Patent Description:
In the field of power cables, such as low voltage (LV) cables, often polyurethane cast resins (PUR) are used when jointing such cables. While PVC, which is a common material used for layers in power cables, has an excellent adhesion towards PUR, polyolefins, and amongst them ethylene vinylsilane ethylene copolymers, show almost no adhesion at all towards such jointing material.

Patent application <CIT> discloses to a low voltage power cable comprising an insulation layer with a density below <NUM>/m<NUM> which comprises a polyolefin comprising <NUM> to <NUM> mol% of a compound having polar groups. Furthermore, it discloses the use of a polyolefin comprising <NUM> to <NUM> mol% of a compound having polar groups in the production of an insulation layer for a low voltage power cable.

As polyolefins are also frequently used as layers in power cables there is a need to provide polyolefin, in particular polyethylene, compositions or power cables in which layers comprising polyolefins, in particular polyethylenes, are contained with an enhanced adhesion towards PURs.

The present invention is based on the finding that this object can be achieved if a polyethylene composition is used for producing the cable/a layer of the cable which comprises both an ethylene co-polymer containing hydrolysable silane-groups and an ethylene co-polymer with monomer units comprising hydroxyl groups and/or (meth-)acrylate groups, and/or if a cable comprises a layer which comprises an ethylene co-polymer with monomer units comprising hydroxyl groups and/or (meth-)acrylate groups.

It is disclosed a polyethylene composition comprising.

one or more ethylene co-polymers selected from the group of.

The composition comprising component (B) is according to the invention.

The term "ethylene co-polymer" as used herein is intended to denote a polymer of ethylene in which one or more other type(s) of monomer units than ethylene are present.

Components (A) and (B) may be present in the composition as separate ethylene co-polymers or as one ethylene co-polymer containing the respective groups/monomer units simultaneously.

For example, the polyethylene composition may comprise (A) and (B1) in the form of one ethylene co-polymer comprising hydrolysable silane-groups and monomer units having hydroxyl groups. In the case of (A) and (B) this may be one ethylene co-polymer comprising hydrolysable silane-groups and monomer units having both hydroxyl groups and (meth-)acrylate groups.

The term "(meth)acrylate" is intended to encompass both "acrylate" and "methacrylate".

Component (A) is an ethylene co-polymer containing monomer units with hydrolysable silane-groups. It is known to cross-link polyolefins by means of additives as this improves the properties of the polyolefin such as mechanical strength and chemical heat resistance. Cross-linking may be performed by condensation of silanol groups contained in the composition which can be obtained by hydrolysation of silane groups. A silane-group containing compound can be introduced as a cross-linkable group e.g. by grafting the silane compound onto a polyolefin, i.e. by chemical modification of the polymer by addition of silane groups mostly in a radical reaction, or by copolymerisation of olefin monomers and silane-group containing monomers. Such techniques are known e.g. from <CIT>, <CIT>, <CIT>, <CIT>, <CIT> and <CIT>. If using a graft polymer, this may have been produced e.g. by any of the two methods described in <CIT> and <CIT>, respectively.

Preferably, the silane group containing ethylene co-polymer has been obtained by co-polymerisation. The co-polymerisation is preferably carried out with an unsaturated silane compound represented by the formula.

Special examples of the unsaturated silane compound are those wherein R1 is vinyl, allyl, isopropenyl, butenyl, cyclohexanyl or gamma-(meth)acryloxy propyl; Y is methoxy, ethoxy, formyloxy, acetoxy, propionyloxy or an alkyl-or arylamino group; and R2, if present, is a methyl, ethyl, propyl, decyl or phenyl group.

A preferred unsaturated silane compound is represented by the formula.

wherein A is a hydrocarbyl group having <NUM>-<NUM> carbon atoms, preferably <NUM>-<NUM> carbon atoms.

The most preferred compounds are vinyl trimethoxysilane, vinyl bismethoxyethoxysilane, vinyl triethoxysilane, gamma-(meth)acryloxypropyltrimethoxysilane, gamma(meth)acryloxypropyltriethoxysilane, and vinyl triacetoxysilane.

