WO2022129409A1

WO2022129409A1 - Modification of polyethylene terpolymer

Info

Publication number: WO2022129409A1
Application number: PCT/EP2021/086305
Authority: WO
Inventors: Jingbo Wang; Klaus Bernreitner; Markku Vahteri; Friedrich Berger
Original assignee: Borealis Ag
Priority date: 2020-12-18
Filing date: 2021-12-16
Publication date: 2022-06-23
Also published as: EP4263631A1

Abstract

A process for the reduction of the MFR2 of a polyethylene comprising (i) combining a single site produced polyethylene terpolymer having an MFR2 (starting) of 0.5 to 10 g/10min and a density from 910 to 945 kg/m3 with a radical initiator to form a mixture; (ii) extruding the mixture of step (i) at a temperature above the melting point of the polyethylene terpolymer and at a temperature above the initiation temperature of the radical initiator to form pellets comprising a modified polyethylene terpolymer; wherein said pellets have a density of 910 to 945 kg/m3, a xylene hot insoluble content (XHU) of 0.3 wt% or less; an MFR2 (pellets) of 0.001 to 4.0 g/10min and wherein the MFR2 (pellets) is lower than MFR2 (starting) such that MFR2 pellets/MFR2 starting is 0.5 or less.

Description

MODIFICATION OF POLYETHYLENE TERPOLYMER

Field of the Invention

The present invention is directed to a process for producing modified polyethylene terpolymer having decreased melt flow rate (2.16 kg, 190°C) (MFR2). In particular, the present invention is directed to a process for reducing the MFR2 of a single site produced polyethylene terpolymer without an increase in gel content by extruding said polyethylene terpolymer in the presence of a peroxide.

Background of the Invention

Polyethylene, especially metallocene produced linear low density polyethylene (mLLDPE) is widely used in daily life due to its low cost and high performance. It is known that, depending on the application, different MFRs and density are required. For example, low MFRs are needed for pipe or packaging applications where higher impact is required.

One simple way to produce lower MFR (i.e. higher molecular weight) polyethylene is to use less hydrogen in its manufacture. However, just using hydrogen to control molecular weight is not always an option. Not all catalysts can make lower MFR materials as they do respond to the presence of hydrogen in an appropriate way. This is a particular problem with single site catalysts. Achieving low MFR2 values in polyethylene copolymers using hydrogen molecular weight control is challenging.

The present inventors therefore sought a method to reduce the MFR2 of polyethylene copolymers, in particular LLDPEs prepared using single site catalysis.

The present inventors have now found that MFR2 can be reduced in a single site produced polyethylene copolymer by extrusion with an initiator such as peroxide. Moreover, this reduction in MFR can be achieved without a consequential increase in gels.

WO2017/001384 discloses the use of small quantities of free radical initiator to improve the homogeneity of a polyethylene. In that way the gel content of the materials are lower and other properties like optical and mechanical properties are not destroyed. MFR however is not reduced. WO2017/202802 discloses the use of the peroxides to reduce the MFRs of polyethylene in the context of a Ziegler Natta high density polyethylene.

WO2014/186272 describes ethylene polymers with narrow Mw/Mn and a low Mz/Mw ratio. The polymers are targeted towards blown and cast films.

CN 102308601 discloses a composition comprising a metallocene linear low density polyethylene, a crosslinking agent and benzoyl peroxide.

The present inventors have found that the reduction in MFR2 that can be achieved via extrusion in the presence of a peroxide is more marked for a single site lower density polyethylene terpolymer than for a higher density Ziegler Natta material. There is also no consequential increase in gels. Thus, for a given level of peroxide, the MFR reduction that we observe is higher than for the polymers of ‘802.

Summary of the Invention

Viewed from one aspect the invention provides a process for the reduction of the MFR2 of a polyethylene terpolymer comprising

(i) combining a single site produced polyethylene terpolymer having an MFR2 (starting) of 0.5 to 10 g/10min and a density from 910 to 945 kg/m³ with a radical initiator to form a mixture; and

(ii) extruding the mixture of step (i) at a temperature above the melting point of the polyethylene terpolymer and at a temperature above the initiation temperature of the initiator to form pellets comprising a modified polyethylene terpolymer; wherein said pellets have a density of 910 to 945 kg/m³, a xylene hot insoluble content (XHU) of 0.3 wt% or less; an MFR2 (pellets) of 0.001 to 4.0 g/10min and wherein the MFR2 (pellets) is lower than MFR2 (starting) such that MFR2 pellets/MFR2 starting is 0.5 or less.

Viewed from another aspect the invention provides the use of radical initiator to reduce the MFR2 of single site produced polyethylene terpolymer by at least 50%, wherein the gel content measured as XHU of said polyethylene terpolymer after treatment with said radical initiator is less than 0.1 wt%. Viewed from another aspect the invention provides a process for the reduction of the MFR2 of a polyethylene terpolymer comprising

(i) polymerizing ethylene and at least two C3-10 alpha olefin comonomer in the presence of a single site catalyst to form a polyethylene terpolymer having an MFR2 (starting) of 0.5 to 10 g/10min and a density from 910 to 945 kg/m³ ;

(ii) combining said polyethylene terpolymer with a radical initiator to form a mixture;

(iii) extruding the mixture of step (ii) at a temperature above the melting point of the polyethylene terpolymer and at a temperature above the initiation temperature of the initiator to form pellets comprising a modified polyethylene terpolymer; wherein said pellets have a density of 910 to 945 kg/m³, an XHU of 0.1 wt% or less; an MFR2 of 0.001 to 4.0 g/10min and wherein the MFR2 (pellets) is lower than MFR2 (starting) such that MFR2 pellets/MFR2 (starting) is 0.5 or less.

Detailed Description of the Invention

This invention relates to a process for reducing the MFR2 of a polyethylene terpolymer using a radical initiator such as a peroxide. In particular, this reduction can be effected without an increase in gel content and whilst maintaining beneficial mechanical properties such as high tensile modulus and dart drop impact strength. Optical properties and sealing properties are also important and are retained.

