WO2018107308A1

WO2018107308A1 - Heat conductive pe composition for pipe applications

Info

Publication number: WO2018107308A1
Application number: PCT/CN2016/000687
Authority: WO
Inventors: Xin Zhou; Dongyu FANG; Shih-Ping Chen
Original assignee: Borouge Compounding Shanghai Co., Ltd.
Priority date: 2016-12-16
Filing date: 2016-12-16
Publication date: 2018-06-21
Also published as: CN110036067A

Abstract

Provided is a heat conductive polyethylene composition,an article comprising the heat conductive polyethylene composition as well as processes for preparation of such an article.

Description

Heat conductive PE composition for pipe applications

The present invention relates to heat conductive polyethylene composition， an article comprising the heat conductive polyethylene composition as well as processes for the preparation of such an article.

Polymer pipes such as polyolefin pipes are inter alia used to transport fluids. In particular， polymer pipes are often used in applications requiring elevated temperatures， such as underfloor heating， hot and cold water transport， district heating， industrial applications， etc. In this regard， conventional polyolefin materials such as PE80 and PE100 show a life time of at least 50 years at 20℃ and they are usually used for such applications of heated gas and water transporting pipes. Thus， heat conductive polyethylenes have been developed targeting a life time of at least 50 years at not only 20℃， but also at 70℃ or even at 80℃. Although the known heat conductive polyethylenes can be used for such higher temperature applications， their thermal conductivity coefficient is still the same as that of conventional polyethylene， which is usually 0.38-0.40 W/m·K， which is not high enough.

Thus， there is still an urgent need in the art for a heat conductive polyethylene composition having a thermal conductivity coefficient of＞ 0.40 W/m·K. In particular， it is desirable to have a heat conductive polyethylene composition suitable for high temperature applications， including underfloor heating， geothermal， etc. and which saves the amount of pipes used in such applications.

Accordingly， the present invention is especially directed to a heat conductive polyethylene composition comprising

a) from 35.0 to 75.0 wt. -％of a multimodai ethylene polymer， based on the total weight (100.0 wt. -％) of the polyethylene composition，

b) from 10.0 to 40.0 wt. -％of an elastomeric copolymer comprising units derived from ethylene and C₃ to C₈ α-olefins， based on the total weight (100.0 wt. -％) of the polyethylene composition，

c) from 1.0 to 25.0 wt. -％of graphite， based on the total weight (100.0 wt. -％) of the polyethylene composition，

d) from 0.5 to 2.0 wt. -％of mineral oil， based on the total weight (100.0 wt. -％) of the polyethylene composition， and

e) from 0.5 to 7.0 wt. -％of one or more additive (s) ， based on the total weight (100.0 wt. -％) of the polyethylene composition.

In one embodiment， the polyethylene composition has a) a charpy notched impact strength (-30 ℃) measured according to ISO 179 of at least 10 kJ/m²， and/or b) a charpy notched impact strength (23 ℃) measured according to ISO 179 of at least 30 k J/m²， and/or c) a thermal conductivity coefficient measured according to ASTM E1530 of at least 0.42 W/m·K， and/or d) a density measured according to ISO 1183 in the range from 948 to 1020 kg/m³.

In another embodiment， the multimodal ethylene polymer is an ethylene homo-or ethylene copolymer.

In yet another embodiment， the mnltimodal ethylene polymer is an ethylene copolymer with one or more comonomers selected from C₄ to C₂₀ α-olefins.

In one embodiment， the multimodal ethylene polymer is an ethylene copolymer with two comonomers selected from C₄ to C₂₀ α-olefins.

In another embodiment， the multimodal ethylene polymer is a bimodal ethylene polymer.

In yet another embodiment， the multimodal ethylene polymer has a) a density measured according to ISO 1183 in the range from 930 to 950 kg/m³， and/or b) a MFR₅ (ISO 1133， 5 kg lcad) of 0.3 to 1.5 g/10min， and/or c) a MFR₂₁ (ISO 1133， 21.6 kg load) of 5 to 25 g/10min.

In one embodiment， the elastomeric copolymer has a) a density of equal or less than 935 kg/m³， and/or b) a MFR₂ (ISO 1133， 2.16 kg load) in the range of 0.5 to 30.0 g/10 min.

In another embodiment， the graphite is expanded graphite having a) a bulk density in the range of 0.1 to 0.25 g/cm³， and/or b) a BET surface area in the range of 20 to 100 m²/g， and/or c) a particle size d₉₀ of≤ 120 μm.

In yet another embodiment， the mineral oil comprises paraffinic hydrocarbons.

In one embodiment， the one or more additive (s) is/are selected from the group comprising antioxidants， coupling agents， adhesion promoter， waxes， anti-UVs， antistatic agents， clarifiers， brighteners， utilization agents and mixtures thereof.

The present invention is further directed to an article， preferably a pipe or pipe system， comprising the heat conductive polyethylene composition.

In one embodiment， the article is a heat conductive article.

In another embodiment， the article is suitable for applications at temperatures of ＞ 60 ℃.

The present invention is also directed to a process for the preparation of an article， preferably a pipe， comprising the steps of

a) providing a heat conductive polyethylene composition as defined herein， and

b) heating and extruding the heat conductive polyethylene composition of step a) ， whereby a temperature of up to 260 ℃ is applied in the extruder， such as to obtain the article， preferably the pipe.

The present invention is also directed to a process for the preparation of an article， preferably a pipe system， more preferably a pipe fitting， comprising the steps of

b) heating and injection-moulding the heat conductive polyethylene composition of step a) ， whereby a temperature of up to 260 ℃ is applied in the injection-moulding machine， such as to obtain the article， preferably the pipe system， more preferably the pipe fitting.

The invention is now defined in more detail.

As mentioned above， the heat conductive polyethylene composition comprises， preferably consists of，

a) from 35.0 to 75.0 wt. -％of a multimodal ethylene polymer， based on the total weight (100.0 wt. -％) of the polyethylene composition，

It is appreciated that the sum of the multimodal ethylene polymer， the elastomeric copolymer， the graphite， the mineral oil and the one or more additive (s) is 100.0 wt. -％， based on the total weight of the polyethylene composition.

Thus， the heat conductive polyethylene composition (100.0 wt. -％) comprises， preferably consists of，

a) from 35.0 to 75.0 wt. -％， more preferably from 40.0 to 70.0 wt. -％， and most preferably from 45.0 to 65.0 wt. -％of a multimodal ethylene polymer， based on the total weight (100.0 wt. -％) of the polyethylene composition，

b) from 10.0 to 40.0 wt. -％， more preferably from 20.0 to 40.0 wt. -％， and most preferably from 25.0 to 35.0 wt. -％of an elastomeric copolymer comprising units derived from ethylene and C₃ to C₈ α-olefins， based on the total weight (100.0 wt. -％) of the polyethylene composition，

c) from 1.0 to 25.0 wt. -％， more preferably from 3.0 to 20.0 wt. -％， and most preferably from 5.0 to 15.0 wt. -％of graphite， based on the total weight (100.0 wt. -％) of the polyethylene composition，

d) from 0.5 to 2.0 wt. -％， more preferably from 0.5 to 1.8 wt. -％， and most preferably from 0.5 to 1.5 wt. -％of mineral oil， based on the total weight (100.0 wt. -％) of the polyethylene composition， and

e) from 0.5 to 7.0 wt. -％， more preferably from 1.0 to 7.0 wt. -％， and most preferably from 2.0 to 7.0 wt. -％of one or more additive (s) ， based on the total weight (100.0 wt. -％) of the polyethylene composition.

It is appreciated that the heat conductive polyethylene composition is preferably in the form of pellets. Accordingly， the pellets preferably consist of the heat conductive polyethylene composition.

The heat conductive polyethylene composition preferably has a MFR₅ (ISO 1133， 5 kg load) of 0.5 to 1.5 g/10min， more preferably of 0.5 to 1.3 g/10min and most preferably of 0.6 to 1.1 g/10min.

Additionally or alternatively， the heat conductive polyethylene composition preferably has a MFR₂₁ (ISO 1133， 21.6 kg load) of 5 to 25 g/10min， more preferably of 8 to 21 g/10min and most preferably of 10 to 18 g/10min.

In one embodiment， the heat conductive polyethylene composition has

i) a MFR₅ (ISO 1133， 5 kg load) of 0.5 to 1.5 g/10min， more preferably of 0.5 to 1.3 g/10min and most preferably of 0.6 to 1.1 g/10min， or

ii) a MFR₂₁ (ISO 1133， 21.6 kg load) of 5 to 25 g/10min， more preferably of 8 to 21 g/10min and most preferably of 10 to 18 g/10min.

