Multimodal polyethylene material

The present invention relates to a polyethylene resin with a multimodal molecular weight distribution, a polymer composition containing this resin, and the use of a multimodal polyethylene resin, e.g. for the production of a shaped article. The resin and composition according to the invention are particularly suitable for the production of pipes.

Polyethylene compositions with a multimodal molecular weight distribution (MWD), e.g., a bimodal MWD, can offer significant advantages over unimodal polyethylenes or other polyolefins. For example, bimodal polyethylenes can combine the favorable mechanical properties of high molecular weight polyethylene with good processing properties of low molecular weight polyethylene. It is known in the art that such materials can be successfully used in a variety of applications, including film or pipe applications. Known multimodal polyethylenes suggested for use in pipes include the materials disclosed in PCT applications with publication numbers WO 97/29152, WO 00/01765, WO 00/18814, WO 01/02480 and WO 01/25328.

Due to the potentially catastrophic consequences of material failure, the acceptability of any plastic pipes for water or gas distribution is subject to product standards and performance requirements specified in standards, e.g. DIN (German Industrial Standard, "Deutsche Industrie Norm) or standards established by ISO (International Organization for Standardization, Geneva, Switzerland). For example, currently used polyethylene pipe materials such as pressure pipes or irrigation pipes meet the so-called PE80 or PE100 criteria (PE stands for polyethylene). Pipes manufactured from polyethylenes classified as PE80 or PE100 resins must withstand hoop stress or wrap stress of 8 MPa (PE80) or 10 MPa (PE100) at 20 ° C for 50 years. PE100 resins are grades of high-density polyethylene (HDPE), typically having a density of at least about 0.950 g / cm.³ or above.

The relatively low long term hydrostatic strength (LTHS) at high temperatures is a known disadvantage of traditional polyethylenes, making these materials unsuitable for use in pipes exposed to high temperatures, such as domestic pipes. Household piping systems typically operate at pressures in the range of about 2x10² kPa to about 10³ kPa and a temperature of approximately 70 ° C, with an emergency temperature of approximately 95-100 ° C. Household pipes include pipes for hot and / or cold water in pressurized heating and drinking water networks inside buildings, as well as pipes for snow melting or heat recovery systems. The performance requirements for various classes of hot water pipes, including underfloor heating, radiator connectors and sanitary pipes are given e.g. in the international standard ISO 10508 (first edition on October 15, 1995, "Thermoplastic pipes and fittings for hot and cold water systems).

Materials typically used to manufacture pipes exposed to elevated temperatures include polybutylene, random polypropylene copolymer, and cross-linked polyethylene (PEX). Cross-linking of polyethylene is necessary to achieve the required LTHS at high temperatures. Crosslinking can be carried out during extrusion, resulting in reduced productivity, or after extrusion. In both cases, cross-linking causes a significant increase in costs compared to extrusion of thermoplastic pipes.

Increased Temperature Resistance Polyethylenes (PERT), as defined in ISO-1043-1, are a class of high temperature polyethylene materials that have recently been introduced to the market for pipes. Current PE-RT resins compare unfavorably with PEX materials in some respects, as e.g. the walls of PE-RT-based pipes have to be thicker than those of PEX-based pipes due to the lower load parameters.

There continues to be a need for new polyethylene materials that could provide an advantageously balanced combination of thermal, mechanical and processing properties. In particular, there is still a need for new polyethylene materials that provide higher high temperature resistance (e.g. in the service temperature range from about 40 to about 80 ° C and measurement temperatures up to about 110 ° C), higher stress resistance, good tensile strength and impact strength, and excellent processing properties, without the need for cross-linking. The object of the invention is to meet these and other needs.

The invention provides a polyethylene resin with a multimodal molecular weight distribution. Such a multimodal polyethylene resin is characterized by (a) a density in the range of 0.925

PL 203 162 B1 to 0.950 g / cm³ and (b) a melt index (I2) in the range of 0.1 to 5 g / 10 minutes; and (c) comprises at least one high molecular weight (HMW) ethylene / α-olefin interpolymer and at least one ethylene polymer with low molecular weight (LMW) where (d) the HMW component comprises at least one or more ethylene / α-olefin interpolymers having a density ranging from 0.910 to 0.935 g / cm 2³ and a melt index of 0.02 to 1.0 g / 10 minutes, and (e) the LMW component comprises at least one or more ethylene polymers which are an ethylene homopolymer and an ethylene / α-olefin interpolymer having a density ranging from 0.945 to 0.965 g / cm³ and a melt index of at least 2.0 g / 10 minutes or greater.

