Polyethylene used to produce cross-linked polyethylene (PEX)

Abstract

A polyethylene (PE) for producing cross-linked polyethylene (PEX), the polyethylene (PE) having a beneficial balance between unsaturated properties and processability, a method for producing cross-linked polyethylene (PEX) from the polyethylene (PE), and the cross-linked polyethylene (PEX) produced thereby.

Description

Technical Field

[0001] The present invention relates to a polyethylene (PE) for producing cross-linked polyethylene (PEX), a method for producing such a polyethylene (PE), a method for producing cross-linked polyethylene (PEX) from the polyethylene (PE), and the use of the polyethylene for producing cross-linked polyethylene. Background Art

[0002] It is known to use cross-linked polyethylene (PEX) to produce pipes. Cross-linked polyethylene can be obtained by various routes. If cross-linking is performed using peroxides via the so-called Engel process, cross-linked polyethylene known as "PEXa" is obtained. During heat treatment, the peroxides decompose into free radicals, which in turn extract hydrogen atoms from the polymer chains, generating carbon radicals within the polymer chains. The carbon radicals of adjacent polymer chains can form carbon-carbon bonds, thus connecting the two polymer chains.

[0003] If crosslinking is carried out in the presence of silanes, a crosslinked polyethylene known as "PEXb" is obtained. Adjacent polyethylene chains are linked via Si-O-Si bridges.

[0004] If cross-linking is carried out on solid tubes by electron beam irradiation, a cross-linked polyethylene known as "PEXc" is obtained.

[0005] More recently, other PEX technologies have been developed, such as the so-called Lubonyl process, where the polyethylene is extruded in a hot salt bath and then cross-linked using pre-added azo compounds, forming a cross-linked polyethylene called "PEXd."

[0006] Various methods have also been developed that combine the advantages of PEXa, which crosslinks in the molten state, with the advantages of PEXc, which crosslinks during product formation. This process, primarily developed by Uponor (SE), involves extruding polyethylene with a photoinitiator and, optionally, a crosslinker, followed by a UV-promoted crosslinking step in the molten state. WO2015 / 162155A1, WO2014 / 177435A1, and WO2018 / 054515A1 describe such processes (generally referred to as "PEXe"), among others. In an alternative process that avoids the use of a free radical generator, polyethylene can be extruded with a crosslinker and subsequently crosslinked in an IR oven. WO2016 / 170016A1 describes such a process.

[0007] The choice of polyethylene for each of these technologies is a delicately balancing act. For example, for PEXa applications, EP1587858A1 discloses the use of microparticles containing polyethylene with a certain density and MFR2 for PEXa crosslinking. While these microparticles do possess beneficial properties, the use of new polyethylene in novel forms can further modify and even improve the process.

[0008] The so-called PEXe process requires polyethylene to have a combination of beneficial processing properties (i.e. rheological properties) so that the molten article (usually a pipe) does not sag or deform during crosslinking in the molten state. In addition, due to the nature of crosslinking under PEXe conditions, a certain degree of unsaturation has been found to be beneficial.

[0009] Therefore, there is still a need to develop new polyethylene grades suitable for the newly developed PEXe process as well as the more mature PEXa process.

[0010] The present invention is based on a polyethylene that is suitable for both processes where crosslinking occurs in the melt and more traditional peroxide-based processes, particularly when the peroxide is added to the polyethylene in the form of a reactor powder. Summary of the Invention

[0011] Therefore, the present invention relates to polyethylene (PE) for producing cross-linked polyethylene (PEX), wherein the polyethylene (PE) satisfies inequality (I):

[0012] 1≤UI×PI<20(I)

[0013] The unsaturation index (UI) is defined by formula (i):

[0014]

[0015] In the formula

[0016] Mw is the weight-average molecular weight of polyethylene (PE) (measured by gel permeation chromatography, expressed in g / mol);

[0017] [Vinyl] is the number of CH atoms per 1000 in polyethylene (PE). n Vinyl concentration of carbon (by 1 H-NMR spectroscopy); the processability index (PI) is defined by formula (ii):

[0018]

[0019] In the formula

[0020] MFR 21is the melt flow rate of polyethylene (PE) (measured according to ISO 1333 at 190°C and 21.6 kg load, expressed in g / 10 min);

[0021] F 120 is the melt strength of polyethylene (PE) (measured according to ISO 16790:2021 at a die pressure of 120 bar, expressed in cN).

[0022] In a further aspect, the present invention relates to a first method for producing cross-linked polyethylene (PEX), said first method comprising the steps of:

[0023] a) soaking the polyethylene (PE) of the present invention in the form of reactor powder in liquid peroxide;

[0024] b) Extruding the soaked polyethylene powder in an extruder to obtain cross-linked polyethylene (PEX).

[0025] In another aspect, the present invention relates to a second process for producing a cross-linked polyethylene (PEX), wherein cross-linking is achieved by applying radiation to a composition (C) comprising the polyethylene (PE) of the present invention in the molten state.

[0026] In a further aspect, the present invention relates to a cross-linked polyethylene (PEX) obtainable by the process of the present invention.

[0027] In a further aspect, the present invention relates to a cross-linked polyethylene pipe comprising at least 90 wt. % of cross-linked polyethylene (PEX) according to the invention, wherein the pipe is produced according to the first process according to the invention, wherein step b) is a pipe extrusion step, or according to the second process according to the invention, wherein the pipe extrusion step is performed before the cross-linking step.

[0028] In a final aspect, the present invention relates to the use of the polyethylene (PE) of the present invention for producing cross-linked polyethylene.

[0029] definition

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art in connection with the present invention. Although any methods and materials similar or equivalent to those described herein can be used in the practice of the testing of the present invention, the preferred materials and methods are described herein. In describing and claiming the present invention, the following terminology will be used in accordance with the following definitions.

[0031] Unless expressly stated otherwise, use of the terms "a," "an," etc. means more than one.

[0032] "Ethylene homopolymer" refers to a polymer consisting essentially of ethylene monomer units. Due to the requirements of large-scale polymerization, ethylene homopolymers may contain a small amount of comonomer units, which is usually less than 0.05 mol%, most preferably less than 0.01 mol% of the ethylene homopolymer.

[0033] If a polymer is derived from ethylene monomer units and at least one α-olefin comonomer, the polymer is referred to as an "ethylene copolymer" wherein the ethylene monomer is present in at least 50 mol%. The α-olefin comonomer is preferably typically selected from α-olefin comonomers having 4 to 12 carbon atoms (i.e., C4-C 12 α-olefins).

[0034] After (co)polymerization of ethylene in one or more reactors, the resulting polyethylene is typically removed from the reactors in the form of reactor powder, also known as polyethylene fluff. Other forms of polyethylene powder are known, in which the reactor powder is subsequently pelletized and then reground to a powder form. In the context of the present invention, reactor powder refers to polyethylene powder that has not been subjected to compounding, extrusion, pelletization, or any other process whereby the physical form of the reactor powder is altered. DETAILED DESCRIPTION

[0035] Polyethylene (PE)

[0036] Polyethylene (PE) is primarily defined by the product of its unsaturation index (UI) and processability index (PI), which are defined by equations (i) and (ii), respectively:

[0037]

[0038]

[0039] In the formula

[0040] Mw is the weight-average molecular weight of polyethylene (PE) (measured by gel permeation chromatography, expressed in g / mol);

[0041] [Vinyl] is the number of CH atoms per 1000 in polyethylene (PE). n Vinyl concentration of carbon (by 1 H-NMR spectroscopy);

[0042] MFR 21 is the melt flow rate of polyethylene (PE) (measured according to ISO 1333 at 190°C and 21.6 kg load, expressed in g / 10 min);

[0043] F 120is the melt strength of polyethylene (PE) (measured according to ISO 16790:2021 at a die pressure of 120 bar, expressed in cN).

[0044] The product of the unsaturation index (UI) and the processability index (PI) of polyethylene (PE) must satisfy inequality (I), more preferably inequality (Ia), and most preferably inequality (Ib):

[0045] 1.4≤UI×PI<20(I)

[0046] 3≤UI×PI<17 (Ia)

[0047] 4≤UI×PI<15 (Ib)

[0048] Preferably, the unsaturation index (UI) of the polyethylene (PE) defined in formula (i) is in the range of 70 to 103, more preferably in the range of 75 to 102, most preferably in the range of 80 to 100.