It is appreciated that the heat conductive polyethylene composition provides a thermal conductivity coefficient that is above the thermal conductivity coefficient typically achieved by polyethylene polymer， i.e. of＞ 0.40 W/m·K.

Thus， it is preferred that the heat conductive polyethylene composition of the present invention has a thermal conductivity coefficient measured according to ASTM E1530 of at least 0.42 W/m·K， preferably in the range from 0.42 to 1.0 W/m·K， more preferably from 0.43 to 0.95 W/m·K and most preferably from 0.43 to 0.90 W/m·K.

Thereby， the heat conductive polyethylene composition provides an increased thermal conductivity coefficient， resulting in a material saving when installing the pipes in application due to less pipes being used.

The heat conductive polyethylene composition of the present invention has a density measured according to ISO 1183 in the range from 948 to 1020 kg/m³， preferably from 948 to 1018 kg/m³， more preferably from 948 to 1014 kg/m³， and most preferably from 948 to 1010 kg/m³.

It is preferred that the heat conductive polyethylene composition has a

a) a thermal conductivity coefficient measured according to ASTM E1530 of at least 0.42 W/m·K， preferably in the range from 0.42 to 1.0 W/m·K， more preferably from 0.43 to 0.95 W/m·K and most preferably from 0.43 to 0.90 W/m·K， and

b) a density measured according to ISO 1183 in the range from 948 to 1020 kg/m³， preferably from 948 to 1018 kg/m³， more preferably from 948 to 1014 kg/m³， and most preferably from 948 to 1010 kg/m³.

Furthermore， the impact performance of the heat conductive polyethylene composition is improved greatly as compared with the ethylene polymers.

Preferably， the heat conductive polyethylene composition has a charpy notched impact strength (-30 ℃) meastured according to ISO 179 of at least 10 kJ/m²， preferably in the range from 10 to 60 kJ/m²， more preferably from 12 to 45 kJ/m² and most preferably from 14 to 40 kJ/m².

Additionally or alternatively， the heat conductive polyethylene composition preferably has a charpy notched impact strength (23 ℃) measured according to ISO 179 of at least 30 kJ/m²， preferably in the range from 30 to 99 kJ/m²， more preferably from 34 to 88 kJ/m² and most preferably from 38 to 80 kJ/m².

It is preferred that the heat conductive polyethylene composition has a

a) a charpy notched impact strength (-30 ℃) measured according to ISO 179 of at least 10 kJ/m²， preferably in the range from 10 to 60 kJ/m²， more preferably from 12 to 45 kJ/m² and most preferably from 14 to 40 kJ/m²， and

b) a charpy notched impact strength (23 ℃) measured according to ISO 179 of at least 30 kJ/m²， preferably in the range from 30 to 99 kJ/m²， more preferably from 34 to 88 kJ/m² and most preferably from 38 to 80 kJ/m².

Thus， the heat conductive polyethylene composition preferably has a

a) a charpy notched impact strength (-30 ℃) measured according to ISO 179 of at least 10 kJ/m²， preferably in the range from 10 to 60 kJ/m²， more preferably from 12 to 45 kJ/m² and most preferably from 14 to 40 kJ/m²， or

b) a charpy notched impact strength (23 ℃) measured according to ISO 179 of at least 30 kJ/m²， preferably in the range from 30 to 99 kJ/m²， more preferably from 34 to 88 kJ/m² and most preferably from 38 to 80 kJ/m²， or

c) a thermal conductivity coefficient measured according to ASTM E1530 of at least 0.42 W/m·K， preferably in the range from 0.42 to 1.0 W/m·K， more preferably from 0.43 to 0.95 W/m·K and most preferably from 0.43 to 0.90 W/m·K， or

d) a density measured according to ISO 1183 in the range from 948 to 1020 kg/m³， preferably from 948 to 1018 kg/m³， more preferably from 948 to 1014 kg/m³， and most preferably from 948 to 1010 kg/m³.

Alternatively， the heat conductive polyethylene composition has a

b) a charpy notched impact strength (23 ℃) measured according to ISO 179 of at least 30 kJ/m²， preferably in the range from 30 to 99 kJ/m²， more preferably from 34 to 88 kJ/m² and most preferably from 38 to 80 kJ/m²， and

c) a thermal conductivity coefficient measured according to ASTM E1530 of at least 0.42 W/m·K， preferably in the range from 0.42 to 1.0 W/m·K， more preferably from 0.43 to 0.95 W/m·K and most preferably from 0.43 to 0.90 W/m·K， and

It is required that the heat conductive polyethylene composition comprises a multimodal ethylene polymer.

Usually， an ethylene polymer， comprising at least two polyethylene fractions， which have been produced under different polymerization conditions resulting in different (weight average) molecular weights and molecular weight distributions for the fractions， is referred to as a ″multimodal″ ethylene polymer. Accordingly， in this sense the ethylene polymer of the invention is a multimodal ethylene polymer. The prefix ″multi″ relates to the number of different polymer fractions the polymer is consisting of. Thus， for example， an ethylene polymer consisting of two fractions is called ″bimodal″ . “Multimodal polyethylene polymer” or “Multimodai ethylene polymer” means herein the multimodality of the polyethylene with respect to the weight average molecular weight (in other terms with respect to molecular weight distribution (MWD) ) . Herein below the multimodal polyethylene polymer is also referred to as “multimodal ethylene polymer” or “multimodal ethylene polymer of the invention” .

The multimodal ethylene polymer is preferably bimodal.

The multimodal ethylene polymer is an ethylene homopolymer or an ethylene copolymer， preferably with less than 12.0 mol. -％total comonomer (s) present in the ethylene polymer. Preferably， the multimodal ethylene polymer is an ethylene copolymer with 0.08 to 12.0 mol. -％， more preferably with 0.1 to 5.0 mol. -％and most preferably with 0.1 to 3.0 mol. -％， total comonomer (s) present in the ethylene polymer.

The multimodal ethylene polymer preferably comprises two fractions of ethylene copolymer， and each fraction has a comonomer content of 0.04 to 6.0 mol. -％， more preferably of 0.05 to 2.5 mol. -％.

The comonomer may be one or more of the comonomers selected from the group of C4-C20 alpha olefins， especially 1-butene， 1-hexene， 1-octene， 4-methylpentene， whereby 1-butene and 1-hexene are most common. For example， the multimodal ethylene polymer comprises two of the eomonomers selected from the group of C4-C20 alpha olefins， especially 1-butene， 1-hexene， 1-octene， 4-methylpentene， preferably 1-butene and 1-hexene.

It is appreciated that the heat conductive polyethylene composition comprises the multimodal ethylene polymer in an amount from 35 to 75 wt. -％and more preferably from 40 to 70 wt. -％， based on the total weight (100.0 wt. -％) of the polyethylene composition. For example， the polyethylene composition comprises the multimodal ethylene polymer in an amount from 45 to 65 wt. -％， based on the total weight (100.0 wt. -％) of the polyethylene composition.

The multimodal ethylene polymer according to the present invention preferably has a MFR₅ (ISO 1133， 5 kg load) of 0.3 to 1.5 g/10min， moro preferably of 0.3 to 1.3 g/10min and most preferably of 0.5 to 1.1 g/10min.

Additionally or alternatively， the multimodal ethylene polymer preferably has a MFR₂₁ (ISO 1133， 21.6 kg load) of 5 to 25 g/10min， more preferably of 8 to 21 g/10min and most preferably of 10 to 18 g/10min.

In one embodiment， the multimodal ethylene polymer thus has

i) a MFR₅ (ISO 1133， 5 kg load) of 0.3 to 1.5 g/10min， more preferably of 0.3 to 1.3 g/10min and most preferably of 0.5 to 1.1 g/10min， or

Alternatively， the multimodal ethylene polymer has

i) a MFR₅ (ISO 1133， 5 kg load) of 0.3 to 1.5 g/10min， more preferably of 0.3 to 1.3 g/10min and most preferably of 0.5 to 1.1 g/10min， and

It is appreciated that the density of the multimodal ethylene polymer is below the density of the heat conductive polyethylene composition.

It is thus preferred that the multimodal ethylene polymer preferably has a density in the range from 930 to 950 kg/m³， more preferably from 940 to 948 kg/m³.

The multimodal ethylene polymer according to the present invention is further preferably characterized by a specific molecular weight distribution reflected by shear thinning indices as described below.