Single Site Produced polyethylene terpolymer

The polyethylene terpolymer used as the starting material in the process of the present invention is a polyethylene terpolymer having a density of 910 to 945 kg/m³. Typically, the density is in the range of 910 to 940 kg/m³, especially 912 to 930 kg/m³. It is preferred if the polyethylene terpolymer is a linear low density polyethylene (LLDPE).

The starting melt flow rate (2.16 kg, 190°C) (MFR2) of the polyethylene terpolymer in the process of the present invention is preferably in the range of 0.5 to 10 g /10min, preferably from 0.5 to 5.0 g/10 min, more preferably from 0.75 to 3.0 g/10 min. The use of a polyethylene terpolymer having a density of 912 to 930 kg/m³ and a MFR2 of 0.75 to 3.0 g/10 min is especially preferred. In one embodiment, the MFR2 of the starting material is measured on powder.

The melting point of the single site produced polyethylene terpolymer is preferably at least 120 °C, such as in the range of 120 to 135°C, more preferably 121 to 132 °C, especially 122 to 130 °C.

The polyethylene terpolymer used as starting material in the process of the present invention is a terpolymer of ethylene with two or more alpha-olefin comonomers having from 3 to 10 carbon atoms. Ideally, the comonomer(s) present are selected from the group consisting of is 1 -butene, 1 -hexene or 1 -octene.

The polyethylene terpolymer may contain from 1 to 10% by mole of comonomer(s), e.g. from 0.1 to 5% by mole of comonomer(s). For example, the polyethylene copolymer may contain from 90 to 99.9% by mole, preferably from 92 to 99.5% by mole, of units derived from ethylene and from 0.5 to 8% by mole of units derived from the comonomer(s), the comonomer(s) preferably being one or more alpha-olefins having from 3 to 10 carbon atoms.

The polyethylene terpolymer used as starting material in the process of present invention may be in any form including particles, pellets, or flakes but it is preferably in the form of a powder when added to the extruder.

The polyethylene terpolymer of use in the invention is preferably multimodal, such as bimodal. It is preferred that the polyethylene terpolymer used as a starting material therefore has a molecular weight distribution (Mw/Mn) in the range of 5 to 20, more preferably in the range of from 5 to 18, most preferably in the range of from 5 to 15. It is preferred that the polyethylene terpolymer used as a starting material therefore has a molecular weight distribution (Mw/Mn) in the range of 6 to 20, more preferably in the range of from 6 to 18, most preferably in the range of from 6 to 15.

In one embodiment, the polyethylene terpolymer is a multimodal polyethylene terpolymer of ethylene and at least two alpha-olefin comonomers having from 3 to 10 carbon atoms. The term terpolymer is used herein to define a polyethylene polymer with at least two comonomers. Ideally, the multimodal polyethylene terpolymer comprises a first copolymer component of ethylene and an alpha-olefin comonomer having from 4 to 10 carbon atoms and a second copolymer component of ethylene and an alpha-olefin comonomer having from 6 to 10 carbon atoms. Preferably the multimodal ethylene terpolymer is a terpolymer of ethylene and at least two comonomers selected from 1 -butene, 1 -hexene, 1 -octene. Ideally, the comonomers used in the two components are different.

It is further preferred that the multimodal polyethylene terpolymer is a terpolymer of ethylene and exactly two comonomers selected from 1 -butene, 1 -hexene, or 1 -octene. Especially preferred is a multimodal ethylene terpolymer comprising

- a first copolymer component of ethylene and 1 -butene, and

- a second copolymer component comprising ethylene and 1 -hexene.

Even more preferred is a multimodal polyethylene terpolymer comprising

- a first copolymer component consisting of ethylene and 1 -butene and

- a second copolymer component consisting of ethylene consisting of ethylene and 1- hexene.

By multimodal polyethylene terpolymer is meant a terpolymer which contains at least two distinct components having different average molecular weights, different contents of comonomer or both. Ideally, the GPC curve of such a material will show two distinct peaks. Multimodal polyethylene terpolymers are well known and are widely described in the literature.

The multimodal polyethylene terpolymer of the present invention is preferably produced by copolymerizing ethylene and at least two comonomers in two or more polymerization stages where the polymerization conditions are sufficiently different to allow production of different polymers in different stages. Such polymers are described in, inter alia, WO2016/198273. Full details of how to prepare suitable multimodal polyethylene terpolymers can be found in this reference. The multimodal polyethylene terpolymer comprise a first copolymer component and a second copolymer component.

First copolymer component

The first copolymer component comprises ethylene and a first alpha-olefin comonomer having 4 to 10 carbon atoms, such as 1 -butene, 1 -hexene or 1 -octene, more preferably 1- butene. In a preferred embodiment the first copolymer component consists of ethylene and 1 -butene.

The first copolymer component may have a melt flow rate MFR2 of from 1.0 to 20 g/10min. Furthermore, the first copolymer component may have a density of from 925 to 955 kg/m³, preferably 930 to 955 kg/m³, especially 935 to 955 kg/m³, most especially from 935 to 945 kg/m³.

The first copolymer component is ideally produced in a first polymerization stage which is preferably a slurry polymerization. Hydrogen can be introduced into the first polymerization stage for controlling the MFR2 of the first copolymer component.

The first alpha-olefin comonomer is introduced into the first polymerization stage for controlling the density of the first copolymer component. As discussed above, the comonomer is an alpha-olefin having from 4 to 10 carbon atoms, preferably 1 -butene, 1- hexene or 1 -octene, more preferably 1 -butene.

In a most preferred embodiment, the multimodal polyethylene terpolymer comprises a first and a second copolymer component, wherein the first copolymer component comprises at least a first and a second fraction.

These two or more fractions of the first copolymer component may be unimodal in view of their molecular weight and/or their density or they can be bimodal in respect of their molecular weight and/or their density.

It is preferred that the two or more fractions of the first copolymer component are unimodal in view of their molecular weight and density. It is within the scope of the invention, that the first and the second fraction of the first copolymer component are present in a weight ratio of 4:1 up to 1 :4, such as 3:1 to 1 :3, or 2:1 to 1 :2, or 1 :1.

