Patent Description:
Polyolefins produced in a high pressure (HP) process are widely used in demanding polymer applications where the polymers must meet high mechanical and/or electrical requirements. For instance in power cable applications, particularly in medium voltage (MV) and especially in high voltage (HV) and extra high voltage (EHV) cable applications, the electrical properties of the polymer composition used in the cable has significant importance. Furthermore, the electrical properties of importance may differ in different cable applications, as is the case between alternating current (AC) and direct current (DC) cable applications.

<CIT> discloses non-halogen-containing thermoplastic polyolefin blends which are either heat resistant and are particularly useful in wire and cable coatings, extruded profiles, sheet form or injection molded part or have an elastomeric behavior and are particularly useful in injection molded part.

<CIT> discloses a cable, comprising a conductor surrounded by one or more layer(s), wherein at least one layer comprises a polyolefin composition comprising, an olefin polymer (A) comprising epoxy-groups; at least one crosslinking agent (B) which accelerates the crosslinking reaction of epoxy-groups; and optionally a conductive filler.

A typical power cable comprises a conductor surrounded, at least, by an inner semiconductive layer, an insulation layer and an outer semiconductive layer, in that order. The cables are commonly produced by extruding the layers on a conductor.

The polymer material in one or more of said layers is often crosslinked to improve e.g. heat and deformation resistance, creep properties, mechanical strength, chemical resistance and abrasion resistance. During the crosslinking reaction, crosslinks (bridges) are primarily formed. Crosslinking can be effected using e.g. a free radical generating compound which is typically incorporated into the layer material prior to the extrusion of the layer(s) on a conductor. After formation of the layered cable, the cable is then subjected to a crosslinking step to initiate the radical formation and thereby crosslinking reaction.

Peroxides are very commonly used as free radical generating compounds. Crosslinking using peroxides suffers from some disadvantages, however. For example low-molecular by-products are formed during crosslinking which have unpleasant odor. These decomposition products of peroxides may include volatile by-products which are often undesired, since they may have an negative influence on the electrical properties of the cable. Therefore the volatile decomposition products such as methane are conventionally reduced to a minimum or removed after crosslinking and a cooling step. Such a removal step, generally known as a degassing step, is time and energy consuming causing extra costs.

Furthermore, prior to the extrusion of the polyolefin composition the peroxide has to be added in a separate processing step into the polymer which increases the lead time. In addition, to achieve a high crosslinking density, organic peroxides are often required which release after peroxide degradation a high level of undesired by-products. The peroxide degradation temperature limits the maximum possible melt temperature in the extruder to about <NUM>. Above that temperature, crosslinking will occur in the extruder which will result in gel or scorch particles in the cable. However the maximum melt temperature at <NUM> in the extruder limits the extruder output and might result in a lower production speed.

Thermoplastic LDPE can offer several advantages compared to a thermosetting cross-linked PE, such as no possibility of peroxide initiated scorch and no degassing step is required to remove peroxide decomposition products. The elimination of crosslinking and degassing steps can lead to faster, less complicated and more cost effective cable production. The absence of peroxide at high temperature vulcanisation is also attractive from a safety perspective. Thermoplastics are also beneficial from a recycling point of view. However, the absence of a cross-linked material can lead to a reduced temperature resistance and hence significant problems with creep.

Thus, there is a need for alternative polyolefin compositions which avoid the disadvantages associated with peroxides, but which also offer satisfactory thermomechanical properties. Hence, it is the object of the present invention to provide a new polyolefin composition which can provide such properties suitable for use in cable applications without using peroxide at all.

The present inventors have now found that the combination of a LDPE and a polypropylene with two polyolefins: the first comprising epoxy groups and the second comprising carboxylic acid groups or precursors thereof provides a composition which is ideally suited for cable manufacture and advantageously does not required the use of peroxide.

Without wishing to be bound by any theory, it is believed that the composition provides a compatibilization effect between the compounds by way of the polyolefin comprising epoxy groups and the polyolefin comprising carboxylic acid groups. It is believed that the epoxy groups react with the carboxylic acid groups in the two polyolefins via the mechanism shown in <FIG>. This may occur at temperatures typical for formulation preparation, such as compounding by, for example, extrusion. These new intermolecular bonds occur in situ without the need for the addition of an external crosslinking agent. Surprisingly, this polyolefin "network" may act as a compatibiliser for the thermoplastic LDPE and a polypropylene, leading to a polymer composition with good thermomechanical properties. Thus, the polymer composition offers the attractive properties of both crosslinked and thermoplastic materials.

Thus, the invention provides a polymer composition comprising: polymer composition comprising.

wherein polyolefin (A) and/or polyolefin (B) are each present in an amount of <NUM> to <NUM> wt%, relative to the total weight of the polymer composition.

Viewed from another aspect, the invention provides a process for preparing a polymer composition as hereinbefore defined, wherein said process comprises heating said polymer composition to a temperature greater than the melting point of at least the major polymer component(s) of the composition.

Viewed from a further aspect, the invention provides a cable comprising one or more conductors surrounded by at least one layer comprising the polymer composition as hereinbefore defined.

The invention also provides a process for producing a cable comprising the steps of: applying on one or more conductors, a layer comprising a polymer composition as hereinbefore defined.

Viewed from one aspect the invention provides use of a polymer composition as hereinbefore defined in the manufacture of an insulation layer or semi-conductive layer in a cable, preferably a power cable.

Wherever the term "molecular weight Mw" is used herein, the weight average molecular weight is meant.

The term "polyethylene" will be understood to mean an ethylene based polymer, i.e. one comprising at least <NUM> wt% ethylene, based on the total weight of the polymer as a whole. The terms "polyethylene" and "ethylene-based polymer," are used interchangeably herein, and men a polymer that comprises a majority weight percent polymerized ethylene monomer (based on the total weight of polymerisable monomers), and optionally may comprise at least one polymerised comonomer. The ethylene-based polymer may include greater than <NUM>, or greater than <NUM>, or greater than <NUM>, or greater than <NUM>, or greater than <NUM> weight percent units derived from ethylene (based on the total weight of the ethylene-based polymer).

The term "polypropylene" will be understood to mean a propylene based polymer, i.e. one comprising at least <NUM> wt% propylene, based on the total weight of the polymer as a whole.

The low density polyethylene, LDPE, of the invention is a polyethylene produced in a high pressure process. Typically the polymerization of ethylene and optional further comonomer(s) in a high pressure process is carried out in the presence of an initiator(s). The meaning of the term LDPE is well known and documented in the literature. The term LDPE describes and distinguishes a high pressure polyethylene from low pressure polyethylenes produced in the presence of an olefin polymerisation catalyst. LDPEs have certain typical features, such as different branching architecture. A typical density range for an LDPE is <NUM> to <NUM>/cm<NUM>.

Within the context of the invention, the term "precursor" is intended to mean a chemical moiety or functional group which may be transformed into another moiety or functional group, in this case into a carboxylic acid. Precursors of carboxylic acids are described in more detail below.

The term "conductor" means herein a conductor comprising one or more wires. The wire can be for any use and be e.g. optical, telecommunication or electrical wire. Moreover, the cable may comprise one or more such conductors. Preferably the conductor is an electrical conductor and comprises one or more metal wires.

The present invention relates to a particular polymer composition comprising (i) an LDPE, (ii) a polypropylene, (iii) a polyolefin (A) comprising epoxy groups and (iv) a polyolefin (B) comprising carboxylic acid groups, or precursors thereof.

In one preferred embodiment, at least one of (A) and (B) is polyethylene. Even more preferably, one of (A) and (B) is polyethylene and the other is polypropylene.

Generally, the compatibility between polyethylene and polypropylene is relatively low. Blends between these polymers therefore typically result in phase separated systems. However, the functional groups used in the invention allow polyethylene and polypropylene to react with each other. As a result, an in-situ copolymer compatibiliser is formed. It reduces phase separation, and results in blends with considerably higher thermomechanical performance.

In all embodiments, said polyethylene is preferably a low density polyethylene (LDPE).

The low density polyethylene (LDPE) is an ethylene-based polymer. The term, "ethylene-based polymer," as used herein, is a polymer that comprises a majority weight percent polymerized ethylene monomer (based on the total weight of polymerisable monomers), and optionally may comprise at least one polymerised comonomer. The ethylene-based polymer may include greater than <NUM>, or greater than <NUM>, or greater than <NUM>, or greater than <NUM>, or greater than <NUM> weight percent units derived from ethylene (based on the total weight of the ethylene-based polymer).

The LDPE may be an ethylene homopolymer or an ethylene copolymer. Preferably, the LDPE is a homopolymer.

In embodiments wherein the LDPE does comprise comonomer(s), then these may be polar comonomer(s), non-polar comonomer(s) or a mixture of the polar comonomer(s) and non-polar comonomer(s). Moreover, the LDPE may optionally be unsaturated.

As a polar comonomer for the LDPE copolymer comonomer(s) containing hydroxyl group(s), alkoxy group(s), carbonyl group(s), carboxyl group(s), ether group(s) or ester group(s), or a mixture thereof, can be used. More preferably, comonomer(s) containing carboxyl and/or ester group(s) are used as said polar comonomer. Still more preferably, the polar comonomer(s) of the LDPE copolymer is selected from the groups of acrylate(s), methacrylate(s) or acetate(s), or any mixtures thereof.