The multimodal ethylene polymer preferably has a SHI_2.7/210 of 5 to 50 when determined as described herein， more preferably 10 to 40 and most preferably 12 to 30. This shear thinning index range indicates good processability of the multimodal ethylene polymer.

The molecular weight relationships defined above indicates the specific polymer broadness， i.e. implies a unique relationship between LMW and HMW portions in a MWD curve. This weighting of the molecular weight distribution occurs results in the advantageous properties which are observed in the present application.

The multimodal ethylene polymer of the invention preferably comprises a LMW component (A) and a HMW component (B) . The lower weight average molecular weight polyethylene polymer component (A) ， which is referred herein shortly as LMW component (A) ， has lower weight average molecular weight than higher weight average weight molecular weight polymer component (B) ， which is referred to herein shortly as HMW component (B) . Both LMW and HMW components (A) and (B) are preferably obtainable by polymerisation using Ziegler Natta catalysis， ideally the same Ziegler Natta catalyst.

The weight ratio of LMW component (A) to HMW component (B) in the composition is preferably in the range 30： 70 to 70： 30， more preferably 35： 65 to 65： 35， most preferably 40： 60 to 60： 40. In some embodiments the ratio may be 35 to 45 wt. -％of LMW component (A) and 65 to 55 wt. -％HMW component (B) ， such as 37 to 42 wt. -％of LMW component (A) and 63 to 58 wt. -％HMW component (B) .

LMW component (A) and HMW component (B) of the multimodal ethylene polymer may both be ethylene copolymers or ethylene homopolymers， although preferably at least one of said LMW and HMW components is an ethylene copolymer. Preferably， the multimodal ethylene polymer comprises two ethylene copolymer components. Where one of the LMW or HMW components is an ethylene homopolymer， this is preferably the component with the lower weight average molecular weight (Mw) ， i.e. LMW component (A) .

A preferred multimodal ethylene polymer therefore comprises， preferably consists of， a LMW component (A) which is an ethylene copolymer with butene and/or hexene， preferably butene， as the comonomer， and a HMW component (B) ， which is preferably an ethylene copolymer with hexene as the comonomer.

The LMW component (A) of the multimodal ethylene polymer preferably has an MFR₂ of 10 g/10min or higher， more preferably of 50 g/10min or higher， and most preferably 100 g/10min or higher.

Furthermore， LMW component (A) preferably has an MFR₂ of 1000 g/10 min or lower， preferably 800 g/10 min or lower， and most preferably 600 g/10min or lower. Preferred ranges are fiom 100 to 500 g/10min， preferably from 150 to 400 g/10min.

Preferably， LMW component (A) is an ethylene homo-or copolymer， more preferably ethylene copolymer， with a density of at least 950 kg/m³. Preferably the density of the LMW component (A) is at least 955 kg/m³.

Furthermore， LMW component (A) preferably has a density of 975 kg/m³ or lower. Preferred ranges are from 950 to 975 kg/m³， preferably from 955 to 975 kg/m³.

Most preferably， LMW component (A) of the multimodal ethylene polymer is an ethylene copolymer. If LMW component (A) is a copolymer， the comonomer is preferably l-butene and/or 1-hexene， more preferably 1-butene. In case LMW component (A) is an ethylene copolymer， preferably LMW component (A) is an ethylene copolymer comprising 0.04 to 6.0 mol. -％comonomer， more preferably 0.05 to 2.5 mol. -％comonomer， even more preferably 0.1 to 1.5 mol. -％comonomer.

Preferably， HMW component (B) of the multimodal ethylene polymer is an ethylene homo-or copolymer with a density of less than 950 kg/m³. For example， HMW component (B) of the multimodal ethylene polymer is an ethylene homo-or copolymer with a density in the range of 930 to 945 kg/m³. Most preferably， HMW component (B) of the multimodal ethylene polymer is a copolymer. Preferred ethylene copolymers employ one or more alpha-olefin (e.g. C4-20 alpha-olefins) as comonomer (s) . Examples of suitable alpha-olefins include 1-butene， 1-hexene and 1-octene. 1-Hexene is especially preferred as at least one of the comonomer (s) present in HMW component (B) of the multimodal ethylene polymer. Preferably， HMW component (B) of the multimodal ethylene polymer comprises one comonomer which is 1-hexene. In case HMW component (B) is an ethylene copolymer， preferably HMW component (B) is an ethylene copolymer comprising 0.04 to 6.0 mol. -％ comonomer， more preferably 0.04 to 4.0 mol. -％comonomer， even more preferably 0.5 to 3.0 mol. -％comonomer and most preferably 0.5 to 2.5 mol. -％comonomer.

Where herein features of LMW component (A) and/or HMW component (B) of the multimodal ethylene polymer of the present invention are given， these values are generally valid for the cases in which they can be directly measured on the respective LMW component (A) or HMW component (B) ， e.g. when such components are separately produced. However， the multimodal ethylene polymer may also be and preferably is produced in a multistage process wherein e.g. LMW component (A) and HMW component (B) are produced in subsequent stages. In such a case， the properties of the LMW component (A) or HMW component (B) produced in the second step (or further steps) of the multistage process can either be inferred from polymers， which are separately produced in a single stage by applying identical polymerisation conditions (e.g. identical temperature， partial pressures of the reactants/diluents， suspension medium， reaction time) with regard to the stage of the multistage process in which the fraction is produced， and by using a catalyst on which no previously produced polymer is present. Alternatively， the properties of the LMW component (A) or HMW component (B) produced in a higher stage of the multistage process may also be calculated， e.g. in accordance with B.

Conference on Polymer Processing (The Polymer Processing Society) ， Extended Abstracts and Final Programme， Gothenburg， August 19 to 21， 1997， 4： 13.

Thns， although not directly measurable on the multistage process products， the properties of the LMW component (A) or HMW component (B) produced in higher stages of such a multistage process can be determined by applying either or both of the above methods. The skilled person will be able to select the appropriate method.

It is preferred that the multimodal ethylene polymer is prepared by

i) polymerizing ethylene and optionally at least one C4-20 alpha olefin comonomer such as to form a LMW component (A) ， and

ii) polymerizing ethylene and optionally at least one C4-20 alpha olefin comonomer in the presence of component (A) obtained in step i) such as to form a HMW component (B) ， and

iii) compounding the product obtained in step ii) optionally， and preferably， in the presence of additives to yield pellets.

Preferably， polymerizing steps i) and ii) may be carried out by polymerisation in one reactor using conditions which create a multimodal (e.g. bimodal) polymer product， e.g. using a catalyst system or mixture with two or more different catalytic sites， each site obtained from its own catalytic site precursor， or by polymerisation using a two or more stage， i.e. multistage， polymerisation process with different process conditions in the different stages or zones (e.g. different temperatures， pressures， polymerisation media， hydrogen partial pressures， etc. ) and using same or different catalyst systems， preferably the same catalyst system.

Polymer compositions produced in a multistage process are also designated as ″in-situ″ blends.

Most preferably， polymerizing steps i) and ii) are carried out by in-situ blending in a multistage process. The process for the preparation of the multimodal ethylene polymer of the invention preferably involves：

i) polymerizing ethylene and optionally at least one C4-20 alpha olefin comonomer such as to form a LMW component (A) ， and subsequently

iii) compounding the product obtained in step ii) to yield pellets.

It is preferred if at least one of polymerizing steps i) and ii) is produced in a gas-phase reaction.

It is further preferred， if one of polymerizing steps i) and ii) ， preferably polymerizing step i) ， is carried out in a slurry reaction， preferably in a loop reactor， and one of polymerizing steps i) and ii) ， preferably polymerizing step ii) ， is produced in a gas-phase reaction.

Preferably， the multimodal ethylene polymer is produced by a multistage ethylene polymerisation， e.g. using a series of reactors， with optional comonomer addition preferably in only the reactor (s) used for production of the HMW component (B) or differing comonomers used in each stage. A multistage process is defined generally to be a polymerisation process in which a polymer comprising two or more fractions is produced by producing each or at least two polymer fraction (s) in separate reaction stages respectively， usually with different reaction conditions in each stage， in the presence of the reaction product of the previous stage which comprises a polymerisation catalyst. The polymerisation reactions used in each stage may involve conventional ethylene homopolymerisation or copolymerisation reactions， e.g. gas-phase， slurry phase， liquid phase polymerisations， using conventional reactors， e.g. loop reactors， gas phase reactors， batch reactors etc. (see for example WO97/44371 and WO96/18662) .

Accordingly， it is preferred that polymerizing steps i) and ii) are carried out in different stages of a multistage process.

