MOISTURE CUREABLE POLYMER FOR FLEXIBLE CABLES

Abstract

The invention relates to the use of a polyethylene composition comprising one or more ethylene copolymer(s) wherein the ethylene copolymer is a terpolymer containing monomer units with polar groups and monomer units with hydrolysable silane groups, wherein the monomer units with polar groups are present in an amount of more than 5 mol. % based on the total polyethylene composition, and a silanol condensation catalyst in an amount of 0.0001 to 5 wt. %, based on the total polyethylene composition for improving the adhesion between a layer of a cable comprising the polyethylene composition and a polyurethane resin.

Claims

1. A method, comprising: adhering a layer of a cable comprising a polyethylene composition to a polyurethane resin; wherein the polyethylene composition comprises: a) one or more ethylene copolymer(s) wherein the ethylene copolymer is a terpolymer containing monomer units with polar groups and monomer units with hydrolysable silane groups, wherein the monomer units with polar groups are present in an amount of more than 5 mol. % based on the total polyethylene composition, and b) a silanol condensation catalyst in an amount of 0.0001 to 5 wt. %, based on the total polyethylene composition.

2. The method of claim 1, wherein the monomer units with polar groups are butyl acrylate, ethyl acrylate, methyl acrylate and/or methyl methacrylate.

3. The method of claim 1, wherein the monomer units with polar groups are present in an amount of not more than 25 mol. % based on the total polyethylene composition.

4. The method of claim 1, wherein the monomer units with hydrolysable silane groups comprise vinyl trimethoxy silane, vinyl bismethoxyethoxy silane, vinyl triethoxy silane, gamma-(meth)acryl-oxypropyltrimethoxy silane, gamma(meth)acryloxypropyltriethoxy silane, vinyl triacetoxy silane and mixtures thereof.

5. The method of claim 1, wherein the monomer units with hydrolysable groups are present in an amount of 0.001 wt. % to 15 wt. % based on the total polyethylene composition.

6. The method of claim 1, wherein the silanol condensation catalyst b) comprises a sulphonic acid based catalyst or a tin based catalyst.

7. The method of claim 6, wherein the sulphonic acid based catalyst comprises dodecyl benzene sulphonic acid, tetrapropyl benzene sulphonic acid, alkylated naphthalene sulphonic acid, arylalkyl sulphonic acid, alkylated aryl disulphonic acid or mixtures thereof.

8. The method of claim 6, wherein the polyethylene composition further comprises c) a scorch retardant additive.

9. The method of claim 8, wherein the scorch retardant additive c) is present in an amount of 0.0003 mole/1000 g polyethylene composition to 0.6 mole/1000 g polyethylene composition.

10. The method of claim 8, wherein the scorch retardant additive c) comprises an alkoxy silane.

11. The method of claim 8, wherein the polyethylene composition has an MFR.sub.2 (2.16 kg) of 0.1 to 50 g/10 min measured according to ISO 1133.

12. The method of claim 8, wherein the layer is an insulation layer or a sheath layer.

13. The method of claim 8, wherein the cable further comprises a skin layer.

Description

EXAMPLES

[0060] 1. Determination Methods

[0061] a) Melt Flow Rate (MFR)

[0062] 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.

[0063] The MFR.sub.2 of polyethylene (co-)polymers is measured at a temperature 190° C. and at a load of 2.16 kg.

[0064] b) Density

[0065] Density of the polymer was measured according to ISO 1183-1:2004 Method A on compression moulded specimen prepared according to EN ISO 1872-2 and is given in kg/m.sup.3

[0066] c) FTIR

[0067] The amount of monomer units with polar groups and monomer units with hydrolysable silane-groups can be determined using Fourier Transform Infrared Spectroscopy (FTIR).

[0068] In particular, the amount of butyl acrylate (BA) in the polymers was measured by Fourier Transform Infrared Spectroscopy (FTIR). The wt. %/mole. % of butyl acrylate was determined from the peak for butyl acrylate at 3450 cm.sup.−1, which was compared to the peak of polyethylene at 2020 cm.sup.−1.

[0069] The amount of vinyl trimethoxy silane in the polymers was measured by Fourier Transform Infrared Spektroscopy (FTIR). The wt. % of vinyl trimethoxy silane was determined from the peak for silane at 945 cm.sup.−1, which was compared to the peak of polyethylene at 2665 cm.sup.−1.

[0070] d) Adhesion Strength

[0071] 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).

[0072] 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 iso-propyl alcohol.

[0073] 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 polyurethane resin (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.

[0074] The crosslinking catalyst masterbatch was dry-blended with the polymers/compounds outlined in table 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.