If present in said LDPE copolymer, the polar comonomer(s) is preferably selected from the group of alkyl acrylates, alkyl methacrylates or vinyl acetate, or a mixture thereof. Further preferably, said polar comonomers are selected from C<NUM>- to C<NUM>-alkyl acrylates, C<NUM>- to C<NUM>-alkyl methacrylates or vinyl acetate. Still more preferably, said polyolefin (A) copolymer is a copolymer of ethylene with C<NUM>- to C<NUM>-alkyl acrylate, such as methyl, ethyl, propyl or butyl acrylate, or vinyl acetate, or any mixture thereof.

Preferably, the polar group containing monomer units are selected from acrylates or acetate comonomer units, preferably from alkyl (meth)acrylate or vinyl acetate comonomer units, preferably alkyl (meth)acrylate comonomer units.

In the present invention the term "alkyl (meth)acrylate comonomer units" encompasses alkyl acrylate comonomer units and/or alkyl methacrylate comonomer units. The alkyl moiety in the alkyl(meth)acrylate comonomer units is preferably selected from C<NUM> to C<NUM>-hydrocarbyls, whereby the C<NUM> or C<NUM> hydrocarbyl may be branched or linear.

As the non-polar comonomer(s) for the LDPE copolymer, comonomer(s) other than the above defined polar comonomers can be used. Preferably, the non-polar comonomers are other than comonomer(s) containing hydroxyl group(s), alkoxy group(s), carbonyl group(s), carboxyl group(s), ether group(s) or ester group(s). One group of preferable non-polar comonomer(s) comprise, preferably consist of, monounsaturated (= one double bond) comonomer(s), preferably olefins, preferably alpha-olefins, more preferably C<NUM> to C<NUM> alpha-olefins, such as propylene, <NUM>-butene, <NUM>-hexene, <NUM>-methyl-<NUM>-pentene, styrene, <NUM>-octene, <NUM>-nonene; polyunsaturated (= more than one double bond) comonomer(s); a silane group containing comonomer(s); or any mixtures thereof.

If the LDPE is a copolymer, it preferably comprises <NUM> to <NUM> wt. -%, still more preferably less than <NUM> wt. -%, more preferably less than <NUM> wt. -%, of one or more comonomer(s). Preferred ranges include <NUM> to <NUM> wt%, such as <NUM> to <NUM> wt% comonomer.

The LDPE polymer, may optionally be unsaturated, i.e. may comprise carbon-carbon double bonds (-C=C-). Preferred "unsaturated" LDPEs contains carbon-carbon double bonds/<NUM> carbon atoms in a total amount of at least <NUM>/<NUM> carbon atoms. If a non-cross-linked LDPE is used in the final cable, then the LDPE is typically not unsaturated as defined above. By not unsaturated is meant that the C=C content is preferably less than <NUM>/<NUM> carbon atoms, such as <NUM>/<NUM> C atoms or less.

As well known, the unsaturation can be provided to the LDPE polymer by means of the comonomers, a low molecular weight (Mw) additive compound, such as a CTA or scorch retarder additive, or any combinations thereof. The total amount of double bonds means herein double bonds added by any means. If two or more above sources of double bonds are chosen to be used for providing the unsaturation, then the total amount of double bonds in the LDPE polymer means the sum of the double bonds present. Any double bond measurements are carried out prior to optional crosslinking.

The term "total amount of carbon-carbon double bonds" refers to the combined amount of double bonds which originate from vinyl groups, vinylidene groups and trans-vinylene groups, if present.

If an LDPE homopolymer is unsaturated, then the unsaturation can be provided e.g. by a chain transfer agent (CTA), such as propylene, and/or by polymerization conditions. If an LDPE copolymer is unsaturated, then the unsaturation can be provided by one or more of the following means: by a chain transfer agent (CTA), by one or more polyunsaturated comonomer(s) or by polymerisation conditions. It is well known that selected polymerisation conditions such as peak temperatures and pressure, can have an influence on the unsaturation level. In case of an unsaturated LDPE copolymer, it is preferably an unsaturated LDPE copolymer of ethylene with at least one polyunsaturated comonomer, and optionally with other comonomer(s), such as polar comonomer(s) which is preferably selected from acrylate or acetate comonomer(s). More preferably an unsaturated LDPE copolymer is an unsaturated LDPE copolymer of ethylene with at least polyunsaturated comonomer(s).

The polyunsaturated comonomers suitable as the non-polar comonomer preferably consist of a straight carbon chain with at least <NUM> carbon atoms and at least <NUM> carbons between the non-conjugated double bonds, of which at least one is terminal, more preferably, said polyunsaturated comonomer is a diene, preferably a diene which comprises at least eight carbon atoms, the first carbon-carbon double bond being terminal and the second carbon-carbon double bond being non-conjugated to the first one. Preferred dienes are selected from C<NUM> to C<NUM> non-conjugated dienes or mixtures thereof, more preferably selected from <NUM>,<NUM>-octadiene, <NUM>,<NUM>-decadiene, <NUM>,<NUM>-dodecadiene, <NUM>,<NUM>-tetradecadiene, <NUM>-methyl-<NUM>,<NUM>-octadiene, <NUM>-methyl-<NUM>,<NUM>-decadiene, or mixtures thereof. Even more preferably, the diene is selected from <NUM>,<NUM>-octadiene, <NUM>,<NUM>-decadiene, <NUM>,<NUM>-dodecadiene, <NUM>,<NUM>-tetradecadiene, or any mixture thereof, however, without limiting to above dienes.

It is well known that e.g. propylene can be used as a comonomer or as a chain transfer agent (CTA), or both, whereby it can contribute to the total amount of the carbon-carbon double bonds, preferably to the total amount of the vinyl groups. Herein, when a compound which can also act as comonomer, such as propylene, is used as CTA for providing double bonds, then said copolymerisable comonomer is not calculated to the comonomer content.

If LDPE polymer is unsaturated, then it has preferably a total amount of carbon-carbon double bonds, which originate from vinyl groups, vinylidene groups and trans-vinylene groups, if present, of more than <NUM>/<NUM> carbon atoms, preferably of more than <NUM>/<NUM> carbon atoms. The upper limit of the amount of carbon-carbon double bonds present in the polyolefin is not limited and may preferably be less than <NUM>/<NUM> carbon atoms, preferably less than <NUM>/<NUM> carbon atoms.

If the LDPE is unsaturated LDPE as defined above, it contains preferably at least vinyl groups and the total amount of vinyl groups is preferably higher than <NUM>/<NUM> carbon atoms, still more preferably higher than <NUM>/<NUM> carbon atoms, and most preferably of higher than <NUM>/<NUM> carbon atoms. Preferably, the total amount of vinyl groups is of lower than <NUM>/<NUM> carbon atoms, more preferably lower than <NUM>/<NUM> carbon atoms. More preferably the LDPE contains vinyl groups in total amount of more than <NUM>/<NUM> carbon atoms, still more preferably of more than <NUM>/<NUM> carbon atoms.

It is however, preferred if the LDPE of the invention is not unsaturated and possesses less than <NUM> C=C/<NUM> C atoms, preferably less than <NUM> C=C/<NUM> C atoms. It is also preferred if the LDPE is a homopolymer. As the polymer composition of the invention is not designed for crosslinking, the presence of unsaturation within the LDPE is not required or desired.

The LDPE polymer may have a high melting point, which may be of importance especially for a thermoplastic insulation material. Melting points of <NUM> or more are envisaged, such as <NUM> or more, especially <NUM> or more, such as <NUM> to <NUM>.

The LDPE used in the composition of the invention may have a density of <NUM> to <NUM>/m<NUM>, preferably <NUM> to <NUM>/m<NUM>, especially <NUM> to <NUM>/m<NUM>, such as about <NUM> to <NUM>/m<NUM>.

The MFR<NUM> (<NUM>, <NUM>) of the LDPE polymer is preferably from <NUM> to <NUM>/<NUM>, more preferably is from <NUM> to <NUM>/<NUM>, and most preferably is from <NUM> to <NUM>/<NUM>, especially <NUM> to <NUM>/<NUM>. In a preferred embodiment, the MFR<NUM> of the LDPE is <NUM> to <NUM>/<NUM>, especially <NUM> to <NUM>/<NUM>, especially <NUM> to <NUM>/<NUM>.

The LDPE may have an Mw of <NUM>/mol to <NUM>/mol, such as <NUM> to <NUM>/mol.

The LDPE may have a PDI of <NUM> to <NUM>, such as <NUM> to <NUM>.

It is possible to use a mixture of LDPEs in the polymer composition of the invention however it is preferred if a single LDPE is used.

The LDPE is typically produced in a high pressure (HP) process in a tubular or autoclave reactor or in any combination thereof.

Accordingly, the LDPE of the invention is preferably a LDPE polymer, which is preferably produced at high pressure by free radical initiated polymerisation. The high pressure (HP) polymerisation is widely described in the literature and the adjustment of process conditions for further tailoring the other properties of the polyolefin depending on the desired end application is within the skills of a skilled person.