[0049] Preferably, the polyethylene (PE) defined in formula (ii) has a processability index (PI) in the range of 0.02 to 0.20, more preferably in the range of 0.03 to 0.19, most preferably in the range of 0.05 to 0.17.

[0050] MFR of polyethylene (PE) 21 The molecular weight (measured according to ISO 1333 at 190° C. under a load of 21.6 kg) is preferably in the range of 2.5 to 30.0 g / 10 min, more preferably in the range of 3.0 to 20.0 g / 10 min, most preferably in the range of 4.5 to 10.0 g / 10 min.

[0051] Polyethylene (PE) F 120 The melt strength (measured according to ISO 16790:2021 at a die pressure of 120 bar) is preferably in the range of 40 to 120 cN, more preferably in the range of 45 to 100 cN, most preferably in the range of 50 to 85 cN.

[0052] The weight average molecular weight Mw of the polyethylene (PE) (determined by gel permeation chromatography) is preferably in the range of 150,000 to 300,000 g / mol, more preferably in the range of 170,000 to 270,000 g / mol, most preferably in the range of 200,000 to 250,000 g / mol.

[0053] The number average molecular weight Mn of the polyethylene (PE) (determined by gel permeation chromatography) is preferably in the range of 15,000 to 50,000 g / mol, more preferably in the range of 18,000 to 35,000 g / mol, most preferably in the range of 20,000 to 27,000 g / mol.

[0054] The z-average molecular weight Mz of the polyethylene (PE) (determined by gel permeation chromatography) is preferably in the range of 1,100,000 to 1,500,000 g / mol, more preferably in the range of 1,150,000 to 1,400,000 g / mol, most preferably in the range of 1,210,000 to 1,300,000 g / mol.

[0055] The molecular weight distribution (Mw / Mn) of the polyethylene (PE) (measured by gel permeation chromatography) is preferably in the range of 3-20, more preferably in the range of 5-15, most preferably in the range of 7-12.

[0056] The vinyl concentration of polyethylene (PE) [vinyl] (by 1 H-NMR spectrum) per 1000 CH n The number of vinyl units per 1000 CH n The range of 0.20 to 1.50 vinyl units per 1000 CH n The carbon number is in the range of 0.30 to 1.00 vinyl units.

[0057] The density of polyethylene (PE) (measured according to ISO 1183) is between 935 and 965 kg / m 3 in the range of 945 to 962 kg / m 3 In the range of 950 to 960 kg / m 3 within the range.

[0058] Polyethylene (PE) can be an ethylene homopolymer or a copolymer of ethylene and a comonomer selected from C3-C8 alpha-olefins. If comonomers are present, they must be selected from C3-C8 alpha-olefins, more preferably C4-C6 alpha-olefins, further more preferably 1-butene or 1-hexene, most preferably 1-butene.

[0059] In the case where comonomers are present, the total comonomer content is preferably in the range of 0.01 to 1.0 mol%, more preferably in the range of 0.03 to 0.50 mol%, most preferably in the range of 0.05 to 0.20 mol%.

[0060] The polyethylene (PE) may be unimodal or multimodal, including bimodal. Preferably, the polyethylene (PE) is unimodal or bimodal, most preferably, the polyethylene (PE) is unimodal.

[0061] In one embodiment, the polyethylene (PE) is provided in the form of a reactor powder or granules. Most preferably, the polyethylene (PE) is provided in the form of a reactor powder.

[0062] The median particle size (D 50 ) (determined by sieve analysis) is preferably in the range of 400 to 1400 μm, more preferably in the range of 500 to 1200 μm, most preferably in the range of 600 to 1000 μm.

[0063] The upper cut particle size (D 90 ) (determined by sieve analysis) is preferably in the range of 800 to 1400 μm, more preferably in the range of 900 to 1300 μm, most preferably in the range of 1000 to 1200 μm.

[0064] The cut particle size (D 10 ) (determined by sieve analysis) is preferably in the range of 200 to 500 μm, more preferably in the range of 250 to 450 μm, most preferably in the range of 300 to 400 μm.

[0065] Particle size distribution of polyethylene (PE) reactor powder (D 90- D 10 ) / D 50 ) (determined by sieve analysis) is preferably in the range of 0.80 to 1.30, more preferably in the range of 0.90 to 1.20, most preferably in the range of 0.95 to 1.10.

[0066] Polyethylene (PE) is preferably suitable for the production of cross-linked polyethylene (PEX).

[0067] Preferably, the polyethylene (PE) is suitable for the production of cross-linked polyethylene (PEX), wherein radiation is applied to a composition comprising polyethylene in the molten state. One such process is known in the art as PEXe.

[0068] Alternatively or additionally preferably, the polyethylene (PE) is suitable for producing cross-linked polyethylene (PEX) by a process comprising the steps of:

[0069] a) soaking polyethylene (PE) in the form of reactor powder in liquid peroxide;

[0070] b) Extruding the soaked polyethylene powder in an extruder to obtain cross-linked polyethylene (PEX).

[0071] The cross-linked polyethylene (PEX) thus produced is known in the art as PEXa.

[0072] All preferred embodiments and alternatives given below regarding the process for producing cross-linked polyethylene (PEX) from polyethylene (PE) apply mutatis mutandis to the above-described embodiments, wherein the polyethylene (PE) is suitable for such a process.

[0073] Method for preparing polyethylene (PE)

[0074] The polyethylene (PE) of the present invention can be produced by any method known to those skilled in the art.

[0075] The process may employ catalysts well known for ethylene polymerization, such as single-site catalysts and chromium catalysts.

[0076] Single site catalysts include metallocene catalysts and non-metallocene catalysts. By polymerizing in the presence of a single site polymerization catalyst, optionally, for example, in a solution process, polyethylene (PE) as described herein can be produced. The single site catalyst can be suitably a metallocene catalyst. This catalyst comprises a transition metal compound containing a cyclopentadienyl, indenyl or fluorenyl ligand. The catalyst contains, for example, two cyclopentadienyl, indenyl or fluorenyl ligands, which can be bridged by groups preferably containing silicon and / or carbon atoms. In addition, the ligand can have a substituent, for example, an alkyl, aryl, arylalkyl, alkylaryl, silyl, siloxy, alkoxy, etc. Suitable metallocene compounds are known in the art and are disclosed in WO-A-97 / 28170, WO-A-98 / 32776, WO-A-99 / 61489, WO-A-03 / 010208, WO-A-03 / 051934, WO-A-03 / 051514, WO-A-2004 / 085499, EP-A-1752462 and EP-A-1739103, among others.

[0077] In particular, the metallocene compound must be able to produce polyethylene with a sufficiently high molecular weight. In particular, it has been found that metallocene compounds with hafnium as the transition metal atom or metallocene compounds containing indenyl or tetrahydroindenyl type ligands generally have the desired properties. An example of a suitable metallocene compound is the group of metallocene compounds having zirconium, titanium or hafnium as the transition metal and one or more ligands having an indenyl structure with a siloxy substituent, for example, [ethylenebis(3,7-bis(triisopropylsiloxy)inden-1-yl)]zirconium dichloride (racemic and meso), [ethylenebis(4,7-bis(triisopropylsiloxy)inden-1-yl)]zirconium dichloride (racemic and meso), [ethylenebis(5-tert-butyldimethyl ... [(5-tert-butyldimethylsilyloxy)inden-1-yl)]zirconium dichloride (racemic and meso), bis(5-tert-butyldimethylsilyloxy)inden-1-yl)zirconium dichloride, [dimethylsilylenebis(5-tert-butyldimethylsilyloxy)inden-1-yl)]zirconium dichloride (racemic and meso), N-tert-butylamido)(dimethyl)(η5-inden-4-yloxy)silanetitanium dichloride, and [ethylenebis(2-(tert-butyldimethylsilyloxy)inden-1-yl)]zirconium dichloride (racemic and meso).

[0078] Another example is a group of metallocene compounds: it has hafnium as the transition metal atom and carries a cyclopentadienyl type ligand, for example, bis(n-butylcyclopentadienyl) hafnium dichloride, bis(n-butylcyclopentadienyl) dibenzyl hafnium, dimethylsilylene bis(n-butylcyclopentadienyl) hafnium dichloride (racemic and meso) and bis[1,2,4-tri(ethyl)cyclopentadienyl] hafnium dichloride. Yet another example is a group of metallocene compounds with a tetrahydroindenyl ligand, for example, bis(4,5,6,7-tetrahydroindenyl) zirconium dichloride, bis(4,5,6,7-tetrahydroindenyl) hafnium dichloride, ethylene bis(4,5,6,7-tetrahydroindenyl) zirconium dichloride, dimethylsilylene bis(4,5,6,7-tetrahydroindenyl) zirconium dichloride.

