Low Voltage Power Cable With Insulation Layer Comprising Polyolefin Having Polar Groups, Hydrolysable Silane Groups and Which Includes Silanol Condensation

Abstract

The present invention relates to a low voltage power cable comprising an insulation layer with a density below 1100 kg/m3 which comprises a polyolefin comprising 0.02 to 4 mol % of a compound having polar groups and further comprises a compound having hydrolysable silane groups and include 0.0001 to 3 wt.-% of a silanol condensation catalyst. Furthermore, the present invention relates to a process for the production of said low voltage power cable and to the use of a polyolefin comprising 0.02 to 4 mol % of a compound having polar groups in the production of an insulation layer for a low voltage power cable.

Description

The present invention will now be further illustrated by way of examples and the following figures:

FIG. 1 shows the tensile strength at break as a function of the preheating temperature of the conductor for polymer A (Comp.) and polymer D, and

FIG. 2 shows the elongation at break as a function of the preheating temperature of the conductor for polymer A (Comp.) and polymer D.

EXAMPLES

1. Compositions Used for Production of Insulation Layers

a) Polymer A (comparative) is a ethylene copolymer containing 0.23 mol % (1.25 wt %) of vinyltrimethoxysilane (VTMS), which has been obtained by free radical copolymerisation of ethylene monomers and VTMS comonomers. Polymer A has a density of 922 kg/m³ and an MFR₂ (190° C., 2.16 kg) of 1.00 g/10 min.

b) Polymer B (comparative) is a ethylene copolymer containing 0.25 mol % (1.3 wt %) of vinyltrimethoxysilane (VTMS), which has been obtained in the same way as polymer A. Polymer B has a density of 925 kg/m³ and an MFR₂ (190° C., 2.16 kg) of 1.1 g/10 min.

c) Polymer C is a ethylene copolymer containing 0.25 mol % (1.3 wt %) of vinyltrimethoxysilane (VTMS) and 0.33 mol % (1.5 wt %) of butyl acrylate (BA), which has been obtained in the same way as polymer A, except that during polymerisation butylacrylate comonomers were added. Polymer C has a density of 925 kg/m³ and an MFR₂ (190° C., 2.16 kg) of 0.9 g/10 min.

d) Polymer D is a ethylene copolymer containing 0.26 mol % (1.3 wt %) of vinyltrimethoxysilane (VTMS) and 0.91 mol % (4.0 wt %) of butyl acrylate (BA), which has been obtained in the same way as polymer A, except that during polymerisation butylacrylate comonomers were added. Polymer D has a density of 925 kg/m³ and an MFR₂ (190° C., 2.16 kg) of 0.8 g/10 min.

e) Polymer E is a ethylene copolymer containing 0.30 mol % (1.5 wt %) of vinyltrimethoxysilane (VTMS) and 1.6 mol % (7 wt %) of butyl acrylate (BA), which has been obtained in the same way as polymer A, except that during polymerisation butylacrylate comonomers were added. Polymer E has an MFR₂ (190° C., 2.16 kg) of 1.69 g/10 min.

f) Polymer F is a ethylene copolymer containing 0.34 mol % (1.7 wt %) of vinyltrimethoxysilane (VTMS) and 2.9 mol % (12 wt %) of butyl acrylate (BA), which has been obtained in the same way as polymer A, except that during polymerisation butylacrylate comonomers were added. Polymer F has a density of 925 kg/m³ and an MFR₂ (190° C., 2.16 kg) of 1.50 g/10 min.

g) Polymer G is a ethylene copolymer containing 1.8 mol % (8 wt %) of butyl acrylate (BA), which has been obtained in the same way as polymer A, except that during polymerisation butylacrylate comonomers were added, but no silane group containing comonomers. Polymer G has a density of 923 kg/m³ and an MFR₂ (190° C., 2.16 kg) of 0.50 g/10 min.

h) Polymer H is a ethylene copolymer containing 4.3 mol % (17 wt %) of butyl acrylate (BA), which has been obtained in the same way as polymer A, except that during polymerisation butylacrylate comonomers were added, but no silane group containing comonomers. Polymer H has a density of 925 kg/m³ and an MFR₂ (190° C., 2.16 kg) of 1.20 g/10 min.

