Cross-linkable polyolefin composition comprising a first and a second olefin polymer

Abstract

The present invention relates to a cross-linkable polyolefin composition comprising a first olefin polymer (A) comprising a first comonomer comprising epoxy groups, and a second olefin polymer (B) comprising a second comonomer comprising carboxylic acid groups and/or precursor thereof.

Claims

1. A cable comprising at least one layer comprising a cross-linkable polyolefin composition comprising: 20 wt % to 95 wt % based on the total amount of said polyolefin composition of a first olefin polymer (A) comprising a first comonomer comprising epoxy groups, and 5 to 60 wt % based on the total amount of said polyolefin composition of a second olefin polymer (B) comprising a second comonomer comprising carboxylic acid groups and/or precursor thereof; wherein the cross-linkable polyolefin composition is substantially free of curing agents.

2. The cable according to claim 1, wherein said first comonomer comprising epoxy groups is aliphatic glycidyl methacrylate comonomer.

3. The cable according to claim 1, wherein the amount of said first comonomer is at least 0.1 wt %, or at least 0.5 wt %, or at least 1 wt %, based on the amount of said first olefin polymer (A).

4. The cable according to claim 1, wherein the amount of said first comonomer is 20 wt % or less, or 15 wt % or less, or 10 wt % or less, or 5 wt % or less, based on the amount of said first olefin polymer (A).

5. The cable according to claim 1, wherein said second comonomer comprising carboxylic acid groups is acrylic acid comonomer.

6. The cable accordingly to claim 1, wherein the amount of said second comonomer is from 0.1 to 20 wt %, based on the amount of said second olefin polymer (B).

7. The cable accordingly to claim 1, wherein said cross-linkable polyolefin composition further comprises a third olefin polymer (C).

8. A cable comprising at least one layer comprising a cross-linked polyolefin composition cured in the absence of curing agents comprising: 20 wt % to 95 wt % based on the total amount of said polyolefin composition of a first olefin polymer (A) comprising a first comonomer comprising epoxy groups, and 5 to 60 wt % based on the total amount of said polyolefin composition of a second olefin polymer (B) comprising a second comonomer comprising carboxylic acid groups and/or a precursor thereof.

9. The cable according to claim 8, wherein said cross-linked polyolefin composition has hotset elongation measured according to IEC 60811-2-1 of below 175%.

10. The cable according to claim 8, wherein the gel content of the cross-linked polyolefin composition is at least 50%, or at least 60%, or at least 70%.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) 1. Materials

(2) Below, the materials used in the compositions of the present invention are described. In particular, the polymers (P1-P10) are classified as polymer (A), i.e. a polymer bearing epoxy-groups, polymer (B), i.e. polymer bearing carboxylic acid functionality or its precursor, or polymer (C).

(3) 1.1 P1 (A)

(4) P1 is a 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.

(5) 1.2 P2 (B)

(6) P2 is an ethylene-methacrylic acid copolymer resin having 7 wt % of methacrylic acid comonomer, a density of 0.93 g/cm.sup.3 and MFR.sub.2 (190° C./2.16 kg) of 8 g/10 min, commercially available from Dow.

(7) 1.3 P3 (C)

(8) P3 is an LDPE homopolymer having MFR.sub.2 (190° C./2.16 kg) of 1.9 g/10 min, and density of 0.923 g/cm.sup.3.

(9) 1.4 P4 (A)

(10) P4 is copolymer of ethylene and glycidyl methacrylate produced in a tubular reactor, having 2 wt % GMA, and MFR.sub.2 (190° C./2.16 kg) of 1.9 g/10 min.

(11) 1.5 P5 (B)

(12) P5 is a terpolymer of ethylene, tertbutyl methacrylate and acrylic acid, produced in a tubular reactor, having 5.8 wt % TBMA and 5.8 wt % EAA, and MFR.sub.2 (190° C./2.16 kg) of 1.5 g/10 min.

(13) 1.6 P6 (A)

(14) P6 is a terpolymer of ethylene glycidyl methacrylate/butyl acrylate, produced in a tubular reactor, and having 1.8 wt % GMA, —18 wt % BA, and MFR.sub.2 (190° C./2.16 kg) of 6.6 g/10 min.

(15) 1.7 P8 (A)

(16) P8 is a polymer of ethylene-glycidyl methacrylate having a glycidyl methacrylate content of 4.5 wt %, an MFR.sub.2 (2.16 kg/190° C.) of 2 g/10 min, a density of 930 kg/m.sup.3, commercially available from Arkema.

(17) 1.8 P9 (C)

(18) P9 is HDPE having density of 962 kg/m.sup.3, MFR.sub.2 (2.16 kg/190° C.) of 12 g/10 min.