Preferably， the multistage process comprises at least one gas phase stage in which， preferably， polymerizing step ii) is carried out.

It is further preferred， if polymerizing step ii) is carried out in a subsequent stage in the presence of LMW component (A) which has been produced in previous polymerizing step i) .

It is previously known to produce multimodal， in particular bimodal， olefin polymers， such as multimodal polyethylene， in a multistage process comprising two or more reactors connected in series. As instance of this prior art， mention may be made of EP 517 868， which is hereby incorporated by way of reference in its entirety， including all its preferred embodiments as described therein， as a preferred multistage process for the production of the polyethylene composition according to the invention.

Preferably， the main polymerisation stages， i.e. polymerizing steps i) and ii) ， of the multistage process for producing the polyethylene composition according to the invention are such as described in EP 517 868， i.e. the production of LMW and HMW components (A) and (B) is carried out as a combination of slurry polymerisation for LMW component (A) /gas-phase polymerisation for HMW component (B) . The slurry polymerisation is preferably performed in a so-called loop reactor. Further preferred， the slurry polymerisation stage precedes the gas phase stage.

Optionally， the main polymerisation stages， i.e. polymerizing steps i) and ii) ， may be preceded by a prepolymerisation， in which case up to 20 ％by weight， preferably 1 to 10 ％ by weight， more preferably 1 to 5 ％by weight， of the total composition is produced. The prepolymer is preferably an ethylene homopolymer. At the prepolymerisation， preferably all of the catalyst is charged into a loop reactor and the prepolymerisation is performed as a slurry polymerisation. Such a prepolymerisation leads to less fine particles being produced in the following reactors and to a more homogeneous product being obtained in the end. Where prepolymerisation is used， the prepolymer formed can be regarded as forming part of the lower molecular weight fraction (A) . I.e. the optional prepolymer component is counted to the amount (wt％) of LMW component (A) .

Preferably， the polymerisation conditions in the preferred two-stage method are chosen so that the comparatively low-molecular weight polymer containing a comonomer is produced in one stage， preferably the first stage， whereas the high-molecular weight polymer having a content of comonomer is produced in another stage， preferably the second stage. The order of these stages may， however， be reversed.

In a preferred embodiment， the polymerisation in a loop reactor is followed by a gas-phase reactor， the polymerisation temperature in the loop reactor preferably is 75 to 115 ℃， more preferably is 80 to 105 ℃， and most preferably is 82 to 100 ℃. The temperature in the gas-phase reactor preferably is 70 to 105 ℃， more preferably is 75 to 100℃， and most preferably is 82 to 97℃.

A chain-transfer agent， preferably hydrogen， is added as required to the reactors， and preferably 100 to 800 moles of H₂/kmoles of ethylene are added to the reactor， when the LMW fraction is produced in this reactor， and 50 to 500 moles of H₂/kmoles of ethylene are added to the gas phase reactor when this reactor is producing the HMW fraction.

Polymerizing steps i) and ii) are preferably carried out in the presence ofa polymerisation catalyst. The polymerisation catalyst may be a coordination catalysts of a transition metal， such as Ziegler-Natta (ZN) ， metallocene， non-metailocene， Cr-catalyst etc. The catalyst may be supported， e.g. with conventional supports including silica， Al-containing supports and magnesium dichloride based supports. Preferably the catalyst is a ZN catalyst， more preferably the catalyst is silica supported ZN catalyst.

The Ziegler-Natta catalyst further preferably comprises a group 4 (group numbering according to new-IUPAC system) metal compound， preferably titanium， magnesium dichloride and aluminium.

The catalyst may be commercially available or be produced in accordance or analogously to the literature. For the preparation of the preferable catalyst usable in the invention reference is made to EP688794 A1， EP835887 A2， EP2746298 A1， WO2004055068 and WO2004055069 of Borealis， EP 0 688 794 and EP 0 810 235. The content of these documents in its entirety is incorporated herein by reference， in particular concerning the general and all preferred embodiments of the catalysts described therein as well as the methods for the production of the catalysts. Particularly preferred Ziegler-Natta catalysts are described in EP2746298 A1.

It is preferred that the catalyst used in polymerizing step i) is also used in polymerizing step ii) . It is generally transferred from polymerizing step i) to the polymerizing step ii) .

As well known， the Ziegler-Natta catalyst is used together with an activator. Suitable activators are metal alkyl compounds and especially aluminium alkyl compounds. These compounds include alkyl aluminium halides， such as ethylaluminium dichloride， diethylaluminium chloride， ethylaluminium sesquichloride， dimethylaluminium chloride and the like. They also include trialkylaluminium compounds， such as trimethylaluminium， triethylaluminium， tri-isobutylaluminium， trihexylaluminium and tri-n-octylaluminium. Furthermore， they include alkylaluminium oxy-compounds， such as methylaluminiumoxane (MAO) ， hexaisobutylaluminiumoxane (HIBAO) and tetraisobutylaluminiumoxane (TIBAO) . Also other aluminium alkyl compounds， such as isoprenylaluminium， may be used. Especially preferred activators are trialkylaluminiums， of which triethylaluminium， trimethylaluminium and tri-isobutylaluminium are particularly used.

The amount of activator used depends on the specific catalyst and activator. Typically， triethyl aluminium is used in such amount that the molar ratio of aluminium to the transition metal， like Al/Ti， is from 1 to 1000， preferably from 3 to 100.

The resulting end product， i.e. the multimodal ethylene polymer， consists of an intimate mixture of the polymers (herein LMW component (A) and HMW component (B) ) from the two or more reactors， the different molecular-weight-distribution curves of these polymers together forming a molecular-weight-distribution curve having a broad maximum or two or more maxima， i.e. the end product is a bimodal or multimodal polymer mixture.

The multimodal ethylene polymer is recovered from the polymerisation reactor including conventional post-reactor treatment and then compounded in a conventional extruder to form the multimodal ethylene polymer in pellet form.

Preferably， the multimodal ethylene polymer comprises the multimodal ethylene polymer as the sole polymer component.

It is appreciated that the increase for the thermal conductivity coefficient of＞ 0.40 W/m·K for the heat conductive polyethylene composition of the present invention is achieved by the specific combination of the multimodal ethylene polymer with an elastomeric copolymer， graphite， mineral oil and one or more additive (s) .

It is thus further required that the heat conductive polyethylene composition comprises an elastomeric copolymer comprising units derived from ethylene and C₃ to C₈ α-olefins.

The heat conductive polyethylene composition comprises the elastomeric copolymer in an amount from 10.3 to 35.0 wt. -％， based on the total weight (100.0 wt. -％) of the polyethylene composition. For example， the heat conductive polyethylene composition comprises the elastomeric copolymer in an amount from 18.0 to 35.0 wt.-％， and most preferably from 23.0 to 34.0 wt. -％， based on the total weight (100.0 wt.-％) of the polyethylene composition.

The elastomeric copolymer preferably has a melt flow rate MFR₂ (190 ℃) measured according to ISO 1133 in the range of 0.5 to 30.0 g/10 min， preferably in the range of 0.5 to 20.0 g/10 min and most preferably in the range of 0.5 to 10.0 g/10 min.

The elastomeric copolymer typically has a density of equal or less than 935 kg/m³， preferably of equal or less than 900 kg/m³， more preferably of equal or less than 890 kg/m³， still more preferably in the range of 850 to 890 kg/m³.

The elastomeric copolymer is an ethylene copolymer with comonomers selected from C₃ to C₈ α-olefins. For example， the elastomeric copolymer comprises especially consists of， monomers copolymerizable with ethylene from the group consisting of propylene， 1-butene， 1-hexene and 1-octene.

More specifically， the elastomeric copolymer comprises -apart from ethylene -units derivable from 1-hexene and 1-octene. In a preferred embodiment， the elastomeric copolymer comprises units derivable from ethylene and 1-octene only.

Additionally， it is appreciated that the elastomeric copolymer has preferably a comonomer content in the range from 25.0 to 55.0 wt. -％， more preferably in the range from 30.0 to 50.0 wt. -％， based on the total weight of the elastomeric copolymer.

It is appreciated that the weight ratio of multimodal ethylene polymer (EP) to the elastomeric copolymer (E) [EP/E] is from 3.0∶1.0 to 1.2∶1.0， preferably from 2.2∶1.0 to 1.4∶1.0.

The elastomeric copolymer is also dispersed in the multimodal ethylene polymer.

It is preferred that the elastomeric eopolymer is also present in a specific weight ratio compared to the graphite in the heat conductive polyethylene composition.