In a tubular reactor the polymerisation is effected at temperatures which typically range up to <NUM>, preferably from <NUM> to <NUM> and pressure from <NUM> MPa, preferably <NUM> to <NUM> MPa, more preferably from <NUM> to <NUM> MPa. Pressure can be measured at least after compression stage and/or after the tubular reactor. Temperature can be measured at several points during all steps.

The autoclave process may, for example, be conducted in a stirred autoclave reactor. The stirred autoclave reactor is commonly divided into separate zones. The main flow pattern is from top zone(s) to bottom zone(s), but backmixing is allowed and sometimes desired. The stirrer is preferably designed to produce efficient mixing and flow patterns at a suitable speed of rotation selected by a person skilled in the art. The compressed mixture is commonly cooled and fed to one or more of the reactor zones. Radical initiators may also be injected at one or more zones along the reactor. As radical initiator, any compound or a mixture thereof that decomposes to radicals at an elevated temperature can be used. Usable radical initiators are commercially available. The polymerization pressure is typically <NUM> to <NUM>, such as <NUM> to <NUM>, MPa. The polymerization reaction is exothermic and after startup (at elevated temperature, e.g. from <NUM> to <NUM> to create the first radicals) the exothermic heat generated sustains the reaction. Temperature in each zone is controlled by the cooled incoming feed mixture. Suitable temperatures range from <NUM> to <NUM>. The process is well known to a skilled person.

After the separation the obtained LDPE is typically in a form of a polymer melt which is normally mixed and pelletized in a pelletising section, such as pelletising extruder, arranged in connection to the HP reactor system. Optionally, additive(s), such as antioxidant(s), can be added in this mixer in a known manner.

Further details of the production of ethylene (co)polymers by high pressure radical polymerization can be found i. in the <NPL> and <NPL>.

When an unsaturated LDPE copolymer of ethylene is prepared, then, as well known, the carbon-carbon double bond content can be adjusted by polymerising the ethylene e.g. in the presence of one or more polyunsaturated comonomer(s), chain transfer agent(s), or both, using the desired feed ratio between monomer, preferably ethylene, and polyunsaturated comonomer and/or chain transfer agent, depending on the nature and amount of C-C double bonds desired for the unsaturated LDPE copolymer. <CIT> describes a high pressure radical polymerisation of ethylene with polyunsaturated monomers. As a result the unsaturation can be uniformly distributed along the polymer chain in random copolymerisation manner.

It is most preferred if the LDPE is a low density homopolymer of ethylene.

The LDPE (i) is present in an amount of <NUM> to <NUM> wt%, preferably <NUM> to <NUM> wt%, more preferably <NUM> to <NUM> wt% relative to the total weight of the composition as a whole.

The polypropylene is a propylene-based polymer. The term, "propylene-based polymer," as used herein, is a polymer that comprises a majority weight percent polymerized propylene monomer (based on the total weight of polymerisable monomers), and optionally may comprise at least one polymerised comonomer. The propylene-based polymer may include greater than <NUM>, or greater than <NUM>, or greater than <NUM>, or greater than <NUM>, or greater than <NUM> weight percent units derived from propylene (based on the total weight of the propylene-based polymer).

The polypropylene may be a propylene homopolymer or a propylene copolymer. Preferably, the polypropylene is a homopolymer.

The comonomer may be α-olefin such as ethylene or a C<NUM>-<NUM> linear, branched or cyclic α-olefin. Nonlimiting examples of suitable C<NUM>-<NUM> α-olefins include <NUM>-butene, <NUM>-methyl-<NUM>-pentene, <NUM>-hexene, <NUM>-octene, <NUM>-decene, <NUM>-dodecene, <NUM>-tetradecene, <NUM>-hexadecene, and <NUM>-octadecene. The α-olefins also can contain a cyclic structure such as cyclohexane or cyclopentane, resulting in an α-olefin such as <NUM>-cyclohexyl-<NUM>-propene (allyl cyclohexane) and vinyl cyclohexane. Although not α-olefins in the classical sense of the term, for purposes of this disclosure certain cyclic olefins, such as norbornene and related olefins, particularly <NUM>-ethylidene-<NUM>-norbornene, are α-olefins and can be used in place of some or all of the α-olefins described above. Similarly, styrene and its related olefins (for example, α-methylstyrene, etc.) are α-olefins for purposes of this disclosure. Illustrative propylene polymers include ethylene/propylene, propylene/butene, propylene/<NUM>-hexene, propylene/<NUM>-octene, propylene/styrene, and the like. Illustrative terpolymers include ethylene/propylene/<NUM>-octene, ethylene/propylene/butene, propylene/butene/<NUM>-octene, ethylene/propylene/diene monomer (EPDM) and propylene/butene/styrene. The copolymers can be random copolymers.

In a particularly preferred embodiment, the polypropylene is an isotactic propylene homopolymer.

Typically, the polypropylene has an MFR<NUM> of from <NUM> to <NUM>/l0 min, preferably from <NUM> to <NUM>/l0 min as determined in accordance with ISO <NUM> (at <NUM>; <NUM> load). Most preferably, the MFR is in the range of <NUM> to <NUM>/<NUM>, such as <NUM> to <NUM>/<NUM>.

The density of the polypropylene may typically be in the range <NUM> to <NUM>/m<NUM>, ideally <NUM> to <NUM>/cm<NUM>, preferably from <NUM> to <NUM>/cm<NUM>, and more preferably from <NUM> to <NUM>/cm<NUM> as determined in accordance with ISO <NUM>.

The propylene may have an Mw in the range of <NUM>/mol to <NUM>/mol. The polypropylene polymer preferably has a molecular weight distribution Mw/Mn, being the ratio of the weight average molecular weight Mw and the number average molecular weight Mn, of less than <NUM>, such as <NUM>. <NUM> to <NUM>, e.g. <NUM>.

Usually the melting temperature of the polypropylene is within the range of <NUM> to <NUM>, preferably in the range of <NUM> to <NUM>, more preferably in the range from <NUM> to <NUM> as determined by differential scanning calorimetry (DSC) according to ISO <NUM>-<NUM>. Ideally, the polypropylene has a melting temperature (Tm) of greater than <NUM>, preferably greater than <NUM>.

The polypropylene may be prepared by any suitable known method in the art or can be obtained commercially.

The polypropylene (ii) is present in an amount of <NUM> to <NUM> wt%, preferably <NUM> to <NUM> wt%, more preferably <NUM> to <NUM> wt% relative to the total weight of the composition as a whole.

Polyolefin (A) is an olefin polymer comprising epoxy groups, i.e. an olefin polymer wherein a unit containing at least one epoxy functional group is incorporated. Such unit is referred herein as an "epoxy-group-containing monomer unit" and means an unsaturated compound comprising an epoxy group, preferably a vinyl group containing compound bearing an epoxy group. Such compounds can be used as comonomers for copolymerising epoxy-group-containing monomers units to the polyolefin (A) or can be grafted to the polyolefin (A), as is well known in the polymer field. Grafting and copolymerizing of epoxy-group containing monomer units can be made according to or analogously to the methods described in the literature.

The polyolefin (A) containing epoxy groups as well as the epoxy-group-containing monomer units are well known and commercially available. As preferable examples of epoxy-group-containing monomer units, aliphatic esters and glycidyl ethers such as an allyl glycidyl ether, a vinyl glycidyl ether, a glycidylmaleate, a glycidyl itaconate, a (meth)glycidyl acrylate, and alicyclic esters and glycidyl ethers, such as a <NUM>-cyclohexene-<NUM>-glycidylether, a cyclohexene-<NUM>,<NUM>-diglycidyl carboxylate, a cyclohexene-<NUM>-glycidyl carboxylate, a <NUM>-norbornene-<NUM>-methyl-<NUM>-glycidyl carboxylate and an endo cis-bicyclo (<NUM>,<NUM>,<NUM>)-<NUM>-heptene-<NUM>,<NUM>-diglycidyl dicarboxylate, can be mentioned.

Particularly preferable epoxy-group-containing monomer units include <NUM>,<NUM>-epoxy-<NUM>-decene, <NUM>,<NUM>-epoxy-<NUM>-hexene, <NUM>,<NUM>-epoxy-<NUM>-butene, glycidyl methacrylate, glycidyl acrylate, and allyl glycidyl ether, especially glycidyl methacrylate.

In the present invention the epoxy-group-containing monomer unit is preferably incorporated as a comonomer, i.e. by copolymerising an olefin monomer with the vinyl group containing comonomer bearing an epoxy group (=epoxy-group-containing monomer unit).

Most preferably, the epoxy-group-containing monomer unit is glycidyl methacrylate.

Preferably, the amount of epoxy-group-containing monomer units is at least <NUM> wt%, more preferably at least <NUM> wt%, more preferably at least <NUM> wt%, such as at least <NUM> wt%, based on the total amount of polyolefin (A). The content of epoxy-group-containing monomer units is preferably <NUM> wt% or less, preferably <NUM> wt%, more preferably <NUM> wt% or less and most preferably <NUM> wt% or less, based on the total amount of polyolefin (A).

The suitable polyolefin (A) can be a homopolymer or a copolymer of an olefin, wherein the epoxy-group-containing monomer units are grafted as defined above, or a copolymer of an olefin and at least the epoxy-group-containing monomer units as defined above. Preferably polyolefin (A) is a copolymer of an olefin with at least the epoxy-group-containing monomer units as defined above, more preferably a copolymer of an olefin with at least glycidyl methacrylate comonomer units.