[0079] Single-site catalysts typically also include an activator. Commonly used activators are aluminoxane compounds, such as methylaluminoxane (MAO), tetraisobutylaluminoxane (TIBAO), or hexaisobutylaluminoxane (HIBAO). Boron activators, such as those disclosed in US-A-2007 / 049711, may also be used. These activators may be used alone or in combination with, for example, aluminum alkyls (e.g., triethylaluminum or triisobutylaluminum).

[0080] Depending on the polymerization process, the catalyst can be a supported type. The carrier can be any particulate carrier, including an inorganic oxide carrier, such as silicon dioxide, aluminum oxide or titanium, or a polymer carrier, such as a polymer carrier comprising styrene or divinylbenzene. When using a supported catalyst, it is necessary to prepare the catalyst so that the activity of the catalyst is not affected. In addition, any catalyst residues remaining in the final polymer or product should not have any negative impact on key properties, such as uniformity, electrical properties or mechanical properties. The catalyst can also include a metallocene compound on a cured aluminoxane, or it can also be a solid catalyst prepared according to an emulsion curing technique. These catalysts are disclosed in EP-A-1539775 or WO-A-03 / 051934 etc.

[0081] Chromium catalysts are already well known, and for detailed descriptions, see MPMcDaniel, Advances in Catalysis, Vol. 33 (1985), pp. 47-98 and MPMcDaniel, Ind. Eng. Chem. Res., Vol. 27 (1988), pp. 1559-1569. Typically, chromium catalysts are supported by a carrier (preferably silica). So-called Philips catalysts, which are based on chromium trioxide on a silica carrier, are chromium catalysts that can be appropriately used in the present invention. Phillips catalysts are typically produced by activating silica together with a masterbatch of so-called chromium trioxide or chromium acetate. When chromium acetate is used, it is oxidized to chromium trioxide so that the final product is the same regardless of whether chromium trioxide or chromium acetate is used. Chromium trioxide forms volatile chromic acid, which is evenly distributed on the silica particles. The hexavalent chromium deposited on the silica particles should be reduced to become catalytically active, which occurs when chromium contacts the ethylene in the polymerization reactor. Another type of chromium catalyst useful in the present invention is a so-called chromate-type catalyst. When producing this catalyst, a chromate compound (e.g., silyl chromate) is deposited on an activated silica support. The deposited chromate is reduced by means of an alkoxide (e.g., an aluminum alkoxide, such as diethylaluminum ethoxide).

[0082] According to the invention, the chromium catalyst can be modified by titanation and fluorination, according to the prior art (see, for example, Preparation of Catalysts, VG Orcelet et al., Elsevier Science Publishers, Amsterdam, 1991, pp. 215-227, C. 30 E. Marsden).

[0083] Preferably, the chromium catalyst is used to prepare polyethylene (PE).

[0084] When the polyethylene (PE) is desired to be unimodal, it can be produced by a single-stage polymerization in a single reactor in a well-known and well-documented manner. When multimodal (e.g. bimodal) polyethylene is desired, the polyethylene can be produced by mechanically mixing two or more separate polymer components together, or, for example, by in-situ mixing during the polymerization of the components. Both mechanical and in-situ mixing are well known in the art.

[0085] Single-site polyethylene

[0086] Thus, exemplary in situ mixing refers to the polymerization of polymer components under different polymerization conditions, for example, in a multi-stage (i.e., two or more stage) polymerization reactor system, or by using two or more different single-site polymerization catalysts in a single-stage polymerization, or by using a combination of multi-stage polymerization and two or more different single-site polymerization catalysts. In a multi-stage polymerization process, the polymer is polymerized in a process comprising at least two polymerization stages. Each polymerization stage can be carried out in at least two different polymerization zones in one reactor or in at least two separate reactors.

[0087] Furthermore, the multistage polymerization process may be carried out in at least two cascaded polymerization zones. The polymerization zones may be connected in parallel or, for example, the polymerization zones may be operated in cascade mode.

[0088] The polymerization zone may be operated under bulk, slurry, solution, or gas phase conditions, or any combination thereof. In an exemplary multi-stage process, the first polymerization step is carried out in at least one slurry (e.g., loop) reactor and the second polymerization step is carried out in one or more gas phase reactors. An exemplary multi-stage process is described in EP 517868.

[0089] Typically, the temperature in single-site polyethylene polymerization (which is low-pressure PE polymerization) is typically 50 to 115° C., for example 60 to 110° C. The pressure is 1 to 150 bar, for example 10 to 100 bar. By using different types of catalysts and different comonomers and / or hydrogen feeds, precise control of the polymerization conditions can be achieved.

[0090] Furthermore, as described herein, single site polyethylenes can be prepared by known processes, using solution polymerization in the presence of a single site catalyst, such as a metallocene or constrained geometry catalyst, in a one-stage or two-stage polymerization process, known to those skilled in the art.

[0091] For example, as described herein, the single-site polyethylene can be prepared in a high temperature solution polymerization process at temperatures above 100°C by a one-stage or two-stage solution polymerization process.

[0092] This process is essentially based on the polymerization of monomers and suitable comonomers in a liquid hydrocarbon solvent in which the resulting polymer is soluble. The polymerization is carried out at a temperature above the melting point of the polymer, thereby obtaining a polymer solution. This solution is flash evaporated to separate the polymer from the unreacted monomers and the solvent. The solvent is then recovered and recycled in the process. In addition, the solution polymerization process is a high-temperature solution polymerization process using a polymerization temperature above 100°C. The polymerization temperature is, for example, at least 110°C, for example at least 150°C. The polymerization temperature can be, for example, up to 250°C. The pressure in such a solution polymerization process is, for example, from 10 to 100 bar, for example from 15 to 100 bar, for example from 20 to 100 bar. The liquid hydrocarbon solvent used is, for example, C 5-12 hydrocarbons, which may be unsubstituted or replaced by C 1-4 Alkyl substitution, such as pentane, methylpentane, hexane, heptane, octane, cyclohexane, methylcyclohexane and hydrogenated naphtha. For example, using unsubstituted C 6- C 10 Hydrocarbon solvents. Precise control of the polymerization conditions can be achieved by using different types of catalysts and by using different comonomers and / or hydrogen feeds.

[0093] A known solution technology suitable for the preparation of single-site polyethylene in a solution process is BORCEED TM technology.

[0094] Chromium catalyst polyethylene

[0095] Chromium-catalyzed polyethylene is a unimodal low-pressure PE that can be produced by a single-stage polymerization in a single reactor in a well-known and well-documented manner. Chromium-catalyzed polyethylene (CrPE) is a multimodal (e.g., bimodal) low-pressure PE that can be produced, for example, by mechanically mixing two or more separate polymer components together, or by in-situ mixing during the polymerization of the components. Both mechanical and in-situ mixing are well known in the art.

[0096] Thus, exemplary in situ mixing refers to the polymerization of polymer components under different polymerization conditions, for example, in a multi-stage (i.e., two or more stages) polymerization reactor system, or by using two or more different chromium polymerization catalysts (including multi-site or dual-site catalysts) in a one-stage polymerization, or by using a combination of multi-stage polymerization and two or more different chromium polymerization catalysts. In a multi-stage polymerization process, the polymer is polymerized in a process comprising at least two polymerization stages. Each polymerization stage can be carried out in at least two different polymerization zones in one reactor or in at least two separate reactors. In addition, the multi-stage polymerization process can be carried out in at least two cascaded polymerization zones. The polymerization zones can be connected in parallel, or, for example, the polymerization zones are operated in cascade mode. The polymerization zones can be operated under bulk, slurry, solution or gas phase conditions, or any combination thereof. In an exemplary multi-stage process, the first polymerization step is carried out in at least one slurry (e.g., loop) reactor and the second polymerization step is carried out in one or more gas phase reactors. An exemplary multi-stage process is described in EP517868.

[0097] Typically, the temperature in chromium-catalyzed polyethylene polymerization (which is a low-pressure PE polymerization) is typically 50 to 115° C., for example 60 to 110° C. The pressure is 1 to 150 bar, for example 10 to 100 bar. By using different types of catalysts and using different comonomers and / or hydrogen feeds, precise control of the polymerization conditions can be achieved.