For example， the weight ratio of elastomeric copolymer (E) to the graphite (G) [E/G] is below 10.0. Preferably， the weight ratio of elastomeric copolymer (E) to the graphite (G) [E/G] is from 10.0∶1.0 to 1.0∶1.0， more preferably from 9∶1.0 to 1.5∶1.0， and most preferably from 8.0∶1.0 to 2.0∶1.0.

It is further required that the heat conductive polyethylene composition comprises graphite in an amount ranging from 1.0 to 20.0 wt. -％， based on the total weight (100.0 wt. -％) of the polyethylene composition. Preferably， the heat conductive polyethylene composition comprises the graphite in an amount ranging from 1.5 to 19.0 wt. -％， and most preferably from 2.0 to 18.0 wt. -％， based on the total weight (100.0 wt. -％) of the polyethylene composition.

In this regard， it is appreciated that the graphite can be added to the heat conductive polyethylene composition as such (neat) or in form of a so-called masterbatch (CBG) ， in which graphite is contained in concentrated form in a carrier polymer. The former is preferable.

The optional carrier polymer is present in the heat conductive polyethylene composition in an amount of less than 3.0 wt. -％， more preferably less than 2.0 wt. -％and most preferably less than 1.0 wt. -％， based on the total weight (100.0 wt. -％) of the polyethylene composition

If present， the carrier polymer of the graphite masterbatch is not calculated to the amount of multimodal ethylene polymer or elastomeric copolymer. The carrier polymer of the graphite masterbatch is calculated to the total amount of graphite based on the total amount (100.0 wt.-％) of final polyethylene composition.

The optional carrier polymer can be any polyolefin known as carrier polymer for graphite. Examples include but are not limited to are high density polyethylene (HDPE) ， medium density polyethylene (MDPE) or linear low density ethylene copolymer (LLDPE) ， preferably HDPE carrier polymer. It is well known and within the skills of a skilled person to choose the type of the optional carrier polymer and the properties thereof depending on the properties of the multimodal ethylene polymer to provide suitable dispersion of the graphite masterbatch.

The graphite masterbatch， i.e. the mixture of graphite and the carrier polymer， preferably comprises graphite in an amount of from 20.0 to 70.0 wt. -％， more preferably from 40.0 to 60.0 wt. -％， based on the total weight (100.0 wt. -％) of the graphite masterbatch. It is preferred that the graphite is incorporated into the heat conductive polyethylene composition in the form of a graphite masterbatch. Graphites for the purpose of the present invention are commercially available.

The graphite can be of any type feasible for use in heat conductive pipes or pipe systems. The graphite according to the present invention has preferably a particle size d₉₀ of≤ 120 μm, preferably from 60 to 100 μm， more preferably from 70 to 90 μm.

In one embodiment， the graphite useful for the present invention has preferably a bulk density in the range of 0.1 to 0.25 g/cm³， more preferably of 0.12 to 0.22 g/em³ and most preferably of 0.12 to 0.2 g/cm³.

Additionally or alternatively， the graphite has a BET surface area in the range of 20 to 100 m²/g， preferably from 20 to 50 m²/g， more preferably from 20 to 40 m²/g.

It is preferred that the graphite is preferably expanded graphite.

The term “expanded graphite” encompasses graphite having no significant order as evidenced by X-ray diffraction pattern. Expanded graphite has been treated to increase the inter-planar distance between the individual layers that form the graphite structure. It is intended that the term “expanded graphite” throughout the present description relates to a graphite material where the distances between the graphene layers have been substantially increased compared to pure graphite.

Suitable graphites are commercially available from several suppliers including Imerys Graphite &Carbon Switzerland Ltd (Switzerland) ， and can be selected accordingly by a person skilled in the art. As an example， C-THERM^TM001 can be given.

It is further required that the heat conductive polyethylene composition comprises a mineral oil in an amount ranging from 0.5 to 2.0 wt. -％， based on the total weight (100.0 wt. -％) of the polyethylene composition. Preferably， the heat conductive polyethylene composition comprises the mineral oil in an amount ranging from 0.5 to 1.8 wt. -％， and most preferably from 0.5 to 1.5 wt. -％， based on the total weight (100.0 wt. -％) of the polyethylene composition.

The mineral oil is a known petroleum product.

Mineral oils have a well-known meaning and are used inter alia for lubrication in pipes and pipe systems. The mineral oil can be a synthetic mineral oil which is produced synthetically or a mineral oil obtainable from crude oil refinery processes. Typically， mineral oil， known also as liquid petroleum， is a by-product in the distillation of petroleum to produce gasoline and other petroleum based products from crude oil. The mineral oil of the present invention of the invention is preferably a paraffinic oil. Such paraffinic oil is derived from petroleum based hydrocarbon feedstocks.

Preferably， the mineral oil which is a mineral oil which is conventionally used as lubricant for producing pipes or pipe systems. More preferably the mineral oil is a regular white oil. White oil has a well-known meaning. Moreover， such white oil based lubricants are well known and commercially available.

It is appreciated that the mineral oil， preferably the white (mineral) oil， of the present invention comprises paraffinic hydrocarbons.

The mineral oil， preferably the white (mineral) oil， can be a commercially available mineral oil or can be produced by conventional means， and is preferably a commercial mineral oil used in heat conductive polyethylene compositions. Suitable mineral oils are commercially available from several suppliers including ExxonMobil and Shell Corena， and can be selected accordingly by a person skilled in the art.

The heat conductive polyethylene composition further comprises one or more additive (s) in an amount ranging from 0.5 to 7.0 wt. -％， based on the total weight (100.0 wt. -％) of the polyethylene composition. Preferably， the heat conductive polyethylene composition comprises the one or more additive (s) in an amount ranging from 1.0 to 7.0 wt. -％， and most preferably from 2.0 to 7.0 wt. -％， based on the total weight (100.0 wt. -％) of the polyethylene composition.

According to this invention， the elastomerie copolymer， the graphite and the mineral oil are not considered as an additive.

The one or more additive (s) are selected from the group comprising antioxidants， coupling agents， adhesion promoter， waxes， anti-UVs， antistatic agents， clarifiers， brighteners， utilization agents and mixtures thereof.

In one embodiment of the present invention， the one or more additive (s) comprises， preferably consists of， one additive. Alternatively， one or more additive (s) comprises， preferably consists of， two or more additives. For example， the one or more additive (s) comprises， preferably consists of， two or three or four or five additives.

Preferably， the one or more additive (s) comprises， more preferably consists of， five additive (s) .

Such additives are commercially available and for example described in “Plastic Additives Handbook” ， 6^th edition 2009 of Hans Zweifel (pages 1141 to 1190) .

Furthermore， the term “additives” according to the present invention may also include carrier materials， in particular polymeric carrier materials (PCM) .

In this regard， it is appreciated that the one or more additive (s) can be added to the heat conductive polyethylene composition as such (neat) or in form of a so-called masterbatch， in which the one or more additive (s) is/are contained in concentrated form in a carrier polymer.

The optional carrier polymer (s) is/are present in the heat conductive polyethylene composition in an amount of less than 5.0 wt. -％， more preferably less than 4.0 wt. -％and most preferably less than 2.0 wt. -％， based on the total weight (100.0 wt. -％) of the polyethylene composition.

If present， the carrier polymer of the additive masterbatch is not calculated to the amount of multimodal ethylene polymer or elastomeric copolymer. The carrier polymer of the additive masterbatch is calculated to the total amount of additives based on the total amount (100.0 wt. -％) of final polyethylene composition.

The polymeric carrier material (PCM) is a carrier polymer for the additives to ensure a uniform distribution in the heat conductive polyethylene composition. The polymeric carrier material (PCM) is not limited to a particular polymer. The polymeric carrier material (PCM) is not limited to a particular polymer. The polymeric carrier material (PCM) may be ethylene homopolymer， ethylene copolymer obtained from ethylene and α-olefin comonomer such as C₃ to C₈ α-olefin comonomer， propylene homopolymer and/or propylene copolymer obtained from propylene and α-olefin comonomer such as ethylene and/or C₄ to C₈ α-olefin comonomer.

According to a preferred embodiment the polymeric carrier material (PCM) is a polyethylene homopolymer.

The additive masterbatch， i.e. the mixture of additives and the carrier polymer， preferably comprises the additives in an amount of from 20.0 to 70.0 wt. -％， more preferably from 40.0 to 60.0 wt. -％， based on the total weight (100.0 wt. -％) of the additive masterbatch. It is preferred that the one or more additive (s) is/are incorporated into the heat conductive polyethylene composition in the form of an additive masterbatch.