The silane-group containing ethylene co-polymer preferably contains <NUM> to <NUM> wt. % of monomer units with hydrolysable silane groups, more preferably <NUM> to <NUM> wt. %, and most preferably <NUM> to <NUM> wt.

Preferably, in the composition the monomer units with hydrolysable silane-group are present in an amount of <NUM> to <NUM> mol. %, more preferably of <NUM> to <NUM> mol. %, and most preferably of <NUM> to <NUM> mol.

For cross-linking of such ethylene co-polymers comprising silanol groups, a silanol condensation catalyst must be used. Conventional catalysts are for example tin-organic compounds such as dibutyl tin dilaurate (DBTDL). It is further known that the cross-linking process advantageously is carried out in the presence of acidic silanol condensation catalysts. In contrast to the conventional tin-organic catalysts the acidic catalysts allow cross-linking to quickly take place already at room temperature. Such acidic silanol condensation catalysts are disclosed for example in <CIT> or in <CIT> and <CIT>.

In a preferred embodiment of the invention, the polyethylene composition further comprises a silanol condensation catalyst.

The currently most preferred compounds are dodecyl benzene sulphonic acid and tetrapropyl benzene sulphonic acid.

Preferably, in the polyethylene composition the silanol condensation catalyst is present in an amount of <NUM> to <NUM> wt. %, more preferably of <NUM> to <NUM> wt. %, and most preferably <NUM> to <NUM> wt.

In a preferred embodiment, component (B) is present in an amount of <NUM> wt. % or more, more preferably of <NUM> wt. % or more, and still more preferably of <NUM> wt. % or more in the total polyethylene composition.

Furthermore, it is preferred that component (B) is present in an amount of <NUM> wt. % or less, more preferably of <NUM> wt. % or less, and most preferably of 25wt. % or less in the total polyethylene composition.

Component (B) comprises, or consists of, an ethylene co-polymer containing monomer units with hydroxyl groups and (meth-)acrylate groups.

In said ethylene co-polymer both hydroxyl groups and (meth-)acrylate groups may be present at the same monomer units, or may be present in separate monomer units.

Preferably, in component (B) both hydroxyl groups and (meth-)acrylate groups are present at the same monomer units, more preferably, component (B) comprises, or consists of, an ethylene co-polymer containing (meth-)acrylic acid ester wherein the alcohol component of the ester contains a hydroxyl group, and still more preferably, an ethylene co-polymer containing hydroxyalkyl (meth-)acrylate monomer units.

In a particularly preferred embodiment, component (B) comprises, or consist of, an ethylene co-polymer containing hydroxyalkyl (meth-)acrylate monomer units wherein the alkyl-group is a C<NUM>- to C<NUM>- alkyl group, in particular is methyl, ethyl or propyl.

Further preferred, in component (B) the monomer units having both hydroxyl groups and (meth-)acrylate groups are present in the ethylene co-polymer in an amount of <NUM> mol. % or more, i.e. both hydroxyl groups and (meth-)acrylate groups are each present in the ethylene co-polymer in an amount of <NUM> mol. % or more, more preferably of <NUM> mol. % or more, and still more preferably of <NUM> mol.

Further preferred, in component (B) the monomer units having both hydroxyl groups and (meth-)acrylate groups are present in the ethylene co-polymer in an amount of <NUM> mol. % or less, i.e. both hydroxyl groups and (meth-)acrylate groups are each present in the ethylene co-polymer in an amount of <NUM> mol. % or less, more preferably of <NUM> mol. % or less, and still more preferably of <NUM> mol. % or less, and most preferably <NUM> mol. % and less.

Further preferred, component (B) is present in the composition in an amount so that the monomer units having both hydroxyl groups and (methyl-)acrylate groups are present in the composition in an amount of <NUM> mol. % or more i.e. both hydroxyl groups and (meth-)acrylate groups are each present in the composition in an amount of <NUM> mol. % or more, more preferably of <NUM> mol. % or more, still more preferably of <NUM> mol. % or more, and most preferably of <NUM> mol.

