluminum alkyls, chlorosilanes or SiCl ₄ , or else methylaluminoxane. Appropriate treatment methods are described, for example, in WO 00/31090.

[0031] As joint activator (co-catalyst) for the catalyst components A) and B), preference is given to using an aluminoxane, such as mono-methylaluminoxane (MAO), for instance.

[0032] The molar ratio of the catalyst component A) to catalyst component B) is usually in the range from 100-1: 1, preferably from 20-5: 1 and particularly preferably from 1: 1 to 5: 1.

[0033] The catalyst component A) is preferably applied in such an amount that the concentration of the transition metal from the catalyst component A) in the finished catalyst system is from 1 to 200 μιηοΐ, preferably from 5 to 100 μιηοΐ and particularly preferably from 10 to 70 μιηοΐ, per g of support. The catalyst component B) is preferably applied in such an amount that the concentration of iron from the catalyst component B) in the finished catalyst system is from 1 to 200 μιηοΐ, preferably from 5 to 100 μιηοΐ and particularly preferably from 10 to 70 μιηοΐ, per g of support.

[0034] The molar ratio of catalyst component A) to activator (co-catalyst) can be from 1:0.1 to 1: 10000, preferably from 1: 1 to 1:2000. The molar ratio of catalyst component B) to activator (co-catalyst) is also usually in the range from 1:0.1 to 1: 10000, preferably from 1: 1 to 1:2000.

[0035] Preferably, the catalyst component A), the catalyst component B) and the activator (co-catalyst) are all supported on the same support by contacting them with the said support in suspension in a solvent, preferably an hydrocarbon having from 6 to 20 carbon atoms, in particular xylene, toluene, pentane, hexane, heptane or a mixture thereof. [0036] The process for polymerizing ethylene, alone or with 1-alkenes, can be generally carried out at temperatures in the range from 0 to 200 °C, preferably from 20 to 200 °C and particularly preferably from 25 to 150 °C, and under pressures from 0.005 to 10 MPa. The polymerization can be carried out in a known manner in bulk, in suspension, in the gas phase or in a supercritical medium in the customary reactors used for the polymerization of olefins.

[0037] The mean residence times are usually from 0.5 to 5 hours, preferably from 0.5 to 3 hours. The advantageous pressure and temperature ranges for carrying out the polymerizations usually depend on the polymerization method.

[0038] Among the polymerization processes, particular preference is given to gas-phase polymerization, in particular in gas-phase fluidized-bed reactors, solution polymerization and suspension (slurry) polymerization, in particular in loop reactors and stirred tank reactors.

[0039] Hydrogen is preferably used as a molar mass regulator.

[0040] Furthermore, customary additives such as antistatics, can also be used in the polymerizations.

[0041] The polymerization is most preferably carried out in a single reactor.

[0042] The present invention also concerns a pipe, in particular a hot water pipe or a floor heating pipe, comprising the polyethylene composition of the invention.

[0043] Such pipe can be a monolayer pipe or can comprise two or more layers, wherein at least one layer comprises the polyethylene composition of the invention.

[0044] In particular, for "comprising" it is preferably meant here that the pipe, or the said at least one layer, comprise from 50% to 100% by weight of the polyethylene composition of the invention.

[0045] Hot water pipes and floor heating pipes are well known kinds of pipe commonly produced.

[0046] They are generally prepared by extrusion by using preparation processes and equipment well known in the art.

[0047] For hot water it is generally meant water at a temperature of 60°C or higher. EXAMPLES

[0048] The following examples are included to demonstrate preferred embodiments of the invention. It should be appreciated by those of skill in the art that the techniques disclosed in the examples which follow represent techniques discovered by the inventor to function well in the practice of the invention, and thus can be considered to constitute preferred modes for its practice. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments which are disclosed and still obtain a like or similar result without departing from the spirit and scope of the invention.

[0049] Unless differently stated, the following test methods are used to determine the properties reported in the detailed description and in the examples.

[0050] Density

[0051] Determined according to ISO 1183 at 23°C.

[0052] Melt flow index (MI)

[0053] Determined according to ISO 1133 at 190°C with the specified load.

[0054] Intrinsic viscosity [τιΐ

[0055] Determined according to ISO 1628-1 and -3 in decalin at 135°C by capillary viscosity measurement.

[0056] M _w , M _n and M _w /M„

[0057] The determination of M _w , M _n and M _w /M _n derived therefrom is carried out by high-temperature gel permeation chromatography using a method described in DIN 55672- 1: 1995-02 issue February 1995. The deviations according to the mentioned DIN standard are as follows: Solvent 1,2,4-trichlorobenzene (TCB), temperature of apparatus and solutions 135°C and as concentration detector a PolymerChar (Valencia, Paterna 46980, Spain) IR-4 infrared detector, suited for use with TCB

[0058] Applying the universal calibration method based on the Mark-Houwink constants given may be inferred in detail from ASTM-6474-99, along with further explanation on using an additional internal standard-PE for spiking a given sample during chromatography runs, after calibration.