Each fraction of the first copolymer component is a polyethylene copolymer with one or more alpha-olefins having from 4 to 10 carbon atoms, preferably 1 -butene, 1 -hexene or 1 -octene, more preferably 1 -butene. Ideally each fraction contains a single comonomer. Ideally each fraction is an ethylene 1 -butene copolymer.

It is further preferred, that the two or more fractions of the first copolymer component are produced in two or more consecutive reactors. For a person skilled in the art it will be clear that when producing the first and the second fraction of the first copolymer component in two consecutive reactors, there has to be a certain difference in the MFR2-values and/or densityvalues of each fraction to ensure that these can be distinguished. These must be different. Ideally, the fractions are produced in two consecutive slurry reactors such as loop reactors.

It is hence understood within the meaning of the invention, that MFR2 after loop 1 is preferably higher than the MFR2 after Ioop2 of the first copolymer component. Further, the MFR2 after Ioop2 can be at least 10% lower than the MFR2 after loop! Ideally, the density after Ioop2 is lower than that after loopl , e.g. at least 1 kg/m³ lower.

Second copolymer component

The second copolymer component comprises ethylene and a second alpha-olefin comonomer having 6 to 10 carbon atoms, such as 1 -hexene or 1 -octene, more preferably 1- hexene. It is further preferred that the second alpha-olefin comonomer has more carbon atoms than the first alpha-olefin monomer, i.e. the comonomer in the second copolymer component is higher than the comonomer in the first copolymer component, e.g. 1 -hexene vs 1 -butene.

It is further preferred that the second alpha-olefin comonomer has 2 more carbon atoms than the first alpha-olefin monomer. In a preferred embodiment the second copolymer consists of ethylene and 1 -hexene. The second copolymer component is produced in the presence of any previously produced polymer component. Ideally, it is produced in a gas phase reactor, e.g. as discussed in WO2016/198273.

The melt flow rate of the second copolymer mixture corresponds to the MFR of the starting product.

The ratio (i.e. the split) between the first and the second copolymer within the final multimodal terpolymer of ethylene and at least two alpha-olefin-comonomers has significant effect on the mechanical properties of the final composition.

It is hence envisaged within the scope of the invention that the second copolymer component forms a significant part of the polymer fractions present in the multimodal polyethylene terpolymer, i.e. at least 50 wt% of the final composition, preferably 53 wt% or more, such as 55 wt% or more.

More preferably the second copolymer component may form up to 65 wt% of the multimodal polyethylene terpolymer.

Consecutively the first copolymer component forms at most 50 wt% or less of the multimodal polyethylene terpolymer, preferably 47 wt% or less, such as 45 wt% or less. More preferably the first copolymer component may form 35 wt% or more of the multimodal polyethylene terpolymer.

Polymerization

The multimodal polyethylene terpolymer is preferably produced in a loop loop gas cascade as described in WO2016/198273. Such polymerization steps may be preceded by a prepolymerization step. The purpose of the prepolymerization is to polymerize a small amount of polymer onto the catalyst at a low temperature and/or a low monomer concentration. By prepolymerization it is possible to improve the performance of the catalyst in slurry and/or modify the properties of the final polymer. The prepolymerization step is preferably conducted in slurry.

The catalyst components are preferably all introduced to the prepolymerization step when a prepolymerization step is present. However, where the solid catalyst component and the cocatalyst can be fed separately it is possible that only a part of the cocatalyst is introduced into the prepolymerization stage and the remaining part into subsequent polymerization stages. Also in such cases it is necessary to introduce so much cocatalyst into the prepolymerization stage that a sufficient polymerization reaction is obtained therein.

It is understood within the scope of the invention, that the amount or polymer produced in the prepolymerization lies within 1 to 5 wt% in respect to the final multimodal terpolymer. This can counted as part of the first copolymer component.

Catalyst

The polyethylene terpolymer used in the process of the invention is one made using a single site catalyst, such as a metallocene catalyst. A metallocene catalyst comprises a metallocene complex and a cocatalyst. It is preferred if the metallocene complex comprises an element of a group (IV) metal coordinated to at least one, preferably at least two cyclopentadienyl type ligands.

The cyclopentadienyl type group ligand has been widely described in the scientific and patent literature for about twenty years. Essentially any ligand containing the general structure:

can be employed herein.

The cyclopentadienyl type ligand can be an unsubstituted or substituted and/or fused cyclopentadienyl ligand, e.g. substituted or unsubstituted cyclopentadienyl, substituted or unsubstituted indenyl, substituted or unsubstituted tetrahydroindenyl or substituted or unsubstituted fluorenyl ligand.

Suitable ligands therefore include:

which can obviously be substituted. The use of indenyl ligands is preferred. The metallocene complex preferably does not comprise a single cyclopentadienyl type ligand. Preferably two such cyclopentadienyl type ligands are present, ideally joined by a bridging group. The substitution pattern on the two ligands may be the same or different. Metallocene complexes of use in this invention can therefore be symmetrical or asymmetrical.

The two cyclopentadienyl ligands of the present invention can be bridged or unbridged as is well known in the art. It is generally envisaged that the principles of this invention can be applied to any bis cyclopentadienyl type ligand system.

The metallocene complex will comprise at least one metal ion of group (IV) as is well known. This will be r|-bonded to the cyclopentadienyl type rings. Such r|-bonded metals are typically Zr, Hf or Ti, especially Zr or Hf.

In a preferred embodiment the metallocene complex is a compound of formula (I) (Cp)₂RnMX₂(l) wherein: each Cp independently is an unsubstituted or substituted and/or fused cyclopentadienyl ligand, e.g. substituted or unsubstituted cyclopentadienyl, substituted or unsubstituted indenyl or substituted or unsubstituted fluorenyl ligand;

R is a bridge of 1-7 atoms, e.g. 1 to 2 atoms;

X is a sigma ligand; n is 0 or 1 ;

M is a transition metal of Group 4, e.g. Ti, Zr or Hf, especially Zr or Hf.