Whilst it is within the ambit of the invention for the polyolefin (A) to comprise other comonomers in addition to the epoxy-group-containing comonomer, it is preferred if the epoxy-group-containing comonomer (e.g. the glycidyl methacrylate) is the sole comonomer.

In embodiments wherein the polyolefin (A) does comprise further comonomer(s) different from the epoxy-group containing monomer units, then these may be polar comonomer(s), non-polar comonomer(s) or a mixture of the polar comonomer(s) and non-polar comonomer(s). Moreover, polyolefn (A) may optionally be unsaturated.

As a polar comonomer for the polyolefin (A), comonomer(s) containing hydroxyl group(s), alkoxy group(s), carbonyl group(s), carboxyl group(s), ether group(s) or ester group(s), or a mixture thereof, can be used. More preferably, comonomer(s) containing carboxyl and/or ester group(s) are used as said polar comonomer. Still more preferably, the polar comonomer(s) of the polyolefin (A) copolymer is selected from the groups of acrylate(s), methacrylate(s) or acetate(s), or any mixtures thereof.

If present in said polyolefin (A) copolymer, the polar comonomer(s) is preferably selected from the group of alkyl acrylates, alkyl methacrylates or vinyl acetate, or a mixture thereof. Further preferably, said polar comonomers are selected from C<NUM>- to C<NUM>-alkyl acrylates, C<NUM>- to C<NUM>-alkyl methacrylates or vinyl acetate. Still more preferably, said polyolefin (A) copolymer is a copolymer of ethylene with C<NUM>- to C<NUM>-alkyl acrylate, such as methyl, ethyl, propyl or butyl acrylate, or vinyl acetate, or any mixture thereof.

As the non-polar comonomer(s) for the polyolefin (A) copolymer, comonomer(s) other than the above defined polar comonomers can be used. Preferably, the non-polar comonomers are other than comonomer(s) containing hydroxyl group(s), alkoxy group(s), carbonyl group(s), carboxyl group(s), ether group(s) or ester group(s). One group of preferable non-polar comonomer(s) comprise, preferably consist of, monounsaturated (= one double bond) comonomer(s), preferably olefins, preferably alpha-olefins, more preferably C<NUM> to C<NUM> alpha-olefins, such as propylene, <NUM>-butene, <NUM>-hexene, <NUM>-methyl-<NUM>-pentene, styrene, <NUM>-octene, <NUM>-nonene; polyunsaturated (= more than one double bond) comonomer(s); a silane group containing comonomer(s); or any mixtures thereof.

If polyolefin (A) is a copolymer, it preferably comprises <NUM> to <NUM> wt. -%, still more preferably less than <NUM> wt. -%, more preferably less than <NUM> wt. -%, of one or more comonomer(s). Preferred ranges include <NUM> to <NUM> wt%, such as <NUM> to <NUM> wt% comonomer.

Polyolefin (A) may optionally be unsaturated, i.e. may comprise carbon-carbon double bonds (-C=C-). Preferred "unsaturated" polyolefins contain carbon-carbon double bonds/<NUM> carbon atoms in a total amount of at least <NUM>/<NUM> carbon atoms. Preferably, the polyolefin is not unsaturated as defined above. By not unsaturated is meant that the C=C content is preferably less than <NUM>/<NUM> carbon atoms, such as <NUM>/<NUM> C atoms or less.

As well known, the unsaturation can be provided to the polyolefin by means of the comonomers, a low molecular weight (Mw) additive compound, such as a CTA or scorch retarder additive, or any combinations thereof. The total amount of double bonds means herein double bonds added by any means. If two or more above sources of double bonds are chosen to be used for providing the unsaturation, then the total amount of double bonds in the polymer means the sum of the double bonds present. Any double bond measurements are carried out prior to optional crosslinking.

The unsaturation can be provided by one or more of the following means: by a chain transfer agent (CTA), by one or more polyunsaturated comonomer(s) or by polymerisation conditions. It is well known that selected polymerisation conditions such as peak temperatures and pressure, can have an influence on the unsaturation level. In case of an unsaturated copolymer, it is preferably an unsaturated copolymer of ethylene with at least one polyunsaturated comonomer, and optionally with other comonomer(s), such as polar comonomer(s) which is preferably selected from acrylate or acetate comonomer(s). More preferably an unsaturated copolymer is an unsaturated copolymer of ethylene with at least polyunsaturated comonomer(s).

The polyunsaturated comonomers suitable as the non polar comonomer preferably consist of a straight carbon chain with at least <NUM> carbon atoms and at least <NUM> carbons between the non-conjugated double bonds, of which at least one is terminal, more preferably, said polyunsaturated comonomer is a diene, preferably a diene which comprises at least eight carbon atoms, the first carbon-carbon double bond being terminal and the second carbon-carbon double bond being non-conjugated to the first one. Preferred dienes are selected from C<NUM> to C<NUM> non-conjugated dienes or mixtures thereof, more preferably selected from <NUM>,<NUM>-octadiene, <NUM>,<NUM>-decadiene, <NUM>,<NUM>-dodecadiene, <NUM>,<NUM>-tetradecadiene, <NUM>-methyl-<NUM>,<NUM>-octadiene, <NUM>-methyl-<NUM>,<NUM>-decadiene, or mixtures thereof. Even more preferably, the diene is selected from <NUM>,<NUM>-octadiene, <NUM>,<NUM>-decadiene, <NUM>,<NUM>-dodecadiene, <NUM>,<NUM>-tetradecadiene, or any mixture thereof, however, without limiting to above dienes.

If polyolefin (A) is unsaturated, then it has preferably a total amount of carbon-carbon double bonds, which originate from vinyl groups, vinylidene groups and trans-vinylene groups, if present, of more than <NUM>/<NUM> carbon atoms, preferably of more than <NUM>/<NUM> carbon atoms. The upper limit of the amount of carbon-carbon double bonds present in the polyolefin is not limited and may preferably be less than <NUM>/<NUM> carbon atoms, preferably less than <NUM>/<NUM> carbon atoms.

If polyolefin (A) is unsaturated as defined above, it contains preferably at least vinyl groups and the total amount of vinyl groups is preferably higher than <NUM>/<NUM> carbon atoms, still more preferably higher than <NUM>/<NUM> carbon atoms, and most preferably of higher than <NUM>/<NUM> carbon atoms. Preferably, the total amount of vinyl groups is of lower than <NUM>/<NUM> carbon atoms, more preferably lower than <NUM>/<NUM> carbon atoms. More preferably, polyolefin (A) contains vinyl groups in total amount of more than <NUM>/<NUM> carbon atoms, still more preferably of more than <NUM>/<NUM> carbon atoms.

It is however, preferred if the polyolefin (A) of the invention is not unsaturated and possesses less than <NUM> C=C/<NUM> C atoms, preferably less than <NUM> C=C/<NUM> C atoms.

The polyolefin (A) may have a high melting point, which may be of importance especially for a thermoplastic insulation material. Melting points of <NUM> or more are envisaged, such as <NUM> or more, especially <NUM> or more, such as <NUM> to <NUM>.

Polyolefin (A) may be any polymer comprising olefin monomer units. Examples of polyolefin (A) include polymers of C<NUM>-C<NUM> olefins, such as a polyethylene or polypropylene. In embodiments wherein polyolefin (A) is a polypropylene, said polypropylene preferably does not comprise ethylene monomer units. A particularly preferred polyolefin (A) is polyethylene.

In particular, polyolefin (A) is preferably a polyethylene comprising epoxy-group-containing monomer units, more preferably a copolymer of ethylene with at least the epoxy-group-containing monomer units as defined above, more preferably with at least glycidyl methacrylate comonomer units.

The copolymer of ethylene with at least the epoxy-group-containing monomer units as the preferable polyolefin (A) is referred herein also shortly as ethylene/epoxy copolymer.

The ethylene/epoxy copolymer may further comprise further comonomer units as defined above, however it is preferred if the epoxy-group-containing comonomer is the only comonomer present.

In one embodiment, the polyolefin (A) is a copolymer of ethylene with at least an epoxy-group-containing comonomer and optionally with other comonomer(s), different from the epoxy-group-containing monomer units, which other comonomer is preferably a polar comonomer different from the epoxy-group-containing monomer units, more preferably an acrylate or acetate group containing comonomer units.

The polyolefin (A) may be selected from an ethylene copolymer with glycidyl methacrylate comonomer units or an ethylene copolymer with glycidyl methacrylate comonomer units and a polar comonomer selected from alkyl(meth)acrylate or a vinyl acetate comonomer units, even more preferably from an alkyl acrylate or a vinyl acetate comonomer units, even more preferably from a methyl acrylate, ethyl acrylate, butyl acrylate or vinyl acetate comonomer units, most preferably from a methyl acrylate, an ethyl acrylate or butyl acrylate comonomer units. Most preferably the polyolefin (A) is selected from ethylene copolymer with glycidyl methacrylate comonomer units or ethylene copolymer with glycidyl methacrylate comonomer units and C1-C4 alkyl acrylate comonomer units, preferably methyl acrylate comonomer units. Moreover, the most preferred ethylene/epoxy copolymer for the polyolefin (A) is an ethylene copolymer with glycidyl methacrylate comonomer units.

