Cross-linkable ethylene polymer composition comprising epoxy-groups and a cross-linking agent

Abstract

The present invention relates to an ethylene polymer composition comprising: (A) an ethylene polymer comprising epoxy-groups, and (B) a cross-linking agent comprising: (B1) an organo-metallic Lewis acid, and at least one of: (B2) a compound comprising at least one amino group; and (B3) a compound comprising at least one hydroxyl group.

Claims

1. An ethylene polymer composition comprising: (A) an ethylene polymer comprising epoxy-groups, and (B) a cross-linking agent comprising (B1) an organo-metallic Lewis acid, and at least one of: (B2) a compound comprising at least one amino group; and (B3) a compound comprising at least one hydroxyl group.

2. The ethylene polymer composition according to claim 1, wherein said organo-metallic Lewis acid (B1) is a compound according to formula (I):
M.sup.m+L.sub.n  (I) wherein M is an element selected from lanthanides or an element of groups 2 to 14 of the IUPAC periodic table (1989) except the elements of the group 7 of the IUPAC periodic table (1989) and Be, C, Si, Ge, Tl, Pb, Tc, Hg and Cd; each L is the same or different and is a ligand linked to M; and m is 1 to 4, and n is 1 to 4, with the proviso that m-n is 0.

3. The ethylene polymer composition according to claim 1, wherein said organo-metallic Lewis acid is a compound of formula: TiL.sub.4.

4. The ethylene polymer composition according to claim 1, wherein each L is a saturated hydrocarbyl group, each hydrocarbyl group independently containing one or more hetero atoms selected from N, O, P, S, or Si.

5. The ethylene polymer composition according to claim 1, wherein said compound (B2) is a compound selected from the group consisting of: a saturated aliphatic (mono, di, or tri)amine with up to 50 carbon atoms; an unsaturated aliphatic (mono, di, or tri)amine with up to 50 carbon atoms; and an aromatic hydrocarbyl with up to 50 carbon atoms.

6. The ethylene polymer composition according to claim 1, wherein said compound (B2) comprises at least two amino substituents.

7. The ethylene polymer composition according to claim 1, wherein said compound (B3) is selected from aliphatic di- to hexa-alcohols or aromatic di- to hexa-alcohols.

8. The ethylene polymer composition according to claim 1 wherein the epoxy-group-containing monomer units are glycidyl methacrylate comonomer units.

9. The ethylene polymer composition according to claim 1 wherein the amount of epoxy-group-containing monomer units is at least 0.1 wt %, based on the amount of olefin polymer (A).

10. The ethylene polymer composition according to claim 1, wherein the content of epoxy-group-containing monomer units is 20 wt % or less, based on the amount of olefin polymer (A).

11. A process for cross-linking the ethylene polymer composition of claim 1, the process comprising cross-linking the ethylene polymer comprising epoxy-groups (A) using the cross-linking agent (B).

12. The process according to claim 11, wherein said cross-linking takes place for 2 to 10 minutes.

13. The process according to claim 11, wherein said cross-linking is carried out at a temperature of at least 150° C.

14. A method of use of a cross-linking agent (B) comprising: (B1) an organo-metallic Lewis acid, and at least one of: (B2) a compound comprising at least one amino group; and (B3) a compound comprising at least one hydroxyl group; the method comprising using the cross-linking agent (B) for cross-linking of an ethylene polymer comprising epoxy-groups (A).

15. The ethylene polymer composition according to claim 1, wherein said compound (B2) is a compound selected from the group consisting of: a saturated aliphatic (mono, di, or tri)amine with 1 to 20 carbon atoms; an unsaturated aliphatic (mono, di, or tri)amine with 1 to 20 carbon atoms; and an aromatic hydrocarbyl with 1 to 20 carbon atoms.

16. The ethylene polymer composition according to claim 1, wherein said compound (B3) is selected from aliphatic di-, tri- or tetra-alcohols or aromatic di-, tri- or tetra-alcohols.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) 1. Materials

(2) 1.1 P1

(3) P1 is a random polymer of ethylene-glycidyl methacrylate having a glycidyl methacrylate content of 8 wt %, an MFR.sub.2 (2.16 kg/190° C.) of 5 g/10 min, a density of 940 kg/m.sup.3 and a melting point of 106° C., commercially available from Arkema.

(4) 1.2 Ad1

(5) Ad1 is 1,8-Diaminooctane, CAS nr. 373-44-4, commercially available from Sigma Aldrich.

(6) 1.3 Ad2

(7) Ad2 is trimethylolpropane tris[poly(propylene glycol) amine terminated] ether, CAS nr. 39423-51-3, commercially available from Sigma Aldrich.

(8) 1.4 Ad3

(9) Ad3 is 2,2-Bis(4-hydroxy-3-methylphenyl)propane, CAS nr. 79-97-0, commercially available from Sigma Aldrich.

(10) 1.5 Ti1

(11) Ti1 is Tetrakis(2-ethylhexyl) orthotitanate, CAS nr. 1070-10-6, having Mw of 564 g/mol, commercially available from Dorf Ketal.

(12) 2. Measurement Methods

(13) 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.

(14) 2.1 Melt Flow Rate

(15) The melt flow rate was determined according to ISO 1133 for ethylene copolymers at 190° C., at a 2.16 kg load (MFR2).

(16) 2.2 Density

(17) Density was measured according to ISO 1183-2. The sample preparation was executed according to ISO 1872-2 Table 3 Q (compression moulding).

(18) 2.3 Comonomer Content

(19) Determination of comonomer content is effected using the procedure as described in EP 2 444 980 A1, page 19, line 40 to page 20, line 29.

