POLYETHYLENE COMPOSITION FOR IMPROVING ADHESION TO POLYURETHANE RESINS

Abstract

The present invention concerns a polyethylene composition comprising (A) an ethylene co-polymer containing monomer units with hydrolysable silane-groups, and (B) one or more ethylene co-polymers selected from the group of (B1) an ethylene co-polymer containing monomer units with hydroxyl groups, (B2) an ethylene co-polymer containing monomer units with (meth-)acrylate groups, and (B3) an ethylene co-polymer containing monomer units with hydroxyl groups and (meth-)acrylate groups, a cable comprising a layer (1) which comprises one or more ethylene copolymers selected from the group of (B1), (B2) and (B3) and to the use of one or more ethylene co-polymers selected from the group of (B1), (B2) and (B3) for improving the adhesion between a layer of a cable comprising the ethylene co-polymer(s) and a polyurethane resin.

Claims

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 (alkyl-)acrylate groups are present in the composition in an amount of 0.14 mol. % or more and 7 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.

2. Polyethylene composition according to claim 1, wherein component (B) is present in an amount of 2 wt. % or more and 35 wt. % or less in the total polyethylene composition.

3. Cable comprising a layer which comprises a polyethylene composition according to claim 1.

4. The cable according to claim 3, wherein the layer is a skin layer and/or insulation layer.

5. The cable according to claim 3, wherein a further layer is present adjacent to layer which comprises a polyethylene containing hydrolysable silane-groups.

6. The cable according to claim 3, wherein the cable is a power cable. (Currently Amended) A method for producing a cable, comprising: producing a first cable layer comprising an ethylene co-polymer containing monomer units with (meth-) acrylate groups in an amount of more than 4 mol. % to 15 mol. %; adhering the first cable layer to a second cable layer comprising a polyurethane resin.

8. The method of claim 7, wherein the ethylene co-polymer contains monomers having methyl-, ethyl-, propyl- or butyl acrylate groups.

9. The method of claim 7, wherein the ethylene co-polymer further contains monomer units with hydrolysable silane-groups.

10. The method of claim 9, wherein in the ethylene co-polymer the monomer units with hydrolysable silane-groups are present in an amount of 0.1 to 1 mol. %.

11. The method of claim 9, wherein the monomer units with hydrolysable silane-groups comprise vinyl trimethoxysilane, vinyl bismethoxyethoxysilane, vinyl triethoxysilane, gamma-(meth)acryloxypropyltrimethoxysilane, gamma(meth)acryloxypropyltriethoxysilane, and/or vinyl triacetoxysilane.

12. The method of claim 9, wherein the monomer units with hydrolysable silane-groups comprise vinyl trimethoxysilane.

Description

EXAMPLES

[0081] 1. Determination Methods

[0082] a) Melt Flow Rate

[0083] The melt flow rate (MFR) is determined according to ISO 1133 and is indicated in g/10 min. The MFR is an indication of the flowability, and hence the processability, of the polymer. The higher the melt flow rate, the lower the viscosity of the polymer.

[0084] The MFR.sub.2 of polyethylene (co-)polymers is measured at a temperature 190° C. and at a load of 2.16 kg.

[0085] b) Adhesion Strength

[0086] The adhesion strength is measured according to standard HD 603 S1/A3:2008, see part 5, section G. This standard prescribes a minimum adhesion strength of 1 N/mm width of cable sample between the cable insulation and the joint cast resin (commonly Polyurethane but also epoxy based is existing).

[0087] The data in this invention is based on adhesion to tape samples with a thickness of 0.5 mm and a length of 30 cm. The tapes are prepared on a Collin TeachLine E20T tape extruder with a 4.2:1, 20D Compression screw, D=20 mm, with a temperature profile of 135/165/755° C. at 30 rpm. The tape samples are then conditioned for at least 24 hours in 23° C. and 59% relative humidity and then cleaned with IPA.

[0088] The conditioned tapes are placed on plaques made of HDPE. The plaques contain openings with a width of 10 mm, length of 150 mm and depth of 15 mm. 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 24 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 0472-633.

[0089] The master-batch (MB-CAT) was dry-blended with the polymers/compounds outlined in table 1 and 2. Thereafter 1.8 mm thick tape was extruded with a temperature profile of 135/145/155° C. with 30 rpm on a Collin TeachLine E20T tape extruder with a 4.2:1, 20D Compression screw, D=20 mm.

[0090] 2. Experimental Methods

[0091] a) Crosslinking

[0092] Samples containing the crosslinking catalyst master-batch CM-A were crosslinked in 90° C. water for 24 h prior conditioning for the adhesion test. CM-A was dry-blended into the specific polymer mixture of choice prior the tape extrusion step.

[0093] 3. Materials

[0094] a) Ethylene Co-Polymers

[0095] The ethylene co-polymers with the type and amount of comonomer(s) indicated used in the present invention are given in Table 1 below. Nucrel 0903HC, Nucrel 1202, Surlyn 9320, Surlyn 8320, Escor 6060, Escorene UL00119, Levapren 400, EVAL G156B and EVAL F101A are ethylene co-polymers commercially available from the suppliers as indicated. In table 1 below. Polymer C and D are terpolymers.

[0096] Polymer A-F were produced in a 660 m long split feed high pressure tubular reactor (Union Carbide type A-1). The inner wall diameter is 32 mm. Chain transfer agent (propylene), initiators (t-butylperoxy 2-ethylhexanoate (Luperox 26) and air) and co-monomers were added to the reactor in a conventional manner. Polymerization pressure were 230 MPa for all polymers. The maximum polymerization temperature was 310° C. for polymer A and B, 285° C. for Polymer C-G.