The ethylene polymer as the preferred polyolefin (A) may have a melt flow rate MFR<NUM>, determined according to ISO <NUM> under a load of <NUM> and a temperature of <NUM>, of at least <NUM>/<NUM>, more preferably of at least <NUM>/<NUM>. More preferably such ethylene polymer has a melt flow rate MFR<NUM>, determined according to ISO <NUM> under a load of <NUM> and a temperature of <NUM>, of <NUM>/<NUM> or less, more preferably <NUM>/<NUM> or less, even more preferably <NUM>/<NUM> or less. Typical preferred ranges for the MFR<NUM> of the ethylene polymer are <NUM> to <NUM>/<NUM>, such as <NUM> to <NUM>/<NUM>, e.g. <NUM> to <NUM>/<NUM>.

The ethylene polymer as the preferred polyolefin (A) typically has a density of higher than <NUM>/m<NUM>. Preferably such ethylene polymer has a density of not higher than <NUM>/m<NUM>, and preferably of not higher than <NUM>/m<NUM>. A preferred density range is <NUM> to <NUM>/m<NUM>.

In general, the molecular weight distribution of polyolefin (A) may be in the range <NUM> to <NUM>, such as <NUM> to <NUM>.

The ethylene polymer as polyolefin (A) may be a low density ethylene polymer (LDPE) or a low pressure polymer such as LLDPE, MDPE and HDPE. Low pressure polymers are particularly well suited to embodiments wherein the epoxy-group containing monomer units are grafted to the polymer.

The preferred ethylene polymer as polyolefin (A) is a low density ethylene polymer (LDPE). The LDPE may be produced in a high pressure (HP) process in a tubular or autoclave reactor or in any combination thereof, both in case the epoxy-group-containing monomer units are grafted to a homopolymer or copolymer of ethylene after the production of the ethylene polymer as polyolefin (A), and in case the epoxy-group-containing monomer units are copolymerised with ethylene and optionally with other comonomer(s). Hence, in case the epoxy-group containing monomer units are introduced by grafting the polymer prior to grafting may also be produced by this process.

Accordingly, the polyolefin (A) of the invention is preferably an LDPE polymer, which is preferably produced at high pressure by free radical initiated polymerisation. The high pressure (HP) polymerisation is widely described in the literature and the adjustment of process conditions for further tailoring the other properties of the polyolefin depending on the desired end application is within the skills of a skilled person.

In a tubular reactor the polymerisation is effected at temperatures which typically range up to <NUM>, preferably from <NUM> to <NUM>, and pressures from <NUM> MPa, preferably <NUM> to <NUM> MPa, more preferably from <NUM> to <NUM> MPa. Pressure can be measured at least after compression stage and/or after the tubular reactor. Temperature can be measured at several points during all steps.

Such autoclave polymerisation is preferred when ethylene is copolymerized with the epoxy-group-containing monomer as defined above, preferably with glycidyl methacrylate comonomer, and optionally with other comonomer(s), such as a polar comonomer as defined above.

The LDPE may have a density of <NUM> to <NUM>/m<NUM>, preferably <NUM> to <NUM>/m<NUM>, especially <NUM> to <NUM>/m<NUM>, such as about <NUM> to <NUM>/m<NUM>.

It is possible to use a mixture of LDPEs, however it is preferred if a single LDPE is used.

Polyolefin (A) is preferably present in an amount of <NUM> to <NUM> wt%, more preferably <NUM> to <NUM> wt%, even more preferably <NUM> to <NUM> wt% relative to the total weight of the composition as a whole.

Polyolefin (B) is an olefin polymer comprising carboxylic acid groups, or precursors thereof. In the context of the present invention, carboxylic acid groups and groups being precursors of carboxylic acids will hereafter be referred to as "groups bearing carboxylic functionality".

The carboxylic acid groups or precursors thereof may be present as part of a comonomer unit or may be grafted to the polyolefin. Preferably these groups are grafted to the polyolefin.

In one embodiment, the olefin polymer comprises comonomer units comprising carboxylic acid groups. An example of such comonomer units is acrylic acid.

As an alternative, polyolefin (B) may be an olefin polymer comprising comonomer units comprising functional groups being precursors of carboxylic acid groups, such as esters or anhydrides. Such a polyolefin (B) may be extruded at elevated temperature (for instance <NUM>) without any pre-cross-linking and would then undergo conversion to carboxylic acid functionalities inside the vulcanization tube to react with the epoxy groups. Preferred ester comonomer units are (meth)acrylate comonomer units, more preferably alkyl (meth)acrylate comonomer units.

In the present invention, the term "alkyl (meth)acrylate comonomer units" encompasses alkyl acrylate comonomer units and/or alkyl methacrylate comonomer units. The alkyl moiety in the alkyl(meth)acrylate comonomer units may be selected from C1 to C8-hydrocarbyls, whereby the hydrocarbyl may be branched or linear. In particular, the alkyl moiety is C3 or C4 hydrocarbyl, wherein the C3 or C4 hydrocarbyl may be linear or branched. Particularly preferred alkyl (meth)acrylate comonomer units include tert-butyl acrylate and tert-butyl methacrylate.

Among other possible precursors of carboxylic acids, anhydrides may be mentioned, such as maleic anhydride. The skilled person will appreciate that when we refer to maleic anhydride in this context, we mean the compound which is grafted to the polyolefin. Once grafted the maleic anhydride generates a succinic anhydride group bound to the polyolefin which can in turn be converted to a carboxylic acid group.

Finally, the polyolefin (B) may be a terpolymer comprising comonomer units comprising carboxylic acid groups and comonomer units comprising functional groups being precursors of carboxylic acid groups. Such precursors of a carboxylic acid may e.g. be an ester group. In this case, the cross-linking temperature should be sufficiently high such that all of the ester groups are converted to carboxylic acid functionalities. Alternatively, the precursor may be converted to the carboxylic acid via thermal splitting. An example of a terpolymer that may be used as the polyolefin (B) in the context of the present invention is e.g. a terpolymer comprising tert-butyl acrylate and acrylic acid comonomer units.

The polyolefin (B) may comprise further comonomer(s) different from monomer units containing carboxylic acid groups and/or precursors of carboxylic acids. If present, these further comonomers may be polar comonomer(s). Such polar comonomer(s) may be present in an amount of <NUM> to <NUM> wt%, relative to the total amount of polyolefin (B). In case the polyolefin (B) comprises further polar comonomer(s), then the further polar comonomer(s) may be present in an amount of at least <NUM> wt%, more preferably of at least <NUM> wt%, more preferably of at least <NUM> wt% based on the total amount of the polyolefin (B). In case polyolefin (B) comprises polar comonomers, then, preferably, the polar group containing monomer units are present in an amount of not more than <NUM> wt%, more preferably not more than <NUM> wt%, even more preferably of not more than <NUM> wt%, even more preferably not more than <NUM> wt%, even more preferably not more than <NUM> wt%, and most preferably of not more than <NUM> wt% based on the total amount of the polyolefin (B).

Preferably, the polar group containing monomer units are selected from (meth)acrylates or acetate comonomer units, preferably from alkyl (meth)acrylate or vinyl acetate comonomer units, preferably alkyl (meth)acrylate comonomer units.

In the present invention, the term "alkyl (meth)acrylate comonomer units" encompasses alkyl acrylate comonomer units and/or alkyl methacrylate comonomer units.

The alkyl moiety in the alkyl(meth)acrylate comonomer units may be selected from C1 to C8-hydrocarbyls, whereby the hydrocarbyl may be branched or linear. In particular, the alkyl moiety is C3 or C4 hydrocarbyl, wherein the C3 or C4 hydrocarbyl may be linear or branched.

In the context of the present invention, the polyolefin (B) comprising comonomers bearing carboxylic acid groups or functional groups being precursors of carboxylic acid groups may be a blend of at least two polymers each of which comprises comonomer units bearing carboxylic acid groups or functional groups being precursors of carboxylic acid groups. The carboxylic acid groups or functional groups being precursors of carboxylic acid groups in each of the polymers being a part of the polyolefin (B) may be same or different.

In analogy to the above, the comonomer units of the polyolefin (B) may either be copolymerized or grafted into the olefin polymer. Methods of grafting are well known to those skilled in the art of polymer chemistry.

As previously discussed, in the present invention, the monomer units bearing carboxylic functionality are preferably grafted onto the polyolefin.

In all embodiments, preferable monomer units bearing carboxylic acid functionality are at least one of acrylic acid, maleic anhydride (MAH), or an alkyl (meth)acrylate such as tert-butyl methacrylate or tert-butyl acrylate, in particular maleic anhydride. Whilst it is within the ambit of the invention for more than one type of monomer unit bearing carboxylic acid functionality to be present, preferably only one type is present.

The amount of monomer units bearing carboxylic functionality may be at least <NUM> wt%, more preferably at least <NUM> wt%, more preferably at least <NUM> wt%, based on the amount of polyolefin (B).

The content of monomer units bearing carboxylic functionality may be below <NUM> wt%, preferably below <NUM> wt%, more preferably below <NUM> wt% based on the amount of polyolefin (B).

Polyolefin (B) may be any polymer comprising olefin monomer units. Examples of polyolefin (B) include polymers of C1-C6 olefins, such as a polyethylene or polypropylene.