The invention also provides a polymeric composition comprising such a multimodal polyethylene resin and at least one other additional component which is preferably selected from the group consisting of fillers and additives.

The invention also relates to the use of such a multimodal polyethylene resin for the manufacture of a shaped article selected from the group consisting of film, sheet, fiber, profile, compact and pipe. One specific aspect of the invention relates to a use in the manufacture of products that require high durability, such as pipes.

As used herein, the term "comprising" means "including.

As used herein, the term "interpolymer" refers to polymers made by polymerizing at least two monomers. Accordingly, the generic term "interpolymer" includes the terms copolymer, typically used to denote polymers made from two different monomers, and polymers made from more than two different monomers, such as terpolymers.

Unless otherwise stated, all parts, percentages, and ratios are by weight. The expression "to," used in specifying a numeric range, includes a value that is less than or equal to the numeric value following that expression. The "from" expression used in specifying a numeric range includes a value that is greater than or equal to the numeric value following that expression.

"HMW means high molecular weight and" LMW means low molecular weight.

The abbreviation "cm³ stands for cubic centimeters.

Unless specifically stated otherwise, the term "melt index" means the I2 melt index as determined according to ASTM D1238 under a load of 2.16 kg and a temperature of 190 ° C.

Unless otherwise stated, the term "alpha-olefin (alpha-olefin) refers to aliphatic or cycloaliphatic alpha-olefins containing at least 4, preferably 4-20 carbon atoms.

A multimodal polyethylene resin with a multimodal molecular weight distribution has (a) a density ranging from 0.925 g / cm³preferably from 0.935 g / cm³, up to 0.950 g / cm³preferably up to 0.945 g / cm³and (b) a melt index (I2) in the range of 0.1 g / 10 minutes to 5 g / 10 minutes, preferably up to 1 g / 10 minutes.

Such a multimodal polyethylene resin comprises at least one high molecular weight ethylene (HMW) interpolymer and at least one low molecular weight ethylene polymer (LMW). The HMW interpolymer has a significantly higher weight average molecular weight than the LMW polymer. This difference in molecular weight is reflected in the different melt indexes. A multimodal polyethylene resin which has a trimodal or, most preferably, a bimodal molecular weight distribution is preferred. The preferred polyethylene resin of the invention has a bimodal molecular weight distribution and consists of one unimodal HMW ethylene interpolymer and one unimodal LMW ethylene polymer.

The HMW component of the multimodal polyethylene resin of the invention comprises one or more, preferably one, HMW ethylene interpolymer. Such an ethylene interpolymer has a density ranging from 0.910 g / cm³preferably from 0.915 g / cm³to 0.935 g / cm³preferably up to 0.925 g / cm³, and a melt index of 1.0 g / 10 minutes or less, preferably 0.05 g / 10 minutes or less. Suitably, the HMW ethylene interpolymer has a melt index of 0.02 g / 10 minutes or greater. The HMW ethylene interpolymer comprises ethylene interpolymerized with at least one alpha-olefin, preferably an aliphatic C4-C20 alpha-olefin, and / or an unconjugated C6-C18 diolefin such as 1,4-hexadiene or 1,7-octadiene. While the HMW interpolymer may be a terpolymer, a preferred interpolymer is an ethylene copolymer with an aliphatic alpha-olefin, more preferably an alpha-olefin that contains 4-10 carbon atoms. Particularly preferred aliphatic alpha-olefins are selected from the group consisting of butene, pentene, hexene, heptene and octene. Suitably, the HMW component is present in an amount from 30% by weight, preferably from 40% to 60% by weight, preferably up to 50% (based on the total amount of polymer

PL 203 162 B1 in a multimodal polyethylene resin). More preferably, the HMW component is present in an amount of from 40 to 55% by weight. The molecular weight distribution as reflected by the Mw / Mn ratio of the HMW component is relatively narrow, preferably less than 3.5, more preferably less than 2.4.