[0098] Particularly preferably, the polymerization is carried out in a fluidized bed gas phase reactor.

[0099] In a fluidized bed gas phase reactor, olefins are polymerized in an upward-moving gas stream in the presence of a polymerization catalyst. The reactor typically contains a fluidized bed containing growing polymer particles containing an active catalyst positioned above a fluidizing grid. The polymer bed is fluidized with the aid of a fluidizing gas comprising the olefin monomer, the eventual comonomer, the eventual chain growth controller or chain transfer agent, such as hydrogen, and an eventual inert gas. The fluidizing gas is introduced into an inlet chamber at the bottom of the reactor. One or more of the aforementioned components may be continuously added to the fluidizing gas to compensate for losses caused by the reaction or product withdrawal. From the inlet chamber, the gas stream flows upward through the fluidizing grid into the fluidized bed. The fluidizing gas passes through the fluidized bed. The superficial velocity of the fluidizing gas must be higher than the minimum fluidization velocity of the particles contained in the fluidized bed, otherwise fluidization will not occur. On the other hand, the gas velocity should be lower than the start-up velocity for pneumatic conveying, otherwise the entire bed will be entrained by the fluidizing gas.

[0100] When the fluidizing gas contacts the bed containing the active catalyst, the reactive components of the gas (e.g., monomers and chain transfer agents) react in the presence of the catalyst to produce a polymer product, i.e., chromium-catalyzed polyethylene. Simultaneously, the gas is heated by the heat of reaction. Unreacted fluidizing gas is removed from the top of the reactor and cooled in a heat exchanger to remove the heat of reaction. The gas is cooled to a temperature below the bed temperature to prevent the bed from heating up due to the reaction. The gas can be cooled to a temperature at which a portion of it condenses. When the droplets enter the reaction zone, they are vaporized. The heat of vaporization then helps remove the heat of reaction. The condensing agent is a non-polymerizable component, such as n-pentane, isopentane, n-butane, or isobutane, which is at least partially condensed in the cooler. The gas is then compressed and recycled to the inlet chamber of the reactor. Fresh reactants are introduced into the fluidizing gas stream before entering the reactor to compensate for losses caused by the reaction and product withdrawal. Those skilled in the art generally know how to analyze the composition of the fluidizing gas and how to introduce gas components to keep the composition constant. The actual composition is determined by the desired properties of the product and the catalyst used in the polymerization.

[0101] The catalyst can be introduced into the reactor continuously or intermittently in various ways. The polymer product can be withdrawn from the gas phase reactor continuously or intermittently. Combinations of these methods can also be used.

[0102] Typically, the fluidised bed polymerisation reactor is operated in the temperature range of 50 to 110° C., preferably 65 to 110° C. The pressure is suitably from 10 to 40 bar, preferably from 15 to 30 bar.

[0103] A known gas phase technology suitable for the production of chromium catalyst polyethylene in a fluidized bed gas phase process is UNIPOL TM technology.

[0104] Prepolymerization precedes the actual polymerization step of polyethylene (PE) and is well known in the art.

[0105] The polyethylene powder removed from the reactor may be pelletized with optional additives; however, preferably, the polyethylene powder is not pelletized prior to the PEX forming processes of the present invention, ie, the reactor powder is used in these PEX forming processes as described below.

[0106] As an alternative to addition, optional additives can be added to the reactor powder via a meltblowing system.

[0107] Typical additives can be selected from antioxidants, stabilizers, nucleating agents and antistatic agents. Such additives are generally commercially available and are described, for example, in Hans Zweifel's "Handbook of Plastic Additives", 5th edition, 2001, pages 871 to 873.

[0108] Method for producing cross-linked polyethylene (PEX) from polyethylene (PE)

[0109] The present invention further relates to a process for producing cross-linked polyethylene (PEX) from the polyethylene (PE) of the present invention.

[0110] A variety of possible crosslinking techniques are known in the art, and the polyethylene (PE) of the present invention can be used with each of these techniques. Examples of different methods include peroxide-promoted crosslinking (so-called PEXa), crosslinking based on silanol condensation (so-called PEXb), electron beam crosslinking (so-called PEXc), azo coupling (so-called PEXd) or crosslinking using UV treatment in the melt (so-called PEXe), as well as many other recently developed techniques.

[0111] The polyethylene (PE) of the present invention is particularly suitable for use in methods in which radiation is applied to the polyethylene (PE) in the molten state. These methods include, but are not limited to, PEXe-type processes in which UV light is applied to a composition comprising the polyethylene (PE) and a photoinitiator, or a composition comprising the polyethylene (PE) and a crosslinking agent (e.g., a diene) can be heated in an IR oven (i.e., IR radiation is applied) to achieve crosslinking.

[0112] In one embodiment, the present invention relates to a process for producing cross-linked polyethylene (PEX), wherein cross-linking is achieved by applying radiation to a composition (C) comprising polyethylene (PE) in the molten state.

[0113] In a preferred embodiment, composition (C) further comprises a photoinitiator and optionally a crosslinker, and the radiation applied to the molten composition is UV radiation.

[0114] The photoinitiator may be any photoinitiator capable of being activated upon exposure to radiation, ie upon exposure to UV A, UV B, UV C and the entire visible range, preferably UV A and the visible range, more preferably 355-420 nm.

[0115] Exemplary free radical photoinitiators suitable for use in the process of the present invention include:

[0116] (i) acylphosphine oxides and bisacylphosphine oxides, for example 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide;

[0117] (ii) anisoin;

[0118] (iii) benzoin and benzoin alkyl ethers, for example benzoin ethyl ether, benzoin isobutyl ether, benzoin methyl ether;

[0119] (iv) benzil and benzil dialkyl ketals, for example benzil dimethyl ketal;

[0120] (v) Acetophenones; hydroxyacetophenones, for example 1-hydroxycyclohexylphenyl ketone, 2-hydroxy-2-methyl-1-phenyl-1-propanone, 2-hydroxy-1-[4-(2-hydroxyethoxy)-phenyl]-2-methyl-1-propanone, 3′-hydroxyacetophenone, 4′-hydroxyacetophenone, 2-hydroxy-2-methylpropiophenone; (di)alkoxyacetophenones, for example 2,2-diethoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 4′-ethoxyacetophenone; aminoacetophenones, for example 2-benzyl-2-(dimethylamino)-1-[4-(4-morpholinyl)-phenyl]-1-butanone, 2-methyl-1-[4-(methylthio)-phenyl]-2-(4-morpholinyl)-1-propanone; aryloxyacetophenones, for example 4′-phenoxyacetophenone;

[0121] (vi) benzophenone, 3,3′,4,4′-benzophenonetetracarboxylic dianhydride, benzoylbiphenyl, (di)hydroxybenzophenones, such as 4′-dihydroxybenzophenone, 3-hydroxybenzophenone, and 4-hydroxybenzophenone; (di)alkoxybenzophenones, such as 4′-dimethoxybenzophenone, 3-methoxybenzophenone, and 4-methoxybenzophenone; and (di)alkylbenzophenones, such as 4-(dimethylamino)benzophenone, 2-methylbenzophenone, 3-methylbenzophenone, 2,5-dimethylbenzophenone, and 3,4-dimethylbenzophenone; (di)aminobenzophenones, such as 4,4′-bis(dimethylamino)benzophenone; and 2-benzyl-2-(dimethylamino)-4′-morpholinobutyrophenone and 2-methyl-4′-(methylthio)-2-morpholinopropiophenone;

[0122] (vii) anthraquinone and alkylanthraquinone, such as 2-ethylanthraquinone;

[0123] (viii) thioxanthones; alkylthioxanthones, such as isopropylthioxanthones; and thioxanthen-9-ones, such as 2-chlorothioxanthen-9-one;

[0124] (ix) dibenzosuberenone;

[0125] (x) a-diketones, for example camphorquinone, 9,10-phenanthrenequinone, 1-phenylpropane-1,2-dione, 4,4′-dichlorobenzil, methyl benzoylformate or derivatives thereof;

[0126] (xi) monoacylgermanium compounds and diacylgermanium compounds, for example benzoyltrimethylgermanium, dibenzoyldiethylgermanium, bis(4-methoxybenzoyl)-diethylgermanium;

[0127] (xii) Titanocene, such as bis-(eta 5-2,4-cyclopentadien-1-yl)-bis-[2,6-difluoro-3-(1H-pyrrol-1-yl)phenyl]-titanium.