TABLE-US-00001 TABLE 1 Ethylene co-polymers Comonomer(s) Content, Content, MFR.sub.2, Name Type(s) wt. % mol. % g/10 min Supplier Polymer A VTMS 1.2 0.23 0.9 Borealis Polymer B VTMS 1.9 0.37 0.9 Borealis Polymer C BA/VTMS   4/1.2 0.90/0.24 0.9 Borealis Polymer D MA/VTMS 22.5/1.4  8.7/0.32 3.5 Borealis Polymer E BA 17 4.2 1.5 Borealis Polymer F MA 20 7.4 7.5 Borealis Polymer G HEMA 8 2.6 1.2 Borealis Nucrel MAA 9 3.0 3 Du Pont 0903HC Nucrel 1202 MAA 12 4.3 1.5 Du Pont Surlyn 9320 Zn- n.a. n.a. 0.8 Du Pont ionomer Surlyn 8320 Na- n.a. n.a. 1 Du Pont ionomer Escor 6060 AA 8.5 3.5 8 Exxon Escorene VA 9 0.7 Exxon UL00109 Escorene VA 19 7.1 0.7 Exxon UL00119 Levapren 400 VA 40 18 3 Lanxess EVAL G156B VOH 48 36 6 Kuraray EVAL F101A VOH 32 23 1.6 Kuraray AA - acrylic acid BA - butyl acrylate MA - methyl acrylate MAA - methyl acrylic acid HEMA - hydroxy ethyl methacrylate VA - vinylacetate VOH - vinylalcohol VTMS - vinyl trimethoxy silane n.a. - not available

[0097] b) Crosslinking Catalyst Master Batch CM-A

[0098] CM-A consists of a crosslinking catalyst (1 wt. % dibutyl tin dilaurate) and a stabilizer (2wt. % Irganox 1010) which is compounded into an ethylene butyl acrylate (BA) copolymer with a BA content of 17wt-% and MFR.sub.2=8g/10 min.

[0099] c) Polyurethane Resin (PUR)

[0100] The polyurethane resin (PUR) used in the present invention as cable jointing cast resin is Protolin 2000, commercially available from Lovink-Enertech. It is a two component non-filled and non-colored two-component cast resin

[0101] 4. Results

[0102] The results of adhesion tests for polyethylene compositions to polyurethane resin Protolin 2000 are shown in Table 2 below. Inventive examples 1E1 to 1E3 are polyethylene compositions comprising polyethylene polymer(s) containing hydrolysable silane-groups (A) and ethylene copolymer(s) (B).

TABLE-US-00002 TABLE 2 Adhesion of polyethylene compositions to cable jointing cast resin Protolin 2000 Comono- wt. % mol. % Ad- Exam- mer Active active hesion ple Ethylene copolymer type(s) groups groups N/mm IE1 10 wt. % Polymer G HEMA/ 0.8/1.7 0.26/0.33 7.2 85 wt.% Polymer B VTMS  5 wt. % CM-A IE2 15 wt. % Polymer G HEMA/ 1.2/1.6 0.39/0.31 9 80 wt. % Polymer B VTMS  5 wt. % CM-A IE3 Polymer D MA/ 22.5/1.4   8.7/0.32 >10 VTMS CE1 Polymer A VTMS 1.2 0.23 0.1 CE2 Polymer C BA/   4/1.2  0.9/0.24 0.4 VTMS CE3  5 wt. % Polymer G HEMA/ 7.6/1.8 0.13/0.35 0.4 90 wt. % Polymer B VTMS  5 wt. % CM-A

[0103] The results of adhesion tests for ethylene copolymer(s) (B), which may be used to form layer (1) of the cable of the invention, to polyurethane resin Protolin 2000 are shown in Table 3 below.

TABLE-US-00003 TABLE 3 Adhesion of polyethylene copolymers to cable jointing cast resin Protolin 2000 Comono- w-% Mole-% Ad- Exam- mer Active active hesion ple Ethylene copolymer type(s) groups groups N/mm IE4 EVAL G156B VOH 48 36 >10 IE5 EVAL F101A VOH 32 23 >10 IE6 Polymer G HEMA 8 2.6 >10 IE7 Polymer F MA 20 7.4 1.9 IE8 Polymer E BA 17 4.2 1.0 CE4 Escorene UL00109 VA 9 3.0 <0.1 CE5 Escorene UL00119 VA 19 7.1 <0.1 CE6 Levapren 400 VA 40 18.0 <0.1 CE7 Nucrel 0903 HC MAA 9 3.0 <0.1 CE8 Nucrel 1202 MAA 12 4.3 <0.1 CE9 Escor 6060 AA 8.5 3.5 <0.1 CE10 Surlyn 9320 Zn- n.a. unknown <0.1 ionomer CE11 Surlyn 8320 Na- unknown unknown <0.1 ionomer

[0104] The results presented in tables 2 and 3 show that vinyl trimethoxy silane, vinyl acetate, meth acrylic acid, acrylic acid and ionomer functionalities give no improvement in adhesion towards PUR cast resins (CE 4-11). On the other hand, acrylate (1E3, 7 and 8) and hydroxyl functional copolymers have a great positive effect (IE 4 and 5) and can give adhesion forces by far exceeding 1 N/mm i.e. fulfilling the adhesion requirement of HD603S1. This is also true for copolymers having hydroxy and acrylate functionalities in the same co-monomers (IE1, 2 and 6). It has also been shown that adhesion strength can be reached by using an acrylate or hydroxyl functional polymer as blend into a polyolefin like Polymer A which by itself showing hardly no adhesion towards PUR (IE1).