It is appreciated that the heat conductive polyethylene composition is preferably in the form of pellets.

The pellets of the present invention thus comprise， preferably consist of， a heat conductive polyethylene composition comprising， preferably consisting of，

All preferred ranges and properties as regards the heat conductive polyethylene composition， the multimodal ethylene polymer， the elastomeric copolymer， the graphite， the mineral oil and the one or more additive (s) and preferred embodiments thereof shall also hold for the pellets according to the present invention. The same holds for the proportions of the components.

It is appreciated that the pellets are preferably prepared by compounding the heat conductive polyethylene composition， i.e. the multimodal ethylene polymer， the elastomeric copolymer， the graphite， the mineral oil and the one or more additive (s) .

The compounding of the hea conductive polyethylene composition is preferably carried out at a temperature profile of at least 180 ℃， more preferably in the range from 180 to 260 ℃.

The heat conductive polyethylene composition is preferably pelletized in a step arranged after the compounding， and optional pelletizing， of the multimodal ethylene polymer in the production line of the polymerization process of the multimodal ethylene polymer， the subsequent mixing of the multimodal ethylene polymer with the elastomeric copolymer and the subseqnent mixing of the blend of the mnltimodal ethylene polymer and the elastomerie eopolymer with a mixture of the graphite， the mineral oil and the one or more additive (s) .

Thus， the heat conductive polyethylene composition is preferably prepared by a process comprising the steps of

a) providing a blend of the multimodal ethylene polymer and the elastomeric eopolymer，

b) providing a pre-mix of the graphite， the mineral oil and the one or more additive (s) ，

c) mixing the blend of step a) and the pre-mix of step b) ， and

d) compounding， extruding， and pelleting the mixture obtained in step c) ， whereby a temperature profile of from 180 ℃ to 260 ℃ is maintained over the length of the extruder， such as to obtain the pellets of the heat conductive polyethylene composition.

The extrusion and pelletization of the heat conductive polyethylene composition can be carried out in a known manner using well known extruder equipment supplied by extruder producers and conventional extrusion conditions. As an example of an extruder for the present extrusion and pelletizing step may be those supplied by Japan Steel works， Kobe Steel or Farrel-Pomini， e.g. JSW 460P or JSW CIM90P.

The heat conductive polyethylene composition of the present invention provides a thermal conductivity coefficient of＞0.40 W/m·K and thus is suitable for high temperature pipe applications， including underfloor heating， geothermal， etc.. Furthermore， the heat conductive polyethylene composition of the present invention saves the amount of pipes used in such applications.

The heat conductive polyethylene composition， preferably in the form of pellets， is thus particularly used for the production of article being suitable for applications at temperatures of＞60 ℃.

According to another aspect， the present invention thus refers to an article comprising the heat conductive polyethylene composition. The article is preferably a pipe or pipe system. If the article is a pipe system， the pipe system is preferably a pipe fitting.

Preferably， the article， more preferably the pipe or pipe system， according to the present invention comprises， preferably consists of， a heat conductive polyethylene composition， preferably in the form of pellets， the heat conductive polyethylene composition comprising

b) from 10.0 to 40.0 wt. -％of an elastomeric eopolymer comprising units derived from ethylene and C₃ to C₈ α-olefins， based on the total weight (100.0 wt. -％) of the polyethylene composition，

All preferred ranges and properties as regards the heat conductive polyethylene composition， the multimodal ethylene polymer， the elastomeric copolymer， the graphite and the one or more additive (s) shall also hold for the article according to the present invention. The same holds for the proportions of the components.

A pipe or pipe system denotes all articles used for transporting water or aqueous solutions. This includes the pipes as such as well as fittings. A pipe system means all articles made of polymeric material used for transporting water or aqueous solutions.

The dimensions of the article， preferably of the pipe or pipe system， can vary depending on the size of the intended pipe and on the desired application at the end usesite， and can be chosen accordingly as known in the art.

For example， the article， preferably the pipe or pipe system， according to the present invention has preferably a wall thickness of 0.5 to 50 mm， preferably of 0.8 to 40 mm， even more preferably of 1.0 to 35 mm and most preferably of 1.2 to 28 mm.

Preferably， the article， more preferably the pipe or pipe system， has an outer diameter of 5 to 350 mm， preferably of 10 to 320 mm， more preferably of 12 to 180 mm， and most preferably of 12 to 160 mm.

The article， preferably the pipe or pipe system， preferably has a cross-section of round or ellipse shape. ″Ellipse″ in this regard means that the round cross-section is flattened along one axis of the cross-section to form an ellipse or oval shape.

Due to the increased thermal conductivity coefficient， the heat conductive polyethylene composition is particularly suitable for heat conductive articles， preferably heat conductive pipes or pipe systems. The article is thus preferably a heat conductive article， preferably a heat conductive pipe or pipe system. More preferably， the article is suitable for applications at temperatures of＞60 ℃， preferably from 70℃ to 80℃.

The invention further relates to a process for the preparation of an article， preferably a pipe， comprising the steps of

a) providing a heat conductive polyethylene composition as defined herein，

With regard to the definition of the heat conductive polyethylene composition and preferred embodiments thereof， reference is made to the statements provided above when discussing the technical details of the heat conductive polyethylene composition of the present invention.

Preferably， the article， preferably the pipe or pipe system， of the invention is produced by heating and extruding/injection-molding the heat conductive polyethylene composition using an extruder/injection-molding machine. Preferably， heating and extruding/injection-molding step b) is carried out at a temperature of up to 260 ℃， preferably in the range from 170 to 260 ℃， in a manner well known in the art. Extruder/injection-molding machines are well known in the art and commercially available.

The use of the heat conductive polyethylene composition of the invention results in articles， such as pipes or pipe systems with advantageous thermal conductivity coefficient， i.e. of＞0.40 W/m·K， and thus are suitable for high temperature applications， including underfloor heating， geothermal， etc..

The present invention is further characterized by means of the following examples：

Examples：

1. Test Methods

a) Melt Flow Rate

The melt flow rate (MFR) is determined according to ISO 1133 and is indicated in g/10 min. The MFR is an indication of the flowability， and hence the processability， of the polymer. The higher the melt flow rate， the lower the viscosity of the polymer. The MFR₅ of polyethylene is measured at a temperature 190 ℃ and a load of 5 kg， the MFR₂ of polyethylene at a temperature 190 ℃ and a load of 2.16 kg and the MFR₂₁ of polyethylene is measured at a temperature of 190 ℃ and a load of 21.6 kg.

b) Density

Density is measured according to ISO 1183-1-method A (2004) . Sample preparation is done by compression molding in accordance with ISO 1872-2： 2007. Density is given in kg/m³.

c) Comonomer content

Comonomer content in polyethylene was measured in a known manner based on Fourier trausform infrared spectroscopy (FTIR) calibrated with ¹³C-NMR， using Nicolet Magna 550 IR spectrometer together with Nicolet Omnic FTIR software.

Films having a thickness of about 250 μm were compression molded from the samples. Similar films were made from calibration samples having a known content of the comonomer. The comonomer content was determined from the spectrum from the wave number range of from 1430 to 1100 cm^-1. The absorbance is measured as the height of the peak by. selecting the so-called short or long base line or both. The short base line is drawn in about 1410-1320 cm^-1 through the minimum points and the long base line about between 1410 and 1220 cm^-1. Calibrations need to be done specifically for each base line type. Also， the comonomer content of the unknown sample needs to be within the range of the comonomer contents of the calibration samples.

d) Tensile properties

Stress at yield， strength at yield， strain at break， and modulus were measured on injection molded samples according to ISO 527-2， Specimen type Multipurpose bar IA， 4 mm thick. Tensile modulus was measured on injection molded samples according to ISO 527-2 at a speed of 1 mm/min. Sample preparation was done according to ISO 1872-2.

e) Charpy impact strength

Charpy notched impact strength (-20 ℃) is determined according to ISO 179/leA at 23℃ and at-20 ℃. Charpy notched impact strength (-30 ℃) is determined according to ISO 179/ leA at 23℃ and at -30 ℃. Charpy notched impact strength (23 ℃) is determined according to ISO 179 /leA at 23 ℃. The impact strength was determined by using injection molded test specimens of 80 x 10 x 4 mm³ prepared in accordance with EN ISO 19069-2.

f) Flexural modulus and strength

Flexural modulus and strength were measured according to ISO 178.

g) Thermal conductivity coefficient

The thermal conductivity coefficient was determined according to ASTM E1 530 by using a TA instrument DTC300 at a test temperature of 60 ℃. The sample were prepared in a hot press process in that pellets of the polyethylene compositions were placed in a hot press machine “Collin P400 P/M” ， and then pressed at 210℃ for 5min within a tool with a size 40*40*4mm. Subsequently， the samples were cooled down and tailered in 25mm diameter circle for thermal conductivity test.

h) OIT (oxidizing induced time)

OIT was measured according to ISO 11357-6 at 210 ℃.

i) Particle size d₉₀

The particle size d₉₀ was measured according to ISO 13320-1 by laser light scattering.

j) Shear thinning index SHI (2.7/210)

The characterization of polymer melts by dynamic shear measurements complies with ISO standards 6721-1 and 6721-10 and ASTM D 4440. The measurements were performed on an Anton Paar MCR501 stress controlled rotational rheometer， equipped with a 25 mm parallel plate geometry. Measurements were undertaken on compression molded plates using nitrogen atmosphere and setting a strain within the linear viscoelastic regime. The oscillatory shear tests were done at 190℃ applying a frequency range between 0.01 and 600 rad/s and setting a gap of 1.3 mm.