[0128] Specific examples include acetophenone, alkyl isoquinone, anthraquinone, benzil, benzoin, benzoin ethyl ether, benzoin isobutyl ether, benzoin methyl ether, benzophenone, 1-hydroxycyclohexylphenyl ketone, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, benzoylbiphenyl, 2-benzyl-2-(dimethylamino)-4'-morpholinobutyrophenone, 4,4'-bis(diethylamino)benzophenone, 4,4'-bis(dimethylamino)benzophenone, camphorquinone, 2-chlorothioxanthen-9-one, dibenzosuberenone, 2,2-diethoxyacetophenone, 4,4'-dihydroxybenzophenone, 2,2-dimethoxy-2-phenylacetophenone, 4-(dimethylamino)benzophenone , 4,4'-dimethylbenzil, 2,5-dimethylbenzophenone, 3,4-dimethylbenzophenone, diphenyl (2,4,6-trimethylbenzoyl) phosphine oxide / 2-hydroxy-2-methylpropiophenone, 4'-ethoxyacetophenone, 2-ethylanthraquinone, 3'-hydroxyacetophenone, 4'-hydroxyacetophenone, 3-hydroxybenzophenone, 4-hydroxybenzophenone, 1-hydroxycyclohexylphenyl ketone, 2-hydroxy-2-methylpropiophenone, 2-methylbenzophenone, 3-methylbenzophenone, methyl benzoylformate, 2-methyl-4'-(methylthio)-2-morpholinopropiophenone, phenanthrenequinone, 4'-phenoxyacetophenone, and thioxanthen-9-one.

[0129] Particularly preferably, benzophenone-based photoinitiators are used, the most preferred photoinitiators being alkoxy-substituted benzophenones.

[0130] The photoinitiator is preferably present in the composition in an amount of 0.02 to 3.0 wt%, more preferably 0.2 to 2.5 wt%, and most preferably 0.5 to 2.0 wt%.

[0131] The cross-linking agent may be any suitable cross-linking agent having at least two reactive groups suitable for cross-linking, most preferably two olefinic groups.

[0132] The choice of cross-linking agent is not particularly limited, and suitable cross-linking agents are listed in WO 2015 / 162155 A1.

[0133] The amount of crosslinker present in the composition is preferably from 0.02 to 3.0 wt%, more preferably from 0.2 to 2.5 wt%, most preferably from 0.5 to 2.0 wt%.

[0134] In an alternative embodiment, composition (C) further comprises a crosslinking agent and the radiation applied to the molten composition is IR radiation.

[0135] The cross-linking agent of this embodiment can be any suitable cross-linking agent having at least two reactive groups suitable for cross-linking, most preferably two olefinic groups.

[0136] Particularly preferably, the crosslinking agent is a bismaleimide crosslinking agent, most preferably hexamethylene-1,6-bismaleimide (CAS 4856-87-5).

[0137] The amount of crosslinker present in the composition is preferably from 0.02 to 5.0 wt%, more preferably from 0.2 to 3.0 wt%, most preferably from 0.5 to 2.5 wt%.

[0138] For more detailed information on IR radiation crosslinking, see WO 2016 / 170016 A1.

[0139] In each of the embodiments described above, the radiation is preferably applied to the composition (C) comprising polyethylene (PE) in the molten state after extrusion.

[0140] Particularly preferably, the composition (C) is extruded to form a tube and then crosslinked by applying radiation in the molten state.

[0141] Therefore, the method may comprise the following steps:

[0142] a) adding the polyethylene (PE) of the present invention, optionally a photoinitiator, optionally a crosslinker and optionally additives to an extruder, preferably a twin-screw extruder;

[0143] b) mixing and extruding the obtained composition (C) to form an extruded article, preferably an extruded tube;

[0144] c) applying radiation to the extruded article, preferably the extruded pipe, thereby crosslinking the polyethylene (PE) in the molten state to form crosslinked polyethylene (PEX); and

[0145] d) cooling the article, preferably a pipe, comprising cross-linked polyethylene (PEX) to form a solid article, preferably a solid pipe.

[0146] In one embodiment, the method may include the following steps:

[0147] a) adding the polyethylene (PE) of the present invention, a photoinitiator, an optional crosslinker and optional additives to an extruder, preferably a twin-screw extruder;

[0148] b) mixing and extruding the obtained composition (C) to form an extruded article, preferably an extruded tube;

[0149] c) applying UV radiation to the extruded article, preferably the extruded pipe, thereby crosslinking the polyethylene (PE) in the molten state to form crosslinked polyethylene (PEX); and

[0150] d) cooling the article, preferably a pipe, comprising cross-linked polyethylene (PEX) to form a solid article, preferably a solid pipe.

[0151] In an alternative embodiment, the method may include the following steps:

[0152] a) adding the polyethylene (PE) of the present invention, a crosslinking agent and optional additives to an extruder, preferably a twin-screw extruder;

[0153] b) mixing and extruding the obtained composition (C) to form an extruded article, preferably an extruded tube;

[0154] c) applying IR radiation to an extruded article, preferably an extruded pipe, thereby crosslinking the polyethylene (PE) in the molten state to form crosslinked polyethylene (PEX); and

[0155] d) cooling the article, preferably a pipe, comprising cross-linked polyethylene (PEX) to form a solid article, preferably a solid pipe.

[0156] The compositions used in the PEX process typically contain additional stability additives such as antioxidants, UV absorbers, quenchers, hindered amine light stabilizers (HALS), acid scavengers, and thermal stabilizers. The selection of suitable additives is within the general knowledge and skill of those skilled in the art.

[0157] The polyethylene (PE) of the present invention is also suitable for polyethylene cross-linking processes using thermally activated free radical initiators, such as peroxide-based initiators (PEXa) or azo-based free radical initiators (PEXd).

[0158] The present inventors have found that these methods are particularly effective when the polyethylene (PE) of the present invention is used in the form of a reactor powder.

[0159] Therefore, the present invention also relates to a method for producing cross-linked polyethylene (PEX), comprising the following steps:

[0160] a) soaking the polyethylene (PE) of the present invention in the form of reactor powder in a liquid peroxide or peroxide solution;

[0161] b) extruding the soaked polyethylene powder in an extruder (preferably a twin-screw extruder) to obtain cross-linked polyethylene (PEX).

[0162] As is well known in the art of cross-linked polyethylene, such PEXa type processes typically require elevated temperatures in the extruder (preferably a twin-screw extruder) in the range of 160 to 260°C, more preferably in the range of 180 to 255°C, most preferably in the range of 200 to 250°C.

[0163] The skilled person is aware of suitable peroxides, in particular organic peroxides, by means of which polyethylene can be crosslinked. One or more of the following organic peroxides may be used:

[0164] Diisopropylbenzene peroxide, benzoyl peroxide, dichlorobenzoyl peroxide, di-tert-butyl peroxide, 2,5-dimethyl-2,5-di(peroxybenzoate), hexyn-3,1,4-bis(tert-butylperoxyisopropyl)benzene, lauroyl peroxide, tert-butyl peracetate, tert-butyl perbenzoate, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexyn, and tert-butyl perphenyl acetate.

[0165] In principle, the crosslinkable composition may additionally comprise a non-peroxide crosslinker. In a preferred embodiment, however, the crosslinking is carried out without a non-peroxide crosslinker.

[0166] All preferred embodiments and alternatives of the polyethylene (PE), polyethylene reactor powder and process for the preparation of polyethylene (PE) are applicable mutatis mutandis to the process for producing cross-linked polyethylene (PEX) from the polyethylene (PE) of the present invention.

[0167] The present invention also relates to the cross-linked polyethylene (PEX) obtainable by the process according to the invention.

[0168] The degree of cross-linking of the cross-linked polyethylene (PEX) is preferably at least 40%, more preferably at least 50%, most preferably at least 60%.

[0169] All preferred embodiments and alternatives of the polyethylene (PE), polyethylene reactor powder, process for the preparation of polyethylene (PE) and process for producing cross-linked polyethylene (PEX) from polyethylene (PE) are applicable mutatis mutandis to the cross-linked polyethylene (PEX) obtained according to the invention.

[0170] Products and uses

[0171] The present invention further relates to a cross-linked polyethylene pipe comprising at least 90% by weight of cross-linked polyethylene (PEX), as described above.