In a preferred embodiment the metallocene complex is a compound of formula (II)

(Cp)₂RnMX₂ (II) wherein: each Cp independently is an unsubstituted or substituted and/or fused cyclopentadienyl ligand, e.g. substituted or unsubstituted cyclopentadienyl, substituted or unsubstituted indenyl or substituted or unsubstituted fluorenyl ligand; the optional one or more substituent(s) being independently selected preferably from halogen, hydrocarbyl (e.g. C1-C20-alkyl, C2-C20-alkenyl, C2-C20-alkynyl, C3-C12- cycloalkyl, C6-C20-aryl or C7-C20-arylalkyl), C3-C12-cycloalkyl which contains 1, 2, 3 or 4 heteroatom(s) in the ring moiety, C6-C20-heteroaryl, C1-C20-haloalkyl, -SiR's, -OSiR's, - SR", -PR"₂, OR" or -NR"₂, each R" is independently a hydrogen or hydrocarbyl, e.g. C1-C20-alkyl, C2-C20-alkenyl, C2-C20-alkynyl, C3-C12-cycloalkyl or C6-C20-aryl; or e.g. in case of -NR"₂, the two substituents R" can form a ring, e.g. five- or six-membered ring, together with the nitrogen atom to which they are attached;

R is a bridge of 1-7 atoms, e.g. a bridge of 1-4 C-atoms and 0-4 heteroatoms, wherein the heteroatom(s) can be e.g. Si, Ge and/or O atom(s), wherein each of the bridge atoms may bear independently substituents, such as C1-C20-alkyl, tri(C1-C20-alkyl)silyl, tri(C1-C20- alkyl)siloxy or C6-C20-aryl substituents); or a bridge of 1-3, e.g. one or two, hetero atoms, such as silicon, germanium and/or oxygen atom(s), e.g. -SiR¹⁰ ₂-, wherein each R¹⁰ is independently C1-C20-alkyl, C3-12cycloalkyl, C6-C20-aryl or tri(C1-C20-alkyl)silyl- residue, such as trimethylsilyl;

M is a transition metal of Group 4, e.g. Ti, Zr or Hf, especially Zr or Hf; each X is independently a sigma-ligand, such as H, halogen, C1-C20-alkyl, C1-C20- alkoxy, C2-C20-alkenyl, C2-C20-alkynyl, C3-C12-cycloalkyl, C6-C20-aryl, C6-C20-aryloxy, C7-C20-arylalkyl, C7-C20-arylalkenyl, -SR", -PR"₃, -SiR"₃, -OSiR"₃, -NR"₂ or -CH₂-Y, wherein Y is C6-C20-aryl, C6-C20-heteroaryl, C1-C20-alkoxy, C6-C20-aryloxy, NR"₂, -SR", - PR"₃, -SiR"₃, or -OSiR"₃; each of the above mentioned ring moieties alone or as a part of another moiety as the substituent for Cp, X, R" or R¹ can further be substituted e.g. with C1-C20-alkyl which may contain Si and/or O atoms; n is 0 or 1.

Suitably, in each X as -CH₂-Y, each Y is independently selected from C6-C20-aryl, NR"₂, - SiR"₃ or -OSiR"₃. Most preferably, X as -CH₂-Y is benzyl. Each X other than -CH₂-Y is independently halogen, C1-C20-alkyl, C1-C20-alkoxy, C6-C20-aryl, C7-C20-arylalkenyl or - NR"₂ as defined above, e.g. -N(C1-C20-alkyl) ₂.

Preferably, each X is halogen, methyl, phenyl or -CH₂-Y, and each Y is independently as defined above.

Cp is preferably cyclopentadienyl, indenyl, tetrahydroindenyl or fluorenyl, optionally substituted as defined above. Ideally Cp is a cyclopentadienyl or indenyl.

In a suitable subgroup of the compounds of formula (I), each Cp independently bears 1 , 2, 3 or 4 substituents as defined above, preferably 1 , 2 or 3, such as 1 or 2 substituents, which are preferably selected from C1-C20-alkyl, C6-C20-aryl, C7-C20-arylalkyl (wherein the aryl ring alone or as a part of a further moiety may further be substituted as indicated above), - OSiR"₃, wherein R" is as indicated above, preferably C1-C20-alkyl. R, if present, is preferably a methylene, ethylene or a silyl bridge, whereby the silyl can be substituted as defined above, e.g. a (dimethyl)Si=, (methylphenyl)Si=, (methyylcyclohexyl)silyl= or (trimethylsilylmethyl)Si=; n is 0 or 1. Preferably, R" is other than hydrogen.

A specific subgroup includes the well known metallocenes of Zr, Hf and Ti with two eta5- ligands which may be bridged or unbridged cyclopentadienyl ligands optionally substituted with e.g. siloxy, or alkyl (e.g. C1-6-alkyl) as defined above, or with two unbridged or bridged indenyl ligands optionally substituted in any of the ring moieties with e.g. siloxy or alkyl as defined above, e.g. at 2-, 3-, 4- and/or 7-positions. Preferred bridges are ethylene or -SiMe2.

The preparation of the metallocenes can be carried out according or analogously to the methods known from the literature and is within skills of a person skilled in the field. Thus for the preparation see e.g. EP-A-129 368, examples of compounds wherein the metal atom bears a -NR"2 ligand see i.a. in WO-A-9856831 and WO-A-0034341. For the preparation see also e.g. in EP-A-260 130, WO-A-9728170, WO-A-9846616, WO-A-9849208, WO-A- 9912981 , WO-A-9919335, WO-A-9856831 , WO-A-OO/34341 , EP-A-423 101 and EP-A-537 130.

To form a catalyst, a cocatalyst is used as is well known in the art. Cocatalysts comprising Al or B are well known and can be used here. The use of aluminoxanes (e.g. MAO) or boron based cocatalysts (such as borates) is preferred.

Polyethylene terpolymers made using single site catalysis, as opposed to Ziegler Natta catalysis, have characteristic features that allow them to be distinguished from Ziegler Natta materials. In particular, the comonomer distribution is more homogeneous. This can be shown using TREF or Crystaf techniques. Catalyst residues may also indicate the catalyst used. Ziegler Natta catalysts would not contain a Zr or Hf group (IV) metal for example.