[0075] e) Crosslinking speed

[0076] 5 wt. % of a crosslinking catalyst is added to the formulations given below, and Hot Set elongation in % is evaluated on 1 mm tapes after storage at 23° C. at 55% relative humidity for 4, 7 and 14 days.

[0077] f) Mechanical hardness Shore A and Shore D

[0078] The mechanical hardness Shore A and Shore D are measured according to ISO 868 on 80×10×4 type B specimens. The specimens are moulded according to EN ISO 1872-2 for ethylene based polymers. For Shore D a 30° cone for indentation is used. For both Shore A and D measurements the value 1 sec after indentation is taken.

[0079] g) Flexural Modulus

[0080] Flexural Modulus Flexural modulus was determined according to ISO 178. The test specimens were extruded tapes with a thickness of 2 mm. The length of the span between the supports was 64 mm, the test speed was 2 mm/min and the load cell was 100 N. The equipment used was an Alwetron TCT 25. The specimen were conditioned for minimum 16 hours at 23+/−2° C. and 50% relative humidity prior testing.

[0081] h) Hot Set Elongation (%)

[0082] To determine that the crosslinkable polyethylene composition are properly cured the hot set elongation and permanent set are determined according to IEC 60811-507, by measuring thermal deformation at 200° C. and at a load of 20 N/cm.sup.2 is used. Three dumb-bell test samples are prepared from a tape consisting of a polyethylene composition to be tested by cutting test samples from the tape. Each test sample is fixed vertically from upper end thereof in the oven and the load of 20 N/cm.sup.2 are attached to the lower end of each test sample. After 15 min, 200° C. in oven the distance between the premarked lines is measured and the percentage hot set elongation is calculated and expressed as Hot Set elongation in %.

[0083] For permanent set %, the tensile force (weight) is removed from the test samples and after recovered in 200° C. for 5 minutes and then let to cool in room temperature to ambient temperature. The permanent set % is calculated from the distance between the marked lines.

[0084] i) Tensile Strength at Break and Tensile Strain at Break (Elongation at Break)

[0085] The tensile strength at break and tensile strain at break were measured in accordance with ISO 527-1: 2012 at 23° C. and 50% relative humidity on an Alwetron TCT 10 tensile tester at a speed of 250 mm/min. The extensometer used was MFE-900. The test specimens were extruded tapes with a thickness of 2 mm. The specimens were conditioned for minimum 16 hours at 23+/−2° C. and 50% relative humidity prior testing. The average value out of 6 to 10 samples is reported herein.

[0086] j) Tape Appearance

[0087] The tape appearance is evaluated with the bare eye. Extruded tapes are prepared as described above. The occurrence of many gels on the tape is graded as (−−), occurrence of some gels as (−), a good appearance as (+) and excellent appearance as (++).

[0088] 2. Experimental Methods

[0089] Formulations containing the crosslinking catalyst masterbatch were crosslinked in 90° C. water for 24 h prior conditioning for the adhesion tests. The crosslinking catalyst masterbatch (CM) was dry-blended into the specific formulation of choice prior to the tape extrusion step.

[0090] 3. Materials

[0091] a) Ethylene Copolymers

[0092] The ethylene copolymers with the type and amount of comonomer indicated used in the present invention are given in Table 1 below. In table 1 below, Polymers B and C are terpolymers.

[0093] Polymers A, B and C 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 both polymers. The maximum polymerization temperature was 310° C. for polymer A, 285° C. for Polymer B and C.

TABLE-US-00001 TABLE 1 Ethylene copolymers Material Polymer A Polymer B Polymer C MFR2, 1 0.5 3.5 g/10 min Density, 923 930 945 kg/m.sup.3 VTMS 1.1 1.05 1.4 content, wt. % Polar group — BA MA Polar group 0 9.5/2.3 22.5/8.7 content, wt. %/mol. % BA: butyl acrylate MA: methyl acrylate VTMS: vinyl trimethoxy silane

[0094] The scorch retarding agent (SRA) was hexadecyl trimethoxy silane (HDTMS) and was added in the amounts as indicated to Polymers A to C by preheating the pellets to 60° C. for 12 hours. Thereafter the pellets were forwarded to a drum blender in which the pellets were impregnated with the given amount of HDTMS and mixing performed for 20 minutes. The impregnated pellets were then kept at 60° C. for further 24 hours. Thereby, seven formulations were obtained as shown in table 2 below.