[0172] In one embodiment, the cross-linked pipe is produced by a PEXa type process.

[0173] In this embodiment, the extrusion step b) is a tube extrusion step.

[0174] Thus, the cross-linked pipe can be produced by a method comprising the following steps:

[0175] a) soaking the polyethylene (PE) of the present invention in the form of reactor powder in a liquid peroxide or peroxide solution;

[0176] b) Extruding the soaked polyethylene powder in an extruder (preferably a twin-screw extruder) to form a tube, thereby obtaining a cross-linked polyethylene tube.

[0177] In an alternative embodiment, the cross-linked tube is produced by a process involving the application of radiation to the extruded tube in the molten state.

[0178] In this embodiment, the tube extrusion step is performed before the cross-linking step.

[0179] Thus, the cross-linked pipe can be produced by a method comprising the following steps:

[0180] a) adding the polyethylene (PE) of the present invention, optionally a photoinitiator, optionally a crosslinker and optionally additives to an extruder, preferably a twin-screw extruder;

[0181] b) mixing and extruding the obtained composition (C) to form an extruded tube;

[0182] c) applying radiation to the extruded tube, thereby crosslinking the polyethylene (PE) in the molten state to form cross-linked polyethylene (PEX);

[0183] d) Cooling the tube comprising cross-linked polyethylene (PEX) to form a solid tube.

[0184] In one embodiment, the method comprises the following steps:

[0185] a) adding the polyethylene (PE) of the present invention, a photoinitiator, an optional crosslinker and optional additives to an extruder, preferably a twin-screw extruder;

[0186] b) mixing and extruding the obtained composition (C) to form an extruded tube;

[0187] c) applying UV radiation to the extruded tube, thereby crosslinking the polyethylene (PE) in the molten state to form crosslinked polyethylene (PEX); and

[0188] d) Cooling the tube comprising cross-linked polyethylene (PEX) to form a solid tube.

[0189] In an alternative embodiment, the method comprises the following steps:

[0190] a) adding the polyethylene (PE) of the present invention, a crosslinking agent and optional additives to an extruder, preferably a twin-screw extruder;

[0191] b) mixing and extruding the obtained composition (C) to form an extruded tube;

[0192] c) applying IR radiation to the extruded tube to crosslink the polyethylene (PE) in the molten state to form crosslinked polyethylene (PEX); and

[0193] d) Cooling the tube comprising cross-linked polyethylene (PEX) to form a solid tube.

[0194] The present invention also relates to the use of the polyethylene (PE) of the present invention for producing cross-linked polyethylene (PEX).

[0195] Preferably, the polyethylene (PE) of the present invention is used for producing cross-linked polyethylene pipes.

[0196] All preferred embodiments and alternatives of the polyethylene (PE), the process for the preparation of polyethylene (PE) and the process for producing cross-linked polyethylene (PEX) from polyethylene (PE) are applicable mutatis mutandis to the use according to the invention.

[0197] Example

[0198] 1. Definition / Measurement Method

[0199] Unless otherwise defined, the following definitions of terms and determination methods apply to the above general detailed description of the present invention as well as the following examples.

[0200] Melt flow rate (MFR)

[0201] The melt flow rate (MFR) is measured according to ISO 1133 and is expressed in g / 10 min. The MFR is an indicator of the viscosity of the polymer melt. The MFR of PE is measured at 190°C. The load under which the melt flow rate is measured is usually indicated by a subscript, for example, MFR2 is measured under a load of 2.16 kg (condition D), MFR5 is measured under a load of 5 kg (condition T) or MFR 21 Measured under a load of 21.6 kg (Condition G).

[0202] density

[0203] The density of the polymer is measured according to ISO 1183 / 1872-2B.

[0204] The amount of carbon-carbon double bonds, i.e. [vinyl]

[0205] The vinyl content of the polymer was quantified using quantitative nuclear magnetic resonance (NMR) spectroscopy.

[0206] Quantitative measurements were recorded in solution using a Bruker AVNEO 400 NMR spectrometer operating at 400.15 MHz. 1 H NMR spectroscopy. All spectra were obtained using 13Recordings were made at 125°C using a C-optimized 10 mm selective excitation probehead, with nitrogen used for all pneumatics. Approximately 250 mg of material was dissolved in 1,2-tetrachloroethane-d2 (TCE-d2) using approximately 3 mg of Hostanox 03 (CAS 32509-66-3) as a stabilizer. Standard single-pulse excitation was employed, using a 30-degree pulse, a 10-s relaxation delay, and 10 Hz sample rotation. Four virtual scans were used, yielding a total of 128 transients per spectrum. This setup was chosen primarily due to the high resolution required for quantification and stabilization of the unsaturation of the vinylidene groups {he10a, busico05a}.

[0207] Quantitative analysis using specialized computer programs 1 H spectra were processed, integrated, and relevant quantitative properties determined. All chemical shifts were indirectly referenced to TMS at 0.00 ppm using the signal arising from residual protonated solvent at 5.95 ppm.

[0208] Characteristic signals corresponding to the presence of aliphatic vinyl groups (R-CH=CH2) were observed and their amounts were quantified using the integration of two coupled inequivalent terminal CH2 protons (Va and Vb) at 4.95, 4.98, 5.00, and 5.05 ppm, which illustrate the reporting sites for each functional group:

[0209] N 乙烯基 =IVab / 2

[0210] Hostanox 03 stabilizers were quantified using multiplet integration of aromatic protons (A) at 6.92, 6.91, 6.69, and 6.89 ppm, which account for the reporting sites for each molecule:

[0211] H=IA / 4

[0212] As is typical for the quantification of unsaturation in polyolefins, even by 1 H NMR spectroscopy is quantitative and the amount of unsaturation is determined relative to the total number of carbon atoms. This allows comparison with direct 13 C NMR spectra were directly compared with other microstructural quantities.

[0213] The total amount of carbon atoms was calculated from the integration of the bulk aliphatic signal between 2.85 and -1.00 ppm, with compensation for the methyl-containing signal of the stabilizer and the exclusion of unsaturated derivatization sites.

[0214] NC 总 =((I 本体 -42*H) / 2)+2*N 乙烯基

[0215] The content of vinyl groups (U 乙烯基) is calculated as per thousand total carbons in the polymer (kCH n ) the number of unsaturated groups (N 乙烯基 ):

[0216] U 乙烯基 =1000*N 乙烯基 / NC 总

[0217] References :

[0218] he10a

[0219] He, Y., Qiu, X, and Zhou, Z., Mag. Res. Chem. 2010, 48, 537-542.

[0220] busico05a

[0221] Busico,V.et.al.Macromolecules,2005,38(16),6988-6996

[0222] Molecular weight and molecular weight distribution

[0223] The average molecular weight (M) was determined by gel permeation chromatography (GPC) according to ISO 16014-1:2003, ISO 16014-2:2003, ISO 16014-4:2003 and ASTM D 6474-12 using the following formula: z 、M w and M n ), molecular weight distribution (MWD) and its breadth (measured by the polydispersity index M w / M n (Among them, M n is the number average molecular weight, M w is the weight average molecular weight) description):

[0224]

[0225]

[0226]

[0227] For a constant elution volume interval ΔV i , where A i and M i and elution volume V, respectively. i Correlate the chromatographic peak slice area and the polyolefin molecular weight (MW), where N is equal to the number of data points between the integration limits obtained from the chromatogram.

[0228] A high-temperature GPC instrument was used, equipped with either an infrared (IR) detector (IR4 or IR5) from PolymerChar (Valencia, Spain) or an Agilent Technologies differential refractometer (RI), equipped with three Agilent-PLgel Olexis and one Agilent-PLgel Olexis Guard columns. A mobile phase of 1,2,4-trichlorobenzene (TCB) stabilized with 250 mg / L 2,6-di-tert-butyl-4-methylphenol was used. The chromatographic system was operated at 160°C at a constant flow rate of 1 mL / min. A 200 μL sample solution was injected for each analysis. Data acquisition was performed using Agilent Cirrus software version 3.3 or PolymerChar GPC-IR control software.