(20) 2.4 Hotset Elongation and Hotset Permanent Deformation

(21) Hot set elongation and permanent deformation are determined on dumbbells prepared according to ISO-527-2-5A. Dumbbells were taken from already cross-linked compressed plaques prepared as described below.

(22) The hot set elongation was determined according to IEC 60811-2-1.on dumbbell samples as prepared as described above. The nature of the samples is specified in context. In the hot set test, a dumbbell of the tested material is equipped with a weight corresponding to 20 N/cm2. This specimen was put into an oven at 200° C. and after 5 minutes the elongation was measured. The specimen was then left in the oven with the weight for additional 10 min while the elongation was monitored, usually without indicating any changes. Subsequently, the weight was removed and the specimen was left to recover in the oven for additional 5 min before being extracted. Then, the specimen was taken out from the oven and cooled down to room temperature. The permanent deformation was determined.

(23) Compressed plaques are prepared as follows: Pellets of the test polyethylene composition were compression moulded using the following conditions: First, the pellets were melted at 120° C. at around 20 bar for 1 minutes. Then the pressure was increased to 200 bar, and kept at the pressure and temperature for 6 min. Then material was cooling down to room temperature at rate of 15° C./min at 200 bars. The thickness of the plaque was around 1.8 mm.

(24) The cross-linking density was measured with Hot-set on plaques. This method is use to evaluate curing speeds and screen new curing agents and catalyst without having to extrude complete power cables. Plaques were first melted at 140° C. followed by hot pressing at various temperatures (180-240° C., see table below), a pressure of 100 bar (10 MPa), and various reaction times (2-20 min, see Table below). Thickness of the plaques was 1.25 mm. That hot pressing achieves cross-linking of the composition which simulates a commercial average cable extrusion speed.

(25) 2.5 Gel Content

(26) The gel-content of cross-linked samples was determined gravimetrically using a solvent extraction technique. The samples (˜150 mg) were placed in pre-weighed 100 mesh stainless steel baskets and extracted in 1.1 dm3 by refluxing decalin for 6 h. An antioxidant, 10 g Irganox 1076 from Ciba-Geigy, was added to the solvent to prevent degradation. Then, the solvent was exchanged with 0.9 dm3 of additive free, pre-heated decalin and the extraction continued for 1 h. Finally, the samples were dried first at ambient overnight and then under vacuum for about 8 hours at 50° C. After this period the non-soluble fraction that remained in the basket reached a constant weight, which was used to calculate the gel-content.

(27) 2.6 Compounding

(28) Copolymer/crosslinking agent formulations were compounded through extrusion for 10 minutes at 120° C. using a Haake Minilab Micro Compounder. The extruded material was first molten at 130° C., followed by crosslinking at 180 to 260° C. and a pressure of 25 bar for 2 to 120 min, resulting in 1.25 mm thick plates. Thin films for optical microscopy and FTIR were prepared by drop-casting from 10 g/l hot p-xylene solutions. Films for UV-vis were prepared by melt pressing (0.05 mm thick films melt pressed at 140° C. for 5 minutes).

(29) 3. Results

(30) In order to show the effects provided by the present invention, reference compositions (RE1-RE4) and compositions according to the invention (IE1-IE4) were prepared using the materials and the conditions below. These samples were then cross-linked under the conditions and with the results as given in Table 1 below.

(31) RE1 to RE4 comprises a composition with epoxy polymer and a titanate or a curing agent (Ad1 to Ad3). Those samples were cross-linked at operating MV insulation temperatures and times. The results given in Table 1 show that in all cases the samples broke during hotsets testing at 220° C. Only the composition comprising Ad3 (bisphenol additive, RE4) provided sufficiently low elongation during hotsets when the cross-linking time was 20 min at the cross-linking temperature of 240° C., the conditions that are not feasible for the commercial production of insulation layers.

(32) IE1 to IE4 comprise an epoxy polymer together with a small amount of a titanate and an additive (Ad1 to Ad3). The compositions of IE1 and IE2 were cross-linked at commercial conditions for MV cable insulation layers (temperature 220° C. and time 5 min). Further, the composition of IE3 and IE4 was cross-linked at 240° C. for 2 min and 180° C. for 5 min, respectively.

(33) In all cases, the elongation hotsets of IE1 to IE4 met standards (<100% elongation) and provided excellents gel content values, indicating a high degree of cross-linking.

(34) The comparison of the reference examples and the examples according to the invention shows the synergistic advantageous effects of the use of component (B1) in combination with either or both of (B2) and (B3) as cross-linking agent.

(35) TABLE-US-00001 TABLE 1 RE1 RE2 RE3 RE4 IE1 IE2 IE3 IE4 P1 (wt %) 99 98 99.5 97 98.5 97.5 96.5 96.5 Ad1 (wt %) 1 — — — 1 — — — Ad2 (wt %) — 2 — — — 2 — — Ti1 (wt %) — — 0.5 — 0.5 0.5 0.5 0.5 Ad3 (wt %) — — — 3 — — 3 3 Cross-linking 220 220 220 240 220 220 240 180 temperature (° C.) Cross-linking 5 5 5 20 5 5 2 5 time (min) Elongation broke broke broke 55 59 55 57 63 Hot Sets (%) Gel Content 63 61 <40 86 90 89 90 85 (%)

(36) Although the present invention has been described with reference to various embodiments, those skilled in the art will recognize that changes may be made without departing from the scope of the invention. It is intended that the detailed description be regarded as illustrative, and that the appended claims including all the equivalents are intended to define the scope of the invention.