Process for modification

In step (i) of the process of the invention, the polyethylene terpolymer is combined with other components to form a mixture. These components must include a radical initiator. This mixture preferably comprises at least 95 wt% of the polyethylene terpolymer, such as at least 97 wt%. The combination of the polyethylene terpolymer and the radical initiator can be effected in any convenient way. These may be combined before extrusion via a simple mixing process or, conveniently combined within the extruder. The polyethylene terpolymer and the radical initiator can be fed separately or together into the extruder.

The mixture to be extruded contains the initiator described below as well as optional additives such as antioxidants, nucleating agents, UV stabilisers and so on. Any conventional additive may be present. The amount of additives present (not counting the initiator) may be up to 2 wt% of the mixture. Additives can be added before extrusion, during extrusion or after extrusion, preferably before.

Radical Initiator

The process of the invention requires that the polyethylene terpolymer is contacted with a radical initiator in the extruder. It is essential in the process of the present invention that a radical initiator such as a peroxide is added to generate free radicals allowing modification of the polyethylene terpolymer. Preferably, the free radical generator is selected from acyl peroxide, alkyl peroxide, hydroperoxide, perester, peroxycarbonate, and mixtures thereof.

Examples of suitable organic peroxides include di-tert-amylperoxide, 2,5-di(tert-butylperoxy)- 2,5-dimethyl-3-hexyne, 2,5- di(tert-butylperoxy)-2,5-dimethylhexane, tert-butylcumylperoxide, di(tert-butyl)peroxide, dicumylperoxide, butyl-4,4-bis(tert-butylperoxy)-valerate, 1 , 1 -bis(tert- butylperoxy)-3,3,5-trimethylcyclohexane, tert-butylperoxybenzoate, dibenzoylperoxide, bis(tertbutylperoxyisopropyl)benzene, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, 1,1- di(tertbutylperoxy) cyclohexane, 1 ,1-di(tert amylperoxy)cyclohexane, and any mixtures thereof; for example, the peroxide may be selected from 2,5-di(tert-butylperoxy)-2,5- dimethylhexane, di(tert-butylperoxyisopropyl)benzene, dicumylperoxide, tertbutylcumylperoxide, di(tert-butyl)peroxide, and mixtures thereof, for example, the peroxide is dicumylperoxide.

Preferably, the peroxide is selected from 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, 2,5- dimethyl-2,5-di(tert-butylperoxy)hexyne-3, 3,3,5,7,7-pentamethyl-1 ,2,4-trioxepane, 3,6,9- triethyl-3,6,9-trimethyl-1,4,7-triperoxonane, and di-tert-butyl peroxide. The use of 2,5- Bis(tert-butylperoxy)-2,5-dimethylhexane is especially preferred. The person skilled in the art knows how to choose appropriate peroxide that will thermally decompose during the reactive modification process according to the present invention.

The initiator is preferably present in an amount of 0.01 to 1.0 wt% in the mixture in step (i), preferably 0.01 to 0.25 wt%, especially 0.02 to 0.20 wt%.

It will be appreciated that the mixture in step (i) can be formed before the mixture is added to the extruder or formed within the extruder as components of the mixture are added into the extruder via separate channels.

The initiator may be used in the form of a masterbatch wherein the initiator is fed as a premix (masterbatch). Preferably, the initiator is pre-mixed with a carrier which can be a polymer, e.g. polyethylene and polypropylene, or other materials, e.g. silica and CaCOs, forming a masterbatch and then fed into the extruder. The wt% of initiator above refers to the wt% of the actual initiator not the wt% of masterbatch.

Extrusion Device / Extruder

The process according to the present invention is suitably carried out in melt mixing equipment known to a person skilled in the art. Preferably, an extrusion device, also referred to as an extruder, or kneader is used. The streams of the polyethylene terpolymer and the initiator are suitably passed to the extruder simultaneously. The extruder may be any extruder known in the art. The extruder may thus be a single screw extruder, a twin screw extruder, such as a co-rotating twin screw extruder or a counter-rotating twin screw extruder, or a multi-screw extruder, such as a ring extruder. Furthermore, the extruder may be an internal mixer, such as a Banbury type mixer, a counter-rotating continuous intensive mixer (CIM), or a special single screw mixer, such as the Buss co-kneader or a TriVolution kneader. A static mixer, such as Kenics, Koch, etc., can also be used in addition to the extruder units mentioned in order to improve the distributive mixing with comparatively low heat generation. Especially preferably extruder is a co-rotating twin screw extruder or a continuous intensive mixer (CIM). Examples of suitable extruders according to the present invention include those supplied by Coperion Werner & Pfleiderer, Berstorff, Japan Steel works, Kobe Steel, and Farrel. The extruder typically comprises a feed zone, a melting zone, a mixing zone and a die zone. Further, the melt pressed through the die is typically solidified and cut to pellets in a pelletiser.

Optionally, additives or other polymeric components can be added to the composition before, during or after the compounding (extrusion) step.

The screw speed of the extruder is preferably 140 rpm to 450 rpm, more preferably 170 rpm to 400 rpm and even more preferably 190 rpm to 380 rpm. The residence time of the polyethylene terpolymer in the extrusion device I extruder may vary within wide limits; usually the residence time is at least 25, preferably at least 30 sec, e.g. 25 to 75 secs, and more preferably about 35 seconds.

The temperature in the extruder is greater than the melting temperature of the polyethylene terpolymer and the initiator. The temperature needs to be less than the decomposition temperature of the polyethylene terpolymer. Suitably, the temperature is from about 5°C greater than the melting temperature of the polyethylene terpolymer, preferably from about 10°C greater than the melting temperature of the polyethylene terpolymer to preferably about 280°C, more preferably to about 250°C and especially preferably to about 240°C. For instance, the temperature should be preferably in the range of from 165°C to 280°C, more preferably in the range of from 170°C to 250°C, like in the range of from 180°C to 240°C, and even more preferably between 180°C and 230°C .

Modified polyethylene

The polyethylene terpolymer that exits the extruder is called the modified polyethylene terpolymer herein. It will be converted into pellets by a pelletiser after the extrusion process.