[0229] The column set was calibrated using universal calibration (according to ISO 16014-2:2003) with 19 narrow MWD polystyrene (PS) standards ranging from 0.5 kg / mol to 11,500 kg / mol. The PS standards were dissolved at room temperature for several hours. The conversion of polystyrene peak molecular weight to polyolefin molecular weight was accomplished using the Mark Houwink equation and the following Mark Houwink constants:

[0230] K PS =19x 10 -3 mL / g,α PS =0.655

[0231] K PE =39x 10 -3 mL / g,α PE =0.725

[0232] The calibration data were fitted using a third-order polynomial fit.

[0233] All samples were prepared in a concentration range of approximately 0.1 mg / ml and dissolved in freshly distilled TCB stabilized with 1000 ppm Irgafos 168 at 160°C for 6 h with continuous gentle shaking.

[0234] F 120 Melt strength and V 120 Melt ductility

[0235] The testing documented in this article complies with ISO 16790:2021.

[0236] The strain hardening behavior was determined by the method described in the document "Rheotens-Mastercurves and Drawability of Polymer Melts", MH Wagner, Polymer Engineering and Science, Vol. 36, pp. 925 to 935. The content of this document is incorporated by reference. The strain hardening behavior of the polymer was determined by the Rheotens device ( 2, 74711 Buchen, Germany), in which the melt strand is elongated by drawing it downwards at a defined acceleration.

[0237] The Rheotens experiment simulates industrial rotation and extrusion processes. In principle, the melt is pressed or extruded through a circular die, and the resulting strands are then pulled. The stress on the extrudate is recorded as a function of the melt characteristics and measurement parameters (in particular, the ratio between the output and pull-off speeds, which is actually a measure of the elongation). For the results shown below, the materials were extruded using a laboratory extruder instrument: ALR-M; X-trude 300NM with MBR 71.05 (melt pump) and Rheotens 71.97, and a gear pump with a cylindrical die (L / D = 6.0 / 2.0 mm / 60°). To measure the F30 melt strength and v30 melt ductility, the pressure at the extruder outlet (= gear pump inlet) was set to 30 bar by bypassing a portion of the extruded polymer. In a similar manner, to measure the F 120 Melt strength and V 120 For melt extensibility, the pressure at the extruder outlet (=gear pump inlet) was set to 120 bar, while for measurements of F200 melt strength and v200 melt extensibility, the pressure at the extruder outlet (=gear pump inlet) was set to 200 bar.

[0238] The gear pump was pre-adjusted to an output of 2.10 + / - 0.2 g / min and the melt temperature was set to 200°C. The length of the rotation line between the die and the Rheotens wheel was 100 mm. At the start of the experiment, the take-up speed of the traction wheel was adjusted to the speed of the extruded polymer strand (tension < 0.5 cN). The acceleration of the traction wheel was 120 mm / s 2 .

[0239] Rheotens is run in conjunction with the PC program EXTENS. This is a real-time data acquisition program that displays and stores the measured data of the pulling force and the downward pulling speed. Depending on the measurement results, the end points of the Rheotens curve (force versus pulley speed) at which the polymer strand breaks are taken as F 30 Melt strength and V30 The value of melt ductility, or F 120 Melt strength and V 120 Melt ductility, or F 200 Melt strength and V 200 Value of melt ductility.

[0240] Comonomer content

[0241] Quantitative nuclear magnetic resonance (NMR) spectroscopy was used to quantitatively analyze the comonomer content of the polymers.

[0242] Quantitative measurements were recorded in the melt using a Bruker Avance III 500 NMR spectrometer. 13 C{ 1 H}NMR spectrum, 1 H and 13 C operated at 500.13 and 125.76 MHz, respectively. All spectra were taken using 13Recordings were made at 150°C using a C-optimized 7 mm magic angle spinning (MAS) probehead, with nitrogen used for all pneumatics. Approximately 200 mg of material was loaded into a 7 mm outer diameter zirconium oxide MAS rotor and spun at 4 kHz. This setup was chosen primarily due to the high sensitivity required for rapid identification and accurate quantification (Klimke, K., Parkinson, M., Piel, C., Kaminsky, W., Spiess, H.W., Wilhelm, M., Macromol. Chem. Phys. 2006; 207: 382., Parkinson, M., Klimke, K., Spiess, H.W., Wilhelm, M., Macromol. Chem. Phys. 2007; 208: 2128., Castignolles, P., Graf, R., Parkinson, M., Wilhelm, M., Gaborieau, M., Polymer 50 (2009) 2373). Standard single-pulse excitation was used, using transient NOE with a recycle delay as short as 3 s (Pollard, M., Klimke, K., Graf, R., Spiess, H.W., Wilhelm, M., Sperber, O., Piel, C., Kaminsky, W., Macromolecules 2004; 37:813., Klimke, K., Parkinson, M., Piel, C., Kaminsky, W., Spiess, H.W., Wilhelm, M., Macromol. Chem. Phys. 2006; 207:382.) and the RS-HEPT decoupling scheme (Filip, X., Tripon, C., Filip, C., J. Mag. Resn. 2005, 176, 239, Griffin, J. M., Tripon, C., Samoson, A., Filip, C., and Brown, SP, Mag. Res. in Chem. 2007 45, S1, S198). A total of 16,384 (16k) transients were collected for each spectrum. This setting was chosen because it has a high sensitivity to low comonomer contents.

[0243] Quantitation using a custom spectral analysis automation program 13 C{ 1 H} NMR spectra were processed, integrated, and quantitatively characterized. All chemical shifts were internally referenced to the bulk methylene signal (δ+) at 30.00 ppm (J. Randall, Macromol. Sci., Rev. Macromol. Chem. Phys. 1989, C29, 201).

[0244] A characteristic signal corresponding to the incorporation of 1-butene was observed (J. Randall, Macromol. Sci., Rev. Macromol. Chem. Phys. 1989, C29, 201.) and all contents were calculated relative to all other monomers present in the polymer.

[0245] Characteristic signals resulting from isolated 1-butene incorporation (i.e., EEBEE comonomer sequences) were observed. Isolated 1-butene incorporation was quantified using the integral of the signal at 39.84 ppm assigned to the *B2 site, which illustrates the reported site for each comonomer:

[0246] B=I *B2

[0247] When a characteristic signal resulting from continuous 1-butene incorporation (i.e., EBBE comonomer sequence) is observed, this continuous 1-butene incorporation is quantified using the integral of the signal at 39.4 ppm assigned to the ααB2B2 site, which accounts for the reported site for each comonomer:

[0248] BB=2*I ααB2B2

[0249] When a characteristic signal arising from discontinuous 1-butene incorporation (i.e., EBEBE comonomer sequences) was also observed, this discontinuous 1-butene incorporation was quantified using the integration of the signal at 24.7 ppm assigned to the ββB2B2 site, which accounts for the reported site for each comonomer:

[0250] BEB=2*I ββB2B2

[0251] Since the *B2 and *βB2B2 sites of isolated (EEBEE) and discontinuously introduced (EBEBE) 1-butene, respectively, overlap, the total amount of isolated 1-butene introduction was corrected based on the amount of discontinuous 1-butene present:

[0252] B=I *B2 -2*I ββB2B2

[0253] In the absence of other signals indicating other comonomer sequences (i.e., butene chain initiation), it was observed that the total 1-butene comonomer content was calculated based solely on the amounts of isolated (EEBEE), continuous (EBBE), and discontinuous (EBEBE) 1-butene comonomer sequences:

[0254] B 总 =B+BB+BEB

[0255] Characteristic signals arising from saturated end groups were observed. The amount of such saturated end groups was quantified using the average of the integrals of the signals at 22.84 and 32.23 ppm, assigned to the 2s and 3s sites, respectively:

[0256] S=(1 / 2)*(I 2S +I 3S )

[0257] The relative content of ethylene was quantified using the integral of the bulk methylene (δ+) signal at 30.00 ppm:

[0258] E=(1 / 2)*I δ+

[0259] The total ethylene comonomer content was calculated based on the bulk methylene signal, which accounts for the presence of ethylene units in other observed comonomer sequences or end groups:

[0260] E 总 =E+(5 / 2)*B+(7 / 2)*BB+(9 / 2)*BEB+(3 / 2)*S

[0261] The total mole fraction of 1-butene in the polymer is then calculated as:

[0262] fB=B 总 / (E 总 +B 总 )

[0263] The mole percent of total comonomer incorporation of 1-butene is calculated in the usual manner from the mole fractions:

[0264] B [mol%] = 100 * fB

[0265] The weight percent of total comonomer incorporation of 1-butene was calculated from the mole fractions in the standard manner:

[0266] B [weight %] = 100*(fB*56.11) / ((fB*56.11)+((1-fB)*28.05))

[0267] Particle size distribution (d 10 d 50 d 90 ,span)

[0268] The particle size distribution was determined using a sieving column consisting of the following sieves:

[0269] 20μm, 32μm, 63μm, 100μm, 125μm, 160μm, 200μm, 250μm, 315μm, 400μm, 500μm, 710μm , 1mm (=1000μm), 1.4mm (1400μm), 2mm (=2000μm), 2.8mm (=2800μm) and 4mm (=4000μm).