The LMW component of the multimodal polyethylene resin of the invention comprises one or more, preferably one LMW ethylene polymer. The LMW ethylene polymer has a density ranging from 0.945 to 0.965 g / cm³ and a melt index of at least 2.0 g / 10 minutes or greater, preferably at least 5 g / 10 minutes, more preferably at least 15 g / 10 minutes or greater. Suitably, the LMW component has a melt index of less than 2000 g / 10 minutes, preferably less than 200 g / 10 minutes. A preferred LMW ethylene polymer is an ethylene interpolymer having a density ranging from 0.950 to 0.960 g / cm3.³ and a melt index of at least 2 g / 10 minutes, preferably in the range of about 10 to 150 g / 10 minutes. Preferred LMW ethylene interpolymers are ethylene / α-olefin copolymers, especially those copolymers wherein the aliphatic α-olefin comonomer contains 4-10 carbon atoms. The most preferred aliphatic aolefin comonomers are selected from the group consisting of butene, pentene, hexene, heptene and octene. Suitably, the LMW component is present in an amount from about 40% by weight, preferably from about 50%, to about 70% by weight, preferably up to about 60% (based on the total amount of polymers contained in the multimodal polyethylene resin of the invention). More preferably, the LMW component is present in an amount from about 45 to about 60% by weight.

While the α-olefins incorporated into the HMW component and the LMW component contained in the multimodal polyethylene resin of the invention may be different, multimodal polyethylene resins are preferred in which the HMW and LMW interpolymers contain the same type of α-olefin, preferably 1-butene. 1-pentene, 1-hexene, 1-heptene or 1-octene. Typically, the comonomer content of the HMW ethylene interpolymer is higher than that of the LMW polymer.

The multimodality of the polyethylene resin according to the invention can be determined by known methods. The multimodal molecular weight distribution (MWD) is seen in a gel permeation chromatography (GPC) curve showing the presence of two or more constituent polymers, with the number of constituent polymers corresponding to the number of perceivable peaks, or one constituent polymer may be present as a hump, shoulder, or tail in relation to to the MWD of the other constituent polymer.

For example, a bimodal MWD can be deconvolution into two components: the HMW component and the LMW component. After deconvolution, the half-maximum peak width (WAHM) and the weight average molecular weight (Mw) of each component can be determined. Then the degree of separation ("DOS) between the two components can be calculated from the following equation:

DOS =

M.^H.-M

WAHM^H. + WAHM ^L. Where's m_in^H. them _in^L. are the weight average molecular weight of the HMW component and the LMW component, respectively; and WAHM^H. and WAHM^L. are the peak width at half maximum on the deconvolved molecular weight distribution curve for the HMW component and the LMW component, respectively. The DOS of the bimodal resins of the invention is at least 0.01 or greater, preferably greater than about 0.05, 0.1, 0.5, or 0.8.

WO 99/14271 also describes a suitable deconvolution technique for multi-component polymer blend compositions.

Preferably, both the HMW component and the LMW component are unimodal. The MWD in the GPC curves of the individual components, e.g., the HMW component and the LMW component, respectively, shows substantially no multicomponent polymers (i.e., no humps, shoulders, or tails are present in the GPC curve). Each molecular weight distribution is narrow enough and the average molecular weight values ​​are different. Ethylene interpolymers suitable for use as both HMW and / or LMW components include both homogeneously branched (homogeneous) interpolymers and heterogeneously branched (heterogeneous) interpolymers.

Homogeneous ethylene interpolymers for use in the resin of the invention include ethylene-based interpolymers in which any comonomer is randomly distributed within a given interpolymer molecule and the ethylene / comonomer ratio is substantially the same in all interpolymer molecules. Homogeneous ethylene interpolymers are typically characterized by a substantially single peak (point) of melting between -30 ° C and 150 ° C as determined by Differential Scanning Calorimetry (DSC). Typically, homogeneous ethylene interpolymers also have a relatively narrow molecular weight distribution (MWD) compared to corresponding heterogeneous ethylene interpolymers. Preferably, the molecular weight distribution, defined as the ratio of the weight average molecular weight to the number average molecular weight (Mw / Mn), is less than about 3.5. Moreover, the homogeneity of the ethylene interpolymers is reflected in a narrow composition distribution which can be measured and represented using known methods and parameters such as SCBDI (Short Chain Branch Distribution Index) or CDBI (Wide Composition Distribution Index). The SCBDI of the polymer is readily calculated from data obtained by known techniques such as e.g. temperature-elevated elution fractionation (usually abbreviated as "TREF), as described e.g. in Wild et al., Journal Polymer Science, Poly. Phys. Ed., Vol. 20, p. 441 (1982), in U.S. Patent No. 4,798,081 (Hazlitt et al.) Or in U.S. Patent No. 5,089,321 (Chum et al.), The disclosures of all of these publications being incorporated by reference . CDBI is defined as the% by weight of polymer particles having a comonomer content within 50% of the median total molar comonomer content. Typically, the SCBDI or CDBI values ​​of the homogeneous ethylene / α-olefin interpolymers used in the present invention are greater than about 50%.