In a dynamic shear experiment the probe is subjected to a homogeneous deformation at a sinusoidal varying shear strain or shear stress (strain and stress controlled mode， respectively) . On a controlled strain experiment， the probe is subjected to a sinusoidal strain that can be expressed by

γ (t) ＝ γ₀ sin (ωt) (1)

If the applied strain is within the linear viscoelastic regime， the resulting sinusoidal stress response can be given by

σ (t) ＝ σ₀ sin (ωt +δ) (2)

where σ₀， and γ₀ are the stress and strain amplitudes， respectively； ω is the angular frequency； δ is the phase shift (loss angle between applied strain and stress response) ； t is the time.

Dynamic test results are typically expressed by means of several different rheological functions， namely the shear storage modulus， G’ ， the shear loss modulus， G” ， the complex shear modulus， G*， the complex shear viscosity， η*， the dynamic shear viscosity， η′， the out-of-phase component of the complex shear viscosity， η″and the loss tangent， tan η， which can be expressed as follows：

G*＝ G‘+ iG“ [Pa] (5)

η*＝ η′-iη″ [Pa·s] (6)

The determination of so-called Shear Thinning Index， which correlates with MWD and is independent of Mw， is done as described in equation 9.

For example， the SHI _(2.7/210) is defined by the value of the complex viscosity， in Pa s， determiued for a value of G*equal to 2.7 kPa， divided by the value of the complex viscosity， in Pa s， determined for a value of G*equal to 210 kPa.

The values of storage modulus (G′) ， loss modulus (G″) ， complex modulus (G*) and complex viscosity (η*) were obtained as a function of frequency (ω) .

Thereby， e.g. η*_300rad/s (eta*_300rad/s) is used as abbreviation for the complex viscosity at the frequency of 300 rad/s and η*_0.05rad/s (eta*_0.05rad/s) is used as abbreviation for the complex viscosity at the frequency of 0.05 rad/s.

The loss tangent tan (delta) is defined as the ratio of the loss modulus (G″) and the storage modulus (G′) at a given frequency. Thereby， e.g. tan_0.05 is used as abbreviation for the ratio of the loss modulus (G″) and the storage modulus (G′) at 0.05 rad/sand tan₃₀₀ is used as abbreviation for the ratio of the loss modulus (G″) and the storage modulus (G′) at 300 rad/s. The elasticity balance tan_0.05/tan₃₀₀ is defined as the ratio of the loss tangent tan_0.05 and the loss tangent tan₃₀₀.

Besides the above mentioned rheological functions one can also determine other rheological parameters such as the so-called elasticity index EI (x) . The elasticity index EI (x) is the value of the storage modulus (G′) determined for a value of the loss modulus (G″) of x kPa and can be described by equation 10.

EI (x) ＝ G′for (G″＝ x kPa) [Pa] (10)

For example， the EI (5kPa) is the defined by the value of the storage modulus (G’) ， determined for a value of G″equal to 5 kPa.

The viscosity eta₇₄₇ is measured at a very low， constant shear stress of 747 Pa and is inversely proportional to the gravity flow of the polyethylene composition， i.e. the higher eta₇₄₇ the lower the sagging of the polyethylene composition.

The polydispersity index， PI， is defined by equation 11.

where ω_COP is the cross-over angular frequency， determined as the angular frequency for which the storage modulus， G′， equals the loss modulus， G″.

The values are determined by means of a single point interpolation procedure， as defined by Rheoplus software. In situations for which a given G*value is not experimentally reached， the value is determined by means of an extrapolation， using the same procedure as before. In both cases (interpolation or extrapolation) ， the option from Rheoplus ″Interpolate y-values to x-values from parameter″ and the ″logarithmic interpolation type″ were applied.

References：

[1] “Rheological characterization of polyethylene fractions″ ， Heino， E.L. ， Lehtinen， A.， Tanner J.，

J.， Neste Oy， Porvoo， Finland， Theor. Appl. Rheol.， Proc. Int. Congr. Rheol， 11th (1992) ， 1， 360-362.

[2] “The influence of molecular structure on some rheological properties of polyethylene″ ， Heino， E.L.， Borealis Polymers Oy， Porvoo， Finland， Annual Transactions of the Nordic Rheology Society， 1995.

[3] “Definition of terms relating to the non-ultimate mechanical properties of polymers” ， Pure &Appl. Chem.， Vol. 70， No. 3， pp. 701-754， 1998.

2. Examples

The catalyst used in the polymerization process for the ethylene polymer (PE) of the inventive examples IE 1 to 3 and CE was prepared as follows：

Used chemicals

Silica -Grace Davison ES 757，

EADC (ethyl-aluminium-di-chloride) -supplier Sigma-Aldrich

BOMAG (octyl-butyl-Mg) - (Mg (Bu) 1， 5 (Oct) _0.5) -supplier Chemtura

Preparation of the catalyst and the ethylene polymer

Silica activated at 600 ℃ for 6 h is used as carrier material. 5 g of silica is used for the synthesis. 1.1 mol of 25 ％ethyl-aluminium-di-chloride (EADC) in heptane is added per gram of silica. The EADC is allowed to react with the silica at a temperature between 30 ℃and 40 ℃ for 1 h. Subsequently， 1.0 mol of a Mg-alcoholate solution is added per gram of silica. The Mg-solution is prepared by adding 2-ethyl-hexanol to an octyl-butyl-Mg (BOMAG) solution in a molar ratio of 1.83 to 1. The Mg-reagent is allowed to react with the EADC for

h at a temperature between 30 ℃ and 40 ℃. Heptane is added to create a slurry. The reaction temperature during the preparation is kept between 30 ℃ and 40 ℃. Subsequently， 0.5 mmol of TiCl₄ are slowly added per gram of silica during an addition time of 1/2 h. The components are allowed to react with each other for 1 h. The reaction temperature is kept between 40 ℃ and 50 ℃. Finally， the catalyst is dried under a stream of nitrogen at a temperature between 60 ℃ and 90 ℃.

40 to 50 mg of the catalyst is used in the polymerization reaction and tri-ethylaluminium (TEA) is used as co-catalyst with an Al/Ti molar ratio of 30.

The polymerization conditions for the ethylene polymer (PE) are indicated in table 1.

Table 1： Preparation of the PE

	PE
Loop
Temperature [℃]	85
Pressure [kPa]	5858
Split [wt.-％]	40.4
H2/C2 ratio [mol/kmol]	314.4
C4/C2 ratio [mol/kmol]	309.4
MFR₂ [g/10 min]	302
Density [kg/m³]	958.8
Comonomer type	C4
Comonomer content [wt.-％]	1.5
GPR
Temperature[℃]	85
Pressure [kPa]	2000
Split [wt.-％]	59.6
H2/C2 ratio [mol/kmol]	35
C6/C2 ratio [mol/kmol]	30.7
Density [kg/m³]	944.5
Comonomer type	C6
Final properties
Comonomer content[wt.-％]	4.0
MFR₅[g/10 min]	0.54
MFR_21.6 [g/10 min]	14
Natural density [kg/m³]	946
Modulus [MPa]	800
tensile stress at yield [MPa]	22
tensile strain at break [％]	＞800
NIS (23℃) [kJ/m²]	18
NIS (-20℃)[kJ/m²]	7.5
OIT (210℃) [min]	≥20

Preparation of polyethylene composition

Three examples 1 to 3 of the inventive polyethylene compositions were prepared by premixing the graphite， the mineral oil and the additives and (wax， coupling agent， compatibilizer， and antioxidants) followed by a blending of the premix with a blend of the ethylene polymer (PE) and the elastomeric copolymer (EC) . The mixture was than fed into a twin screw extruder with an L/D ratio of 30∶1 by a feeder and heated and mixed homogeneously in the extruder at a temperature range of 180-260 ℃. The mixture thus formed was extruded from the extruder and pelletized to form pellets of the compositions. The compositions are shown in Table 2 below.