The modified polyethylene terpolymer is characterised by the correlation between the final melt flow rate (2.16 kg, 190°C) (MFR2) and the starting melt flow rate. The reduction achieved is linked to the initiator content. The more initiator the more the MFR2 is reduced.

The final melt flow rate of the pellets produced by the process of the invention is usually in the range of from 0.001 to 4.0, suitably from 0.01 to 4.0, preferably from 0.02 to 1.0, and more preferably from 0.02 to 0.75 g/10min. It will be appreciated that this MFR is measured in the presence of any additives present. These have no material effect on the measured MFR.

Preferably, the modified polyethylene obtained from the process of the present invention has a gel content characterized by xylene hot insoluble content (XHU) of 0.3 wt% or less, such as 0.2 wt% or less, preferably 0.1 wt% or less and more preferably of 0.05 wt% or less.

The ratio of the MFR2 pellets/MFR2 starting is 0.5 or less, preferably 0.4 or less, such as 0.3 or less, especially MFR2 pellets/MFR2 starting is 0.1 or less. It is thus preferred if the MFR2 of the starting polyethylene terpolymer is reduced by at least a factor of 10 during the extrusion process.

Viewed from another aspect the invention provides the use of radical initiator to reduce the MFR2 of single site produced polyethylene terpolymer by at least 50% wherein the gel content measured as XHU of said polyethylene terpolymer after treatment with said radical initiator is less than 0.1 wt%. Preferably the MFR2 of the single site produced polyethylene terpolymer is reduced by at least 10 times, such as at least 20 times.

It is especially preferred if the XHU value is 0.1 wt% or less and the ratio of the MFR2 pellets/MFR2 starting is 0.1 or less.

In one embodiment, it is preferred if the ratio MFR2(pellets/starting) < O,9282e'°’^oo1x where x is the peroxide content in ppm.

In one embodiment, it is preferred if the ratio MFR2(pellets/starting) < 1.031 e'^0002x where x is the peroxide content in ppm.

In one embodiment, the XHU < [3E-08x²] + [4E-05x] - 0,0096 where x is the peroxide content in ppm.

It is especially preferred if the initiator is present in an amount of 0.01 to 0.20 wt% and the MFR2 ratio of MFR2 pellets/MFR2 starting is 0.1 or less.

The modified polyethylene terpolymer of the invention may be used to form a variety of final articles such as pipes, mouldings or films. It is most preferred if the modified polyethylene of the invention is used to form a film. Thus, viewed from another aspect the invention provides a process for the production of a film comprising (i) combining a single site polyethylene terpolymer having an MFR2 (starting) of 0.5 to 10 g/10min and a density from 910 to 945 kg/m³ with a radical initiator to form a mixture;

(ii) extruding the mixture of step (i) at a temperature above the melting point of the polyethylene terpolymer and at a temperature above the initiation temperature of the initiator to form pellets comprising a modified polyethylene terpolymer; wherein said pellets have a density of 910 to 945 kg/m³, an XHU of 0.1 wt% or less; an MFR2 of 0.001 to 4.0 g/10min and wherein the MFR (pellets) is lower than MFR (starting) such that MFR pellets/MFR (starting) is 0.5 or less;

(iii) extruding and film blowing or casting said pellets to form a film.

Films

Films comprising the peroxide treated polyethylene of the invention can be produced with several known conversion techniques, such as extrusion via blown or cast film technology, wherein blown films are preferred.

Films according to the present invention may be subjected to post-treatment processes, e.g. surface modifications, lamination or orientation processes or the like. Such orientation processes can be mono-axially (MDO) or bi-axially orientation, wherein mono-axial orientation is preferred.

The films according to the present invention typically have a thickness of 100 pm or below, such as 10 pm to 80 pm, e.g. 20 to 60 pm.

Films according to the present invention may be mono- or multilayer films, comprising one or more layers, like two, three or five layers, even up to seven, up to 9 or up to 12 layers. The modified polyethylene of the invention may be present in one or more layers of the film.

It is further within the scope of the present invention, that any film layer may comprise at least 80 wt% of the modified polyethylene terpolymer of the invention. Films of the invention may be characterized by a high dart drop index (DDI), e.g. a DDI of at least 400 g or higher, such as 400 to 550 g when measured as described herein on a 40 micron film.

It is within the scope of the invention that the films are characterized by a tensile modulus in the machine direction (MD) of at least 150 MPa, preferably at least 180 MPa, e.g. 150 to 300 MPa.

It is within the scope of the invention that the films are characterized by a tensile modulus in the transverse direction (TD) of at least 200 MPa, preferably at least 220 MPa, e.g. 200 to 400 MPa.

The films according to the present invention are highly useful to being used in various packaging applications, wherein applications related to food packaging are preferred. Films comprising the multimodal terpolymer of the current invention comprise shrink films, collation shrink films, wrap films, lamination films, etc.

Packaging articles comprising the multimodal terpolymer of the current invention comprise bags, pouches, wrapping or collation films, and the like.

It is within the scope of the present invention that the polyethylene may be combined with additives, such as phenolic stabilizers, antioxidants, slip and antistatic agents, antiblock agents processing aids, colorants and the like. The peroxide treated polyethylene may also be combined with other polymer components, e.g. LDPE.

The invention will be further described with reference to the following non limiting examples and figures.

Figure 1 draws MFR ratio vs peroxide content in ppm and draws the lines y = 1.031e'^0002x and y=0.9282e'° ^001x for the working examples and comparative examples. Advantageous materials lie below one or both of these lines.

Figure 2 draws XHU vs peroxide content in ppm and shows the line XHU = [3E-08x²]+ [4E- 05x] - 0,0096 where x is the peroxide content in ppm. Advantageous materials lie below this line. In figures 1 and 2, the dots are examples IE1-3, squares are examples A-C and triangles are examples D-K.

Examples

The following definitions of terms and determination methods apply for the above general description of the invention as well as to the below examples unless otherwise defined.