Further preferred, component (B) is present in the composition in an amount so that the monomer units having both hydroxyl groups and (methyl-)acrylate groups are present in the composition in an amount of <NUM> mol. % or less i.e. both hydroxyl groups and (meth-)acrylate groups are each present in the composition in an amount of <NUM> mol. % or less, more preferably of <NUM> mol. % or less, still more preferably of <NUM> mol. % or less, and most preferably of <NUM> mol.

In A component (B1), i.e. an ethylene co-polymer containing monomer units with hydroxyl groups is disclosed.

Component (B1) may comprise, or consist of, an ethylene vinyl alcohol co-polymer.

The vinyl alcohol comonomer units are present in the ethylene vinyl alcohol co-polymer in an amount of <NUM> mol. % or more, of <NUM> mol. % or more, of <NUM> mol. % or of <NUM> mol.

The vinyl alcohol comonomer units are present in the ethylene vinyl alcohol co-polymer in an amount of <NUM> mol. % or less, of <NUM> mol. % or less, of <NUM> mol. % or less and of <NUM> mol.

Preferably, component (B2) comprises, or consists of, an ethylene co-polymer containing monomer units having methyl-, ethyl-, propyl- or butyl-acrylate groups.

In component (B2) the monomer units having (meth-)acrylate groups are preferably present in the ethylene co-polymer in an amount of <NUM> mol. % or more, more preferably of <NUM> mol. % or more, more preferably of <NUM> mol. % or more, more preferably of <NUM> mol. % or more, more preferably of <NUM> mol. % or more, more preferably of <NUM> mol. % or more, more preferably of <NUM> mol. % or more, more preferably of <NUM> mol. % or more, and most preferably of <NUM> mol.

In component (B2) the monomer units having (meth-)acrylate groups are preferably present in the ethylene co-polymer in an amount of <NUM> mol. % or less, more preferably of <NUM> mol. % or less, and still more preferably of <NUM> mol.

Preferably, component (B2) is present in the composition in an amount so that the monomer units having (meth-)acrylate groups are present in the composition in an amount of <NUM> mol. % or more, more preferably of <NUM> mol. % or more, and still more preferably of <NUM> mol.

Preferably, component (B2) is present in the composition in an amount so that the monomer units having (meth-)acrylate groups are present in the composition in an amount of <NUM> mol. % or less, more preferably of <NUM> mol. % or less, and still more preferably of <NUM> mol.

Component (B2) has preferably been produced in a tubular reactor.

In a preferred embodiment, the adhesion strength between the composition and a standard polyurethane resin according to standard test as defined in the experimental section below is at least <NUM> N/mm. Typically, the adhesion strength is not more than <NUM> N/mm, preferably not more than <NUM> N/mm The standard polyurethane resin according to the present application is Protolin <NUM>, commercially available from Lovink-Enertech.

In one embodiment, components (A) and (B), in any of the above-described embodiments, make up at least <NUM> wt. % of the polyethylene composition of the invention, in a further embodiment make up at least <NUM> wt. % of the composition, and in still a further embodiment make up at least <NUM> wt. % of the composition.

It is disclosed a cable comprising a layer (<NUM>) which comprises, or consists of, one or more ethylene co-polymers selected from the group of.

The cable comprising a layer (<NUM>) which comprises component (B) is according to the invention.

All embodiments and preferred embodiments as described for component ( (B) hereinbefore apply also to component (B) of the layer (<NUM>) of the cable of the invention.

For example, the cable may comprise a layer (<NUM>) which comprises, or consists of, component (B) in any of the embodiments as described herein, wherein the layer is a skin layer (i.e. the outermost layer of the cable).

In a preferred embodiment, the adhesion strength between the cable and a standard polyurethane resin according to standard test as defined in the experimental section below is at least <NUM> N/mm.

In one embodiment, the one or more ethylene co-polymers (B) in any of the above-described embodiments, make up at least <NUM> wt. % of layer (<NUM>), in a further embodiment make up at least <NUM> wt. % of layer (<NUM>), and in still a further embodiment make up at least <NUM> wt. % of layer (<NUM>).