The homogeneous ethylene interpolymers that can be used in the resin of the invention fall into two categories, linear homogeneous ethylene interpolymers and substantially linear homogeneous ethylene interpolymers. Both categories are known and commercially available.

Homogeneous linear ethylene interpolymers are interpolymers with a homogeneous short chain branching distribution having no measurable or detectable long chain branching. Such homogeneous linear ethylene interpolymers can be made by polymerization methods that provide a uniform branching distribution, e.g., as disclosed by Elston in US Patent No. 3,645,992, which uses soluble vanadium catalyst systems. Other single site catalyst systems include metallocene catalyst systems of the type disclosed, for example, in U.S. Patent No. 4,937,299 to Ewena et al. or in U.S. Patent No. 5,218,071 to Tsutsui et al. they are also useful for the preparation of homogeneous linear ethylene interpolymers.

Substantially linear ethylene interpolymers (SLEPs) are homogeneous long chain branched interpolymers, meaning that in bulk the ethylene interpolymer is substituted with an average of from about 0.01 to about 3 long chain branches / 1000 carbon atoms in total (where "the carbon atoms collectively include the carbon atoms of both in the main chain as well as in branches). Preferably the polymers are substituted with from about 0.01 to about 1 long chain branch / 1000 carbon atoms in total, more preferably from about 0.05 to about 1 long chain branch / 1000 carbon atoms in total, especially from about 0.3 to about 1 long chain branch / 1,000 carbon atoms in total. The presence of long chain branching in such ethylene interpolymers can be determined by known methods such as gel permeation chromatography coupled with a narrow angle laser light scattering detector (GPC-LALLS) and gel permeation chromatography coupled with a differential viscometer detector (GPC-DV).

In the case of substantially linear ethylene polymers, a symptom of the presence of long chain branching is an increase in rheological properties, which can be quantified and expressed e.g. by gas extrusion rheometry (GER) and / or as an increase in the ratio (I10 / I2). The melt flow ratio of the substantially linear ethylene / α-olefin interpolymers can vary substantially independently of the molecular weight distribution (Mw / Mn ratio).

Substantially linear ethylene polymers are a unique class of compounds that have been described in numerous publications, including, for example, U.S. Patent Nos. 5,272,236, 5,278,272, and 5,665,800, each of which is incorporated by reference. Such SLEPs are available, e.g., from The Dow Chemical Company as polymers produced by the INSITE ™ catalyst process and technology, such as AFFINITY ™ (POP) polyolefin plastomers.

Preferably, the SLEP is prepared using a constrained geometry catalyst. Such a catalyst can be more accurately described as having a metal-to-metal coordination complex of Groups 3-10 or a series of lanthanides on the Periodic Table of the Elements and a delocalized, pi (π) bonded group substituted with a voltage-inducing moiety, the complex exhibiting a stiffened structure around the metal atom. , so that the angle at the metal between the center of mass of the delocalized, π-linked substituted group, and the center of at least one other substituent is less than such an angle in a similar complex containing the like

A pi-linked group not containing such a voltage inducing substituent, where in the case of such complexes having more than one delocalized π-linked group, only one of them for each metal atom in the complex is a cyclic delocalized substituted-linked group the π bond. Suitable constrained catalysts for the preparation of substantially linear ethylene polymers include e.g. the catalysts disclosed in US Patent Nos. 5,055,438, 5,132,380, 5,064,802, 5,470,993, 5,453,410, 5,374,696, 5,532,394, 5,494,874, and 5,189,192, all of the disclosures being incorporated by reference.