Measuring Methods

Density

Density of the polyethylene was measured according to ISO 1183-1 :2004 (method A) on compression moulded specimen prepared according to EN ISO 1872-2 (Feb 2007) and is given in kg/m³.

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 / polyethylene for specific conditions. The higher the melt flow rate, the lower the viscosity of the polymer / polyethylene. The MFR is determined at 190 °C for polyethylene and at a loading of 2.16 kg (MFR₂), 5.00 kg (MFR₅) or 21.6 kg (MFR21).

The quantity FRR (flow rate ratio) is an indication of molecular weight distribution, particularly important to reflect key parts for the melt processing behaviour of the polymer/ polyethylene, e.g. for indication of the melt shear thinning properties and denotes the ratio of flow rates at different loadings. Thus, FRR₂I/5 denotes the value of MFR₂I/MFRS.

XHU

About 2 g of the polyethylene (mp) are weighed and put in a mesh of metal and the combined weight of the polyethylene and the mesh is determined (mp+m). The polyethylene in the mesh is extracted in a Soxhlet apparatus with boiling xylene for 5 hours. The eluent is then replaced by fresh xylene and the boiling is continued for another hour. Subsequently, the mesh is dried and weighed again for obtaining the combined mass of hot xylene insoluble polymer / polyethylene (XHU) and the mesh (mXHU+m). The mass of the xylene hot insoluble polymer I polyethylene (mXHU) obtained by the formula (mXHU+m) - m = mXHU is put in relation to the weight of the polymer I polyethylene (mp) to obtain the fraction of xylene insoluble polymer / polyethylene mXHU/mp. This fraction of xylene insoluble polymer I polyethylene is then taken as the gel content.

Haze

Was measured according to ASTM D1003 on 40 micron films.

Sealing initiation temperature (SIT); sealing end temperature (SET), sealing range:

The method determines the sealing temperature range (sealing range) of polyethylene films, in particular blown films or cast films. The sealing temperature range is the temperature range, in which the films can be sealed according to conditions given below.

The lower limit (heat sealing initiation temperature (SIT)) is the sealing temperature at which a sealing strength of > 5 N is achieved. The upper limit (sealing end temperature (SET)) is reached, when the films stick to the sealing device.

The sealing range is determined on a J&B Universal Sealing Machine Type 4000 with a film of 40 pm thickness with the following further parameters:

Specimen width: 25.4 mm

Seal Pressure: 0.1 N/mm²

Seal Time: 0.1 sec

Cool time: 99 sec

Peel Speed: 10 mm/sec

Start temperature: 80 °C

End temperature: burn through Increments: 5 °C

Dart drop strength (DPI)

Dart-drop is measured using ASTM D1709, method A (Alternative Testing Technique) from the film samples. A dart with a 38 mm diameter hemispherical head is dropped from a height of 0.66 m onto a film clamped over a hole. Successive sets of twenty specimens are tested. One weight is used for each set and the weight is increased (or decreased) from set to set by uniform increments. The weight resulting in failure of 50 % of the specimens is calculated and reported.

DDI40 denominates the Dart Drop Impact determined on a 40 pm blown film.

Tensile modulus on films

Tensile moduli in machine/transverse direction were determined acc. to ISO 527-3 on films with a thickness of 40 pm at a cross head speed of 1 mm/min.

Preparation Example 1

Catalyst A

130 grams of a metallocene complex bis(1-methyl-3-n-butylcyclopentadienyl) zirconium (IV) dichloride (CAS no. 151840-68-5) and 9.67 kg of a 30% solution of commercial methylalumoxane (MAO) in toluene were combined and 3.18 kg dry purified toluene was added. Thus, obtained complex solution was added onto 17 kg silica carrier Sylopol 55 SJ (supplied by Grace) by very slow uniform spraying over 2 hours. The temperature was kept below 30°C. The mixture was allowed to react for 3 hours after complex addition at 30°C.

The polyethylene used in the modification process is obtained via the following process. It is a polyethylene terpolymer comprising first and second copolymer components wherein the first copolymer component comprises two fractions.

Preparation Example 1 powder is produced as described above and is used as base polymer. The base polymer from example 1 is combined with the following components to form a powder:

POX1 : 2,5-Dimethyl-2,5-di(tert-butylperoxy)hexane (commercial name Trigonox 101 , produced and supplied by Nouryon Polymer chemistry)

Antioxidant used is Irganox® B 215, produced and supplied by BASF.

AS011 is Calcium Stearate, it has commercial name of CEASIT Fl, produced and supplied by Barlocher.

The following material is formulated with the modified terpolymer: FT5230, is a unmodified low density polyethylene based on the tubular technology for film extrusion. It is produced by Borealis. It has MFR2 of 0,75 g/10min and density of 923 kg/m³. The recipe is listed in Table 2. Each recipe was compounded on a ZSK 18 twin screw extruder. The throughput is 7 kg/h and melt temperature is fixed at 210°C. Final properties are reported in Table 2.

Table 2 Recipe

The peroxide reduces the MFR2 whilst keeping an exceedingly low gel content (measured as XHU). Gels are essentially not detectable even with MFR2 0.05 g/10min.

Example 2

CE1, IE1 and IE2 are further used for film tests. The film was produced on a Collin blow film line, with 40 pm thickness and 1 :2.5 BUR. The materials were optionally pre-blended with 10wt% of LDPE (FT5230). The film results are shown in Table 2.

Table 3 Film properties

As can be seen, the DDI increases with reduction of MFR2 and the haze and SIT are still at a good level. Even without LDPE, IE1 gives excellent performance.

Comparative Example 3

The data above can be compared to that of WO2017/202802. Table 4

As can be seen from the data presented, there is a relationship between the MFR ratio and the peroxide content. Higher peroxide content tends to lead to a reduced MFR ratio. Higher peroxide content also tends to increase the XHU value.

When comparing the inventive examples and those of table 4, for a given peroxide content, the XHU value of the inventive examples is lower. For a given peroxide content the MFR ratio is reduced.

For example in IE3, there is 0.16 wt% of peroxide which can be readily compared with example G in table 4 where there is 0.15 wt% peroxide. It is clear that IE3 has a much reduced MFR ratio without an increase in XHU. IE2 also outperforms both examples B and E of table 4 in terms of the observed MFR ratio.