i) Polymer I is an ethylene copolymer containing 0.43 mol % (1.9 wt %) vinyltrimethoxysilane (VTMS) and 4.4 mol % (17 wt %) of butylacrylate (BA), which has been obtained in the same way as polymer A, except that polymerisation butylacrylate comonomers were added. Polymer I has an MFR₂ (190° C., 2.16 kg) of 4.5 g/10 min and a density of 928 kg/m³.

j) Catalyst masterbatch CM-A consists of 1.7 wt % dodecylbenzenesulphonic acid crosslinking catalyst, drying agent and antioxidants compounded into an ethylene butyl acrylate (BA) copolymer with an BA content of 17 wt-% and MFR₂=8 g/10 min.

k) Polyurethane based cast resin PU 300 is a naturally coloured unfilled two component system intended to be used for 1 kilovolt cable joints (in accordance with VDE 0291 teil 2 type RLS-W). It has a density of 1225 kg/m³ and a hardness (Shore D) of 55. The cast resin is produced by Höhne GmbH.

l) Polyurethane based cast resin PU 304 is a blue filled two component system intended to be used for 1 kilovolt cable joints. It has a density of 1340 kg/m³ and a hardness (Shore D) of 60. The cast resin is produced by Höhne GmbH.

The amount of butyl acrylate in the polymers was measured by Fourier Transform Infrared Spektroscopy (FTIR). The weight-%/mol-% of butyl acrylate was determined from the peak for butyl acrylate at 3450 cm⁻¹, which was compared to the peak of polyethylene at 2020 cm⁻¹.

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

2. Production of the Low Voltage Power Cables

Cables consisting of an 8 mm² solid aluminium conductor and an insulation layer thickness of 0.8 mm (for the samples in table 1) and 0.7 mm (for the samples in FIG. 1 and FIG. 2) were produced in a Nokia-Maillefer 60 mm extruder at a line speed of 75 m/min by applying the following conditions:

• Die: Pressure (wire guide with a diameter of 3.65 and a pressure die with a diameter of 5.4 mm for the samples in table 1 and wire guide with a diameter of 3.0 and a pressure die with a diameter of 4.4 mm for the samples in FIG. 1 and FIG. 2).
• Conductor: Non-preheated, if not anything else mentioned.
• Cooling bath temperature: 23° C.
• Screws: Elise
• Temperature profile: 150, 160, 170, 170, 170, 170, 170, 170° C. for the samples in Table 1, FIG. 1 and FIG. 2.

For the crosslinked samples, the catalyst masterbatch was dry blended into the polymers prior to extrusion.

3. Test Methods

a) Mechanical and Adhesive Properties

The mechanical evaluation of the cables was performed according to ISO 527 and the test of adhesion to polyurethane was based on VDE 0472-633.

b) Ageing with PVC

A plaques of the insulation material is placed in an oven at 100° C. for 168 hours. PVC plaques are placed on both side of the insulation material plaque. Dumbells are punched out from the plaques after the testing and then conditioned in 23° C. and 50% humidity for 24 hours. The tensile tests are then performed according to ISO 527. The samples that have been aged together with PVC are also weighten before and after ageing. Samples that have been aged in an oven at 100° C. for 168 hours without contact to PVC and also other samples that are unaged have been tested according to ISO 527.

4. Results

The results given in Table 1 show that both for crosslinked and for non-crosslinked (thermoplastic) polymers E, F and G, H, respectively, the mechanical properties are improved upon incorporation of the polar group containing butyl acrylate comonomers into the polymers.

Furthermore, in Table 2 it is shown that the adhesion to polyurethane of polymers C and D is improved even for low amounts of incorporated butylacrylate so that good adhesion to polyurethane according to VDE 0472-633 is obtained.

FIG. 1 and FIG. 2 show that the mechanical properties of low voltage power cables according to the invention are improved when the insulation layer is extruded at the same conductor preheating temperature as the comparative material. In particular, for the elongation at break, this applies also for the case where no preheating at all is applied.

Table 3 shows, surprisingly, that polar groups containing insulation materials have improved resistance to the deterioration of the mechanical properties caused by the plasticiser in the PVC even then the polar groups containing insulation material adsorb more plasticiser compared to the reference.