The catalyst system further comprises a suitable activating cocatalyst.

Suitable cocatalysts for this purpose include polymeric or oligomeric aluminoxanes, especially methylaluminoxanes, as well as neutral, compatible, non-coordinating ion-forming compounds. The so-called modified methylaluminoxane (MMAO) is also suitable for use as a cocatalyst. When aluminoxanes, including modified methylaluminoxanes, are used in the polymerization, they are preferably used in such an amount that the residual catalyst remaining in the (finished) polymer is preferably from about 0 to about 20 ppm aluminum, especially from about 0 to about 10 ppm aluminum. , more preferably from about 0 to about 5 ppm aluminum. To measure the properties of the bulk polymer, an aqueous HCl solution is used to extract the aluminoxane from the polymer. Preferred cocatalysts, however, are inert, non-coordinating boron compounds, such as those disclosed in EP-A-0520732, the disclosure of which is hereby incorporated by reference.

Substantially linear ethylene interpolymers are made by a continuous (as opposed to batch) controlled polymerization process using at least one reactor (as disclosed in e.g. as literature sources), but can also be produced using multiple reactors (e.g. using a multi-reactor system described in U.S. Patent No. 3,914,342, the disclosure of which is incorporated by reference) at polymerization temperature and pressure conditions sufficient to provide interpolymers with the desired properties. Multiple reactors may be connected in series or in parallel, with at least one constrained geometry catalyst being used in at least one of the reactors.

Substantially linear ethylene polymers can be prepared by continuous solution, slurry or gas phase polymerization in the presence of a constrained geometry catalyst, e.g., according to the process disclosed in EP-A-416,815, the disclosure of which is incorporated by reference. Polymerization can typically be performed in any known reactor system including, but not limited to, vessel reactor (s), spherical reactor (s), loop loop reactor (s), or combinations thereof, etc. with any or all reactors partially operating. or completely adiabatic, non-adiabatic or a combination thereof, etc. Preferably, a continuous solution polymerization process in a loop reactor is used to prepare the substantially linear ethylene polymer used in the present invention.

The continuous polymerization required to produce substantially linear ethylene polymers can generally be carried out under well-known Ziegler-Natta or Kaminsky-Sinn type polymerization reaction conditions, i.e. at 0-250 ° C and atmospheric pressure to 1000 atmospheres (100 MPa) . If desired, the reaction can be carried out in suspension, in solution, in suspension, in the gas phase or under other conditions.

The carrier may be used in the polymerization, although catalysts are preferably used under homogeneous (i.e., dissolved) conditions. It should of course be understood that the catalyst system is formed in situ when the catalyst and cocatalyst components are added directly to the polymerization process and a suitable solvent or diluent, including condensed monomer, is used in the polymerization process. Preferably, however, the active catalyst is prepared in a separate step in a suitable solvent prior to addition to the polymerization mixture.

Heterogeneous ethylene-based polymers include ethylene / α-olefin interpolymers characterized by a linear backbone and a DSC melting curve with a distinct melting point peak above 115 ° C attributable to the high density fraction. Such heterogeneous interpolymers typically have a broader molecular weight distribution than comparable homogeneous interpolymers. Typically, heterogeneous ethylene interpolymers have a CDBI of about 50% or less, indicating that such interpolymers are a mixture of molecules with different comonomer content and varying amounts of short chain branching. The heterogeneous ethylene polymers that can be used in the practice of the invention include those made with a coordination catalyst at high temperature and relatively low pressure. Ethylene polymers and copolymers prepared using a (multi-site) coordination catalyst, such as a Ziegler-Natta catalyst or a Phillips catalyst, are generally known as linear polymers due to the substantial absence of branched polymerized monomer chains, side to the backbone. .

The HMW ethylene interpolymer may be a heterogeneous interpolymer or a homogeneous interpolymer, a homogeneous interpolymer being preferred. Particularly preferred HMW ethylene interpolymers are homogeneous, substantially linear HMW ethylene interpolymers. The LMW ethylene interpolymer may be a heterogeneous interpolymer or a homogeneous interpolymer, with a heterogeneous interpolymer being preferred.