Example 4

Comparative Preparative Example 4 powder is produced as described above and is used as base polymer. The base polymer is combined with the following components to form a powder: POX1 : 2,5-Dimethyl-2,5-di(tert-butylperoxy)hexane (commercial name Trigonox 101 , produced and supplied by Nouryon Polymer chemistry)

Comparative preparative example 4 is a bimodal copolymer with butene only. Table 5

This data demonstrates that the reduction in MFR is greater for the multimodal polyethylene terpolymers than multimodal polyethylene copolymers. CE4 shows limited MFR reduction in comparison to IE1 above.

Claims

29 Claims

1 . A process for the reduction of the MFR2 of a polyethylene terpolymer comprising

(i) combining a single site produced polyethylene terpolymer having an MFR2 (starting) of 0.5 to 10 g/10min (ISO 1133, 2.16 kg load 190°C) and a density from 910 to 945 kg/m³ (ISO 1183) with a radical initiator to form a mixture;

(ii) extruding the mixture of step (i) at a temperature above the melting point of the polyethylene terpolymer and at a temperature above the initiation temperature of the radical initiator to form pellets comprising a modified polyethylene terpolymer; wherein said pellets have a density of 910 to 945 kg/m³ (ISO 1183), a xylene hot insoluble content (XHU) of 0.3 wt% or less; an MFR2 (pellets) of 0.001 to 4.0 g/10min (ISO 1133, 2.16 kg load 190°C) and wherein the MFR2 (pellets) is lower than MFR2 (starting) such that MFR2 pellets/MFR2 starting is 0.5 or less.

2. A process as claimed in claim 1 wherein the single site polyethylene terpolymer is obtained using a metallocene catalyst.

3. A process as claimed in any preceding claim wherein the polyethylene terpolymer is an LLDPE having a density of 912 to 930 kg/m³.

4. A process as claimed in any preceding claim wherein the initiator is a peroxide, preferably 2,5-dimethyl-2,5-di(tert-butylperoxy)-hexane, 2,5-dimethyl-2,5-di(tert- butylperoxy)hexyne-3, 3,3,5,7,7-pentamethyl-1 ,2,4-trioxepane, 3,6, 9-triethyl-3,6, 9- trimethyl-1 ,4,7-triperoxonane, and di-tert-butyl peroxide.

5. A process as claimed in any preceding claim wherein the mixture in step (i) comprises 0.01 to 1 .0 wt% initiator and at least 95 wt% polyethylene terpolymer based on the total weight of the mixture.

6. A process as claimed in any preceding claim wherein the MFR pellets/MFR starting is 0.4 or less, such as 0.3 or less, especially MFR pellets/MFR starting 0.1 or less. 30

7. A process as claimed in any preceding claim wherein the polyethylene terpolymer is multimodal, such as bimodal.

8. A process as claimed in any preceding claim wherein the XHU is 0.1 wt% or less, preferably 0.05 wt% or less.

9. A process as claimed in any preceding claim wherein the mixture in step (i) comprises 0.01 to 0.25 wt% initiator based on the total weight of the mixture.

10. A process as claimed in any preceding claim wherein the polyethylene terpolymer in step (i) is a powder.

11. A process as claimed in any preceding claim wherein the polyethylene terpolymer comprises a lower MW component and a higher MW copolymer component; wherein said LMW component comprises two fractions, a first copolymer fraction and a second copolymer fraction.

12. A process as claimed in any preceding claim wherein the polyethylene terpolymer is a terpolymer of ethylene and exactly two comonomers selected from 1 -butene, 1- hexene, or 1 -octene.

13. A process as claimed in claim 12 wherein the polyethylene terpolymer comprises a first copolymer component comprising ethylene and 1 -butene, and a second copolymer component comprising ethylene and 1 -hexene.

14. A process as claimed in any preceding claim wherein the mixture is extruded at a temperature of 165°C to 280°C.

15. Use of radical initiator to reduce the MFR2 of single site produced polyethylene terpolymer by at least 50% wherein the gel content measured as XHU of said polyethylene terpolymer after treatment with said radical initiator is less than 0.1 wt%. 16. A process for the reduction of the MFR2 of a polyethylene terpolymer comprising

(i) polymerizing ethylene and at least two C3-10 alpha olefin comonomers in the presence of a single site catalyst to form a polyethylene terpolymer having an MFR2 (starting) of 0.5 to 10 g/10min (ISO 1133, 2.16 kg load 190°C) and a density from 910 to 945 kg/m³ (ISO 1183);

(iii) extruding the mixture of step (ii) at a temperature above the melting point of the polyethylene terpolymer and at a temperature above the initiation temperature of the initiator to form pellets comprising a modified polyethylene terpolymer; wherein said pellets have a density of 910 to 945 kg/m³ (ISO 1183), an XHU of 0.1 wt% or less; an MFR2 of 0.001 to 4.0 g/10min (ISO 1133, 2.

16 kg load 190°C) and wherein the MFR2 (pellets) is lower than MFR2 (starting) such that MFR2 pellets/MFR2 (starting) is 0.5 or less.

17. A process for the production of a film comprising

(i) combining a single site polyethylene terpolymer having an MFR2 (starting) of 0.5 to 10 g/10min (ISO 1133, 2.16 kg load 190°C) and a density from 910 to 945 kg/m³ (ISO 1183) with a radical initiator to form a mixture;

(ii) extruding the mixture of step (i) at a temperature above the melting point of the polyethylene terpolymer and at a temperature above the initiation temperature of the initiator to form pellets comprising a modified polyethylene terpolymer; wherein said pellets have a density of 910 to 945 kg/m³ (ISO 1183), an XHU of 0.1 wt% or less; an MFR2 of 0.001 to 4.0 g/10min (ISO 1133, 2.16 kg load 190°C) and wherein the MFR2 (pellets) is lower than MFR2 (starting) such that MFR2 pellets/MFR2 starting is 0.5 or less;

(iii) extruding and film blowing or casting said pellets to form a film.