Table 2. Recipe of the compoundings of inventive examples 1 to 3

“PE” refers to the ethylene polymer as indicated above in table 1.

“EC” is the commercial product Engage 8100 of Dow (China) ， which is an ethylene-1-octene copolymer having a density of 870 kg/m³ and a melt flow rate MFR₂ (190℃) of 1.0 g/10min.

“graphite” is the commercial product C-THERM^TM001 of Imery Graphite & Carbon Switzerland Ltd having a BET of 25 m²/g and an average particle size (d₉₀) of 81 μm， and a bulk density of 0.15g/cm³.

“mineral oil” is a commercially available white oil of Exxon Mobil (China) .

“additives” comprise a mixture of the commercial polyethylene wax

C of Lonza Ltd. (Swiss)， the commercial titanate coupling agent KR-TTS of Kenrich Petrochem. Inc. (USA). The commercial ethylene polypropylene copolymer (functionalized with maleic anhydride) TPPP8112 GA of BYK Co. Ltd， Germany， having a MFR₂ (190 ℃) of more than 80 g/10min and a maleic anhydride content of 1.4 wt.-％， and the commercial antioxidant

B225 of BASF (Germany).

The process conditions of the compounding step of preparing the pellets of inventive examples 1 to 3 are shown in table 3 below.

Table 3. Process conditions for preparing the compoundings of inventive examples 1 to 3 in the twin-screw extruder

	IE1	IE2	IE3
temperature (℃)
Zone 1 (feed opening)	RT	RT	RT
zone2 (℃)	180	180	180
zone 3 (℃)	210	215	220
zone 4 (℃)	210	215	220
zone 5 (℃)	210	215	220
zone 6 (℃)	215	220	225
zone 7 (℃)	220	225	230
zone 8 (℃)	220	225	230
zone 9 (℃)	220	225	230
zone 10 (℃)	220	225	230
zone 11 (℃)	215	220	225
Die (℃)	210	215	220
melt temp. (℃)	210	215	220
throughput (kg/hour)	60	60	60
screw speed (rpm)	580	580	580
torque (％)	52	52	52
vacuum (MPa)	-0.6	-0.6	-0.6

The properties of the inventive and comparative examples are outlined in table 4 below.

Table 4. Properties of comparative and inventive examples.

	IE1	IE2	IE3	CE
MFR₂ [g/10 min]	0.9	0.6	0.4	nd
MFR₅ [g/10 min]	nd	nd	nd	0.8
Density [kg/m³]	950	980	1000	944
Tensile strength at yield [MPa]	13.4	14	15.5	22
Tensile modulus [MPa]	446	590	720	800
Flexural modulus [MPa]	467	618	684	nd
Flexural strength [MPa]	12.1	13.8	14.8	nd
Notched Charpy impact (-30℃) [kJ/m²]	26	20.9	18.4	7.5 (-20℃)
Notched Charpy impact (23℃) [kJ/m²]	74.5	58.8	43.8	18
Thermal conductivity coefficient [W/m·K]	0.45	0.66	0.80	0.38-0.40

nd： not determined

“CE” is the same base resin as used for inventive IEs 1-3， i.e. the ethylene polymer (PE) as indicated in table 1 above.

From table 4， it can be gathered that the heat conductivity coefficient of the inventive examples 1 to 3 is almost double over the comparative example， i.e. the base resin used for preparing the inventive examples， which results in material savings in pipe application. Furthermore， the impact performance of the inventive examples 1 to 3 is greatly improved compared to the comparative example. In this regard， it is to be noted that even though the tensile properties are lowered， they are sufficient for typical pipe applications.

Claims

Heat conductive polyethylene composition comprising

a) from 35.0 to 75.0 wt. -％ of a multimodal ethylene polymer， based on the total weight (100.0 wt. -％) of the polyethylene composition，

b) from 10.0 to 40.0 wt. -％ of an elastomeric copolymer comprising units derived from ethylene and C₃ to C₈ α-olefins， based on the total weight (100.0 wt. -％) of the polyethylene composition，

c) from 1.0 to 25.0 wt. -％ of graphite， based on the total weight (100.0 wt. -％) of the polyethylene composition，

d) from 0.5 to 2.0 wt. -％ of mineral oil， based on the total weight (100.0 wt. -％) of the polyethylene composition， and

e) from 0.5 to 7.0 wt. -％ of one or more additive (s) ， based on the total weight (100.0 wt. -％) of the polyethylene composition.
The heat conductive polyethylene composition according to claim 1， wherein the polyethylene composition has

a) a charpy notched impact strength (-30 ℃) measured according to ISO 179 of at least 10 kJ/m²， and/or

b) a charpy notched impact strength (23 ℃) measured according to ISO 179 of at least 30 kJ/m²， and/or

c) a thermal conductivity coefficient measured according to ASTM E1530 of at least 0.42 W/m·K， and/or

d) a density measured according to ISO 1183 in the range from 948 to 1020 kg/m³.
The heat conductive polyethylene composition according to claim 1 or 2， wherein the multimodal ethylene polymer is an ethylene homo- or ethylene copolymer.
The heat conductive polyethylene composition according to any one of claims 1 to 3， wherein the multimodal ethylene polymer is an ethylene copolymer with one or more comonomers selected from C₄ to C₂₀ α-olefins.
The heat conductive polyethylene composition according to claim 4， wherein the multimodal ethylene polymer is an ethylene copolymer with two comonomers selected from C₄ to C₂₀ α-olefins.
The heat conductive polyethylene composition according to any one of claims 1 to 5， wherein the multimodal ethylene polymer is a bimodal ethylene polymer.
The heat conductive polyethylene composition according to any one of claims 1 to 6， wherein the multimodal ethylene polymer has

i) a density measured according to ISO 1183 in the range from 930 to 950 kg/m³， and/or

ii) a MFR₅ (ISO 1133， 5 kg load) of 0.3 to 1.5 g/10min， and/or

iii) a MFR₂₁ (ISO 1133， 21.6 kg load) of 5 to 25 g/10min.
The heat conductive polyethylene composition according to any one of claims 1 to 7， wherein the elastomeric copolymer has

a) a density of equal or less than 935 kg/m³， and/or

b) a MFR₂ (ISO 1133， 2.16 kg load) in the range of 0.5 to 30.0 g/10 min
The heat conductive polyethylene composition according to any one of claims 1 to 8， wherein the graphite is expanded graphite having

a) a bulk density in the range of 0.1 to 0.25 g/cm³， and/or

b) a BET surface area in the range of 20 to 100 m²/g， and/or

c) a particle size d₉₀ of≤ 120 μm
The heat conductive polyethylene composition according to any one of claims 1 to 9， wherein the mineral oil comprises paraffinic hydrocarbons.
The heat conductive polyethylene composition according to any one of claims 1 to 10， wherein the one or more additive (s) is/are selected from the group comprising antioxidants， coupling agents， adhesion promoter， waxes， anti-UVs， antistatic agents， clarifiers， brighteners， utilization agents and mixtures thereof.
An article， preferably a pipe or pipe system， comprising the heat conductive polyethylene composition according to any one of claims 1 to 11.
The article according to claim 12， wherein the article is a heat conductive article.
The article according to claim 12 or 13， wherein the article is suitable for applications at temperatures of＞ 60 ℃.
A process for the preparation of an article， preferably a pipe， comprising the steps of

a) providing a heat conductive polyethylene composition according to any one of claims 1 to 11， and

b) heating and extruding the heat conductive polyethylene composition of step a) ， whereby a temperature of up to 260 ℃ is applied in the extruder， such as to obtain the article， preferably the pipe.
A process for the preparation of an article， preferably a pipe system， comprising the steps of

a) providing a heat conductive polyethylene composition according to any one of claims 1 to 11， and

b) heating and injection-moulding the heat conductive polyethylene composition of step a) ， whereby a temperature of up to 260 ℃ is applied in the injection-moulding machine， such as to obtain the article， preferably the pipe system.