Wherein the polyolefin (B) is a polyethylene, it may have the properties as defined above for polyolefin (A).

In a particularly preferable embodiment, polyolefin (B) is a polypropylene.

In one embodiment wherein polyolefin (B) is a polypropylene, said polypropylene preferably does not comprise ethylene monomer units.

The polypropylene typically has a melt flow rate (MFR<NUM>) determined according to ISO <NUM> under a load of <NUM> and a temperature of <NUM>, of <NUM> to <NUM>/<NUM>, preferably from <NUM> to <NUM>/l0 min. Most preferably, the MFR is in the range of <NUM> to <NUM>/<NUM>, such as <NUM> to <NUM>/<NUM>.

The polypropylene may be prepared by any suitable known method in the art or can be obtained commercially. The skilled worker will be familiar with appropriate methods. Where the polypropylene comprises grafted carboxylic acid groups or precursors thereof, the grafting reaction will usually be carried out after polymerisation. Where the carboxylic acid groups or precursors thereof are incorporated as a comonomer, they will be added during polymerisation.

Polyolefin (B) is preferably present in an amount of <NUM> to <NUM> wt%, more preferably <NUM> to <NUM> wt%, even more preferably <NUM> to <NUM> wt% relative to the total weight of the composition as a whole.

Whilst it is within the ambit of the invention for the polyolefin composition to comprise other polymer components in addition to the LDPE, polypropylene and polyolefin (A) and (B), it is preferable if the composition consists of the LDPE, polypropylene and polyolefins (A) and (B) as the only polymer components.

In one particularly preferable embodiment, polyolefins (A) and (B) are present in equal wt% amounts, relative to the total weight of the composition as a whole.

In any of the above embodiments the use of peroxide with the undesired problems as discussed above can be markedly reduced or completely avoided.

Hence, the polymer composition of the invention preferably comprises less than <NUM> wt% peroxide, more preferably less than <NUM> wt% peroxide, such as less than <NUM> wt% peroxide, relative to the total weight of the composition. Even more preferably, the polymer composition is free of any added peroxide (i.e. contains <NUM> wt% peroxide, relative to the total weight of the composition) and most preferably free of any radical forming agent.

In one embodiment, the composition is thermoplastic. In the context of the present invention, whilst the new covalent bonds formed by the reaction of the epoxy groups with the carboxylic acid groups may be considered crosslinks (since they are new C-O-C bonds), this polyolefin "network" is present together with the thermoplastic LDPE and polypropylene which are typically not crosslinked and thus the material as a whole behaves as a thermoplastic.

Thus, in a further embodiment, the invention provides a process for preparing the polymer composition of the invention, said process comprising heating the composition to a temperature greater than the melting temperature of at least the major component of the composition, more preferably to a temperature greater than the melting temperature of all polymer components (including the LDPE) in the composition, e.g. at least <NUM> above the melting temperature. According to an example embodiment, the polymer composition is heated to the melting temperature of polypropylene, i.e. around <NUM>.

Typically, said process will be carried out by compounding by, for example, extrusion. Preferably, said process does not involve the use of peroxide. Thus, the composition of the invention is substantially free of peroxide (e.g. comprises less than <NUM> wt% peroxide, preferably less than <NUM> wt% peroxide, such as less than <NUM> wt% peroxide, relative to the total weight of the composition) and associated decomposition products. As a result of this the process for preparing the polymer composition of the invention typically does not comprise a degassing step.

Typically, the process involves heating to a temperature of at least <NUM>, preferably at least <NUM>, such as at least <NUM>. The process will generally involve heating to <NUM> or less, such as <NUM> or less.

The tensile creep strain measured after <NUM> minutes is preferably less than <NUM> % (as measured by the test method is the test methods section below).

According to one example embodiment, LDPE is present in the polyolefin composition of the invention in the range <NUM> to <NUM> wt%, such as e.g. about <NUM> wt %, or even <NUM> wt% relative to the total weight of the composition as a whole, and PP, such as e.g. iPP, is present in the polyolefin composition of the invention in an amount in the range <NUM> to <NUM> wt%, such as e.g. <NUM> wt %, or even <NUM> wt%, relative to the total weight of the composition as a whole.

The polyolefin (A) and/or polyolefin (B) are each present in an amount of <NUM> to <NUM> wt%, such as e.g. about <NUM> wt%.

The combination of a polyolefin comprising epoxy groups and a polyolefin comprising carboxylic acid groups or precursors thereof provides a composition which is ideally suited for cable manufacture without using peroxide.

The cable of the invention is typically a power cable, such as an AC cable or a DC cable. A power cable is defined to be a cable transferring energy operating at any voltage level, typically operating at voltages higher than <NUM> kV. The power cable can be a low voltage (LV), a medium voltage (MV), a high voltage (HV) or an extra high voltage (EHV) DC cable, which terms, as well known, indicate the level of operating voltage.

Preferably the HV DC power cable of the invention is one operating at voltages of <NUM> kV or higher, even at voltages of <NUM> kV or higher. More preferably, the HV DC power cable operates at voltages of <NUM> kV or higher. The invention is also highly feasible in very demanding cable applications and further cables of the invention are HV DC power cable operating at voltages higher than <NUM> kV. Voltages of <NUM> kV or more are targeted, such as <NUM> kV or more, more preferably <NUM> KV or more, especially <NUM> kV or more, more especially <NUM> kV or more. Voltages of 640KV or more, such as <NUM> kV are also envisaged. The upper limit is not limited. The practical upper limit can be up to <NUM> kV, such as <NUM> kV. The cables of the invention operate well therefore in demanding extra HV DC power cable applications operating <NUM> to <NUM> kV, such as <NUM> to <NUM> kV.

A cable, such as a power cable (e.g. a DC power cable) comprises one or more conductors surrounded by at least one layer. The polymer composition of the invention may be used in that at least one layer.

Preferably, the cable comprises an inner semiconductive layer comprising a first semiconductive composition, an insulation layer comprising the polymer composition of the invention and an outer semiconductive layer comprising a second semiconductive composition, in that order.

The polymer composition of the invention may be used in one or more of the semiconductive layer(s) of the cable. In such embodiments, a conductive filler, such as carbon black, may be added to the composition.

The polymer composition of the invention is preferably used in the insulation layer of the cable. Ideally, the insulation layer comprises at least <NUM> wt%, such as at least <NUM> wt% of the polymer composition of the invention, such as at least <NUM> wt%, relative to the total weight of the layer as a whole. It is preferred therefore if the polymer composition of the invention is the only non-additive component used in the insulation layer of the cables of the invention. Thus, it is preferred if the insulation layer consists essentially of the composition of the invention. The term consists essentially of is used herein to mean that the only polymer composition present is that defined herein. It will be appreciated that the insulation layer may contain standard polymer additives such as water tree retarders, antioxidants and so on. These are not excluded by the term "consists essentially of". Note also that these additives may be added as part of a masterbatch and hence carried on a polymer carrier. The use of masterbatch additives is not excluded by the term consists essentially of.

The insulation layer is preferably not cross-linked. It will be understood that the term "non-crosslinked" used herein does not exclude the presence of the "network" formed between polyolefins (A) and (B). It is preferred if the insulation layer comprises no crosslinking agent. The insulation layer is thus ideally free of peroxides and hence free of by-products of the decomposition of the peroxide.

Naturally, the non cross-linked embodiment also simplifies the cable production process. Also, it is generally required to degas a cross-linked cable layer to remove the by-products of these agents after crosslinking. Where these are absent, no such degassing step is required. Another advantage of not using an external crosslinking agent is the elimination of the health and safety issues associated with the handling and storage of these agents, particularly peroxides.

The insulation layer may contain, in addition to the polymer composition of the invention further component(s) such as additives, e.g. antioxidant(s), scorch retarder(s) (SR), crosslinking booster(s), stabiliser(s), processing aid(s), flame retardant additive(s), water tree retardant additive(s), acid or ion scavenger(s), inorganic filler(s), dielectric liquids and voltage stabilizer(s), as known in the polymer field. Typically, however, no scorch retarder will be present.

The insulation layer may therefore comprise conventionally used additive(s) for W&C applications, such as one or more antioxidant(s). As non-limiting examples of antioxidants e.g. sterically hindered or semi-hindered phenols, aromatic amines, aliphatic sterically hindered amines, organic phosphites or phosphonites, thio compounds, and mixtures thereof, can be mentioned.

Preferably, the insulation layer does not comprise a carbon black. Also preferably, the insulation layer does not comprise flame retarding additive(s), e.g. a metal hydroxide containing additives in flame retarding amounts.

The used amounts of additives are conventional and well known to a skilled person, e.g. <NUM> to <NUM> wt%.