The multimodal polyethylene resin of the invention can be prepared by any suitable method suitable for homogeneously blending ethylene-based polymers. For example, the HMW component and the LMW component may be mixed by solid mechanical means, e.g. in the form of a powder or granules, and then one or both, preferably both, components may be melted using known means and devices. Preferably, the multimodal resin of the invention is prepared by in situ mixing the HMW component with the LMW component, e.g. by using two or more reactors, connected in series or in parallel. According to a preferred technique, the multimodal polyethylene resin of the invention is produced by interpolymerizing ethylene and the desired comonomer or comonomers, such as aliphatic C₄-C₁₀ α-olefin, using a single site catalyst, e.g. a constrained geometry catalyst in at least one reactor, and a multi site catalyst in at least one other reactor. The reactors may be connected in parallel or, preferably, in series. Preferably, a single site catalyst, e.g. a constrained geometry catalyst, is provided in the first reactor and a multi site catalyst in a second reactor.

In particular, a dual series polymerization system is used. In a preferred embodiment of the invention, the serial polymerization is carried out in such a way that fresh catalyst is injected into each reactor separately. Preferably, when the catalyst is injected separately into each reactor, no (or essentially no) living polymer or active catalyst is introduced from the first reactor into the second reactor since polymerization in the second reactor is only achieved by injecting fresh catalyst and monomer (and comonomer).

In another preferred embodiment, the composition is prepared using a multi-reactor system (preferably a two-reactor system) in series with the fresh soluble catalyst system injected into the first reactor only, the process being operated such that the living polymer and / or the components are of the catalyst is passed from the first reactor to the next reactor to effect polymerization with fresh monomer and optionally comonomer.

Most preferably, whether separate injection into each reactor or injection into the first reactor is used, the resulting resin is characterized in that it comprises constituent polymers with different unimodal molecular weight distributions.

Most preferred is a multimodal polyethylene resin comprising a HMW interpolymer as defined herein as preferred, more preferred or extremely preferred and an LMW polymer identified herein as being preferred, more preferred or extremely preferred, including a bimodal polyethylene resin used to illustrate the invention.

Also within the scope of the invention is a composition comprising the multimodal polyethylene resin of the invention and at least one other additional component. Preferably, such an additional component is added to the multimodal polyethylene resin of the invention. Suitable additional ingredients are e.g. other polymers, fillers, or additives, provided that these additional ingredients do not adversely affect the desired beneficial properties of the multimodal polyethylene resin of the invention. Rather, the additional ingredients are selected to support the beneficial properties of the multimodal ethylene resin of the invention and / or to support or enhance its particular suitability for a desired application. Other polymers included in the composition of the invention are polymers that do not qualify as an HMW interpolymer or an LMW polymer as defined herein. Conveniently, such polymers are compatible with the multimodal polyethylene resin of the invention. Preferred additional ingredients are non-polymeric ingredients. Additives include processing aids, UV stabilizers, antioxidants, pigments or colorants. Compositions comprising the preferred, more preferred or most preferred multimodal polyethylene resin according to the invention are most preferred.

PL 203 162 B1

The inventive resins can be used to make a shaped article selected from the group consisting of film, sheet, fiber, profile, compact and pipe, and such use is also within the scope of the invention. Such an article can be a monolayer or multilayer article produced by any suitable known conversion technique using heat, pressure or a combination thereof to obtain a shaped article. Suitable conversion techniques include e.g. blow molding, coextrusion blow molding, injection molding, injection stretch blow molding, compression molding, extrusion, pultrusion, calendering and thermoforming. A shaped article made from the preferred, more preferred or particularly preferred resin or composition according to the invention is most preferred.

The multimodal polyethylene resins and compositions of the invention are particularly useful in long-life applications, especially in pipes, without the need for cross-linking. Pipes containing at least one multimodal polyethylene resin are another application aspect of the invention and include monolayer pipes as well as multilayer pipes including multilayer composite pipes. Typically, these pipes contain a multimodal polyethylene resin in the form of a composition (blend) that also contains a suitable additive package, e.g. an additive package for use in pipes, and / or one or more fillers. Such additions and additive kits are known.