TABLE-US-00002 TABLE 2 Formulations Formulation 1 2 3 4 5 6 7 Material Polymer A Polymer A Polymer B Polymer C Polymer C Polymer C Polymer C SRA, wt. % 0.35 0.35 1 0 1 2 3

[0095] b) Crosslinking Catalyst Masterbatch CM-A

[0096] CM-A consists of 1.7 wt. % dodecylbenzene sulphonic acid and a stabilizer, 2 wt. % Irganox 1010, and 3 wt. % of HDTMS which are compounded into an ethylene butylacrylate (BA) copolymer with a BA content of 17 wt. % and MFR.sub.2=8 g/10 min.

[0097] c) Crosslinking Catalyst Masterbatch CM-B

[0098] CM-B consists of 3.6 wt. % dioctyl tin dilaureate (DOTDL) and a stabilizer, 2 wt. % Irganox 1010 and 1 wt. % HDTMS which are compounded into an ethylene butylacrylate (BA) copolymer with a BA content of 17 wt. % and MFR.sub.2=8 g/10 min.

[0099] d) 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 comparative (CE) and inventive examples (IE) were prepared by dry-blending the crosslinking silanol condensation catalyst masterbatch as indicated to Formulations 1 to 7 before extrusion. The amounts and type of catalysts added are given in table 3 below.

TABLE-US-00003 TABLE 3 Compositions of comparative and inventive examples CE1 CE2 CE3 IE1 IE2 IE3 IE4 Formulation 1 2 3 4 5 6 7 catalyst, wt. % CM-A, 5 CM-B, 5 CM-A, 5 CM-A, 5 CM-A, 5 CM-A, 5 CM-A, 5

[0103] Formulations 1 to 7 were crosslinked at ambient conditions (23° C., 55% relative humidity) for 10 days. The results after crosslinking the examples are shown in table 4 below.

TABLE-US-00004 TABLE 4 Properties of examples after crosslinking CE1 CE2 CE3 IE1 IE2 IE3 IE4 SRA, wt. % 0.35 0.35 1 0 1 2 3 Scorch Test: ++ ++ ++ −− − + ++ tape appearance Shore D 52 52 46 25 Shore A 82 93 Flexural 170 236 100 22 26 24 25 Modulus, MPa Tensile 21 16 19 14 15 15 19 strength at break, MPa Tensile 439 526 224 344 375 390 565 strain at break, % Hot Set 82 448 32 29 23 25 26 elongation, % Tape appearance: Excellent (++), Good (+), gels (−), many gels (−−)

[0104] The mechanical properties and hot-set data of the inventive examples such as the tensile strength and elongation at break are far over the requirement for flexible cables as expressed in e.g. EN 506363-1 (insulations) and EN50363-2-1 (jacketing) with respect to tensile strength. The requirement is between 5-7 MPa for the different EPR or EVA type of insulations. The flexural modulus is significantly improved for the inventive examples versus the comparative examples. The inventive examples also show a high tensile strain at break (elongation at break) of more than 200% and a tensile strength of more than 6 MPa.

[0105] The inventive examples meet, at the same time, the EN 50525 standards for a typical flexural modulus of below 30 MPa.

[0106] Furthermore, all inventive examples IE1 to IE4 show a high crosslinking degree as evidenced by the Hot Set elongation after 15 min, see table 4. The amount of SRA has only minor effects on the Hot Set results of the inventive examples. Increasing the amount of SRA (1E2 to IE4) lowers the Hot Set value versus the inventive example without SRA (IE1).

[0107] Table 5 shows the results of the crosslinking speed of comparative examples CE1 and CE3 in comparison to IE4 after adding 5 wt. % of crosslinking catalyst CM-A.

TABLE-US-00005 TABLE 5 Crosslinking speed Days at ambient conditions (23° C., 55% relative humidity) 4 7 14 CE1, % 140 94 67 CE3, % 37 31 30 IE4, % 27 26 25

[0108] The inventive terpolymer IE4 shows an outstanding crosslinking speed and is fully crosslinked after 4 days. Also the final Hot Set level is decreased with increasing acrylate concentration, as can be seen from the comparison of examples CE3 with IE4.

[0109] Table 6 shows the results of the adhesion to PUR cast resin Protolin 2000 comparative examples CE1 and CE3 in comparison to IE4 after adding 5 wt. % of crosslinking catalyst CM-A.

TABLE-US-00006 TABLE 6 Adhesion towards PUR joint cast resin Adhesion, N/mm CE1 0.1 CE3 0.5 IE4 >10

[0110] According to standard HD 603 S1/A3:2008 an adhesion strength of at least 1 N/mm is required between the insulation of the cable and the PUR case resin. As can be seen from table 6, the adhesion of IE4 to PUR is significantly higher than this lower limit.