In a preferred embodiment, layer (<NUM>) comprises, or consists of, the polyethylene composition according to the present invention in any of the above-described embodiments.

The cable is disclosed that may comprise a layer (<NUM>) which comprises, or consists of, a polyethylene composition comprising, or consisting of, components (A) and (B2) in any of the embodiments as described herein, wherein the layer is a skin layer (i.e. the outermost layer of the cable), and wherein (A) and (B2) may be present in the composition as a ethylene co-polymer comprising both monomer units with hydrolysable silane groups and monomer units with (meth-) acrylate groups.

In the cable of the invention further layer(s) adjacent to layer (<NUM>) may be present which may comprise, or consist of, an ethylene copolymer with hydrolysable silane-groups, a polypropylene, a polyethylene, such as a LLDPE or a HDPE, and/or a thermoplastic.

Preferably, in the cable according to the invention a further layer is present adjacent to layer (<NUM>) which comprises, or consists of, a polyethylene containing hydrolysable silane-groups.

Layer (<NUM>) is preferably a skin layer and/or insulation layer, more preferably is a skin layer.

Preferably, the cable of the invention is a power cable, e.g. a low voltage power cable.

The present invention furthermore relates to the use of one or more ethylene co-polymers selected from the group of.

in any of the embodiments as described herein, for improving the adhesion between a layer of a cable comprising the ethylene co-polymer(s) and a polyurethane resin.

The present invention furthermore relates to the use of an ethylene co-polymer containing monomer units with (meth-)acrylate groups in an amount of more than <NUM> mol. % to <NUM> mol. % or less for improving the adhesion between a layer of a cable comprising the ethylene co-polymer and a polyurethane resin. All embodiments of the ethylene co-polymer containing monomer units with (meth-) acrylate groups as described above are also preferred embodiments of the use of the ethylene co-polymer containing monomer units with (meth-) acrylate groups.

Preferably, the monomer units with (meth-) acrylate groups are present in an amount of <NUM> mol. % or more, more preferably of <NUM> mol. % or more, more preferably of <NUM> mol. % or more, more preferably of <NUM> mol. % or more, more preferably of <NUM> mol. % or more, more preferably of <NUM> mol. % or more, and most preferably <NUM> mol. % or more, in the ethylene co-polymer containing monomer units with (meth-) acrylate groups.

Preferably, the monomer units with (meth-) acrylate groups are present in an amount of <NUM> mol. % or less, more preferably <NUM> mol. % or less, in the ethylene co-polymer containing monomer units with (meth-) acrylate groups.

Preferably, the ethylene co-polymer contains monomers having methyl-, ethylpropyl- or butyl acrylate groups, more preferably methyl acrylate groups.

Preferably, the ethylene co-polymer further contains monomer units with hydrolysable silane-groups. Especially, it is preferable that the monomer units with hydrolysable silane-groups are present in the ethylene co-polymer in an amount of <NUM> to <NUM> mol. %, more preferably in an amount of <NUM> to <NUM> mol. %, and most preferably in an amount of <NUM> to <NUM> mol.

Furthermore, said monomer units with hydrolysable silane-groups may comprise, or consist of, vinyl trimethoxysilane, vinyl bismethoxyethoxysilane, vinyl triethoxysilane, gamma-(meth)acryloxypropyltrimethoxysilane, gamma(meth)acryloxypropyltriethoxysilane, and/or vinyl triacetoxysilane.

In a preferred embodiment of the invention, the monomer units with hydrolysable silane-groups comprise, or consist of, vinyl trimethoxysilane.

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<NUM> of polyethylene (co-)polymers is measured at a temperature <NUM> and at a load of <NUM>.

The adhesion strength is measured according to standard HD <NUM> S1/A3:<NUM>, see part <NUM>, section G. This standard prescribes a minimum adhesion strength of <NUM> N/mm width of cable sample between the cable insulation and the joint cast resin (commonly Polyurethane but also epoxy based is existing).