Single-layer pipes contain a single layer made of a composition according to the invention containing a multimodal polyethylene resin according to the invention and suitable additives usually used or suitable for pipe applications. Such additives include colorants and materials useful to protect the bulk polymer from certain adverse environmental factors, e.g., oxidation during extrusion or degradation under operating conditions, such as e.g. stabilizers used in processing, antioxidants, pigments, metal deactivating agents, additives increasing resistance to the action of chlorine and agents protecting against UV radiation. Preferred multilayer composite pipes include metal-plastic composite pipes, which are pipes comprising one or more, e.g., one or two layers, comprising the composition of the invention and a barrier layer. Such pipes include e.g. three-layer composite pipes with general structure PE / adhesive layer / barrier layer or barrier layer / adhesive layer / PE, or five-layer composite pipes with general structure PE / adhesive layer / barrier layer / adhesive layer / PE or polyolefin / adhesive layer / barrier layer / adhesive layer / PE. In such structures, PE means polyethylene layers, which may be made of the same or different polyethylene compositions, preferably compositions containing PE-RT, including at least one multimodal polyethylene composition according to the invention. Suitable polyolefins include, for example, high-density polyethylene, and polypropylene and polybutylene homopolymers and interpolymers. A multilayer composite pipe in which at least the inner layer comprises the multimodal polyethylene resin of the invention in uncrosslinked form is preferred. A more preferred is a multilayer composite pipe in which both PE layers contain the multimodal polyethylene resin of the invention. In multilayer pipes, e.g. in the three-layer and five-layer structures exemplified above, the barrier layer may be an organic polymer capable of providing suitable barrier properties such as ethylene vinyl alcohol (EVOH) or a metal, e.g. aluminum or stainless steel.

The resins and compositions of the invention are particularly suitable for domestic and technical pipes operated at elevated temperatures, e.g. above 40 ° C, especially in the range from greater than 40 ° C to about 80 ° C. Such pipe applications include e.g. hot water pipes, e.g. drinking and / or sanitary water pipes, or pipes for underfloor heating. Such pipes can be single-layer or multi-layer. Preferred pipes according to the invention meet the performance requirements set out in the standards for hot water pipes, e.g. ISO 10508. The multimodal polyethylene resins according to the invention allow the production of pipes combining excellent high-temperature performance, which is reflected e.g. in excellent long-term hydrostatic resistance at elevated temperatures ( well above 20 ° C), with good flexibility. Good flexibility makes it easier, for example, to install pipes. Pipes can be produced without cross-linking, which improves processing economy and allows subsequent welding operations.

An important requirement for plastic pipes is their behavior under hoop stress (wrap), in accordance with ISO 9080 and ISO 1167. Long-term service life

Plastic pipes can be predicted from the creep rupture data and curves defining the allowable wrap stress (hoop stress) that the pipe can withstand without failing. Typically, in tests to determine long-term predicted performance properties, potential pipe materials are subjected to various pressures (stresses) and the service life at a given temperature is determined. To extrapolate to a service life of 50 years, e.g. at 20-70 ° C, tests are also carried out at higher temperatures. The determined service life curves at each temperature typically include a high stress malleable fracture region corresponding to a shorter life, and a lower brittle fracture stress region corresponding to a longer service life. A schematic representation of typical service life curves can be found on page 412, Fig. 5, J. Scheirs et al., TRIP 4 (12), 1996, pp. 408-415. The curves can be divided into three stages, Stage I representing the ductile fracture stage, Stage II (elbow) representing the gradual change in fracture character from ductile to brittle, and Stage III representing the brittle fracture stage. The stages II and III are of particular interest because they determine the life of the pipe in practice. The pipes according to the invention are characterized by an excellent wrap-around tension, especially at high temperatures.

The invention is further illustrated by the following examples which should not, however, be considered as limiting the invention.

Examples

Melt indices are expressed as I2 (determined according to ASTMD-1238, condition E, 190 ° C / 2.16 kg). The ratio of I10 (determined according to ASTM D-1238, condition N, 190 ° C / 10 kg) to I2 is the ratio of the melt flow rate and is denoted as I10 / I2

Tensile properties such as yield point, yield stress, maximum tensile stress and maximum elongation, stress at break and strain at break are determined according to ISO 527 on 5A moldings at a measurement speed of 50 mm / minute.

The Izod impact strength was measured in accordance with ASTM D-256.

The flexural modulus was measured according to the ASTM D-790 standard and the mean hardness D was determined according to the ASTM D-2240 standard.