	TABLE 1
	Material
	Polymer
	A + 5	Polymer	Polymer
	weight-%	E + 5	F + 5
	CM-A	weight-%	weight-%	Polymer A
	(Comparative)	CM-A	CM-A	(Comparative)	Polymer G	Polymer H
Comments	Crosslinked	Thermoplastic
MFR2 (g/	1.00	1.69	1.50	1.00	0.50	1.20
10 min)
Density (kg/m3)	922	—	925	922	923	925
VTMS-	1.25	1.5	1.7	1.25	0	0
content
(weight-%)
BA-content	0	7	12	0	8	17
(weight-%)
Elongation	229	285	272	279	403	530
at break (%)
Tensile	15.5	15.9	17.7	11.0	11.9	11.2
strength at
break (MPa)

	TABLE 2
	Relative adhesion
	to polyurethane, %
	Giessharz PU300	Giessharz PU304
Cast resin type	1 kV, unfilled	Blau 1 kV, filled
Polymer A + 5 weight-% CM-A	100	100
(Comparative)
Polymer C + 5 weight-% CM-A	120	500
Polymer D + 5 weight. % CM-A	290	360
85 weight-% Polymer A + 10	No data available	290
weight-%
Polymer I + 5 weight-% CM-A

TABLE 3
	Polymer A + 5
	weight-%	Polymer D + 5
	CM-A	weight-%
Material	(comparative)	CM-A
BA-content (weight-%)	0	4
Elongation at break
Difference after 168 hours in 100 degrees C. without	−11	−19
PVC (%)
Difference after 168 hours in 100 degrees C. with	−42	−14
PVC (%)
Tensile stress at break
Difference after 168 hours in 100 degrees C. without	1	−12
PVC (%)
Difference after 168 hours in 100 degrees C. with	−39	−13
PVC (%)
Plasticiser adsorption
Weight increase after 168 hours in 100 degrees C.	19	31
with PVC (%)

Claims

1. A low voltage power cable comprising an insulation layer with a density below 1100 kg/m3 which comprises a polyolefin having incorporated 0.02 to 4 mol % of a compound having polar groups, and further having incorporated a compound having hydrolysable silane groups, and which further comprises 0.0001 to 3 wt.-% of a silanol condensation catalyst.

2. A low voltage power cable according to claim 1, wherein the polar groups are selected from siloxane, amide, anhydride, carboxylic, carbonyl, hydroxyl, ester and epoxy groups.

3. A low voltage power cable according to claim 2, wherein the compound having polar groups is butyl acrylate.

4. A low voltage power cable according to claim 1, wherein the polyolefin comprises 0.1 to 2.0 mol % of the compound having polar groups.

5. A low voltage power cable according to claim 1, wherein the polyolefin comprises 0.001 to 15 wt. % of the compound having silane groups.

6. A low voltage power cable according to claim 1, wherein the polymer composition further comprises a sulphonic acid or an organic tin compound as a silanol condensation catalyst.

7. A low voltage power cable according to claim 1, wherein the thickness of the insulation layer is 0.4 to 3 mm.

8. A process for producing a low voltage power cable comprising a conductor and an insulation layer, which layer comprises a polyolefin having incorporated 0.02 to 4 mol % of a compound having polar groups, and further having incorporated a compound having hydrolysable silane groups, and which further comprises 0.0001 to 3 wt % of a silanol condensation catalyst, which process comprising extrusion of an insulation layer on a conductor which is preheated to a maximum temperature of 65° C.

9. A process according to claim 8 wherein the extrusion of the insulation layer is performed on the non-preheated conductor.

10. The production of an insulation layer for a low voltage power cable comprising forming said insulation layer from a polyolefin comprising 0.02 to 4 mol % of a compound having polar groups and further having incorporated a compound having hydrolysable silane groups, and which further comprises 0.0001 to 3 wt % of a silanol condensation catalyst.

11. A low voltage power cable according to claim 5, wherein the polymer composition further comprises a sulphonic acid or an organic tin compound as a silanol condensation catalyst.

12. A low voltage power cable according to claim 2 wherein the thickness of the insulation layer is 0.4 to 3 mm.

13. A low voltage power cable according to claim 3 wherein the thickness of the insulation layer is 0.4 to 3 mm.

14. A low voltage power cable according to claim 4 wherein the thickness of the insulation layer is 0.4 to 3 mm.

15. A low voltage power cable according to claim 5 wherein the thickness of the insulation layer is 0.4 to 3 mm.

16. A low voltage power cable according to claim 6 wherein the thickness of the insulation layer is 0.4 to 3 mm.