[0270] The individually peeled sieves are stacked on top of each other on a sieving machine (= sieving machine = vibrating plate). The sieves are arranged so that the sieve with the largest mesh size is at the top and the sieve with the smallest mesh size is at the bottom. The residue after the last sieve is called the sieve residue (= particles < 20 μm).

[0271] Place approximately 100 g of sample in the top sieve (= sieve with the largest mesh size). Note the exact weight = initial weight. After 20 minutes, stop the vibration again, remove the sieves one by one from the sieving machine and weigh them individually.

[0272]

[0273] This calculation is performed for each individual sieve to determine the particle size distribution obtained by sieving.

[0274] Once the experimental particle size distribution is obtained, the cumulative distribution from 0 to 100% can be evaluated. The cumulative curve is fitted by a Boltzmann-type equation:

[0275]

[0276] Where:

[0277] A1, A2, x0, dx are Boltzmann parameters, and D is the particle diameter (in μm).

[0278] The Boltzmann equation parameters were obtained by minimizing the sum of squared errors between the fitted function and the experimental values.

[0279]

[0280] Where n is the number of particle classes defined by sieving, y i is the weight of the cumulative Boltzmann function in the i-th class, y exp,i is the weight % of the cumulative experimental value in class i.

[0281] From the fit function, the following values ​​can be calculated:

[0282] D 10 : The fraction (weight %) of particles with diameters smaller than this value is 10%

[0283] D50 : The fraction (weight %) of particles with diameters smaller and larger than this value is 50%. This is also called the median diameter.

[0284] D 90 : The fraction (weight %) of particles having a diameter smaller than this value is 90%.

[0285] The distribution width is usually defined by the following formula:

[0286]

[0287] 2. Examples

[0288] Aggregation conditions :

[0289] All examples (inventive examples and comparative examples) were polymerized in a fluidized bed gas phase reactor using the Unipol process under the conditions given in Table 1 using a commercially available chromium catalyst BCF01E provided by Grace Catalyst AB. BCF01E is a silica-supported catalyst based on chromium trioxide. 50 The median particle size is 55 μm and the BET surface area is 315 m 2 / g, and the chromium content is 0.085% by weight.

[0290] Upon exiting the reactor, 300 ppm of a stabilizer in the form of Songnox 1076CP (CAS No. 2082-79-3, commercially available from Songwon) was added to each example (inventive and comparative) via a meltblown system in a transfer line.

[0291] Table 1: Polymerization conditions and properties of polyethylene of inventive examples and comparative examples

[0292]

[0293] As can be seen from Table 1, the polyethylene of the present invention has significantly improved performance for the PEX process.

[0294] In particular, the UI is significantly lower than that of CE2, which is a key parameter indicating the suitability of the PEX process, where a higher level of unsaturation (ie, lower UI) helps to achieve crosslinking.

[0295] The inventive examples also showed a low PI parameter, a key indicator of melt stability, a factor required in PEX processes where crosslinking occurs on the melt-extruded article (e.g., pipe), such as the so-called PEXe process. Premature crosslinking should be avoided in such processes, as the extrusion temperature for non-crosslinked PE is typically around 200°C. Therefore, high melt stability is crucial to prevent excessive deformation of the melt-extruded article during crosslinking.

[0296] Although those skilled in the art will understand in a general manner that [vinyl], Mw and F 120 should be increased, and MFR 21 should be reduced, but the inventors have found that the [vinyl], Mw, F 120 and MFR 21 The polymers of these parameters represent the sweet spot for achieving particularly effective PEXe crosslinking, the effects of which cannot be achieved by considering only a single feature in view of the synergistic interaction between these features in achieving the improvements of the present invention.

[0297] The particle sizes of IE1, IE2, and CE2 are beneficial for the PEXa process, where the PE is pre-soaked with peroxide before extrusion. The smaller the particles (within reason), the easier it is for the peroxide to penetrate the entire particle, not just its surface area.

[0298] Furthermore, the specific "fluffy" form of the reactor powder provides a particularly advantageous high surface area to volume ratio, which allows for greater peroxide penetration compared to similarly sized powders formed by grinding granulated samples. Surprisingly, the reactor powder also allows for better homogeneity of any optional additives in the final crosslinking composition.

Claims

1. A polyethylene (PE) for producing cross-linked polyethylene (PEX), wherein: The polyethylene PE has a molecular weight distribution Mw / Mn of 7-12 as measured by gel permeation chromatography, and the polyethylene PE also satisfies inequality (I): 1.4≤UI×PI<20 (I) The unsaturation index UI is defined by formula (i): In the formula Mw is the weight-average molecular weight of polyethylene (PE) measured by gel permeation chromatography, expressed in g / mol; [Vinyl] is through 1 The H-NMR spectrum measured the CH n vinyl concentration of carbon; The processability index PI is defined by formula (ii): In the formula MFR 21 It is the melt flow rate of polyethylene (PE) measured at 190°C and 21.6 kg load according to ISO 1133, expressed in g / 10 min; F 120 It is the melt strength of polyethylene (PE) measured at a die pressure of 120 bar according to ISO 16790:2021 and is expressed in cN.

2. The polyethylene (PE) according to claim 1, wherein The unsaturation index UI of the polyethylene PE defined by formula (i) is in the range of 70 to 103.

3. The polyethylene (PE) according to claim 1, wherein The polyethylene PE has a processability index PI defined by formula (ii) in the range of 0.02 to 0.

20.

4. The polyethylene (PE) according to claim 1, wherein The melt flow rate (MFR) of the polyethylene (PE) measured at 190°C and a load of 21.6 kg according to ISO 1133 is: 21 In the range of 2.5 to 30.0 g / 10 min.

5. The polyethylene (PE) according to claim 1, wherein The polyethylene PE is measured according to ISO 16790:2021 at a die pressure of 120 bar. 120 The melt strength ranged from 40 to 120 cN.

6. The polyethylene (PE) according to claim 1, wherein: The polyethylene PE has a weight average molecular weight Mw measured by gel permeation chromatography in the range of 150,000 to 300,000 g / mol.

7. The polyethylene (PE) according to claim 1, wherein The polyethylene PE is 1 The vinyl concentration expressed as [vinyl] per 1000 CH n The carbon number is in the range of 0.10 to 2.00 vinyl units.

8. The polyethylene (PE) according to claim 1, wherein The polyethylene PE has a density of 935 to 965 kg / m3 as measured according to ISO 1183. 3 within the range.

9. A method for producing cross-linked polyethylene (PEX), wherein: The method comprises the following steps: a) soaking the polyethylene PE according to claim 1 in the form of a reactor powder in a liquid peroxide or a peroxide solution; b) Extruding the soaked polyethylene powder in an extruder to obtain cross-linked polyethylene PEX.

10. A method for producing cross-linked polyethylene (PEX), wherein: The crosslinking is achieved by applying radiation to the composition C in the molten state, said composition C comprising the polyethylene PE according to claim 1 .

11. The method for producing cross-linked polyethylene (PEX) according to claim 10, wherein: The composition C also comprises a photoinitiator, and the radiation applied to the molten composition is UV radiation.

12. A cross-linked polyethylene (PEX) obtained by the method according to claim 9.

13. A cross-linked polyethylene (PEX) obtained by the method according to claim 10.

14. A cross-linked polyethylene pipe comprising at least 90 wt% of the cross-linked polyethylene PEX according to claim 12, wherein: The pipe is produced according to the method of claim 9, wherein the extrusion step b) is a pipe extrusion step.

15. A cross-linked polyethylene pipe comprising at least 90 wt% of the cross-linked polyethylene PEX according to claim 13, wherein: The pipe is produced according to the method of claim 10, wherein the pipe extrusion step is performed before the cross-linking step.

16. Use of the polyethylene (PE) according to claim 1 for producing cross-linked polyethylene (PEX).

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