The data in this invention is based on adhesion to tape samples with a thickness of <NUM> and a length of <NUM>. The tapes are prepared on a Collin TeachLine E20T tape extruder with a <NUM>:<NUM>, 20D Compression screw, D=<NUM>, with a temperature profile of <NUM>/<NUM>/<NUM> at <NUM> rpm. The tape samples are then conditioned for at least <NUM> hours in <NUM> and <NUM>% relative humidity and then cleaned with IPA.

The conditioned tapes are placed on plaques made of HDPE. The plaques contain openings with a width of <NUM>, length of <NUM> and depth of <NUM>. The tape samples are placed above the openings. The tapes are fixed above the openings by another HDPE plaque. The PUR is mixed with the hardener and poured in the openings. The mould is then conditioned for <NUM> hours. The PUR crosslink and hardened during that time. The tape and the PUR sample is removed from the holder and the adhesion force measured in a tensile tester with a special sample holder as described in VDE <NUM>-<NUM>.

The master-batch (MB-CAT) was dry-blended with the polymers/compounds outlined in table <NUM> and <NUM>. Thereafter <NUM> thick tape was extruded with a temperature profile of <NUM>/<NUM>/<NUM> with <NUM> rpm on a Collin TeachLine E20T tape extruder with a <NUM>:<NUM>, 20D Compression screw, D=<NUM>.

Samples containing the crosslinking catalyst master-batch CM-A were crosslinked in <NUM> water for <NUM> prior conditioning for the adhesion test. CM-A was dry-blended into the specific polymer mixture of choice prior the tape extrusion step.

The ethylene co-polymers with the type and amount of comonomer(s) indicated used in the present invention are given in Table <NUM> below. Nucrel 0903HC, Nucrel <NUM>, Surlyn <NUM>, Surlyn <NUM>, Escor <NUM>, Escorene UL00119, Levapren <NUM>, EVAL G156B and EVAL F101A are ethylene co-polymers commercially available from the suppliers as indicated. In table <NUM> below. Polymer C and D are terpolymers.

Polymer A-F were produced in a <NUM> long split feed high pressure tubular reactor (Union Carbide type A-<NUM>). The inner wall diameter is <NUM>. Chain transfer agent (propylene), initiators (t-butylperoxy <NUM>-ethylhexanoate (Luperox <NUM>) and air) and co-monomers were added to the reactor in a conventional manner. Polymerization pressure were <NUM> MPa for all polymers. The maximum polymerization temperature was <NUM> for polymer A and B, <NUM> for Polymer C-G.

CM-A consists of a crosslinking catalyst (<NUM> wt. % dibutyl tin dilaurate) and a stabilizer (2wt. % Irganox <NUM>) which is compounded into an ethylene butyl acrylate (BA) copolymer with a BA content of 17wt-% and MFR<NUM>=<NUM>/<NUM>.

The polyurethane resin (PUR) used in the present invention as cable jointing cast resin is Protolin <NUM>, commercially available from Lovink-Enertech. It is a two component non-filled and non-colored two-component cast resin.

The results of adhesion tests for polyethylene compositions to polyurethane resin Protolin <NUM> are shown in Table <NUM> below. Inventive examples IE1 to IE3 are polyethylene compositions comprising polyethylene polymer(s) containing hydrolysable silane-groups (A) and ethylene copolymer(s) (B).

The results of adhesion tests for ethylene copolymer(s) (B), which may be used to form layer (<NUM>) of the cable of the invention, to polyurethane resin Protolin <NUM> are shown in Table <NUM> below.

Claim 1:
A polyethylene composition comprising
(A) an ethylene co-polymer containing monomer units with hydrolysable silane-groups, and
(B) one or more ethylene co-polymers containing monomer units with hydroxyl groups and (meth-)acrylate groups;
wherein component (B) is present in the composition in an amount so that the monomer units having both hydroxyl groups and (meth-)acrylate groups are present in the composition in an amount of <NUM> mol.% or more and <NUM> mol.% or less; and
wherein components (A) and (B) may be present in the composition as separate ethylene co-polymers or as one ethylene co-polymer containing the respective groups simultaneously.