The multimodal polyethylene resin used in the experiments was a bimodal ethylene interpolymer with I2 0.85 g / 10 minutes, density 0.940 g / cm³ and I10 / I2 9.8. The resin was prepared by in situ mixing by a (continuous) solution process using two reactors connected in series. The HMW ethylene interpolymer was a homogeneous, substantially linear ethylene / octene copolymer made in the first reactor using a constrained geometry catalyst. This HMW interpolymer had an I2 of 0.034 g / 10 minutes and a density of 0.921 g / cm³. The weight average molecular weight was 228,000 and the Mw / Mn ratio was 2.1. The LMW ethylene polymer was a heterogeneous, linear ethylene / octene copolymer with an I2 melt index of 20 g / 10 minutes and a density of 0.953 g / cm.³. The weight average molecular weight of the LMW polymer was 52,100 and the Mw / Mn ratio was 3. The LMW ethylene polymer was prepared in a second reactor using a multi-site Ziegler-Natta (coordination) catalyst. The ratio of the HMW copolymer to the LMW copolymer in the bimodal polyethylene resin was 40-60.

The resin had the following tensile properties, impact strength and other properties (each value reported being the average of 5 measurements):

Yield point [MPa]: 21

Strain at yield [%]: 13

Maximum tensile stress [MPa]: 36

Maximum elongation [%]: 760

Stress at break [MPa]: 36

Strain at break [%]: 760

Modulus of elasticity in bending [MPa]: 955

Hardness D: 61

Izod impact strength at 20 ° C [J / m] 238

Izod impact strength at -40 ° C [J / m]: 8

Monolithic pipes made of the above resin were subjected to hydrostatic pressure tests according to the method specified in ISO 1167 (1996), using water as the internal and external measuring medium. The pipes had nominal dimensions of 16 mm x 2 mm.

PL 203 162 B1

The results of the measurement of the wrap-around stress are given in Table 1.

<td>Temperature [° C]</td><td>Wrap stress [MPa]</td><td>Time to destruction [h] *</td><td>Destruction type *</td>

<td> 20</td><td> 10,57</td><td> &gt; 3096</td><td></td>

<td> 20</td><td> 10,54</td><td> &gt;10344</td><td></td>

<td> 20</td><td> 10,44</td><td> &gt;10344</td><td></td>

<td> 20</td><td> 10,40</td><td> &gt; 4056</td><td></td>

<td> 20</td><td> 10,32</td><td> &gt; 4056</td><td></td>

<td> 80</td><td> 5,65</td><td> 656</td><td>ductile</td>

<td> 80</td><td> 5,59</td><td> 1245</td><td>ductile</td>

<td> 80</td><td> 5,52</td><td> &gt; 5952</td><td></td>

<td> 80</td><td> 5,49</td><td> &gt; 3600</td><td></td>

<td> 80</td><td> 5,45</td><td> &gt; 3600</td><td></td>

<td> 80</td><td> 5,42</td><td> &gt; 5952</td><td></td>

<td> 80</td><td> 5,35</td><td> &gt; 4056</td><td></td>

<td> 80</td><td> 5,34</td><td> &gt; 3600</td><td></td>

<td> 80</td><td> 5,30</td><td> &gt; 5952</td><td></td>

<td> 80</td><td> 5,25</td><td> &gt;3600</td><td></td>

<td> 110</td><td> 2,91</td><td> &gt; 3912</td><td></td>

<td> 110</td><td> 2,89</td><td> &gt; 3912</td><td></td>

<td> 110</td><td> 2,84</td><td> &gt; 2616</td><td></td>

<td> 110</td><td> 2,79</td><td> &gt; 3912</td><td></td>

<td> 110</td><td> 2,47</td><td> &gt;11976</td><td></td>

<td> 110</td><td> 2,11</td><td> &gt;11976</td><td></td>

* "&gt;" Means that the sample is still tested and has not been damaged. In this case, the nature of the destruction cannot be indicated.

Pipes made of bimodal polyethylene resin show excellent resistance to wrap around stress, especially at high (elevated) temperatures. Surprisingly, no elbow (stage II) has appeared so far to reflect the change in failure character from ductile to brittle. The test results have already exceeded the control points for PE-RT according to DIN 16883 (1.9 MPa / 8760 hours at 110 ° C) and PEX according to ISO 10146 (2.5 MPa / 8760 hours at 110 ° C).