The cable of the invention also typically contains inner and outer semiconductive layers. These can be made of any conventional material suitable for use in these layers. The inner and the outer semiconductive compositions can be different or identical and may comprise a polymer(s) which is preferably a polyolefin or a mixture of polyolefins and a conductive filler, preferably carbon black. Suitable polyolefin(s) are e.g. polyethylene produced in a low pressure process (LLDPE, MDPE, HDPE), polyethylene produced in a HP process (LDPE) or a polypropylene. The carbon black can be any conventional carbon black used in the semiconductive layers of a power cable, preferably in the semiconductive layer of a power cable. Preferably the carbon black has one or more of the following properties: a) a primary particle size of at least <NUM> which is defined as the number average particle diameter according ASTM D3849-95a, dispersion procedure D b) iodine number of at least <NUM>/g according to ASTM D1510, c) oil absorption number of at least <NUM>/<NUM> which is measured according to ASTM D2414. Non-limiting examples of carbon blacks are e.g. acetylene carbon black, furnace carbon black and Ketjen carbon black, preferably furnace carbon black and acetylene carbon black. Preferably, the polymer composition of the semiconductive layer(s) comprises <NUM> to <NUM> wt% carbon black, based on the total weight of the composition.

In a preferable embodiment, the outer semiconductive layer is cross-linked. In another preferred embodiment, the inner semiconductive layer is preferably non-cross-linked. Overall therefore it is preferred if the inner semiconductive layer and the insulation layer remain non cross-linked where the outer semiconductive layer is cross-linked. A peroxide crosslinking agent can therefore be provided in the outer semiconductive layer only.

The conductor typically comprises one or more wires. Moreover, the cable may comprise one or more such conductors. Preferably the conductor is an electrical conductor and comprises one or more metal wires. Cu or Al wire is preferred.

As well known the cable can optionally comprise further layers, e.g. screen(s), a jacketing layer(s), other protective layer(s) or any combinations thereof.

The invention also provides a process for producing a cable comprising the steps of applying on one or more conductors, preferably by (co)extrusion, a layer comprising the polymer composition of the invention.

The invention also provides a process for producing a cable comprising the steps of applying on one or more conductors, preferably by (co)extrusion, an inner semiconductive layer, an insulation layer and an outer semiconductive layer, in that order, wherein the insulation layer comprises the composition of the invention.

The invention also provides a process for producing a cable comprising the steps of.

The process may optionally comprise the steps of crosslinking one or both of the inner semiconductive layer or outer semiconductive layer, without crosslinking the insulation layer.

More preferably, a cable is produced, wherein the process comprises the steps of.

Preferably in step (c) the second semiconductive polymer composition of the outer semiconductive layer is cross-linked. Also preferably, the second semiconductive polymer composition of the outer semiconductive layer is cross-linked, without crosslinking the insulation layer or the first semiconductive composition of the inner semiconductive layer.

Melt mixing means mixing above the melting point of at least the major polymer component(s) of the obtained mixture and is carried out for example, without limiting to, in a temperature of at least <NUM> above the melting or softening point of polymer component(s).

The term "(co)extrusion" means herein that in case of two or more layers, said layers can be extruded in separate steps, or at least two or all of said layers can be coextruded in a same extrusion step, as well known in the art. The term "(co)extrusion" means herein also that all or part of the layer(s) are formed simultaneously using one or more extrusion heads. For instance a triple extrusion can be used for forming three layers. In case a layer is formed using more than one extrusion heads, then for instance, the layers can be extruded using two extrusion heads, the first one for forming the inner semiconductive layer and the inner part of the insulation layer, and the second head for forming the outer insulation layer and the outer semiconductive layer.

As well known, the polymer composition of the invention and the optional and preferred first and second semiconductive compositions can be produced before or during the cable production process.

Preferably, the polymers required to manufacture the cable of the invention are provided to the cable production process in form of powder, grain or pellets. Pellets mean herein generally any polymer product which is formed from reactor-made polymer (obtained directly from the reactor) by post-reactor modification to a solid polymer particles.

Accordingly, the components can be premixed, e.g. melt mixed together and pelletized, before mixing. Alternatively, and preferably, these components can be provided in separate pellets to the (melt) mixing step (a), where the pellets are blended together.

The (melt) mixing step (a) of the provided polymer composition of the invention and of the preferable first and second semiconductive compositions is preferably carried out in a cable extruder. The step a) of the cable production process may optionally comprise a separate mixing step, e.g. in a mixer arranged in connection and preceding the cable extruder of the cable production line. Mixing in the preceding separate mixer can be carried out by mixing with or without external heating (heating with an external source) of the component(s).

Any crosslinking agent can be added before the cable production process or during the (melt) mixing step (a). For instance, and preferably, the crosslinking agent and also the optional further component(s), such as additive(s), can already be present in the polymers used. The crosslinking agent is added, preferably impregnated, onto the solid polymer particles, preferably pellets.

It is preferred that the melt mix of the polymer composition obtained from (melt)mixing step (a) consists of the LDPE (i), polypropylene (ii), polyolefin (A) and polyolefin (B) as the sole polymer component(s). The optional and preferable additive(s) can be added to polymer composition as such or as a mixture with a carrier polymer, i.e. in a form of a master batch.

The crosslinking of other layers can be carried out at increased temperature which is chosen, as well known, depending on the type of crosslinking agent. For instance temperatures above <NUM>, such as from <NUM> to <NUM>, are typical, however without limiting thereto.

The processing temperatures and devices are well known in the art, e.g. conventional mixers and extruders, such as single or twin screw extruders, are suitable for the process of the invention.

The thickness of the insulation layer of the cable, more preferably of the power cable is typically <NUM> or more, preferably at least <NUM>, preferably of at least <NUM> to <NUM>, more preferably from <NUM> to <NUM>, and conventionally <NUM> to <NUM>, e.g. <NUM> to <NUM>, when measured from a cross section of the insulation layer of the cable.

The thickness of the inner and outer semiconductive layers is typically less than that of the insulation layer, and in power cables can be e.g. more than <NUM>, such as from <NUM> up to <NUM>, <NUM> to <NUM> of inner semiconductive and outer semiconductive layer. The thickness of the inner semiconductive layer is preferably <NUM> - <NUM>, preferably <NUM> - <NUM>, preferably <NUM> - <NUM>. The thickness of the outer semiconductive layer is preferably from <NUM> to <NUM>, such as <NUM> to <NUM>, preferably <NUM> to <NUM>, preferably <NUM> - <NUM>. It is evident for and within the skills of a skilled person that the thickness of the layers of the power cable depends on the intended voltage level of the end application cable and can be chosen accordingly.

The cable of the invention is preferably a power cable, preferably a power cable operating at voltages up to <NUM> kV and known as low voltage (LV) cables, at voltages <NUM> kV to <NUM> kV and known as medium voltage (MV) cables, at voltages higher than <NUM> kV, known as high voltage (HV) cables or extra high voltage (EHV) cables. The terms have well known meanings and indicate the operating level of such cables.

More preferably the cable is a power cable comprising a conductor surrounded by at least an inner semiconductive layer, an insulation layer and an outer semiconductive layer, in that order, wherein at least one layer comprises, preferably consists of, the polyolefin composition of the invention.

Preferably, the at least one layer is the insulation layer.

In a further embodiment, the invention provides the use of a polyolefin composition as hereinbefore defined in the manufacture of a layer, preferably an insulation layer, of a cable.

Such cable embodiment enables to crosslink the cable without using peroxide which is very beneficial in view of the problems caused by using peroxide as discussed above.

Unless otherwise stated in the description or claims, the following methods were used to measure the properties defined generally above and in the claims and in the examples below. The samples were prepared according to given standards, unless otherwise stated. Wt%: % by weight.

The melt flow rate (MFR) is determined according to ISO <NUM> and is indicated in g/<NUM>. The MFR is an indication of the flowability, and hence the processability, of the polymer. The higher the melt flow rate, the lower the viscosity of the polymer. The MFR is determined at <NUM> for polyethylene and at <NUM> for polypropylene. MFR may be determined at different loadings such as <NUM> (MFR<NUM>) or <NUM> (MFR<NUM>).

Mz, Mw, Mn, and MWD are measured by Gel Permeation Chromatography (GPC) according to the following method:
The weight average molecular weight Mw and the molecular weight distribution (MWD = Mw/Mn wherein Mn is the number average molecular weight and Mw is the weight average molecular weight; Mz is the z-average molecular weight) is measured according to ISO <NUM>-<NUM>:<NUM> and ASTM D <NUM>-<NUM>. A Waters GPCV2000 instrument, equipped with refractive index detector and online viscosimeter was used with <NUM> x GMHXL-HT and 1x G7000HXL-HT TSK-gel columns from Tosoh Bioscience and <NUM>,<NUM>,<NUM>-trichlorobenzene (TCB, stabilized with <NUM>/L <NUM>,<NUM>-Di tert-butyl-<NUM>-methyl-phenol) as solvent at <NUM> and at a constant flow rate of <NUM>/min. <NUM>µL of sample solution were injected per analysis. The column set was calibrated using universal calibration (according to ISO <NUM>-<NUM>:<NUM>) with at least <NUM> narrow MWD polystyrene (PS) standards in the range of <NUM>/mol to <NUM><NUM>/mol. Mark Houwink constants were used as given in ASTM D <NUM>-<NUM>. All samples were prepared by dissolving <NUM> - <NUM> of polymer in <NUM> (at <NUM>) of stabilized TCB (same as mobile phase) and keeping for max. <NUM> hours at a maximum temperature of <NUM> with continuous gentle shaking prior sampling in into the GPC instrument.

The calibration procedure based on results obtained from quantitative <NUM>C-NMR spectroscopy was undertaken in the conventional manner well documented in the literature.