[0059] In detail, A WATERS Alliance 2000 equipped with the precolumn SHODEX UT- G and separation columns SHODEX UT 806 M (3x) and SHODEX UT 807 connected in series was used. The solvent was vacuum distilled under nitrogen and was stabilized with 0.025% by weight of 2,6-di-tert-butyl-4-methylphenol. The flow rate used was 1 ml/min, the injection was 500μ1 and polymer concentration was in the range of 0.01% < cone. < 0.05% w/w. The molecular weight calibration was established by using monodisperse polystyrene (PS) standards from Polymer Laboratories (now Varian, Inc., Essex Road, Church Stretton, Shropshire, SY6 6AX,UK ) in the range from 580g/mol up to 11600000g/mol and additionally hexadecane. The calibration curve was then adapted to Polyethylene (PE) by means of the Universal Calibration method (Benoit H., Rempp P. and Grubisic Z., n J. Polymer Sci., Phys. Ed., 5, 753(1967)). The Mark-Houwing parameters used herefore were for PS: kPS= 0.000121 dl/g, aPS=0.706 and for PE kPE= 0.000406 dl/g, aPE=0.725, valid in TCB at 135°C. Data recording, calibration and calculation was carried out using NTGPC_Control_V6.02.03 and NTGPC_V6.4.24 (HS - Entwicklungsgesellschaft fur wissenschaftliche Hard-und Software mbH , HauptstraBe 36, D-55437 Ober-Hilbersheim) respectively.

[0060] Content of vinyl groups

[0061] The content of vinyl groups/1000 carbon atoms is determined by means of IR, according to ASTM D 6248-98.

[0062] The content of vinyl groups/1000 carbon atoms in the individual polymer mass fractions is determined by the solvent-non-solvent extraction method of Holtrup (W.

Holtrup, Makromol. Chem. 178, 2335 (1977)) coupled with IR.

[0063] Xylene and ethylene glycol diethyl ether at 130°C are used as solvents for such fractionation and 5 g of polyethylene are split up into 8 fractions by Holtrup fractionation.

[0064] Comonomer content

[0065] The comonomer content is determined by means of 13 C-NMR as explained in

James. C. Randall, JMS-REV. Macromol. Chem. Phys., C29 (2&3), 201-317 (1989).

[0066] Pressure Test

[0067] Carried out according to DIN 16 833 at 3.6 MPa, 95°C.

[0068] E-modulus

[0069] Measured according to ISO 527-2/1A/50.

EXAMPLE 1 [0070] Preparation of the individual components of the catalyst system

[0071] Complexes 1 and 2 were used for the catalyst preparation.

[0072] Complex 1 is bis(l-n-butyl- 3-methyl -cyclopentadienyl)zirconium dichloride and is commercially available from Albemarle Inc.

[0073] Complex 2 is 2,6-bis[l-(2-chloro-4,6-dimethylphenylimino)ethyl]pyridine iron

(II) dichloride.

[0074] 2,6-bis[l-(2-chloro-4,6-dimethylphenylimino)ethyl]pyridine was prepared with the same synthetic route as in example 1 of WO2008107135 and reacted in with iron (II) dichloride to form said complex 2, as likewise disclosed in WO2008107135.

[0075] Methylalumoxane (MAO) was received from Chemtura Inc. as a 30% (w/w) toluene solution.

[0076] Support

[0077] XPO-2326A, a spray-dried silica gel from Grace.

[0078] Support pretreatment

[0079] XPO-2326 A was calcinated at 600°C for 6 hours.

[0080] Preparation of the catalyst system

[0081] A solution containing 4459.5 g of complex 1 and 90.425 g of complex 2 in 48.7 kg of MAO (4.75 M in toluene) and 12.4 1 of toluene was prepared. This solution was added within an hour to 40 kg of calcinated XPO-2326A at 0°C and further stirred for another hour. Then 107 1 heptane was added to the reaction mixture so that a slurry was obtained. The slurry of the catalyst was stirred for 30 min. The catalyst has been washed with heptane, filtered and dried with nitrogen flow till obtaining 80.55 kg of a free flowing powder with an ivory colour. The bulk density of powder was 438 g/1 and the residual solvent content was 29.7 weight%.

[0082] Polymerisation process

Polymerization was carried out in a typical Phillips slurry loop process at 4t/h, 75°C, 13% Ethylene, 4 MPa, in isobutene using the above prepared catalyst. 1-hexene (120kg/h) was used a comonomer. Hydrogen (2g/h) was used to adjust the melt flow index of the product. The obtained powder was additivated and pelletized to obtain the product of inventive Example 1. The polymer properties are reported in Table 1.

COMPARATIVE EXAMPLE 1 [0083] The polyethylene of Comparative Example 1 is a sample of the commercial product Hostalen 473 IB, sold by LyondellBasell and prepared by slurry multi-step polymerization with a Ziegler catalyst. The polymer properties are reported in Table 1.

COMPARATIVE EXAMPLE 2

[0084] The polyethylene of Comparative Example 2 is a sample of the commercial product LP3721 C, sold by LyondellBasell and prepared by gas phase polymerization with a Cr-based catalyst. The polymer properties are reported in Table 1.

[0085] Table I

(*) Still running

[0086] As can be seen from the data in Table 1, the inventive polyethylene composition of Example 1 has a very high pressure resistance according to DIN 16 833, and an optimal E-modulus value. The pressure resistance is advantageously higher than for the polyethylene material of Comparative Example 2. [0087] It is to be noted that in the inventive polyethylene composition, such a favourable balance of properties is achieved in combination with a rather high MIP value, which means that the inventive polyethylene composition has a superior process-ability in the molten state.

[0088] It has also been found that, in an ageing test carried out in air atmosphere at 120°C, the MIF value of the inventive polyethylene composition undergoes a much lower decrease with ageing time with respect to a standard PE-RT materials, here represented by the polyethylene material of Comparative Example 1.

[0089] The respective trends are shown in Figure 1, wherein the percentage of MIF decrease (Y axis) with ageing time (minutes, X axis) is reported for the polymer of Example 1 (upper line) and the polymer of Comparative Example 1 (lower line). This property is very much desired for hot water applications with working temperatures higher than 80°C.

[0090] In fact, a drop in melt flow index indicates that the material properties change in the presence of a strong oxidant such as oxygen.

[0091] Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of the ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.