The amount of comonomer (N) was determined as weight percent (wt%) via: <MAT> wherein A is the maximum absorbance defined of the comonomer band, R the maximum absorbance defined as peak height of the reference peak and with k1 and k2 the linear constants obtained by calibration. The band used for ethylene content quantification is selected depending if the ethylene content is random (<NUM>-<NUM>) or block-like (as in heterophasic PP copolymer) (<NUM>-<NUM>). The absorbance at <NUM>-<NUM> was used as a reference band.

b) Quantification of alpha-olefin content in linear low density polyethylenes and low density polyethylenes by NMR spectroscopy:
The comonomer content was determined by quantitative 13C nuclear magnetic resonance (NMR) spectroscopy after basic assignment (<NPL>). Experimental parameters were adjusted to ensure measurement of quantitative spectra for this specific task.

Specifically solution-state NMR spectroscopy was employed using a Bruker AvanceIII <NUM> spectrometer. Homogeneous samples were prepared by dissolving approximately <NUM> of polymer in <NUM> of deuterated-tetrachloroethene in <NUM> sample tubes utilising a heat block and rotating tube oven at <NUM> C. Proton decoupled 13C single pulse NMR spectra with NOE (powergated) were recorded using the following acquisition parameters: a flip-angle of <NUM> degrees, <NUM> dummy scans, <NUM> transients an acquisition time of <NUM>, a spectral width of <NUM>, a temperature of <NUM> C, a bilevel WALTZ proton decoupling scheme and a relaxation delay of <NUM>. The resulting FID was processed using the following processing parameters: zero-filling to <NUM> data points and apodisation using a gaussian window function; automatic zeroth and first order phase correction and automatic baseline correction using a fifth order polynomial restricted to the region of interest.

Quantities were calculated using simple corrected ratios of the signal integrals of representative sites based upon methods well known in the art.

Comonomer content (wt%) was determined in a known manner based on Fourier transform infrared spectroscopy (FTIR) determination calibrated with quantitative nuclear magnetic resonance (NMR) spectroscopy. Below is exemplified the determination of the polar comonomer content of ethylene ethyl acrylate, ethylene butyl acrylate and ethylene methyl acrylate. Film samples of the polymers were prepared for the FTIR measurement: <NUM>-<NUM> thickness was used for ethylene butyl acrylate and ethylene ethyl acrylate and <NUM> film thickness for ethylene methyl acrylate in amount of >6wt%. Films were pressed using a Specac film press at <NUM>, approximately at <NUM> tons, <NUM>-<NUM> minutes, and then cooled with cold water in a not controlled manner. The accurate thickness of the obtained film samples was measured.

After the analysis with FTIR, base lines in absorbance mode were drawn for the peaks to be analysed. The absorbance peak for the comonomer was normalised with the absorbance peak of polyethylene (e.g. the peak height for butyl acrylate or ethyl acrylate at <NUM>-<NUM> was divided with the peak height of polyethylene at <NUM>-<NUM>). The NMR spectroscopy calibration procedure was undertaken in the conventional manner which is well documented in the literature, explained below.

For the determination of the content of methyl acrylate a <NUM> thick film sample was prepared. After the analysis the maximum absorbance for the peak for the methylacrylate at <NUM>-<NUM> was subtracted with the absorbance value for the base line at <NUM>-<NUM> (Amethylacrylate - A<NUM>). Then the maximum absorbance peak for the polyethylene peak at <NUM>-<NUM> was subtracted with the absorbance value for the base line at <NUM>-<NUM> (A<NUM> -A<NUM>). The ratio between (Amethylacrylate-A<NUM>) and (A<NUM>-A<NUM>) was then calculated in the conventional manner which is well documented in the literature.

The weight-% can be converted to mol-% by calculation. It is well documented in the literature.

The comonomer content was determined by quantitative nuclear magnetic resonance (NMR) spectroscopy after basic assignment (e.g. "<NPL>). Experimental parameters were adjusted to ensure measurement of quantitative spectra for this specific task (e. Quantities were calculated using simple corrected ratios of the signal integrals of representative sites in a manner known in the art.

Comonomer content (wt. %) was determined in a known manner based on Fourier transform infrared spectroscopy (FTIR) determination calibrated with quantitative nuclear magnetic resonance (NMR) spectroscopy. Below is exemplified the determination of the polar comonomer content of ethylene butyl acrylate and ethylene methyl acrylate. For the FT-IR measurement a film samples of <NUM> to <NUM> thickness were prepared as described above under method <NUM>). The accurate thickness of the obtained film samples was measured.

After the analysis with FT-IR base lines in absorbance mode were drawn for the peaks to be analysed. The maximum absorbance for the peak for the comonomer (e.g. for methylacrylate at <NUM>-<NUM> and butylacrylate at <NUM>-<NUM>) was subtracted with the absorbance value for the base line at <NUM>-<NUM> (Apolar comonomer - A<NUM>). Then the maximum absorbance peak for polyethylene peak at <NUM>-<NUM> was subtracted with the absorbance value for the base line at <NUM>-<NUM> (A<NUM> - A<NUM>). The ratio between (Acomonomer-A<NUM>) and (A<NUM>-A<NUM>) was then calculated. The NMR spectroscopy calibration procedure was undertaken in the conventional manner which is well documented in the literature, as described above under method <NUM>).

Below is exemplified how polar comonomer content obtained from the above method (<NUM>) or (<NUM>), depending on the amount thereof, can be converted to micromol or mmol per g polar comonomer as used in the definitions in the text and claims:
The millimoles (mmol) and the micro mole calculations have been done as described below.

For example, if <NUM> of the poly(ethylene-co-butylacrylate) polymer, which contains <NUM> wt% butylacrylate, then this material contains <NUM>/Mbutylacrylate (<NUM>/mol) = <NUM> x <NUM>-<NUM> mol. (=<NUM> micromoles).

The content of polar comonomer units in the polar copolymer Cpolar comonomer is expressed in mmol/g (copolymer). For example, a polar poly(ethylene-co-butylacrylate) polymer which contains <NUM> wt. % butyl acrylate comonomer units has a Cpolar comonomer of <NUM> mmol/g.

The used molecular weights are: Mbutylacrylate = <NUM>/mole, Methylacrylate = <NUM>/mole, Mmethylacrylate = <NUM>/mole).

Low density polyethylene (LDPE): The density was measured according to ISO <NUM>-<NUM>. The sample preparation was executed according to ISO <NUM>-<NUM> Table <NUM> Q (compression moulding).

Density of the PP polymer was measured according to ISO <NUM> / <NUM>-2B.

This can be carried out following the protocol in <CIT>.

Melting temperature, Tm, is measured with Mettler TA820 differential scanning calorimetry (DSC) on <NUM>-<NUM> samples. Melting curves are obtained during <NUM>/min cooling and heating scans between <NUM> and <NUM>. Melting temperatures were taken as the peaks of endotherms and exotherms.

The gel content of samples was determined gravimetrically using a solvent extraction technique. The samples (~<NUM>) were placed in pre-weighed <NUM> mesh stainless steel baskets and extracted in <NUM> dm<NUM> decalin by refluxing the solvent for <NUM>. After the extraction, the samples were dried first at ambient overnight and then under vacuum for about <NUM> hours at <NUM>. After this period, the non-soluble fraction that remained in the basket reached a constant weight, which was used to calculate the gel content.

20x5 mm pieces were cut from <NUM> thick melt-pressed films. Creep measurement were carried out using a TA Q800 DMA in tensile mode. First, samples were heated from <NUM> to a final temperature of <NUM>, <NUM> or <NUM> at <NUM> min-<NUM> with a constant preload force <NUM>. 001N corresponding to a stress of <NUM> kPa applied. At the final temperature, a constant stress of <NUM> kPa was applied for <NUM> to the sample and the resulting strain was recorded as a function of time.

A polymer composition was prepared comprising <NUM> wt% LDPE, <NUM> wt% PP, <NUM> wt% LDPE with epoxy groups and <NUM> wt% PP-g-MAH materials as defined above, by compounding through extrusion for <NUM> minutes at <NUM> using an Xplore Micro Compounder MC5. In a hot press, the extruded material was heated to <NUM> and the pressure was increased up to 37000kN/m<NUM>, when the material was left for a further minute before cooling to room temperature. This procedure resulted in <NUM> thick plates.

Creep results are shown in Table <NUM> and <FIG>.

The neat PP-g-MAH was too brittle to press a sample for creep measurement.

The creep measurements clearly illustrate that the inventive examples have considerably higher creep resistance (see Table <NUM>). For example, after <NUM> minutes of loading (<NUM> kPa at <NUM>), the strain in Comparative Example (CE) <NUM> is <NUM> %, whereas Inventive Example <NUM> exhibits a strain of <NUM>%.

Claim 1:
A polymer composition comprising
(i) an LDPE in an amount of <NUM> to <NUM> wt%, relative to the total weight of the polymer composition;
(ii) a polypropylene in an amount of <NUM> to <NUM> wt%, relative to the total weight of the polymer composition;
(iii) polyolefin (A) comprising epoxy groups; and
(iv) polyolefin (B) comprising carboxylic acid groups and/or precursor thereof
wherein polyolefin (A) and/or polyolefin (B) are each present in an amount of <NUM> to <NUM> wt%, relative to the total weight of the polymer composition.