(19) 1.9 P10 (B)

(20) P10 is an ethylene-methacrylic acid copolymer resin having 3.1 wt % of methacrylic acid comonomer, and MFR2 (190° C./2.16 kg) of 10.6 g/10 min, commercially available from Dow.

(21) 1.10 Ad1

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

(23) 1.11 Ad2

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

(25) 1.12 Ad3

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

(27) 1.13 Ti1

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

(29) 2. Measurement Methods

(30) Unless otherwise stated in the description or claims, the following methods were used to measure the properties defined throughout the description and the claims. The samples were prepared according to given standards, unless otherwise stated.

(31) 2.1 Melt Flow Rate

(32) The melt flow rate was determined according to ISO 1133 for ethylene copolymers at 190° C., at a 2.16 kg load (MFR.sub.2).

(33) 2.2 Density

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

(35) 2.3 Comonomer Content

(36) 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.

(37) 2.4 Hotset Elongation and Hotset Permanent Deformation

(38) Hotset 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.

(39) The hotset 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 hotset test, a dumbbell of the tested material is equipped with a weight corresponding to 20 N/cm.sup.2. 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.

(40) 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.

(41) 2.5 Gel Content

(42) 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 dm.sup.3 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 dm.sup.3 of additive free, pre-heated decalin and the extraction continued for 1 h at reflux. Finally, the samples were dried first at ambient overnight and then under vacuum overnight at 50° C. After this period, the non-soluble fraction that remained in the basket reached a constant weight, which was used to calculate gel content.

(43) 2.6 Compounding and Cross-Linking

(44) Copolymer/cross-linking agent formulations were compounded through melt-mixing for 10 minutes at 120° C. using a Haake Minilab Micro Compounder and a string was extruded. The string was used to prepare plaques for crosslinking by first melting said string into a plaque in a preheated first press at 140° C. at above 5 bar for 5 min. The formed plaque was then removed from the first press and put into a second press with the same dimensions, wherein the second press which had been preheated to the desired crosslinking temperature (see Tables below). The plaque was subsequently crosslinked at the desired temperature at 25 bar for the desired time (see Tables below), resulting in a 1.25 mm thick crosslinked plaque. The crosslinked plaque was then removed from the second press at the desired crosslinking temperature and put into a water/ice bath to ensure a rapid cooling of the crosslinked plaque.

(45) 2.7 Tan δ and Conductivity

(46) Measurements ware performed using a Novocontrol Alpha spectrometer in the frequency range of 10.sup.−2 to 10.sup.7 Hz, at different temperatures in the range 20-130° C. with an error of ±0.1° C., at atmospheric pressure and under nitrogen atmosphere. The sample cell consisted of two stainless steel electrodes 40 mm in diameter and the sample with a thickness of 0.1 mm. Each measurement was carried out six times, and average values were recorded. The complex conductivity σ*=σ′+iσ″, the real part of which is used for the analysis herein, can be deducted from the complex dielectric permittivity ε* as σ*=iωε.sub.0ε*, where ε.sub.0 is the permittivity of free space. Both permittivity and conductivity were obtained directly from the instrument. The DC conductivity is extracted from the real part of the conductivity, a′, at the limit of very low frequencies. Only temperatures where a plateau in the spectra (i.e. frequency-independent a′) is observed were considered for this analysis.

(47) The dielectric loss tan(δ) can be derived by the ratio of the real and imaginary part of the permittivity according to the relationship tan (δ)=ε″/ε′. The values of the dielectric loss used in this work were obtained at 56 Hz.

(48) 3. Results

(49) In order to show the effects provided by the present invention, reference compositions (RE1-RE7) and compositions according to the invention (IE1-IE12) were prepared using the materials and the conditions below. The results are summarized in Tables 1-4, and will now be discussed in detail

(50) First, a series of compositions according to the present invention was prepared in order to evaluate cross-linking performance and visual appearance of the final cross-linked samples. The results are summarized in Table 1. The composition of RE1 comprises a first polymer (A), P1, comprising epoxy groups, as well as a titanate and a curing agent (bisphenol derivative, Ad3). The plaque samples prepared from the composition of RE1 have satisfactory cross-linking performance, i.e. <100% elongation and >75% gel content in 5 min at cross-linking temperatures of 180-220° C. However, the samples are coloured with a strong yellowish or even orange colour that in some applications may not be acceptable. In addition, the composition of RE1 requires presence of a catalyst and an additive, which makes the system more expensive and complex and requires special storage and handling conditions in order to avoid hydrolysis of the additive.

(51) On the other hand, the compositions of IE1-IE4 are more simple systems that involves only 2 (IE1) or 3 (IE2-IE4) components in the form of pellets. The inventive compositions comprise a first olefin polymer (A), P1, comprising epoxy groups, and a second olefin polymer (B), P2, comprising methacrylic acid. Cross-linking performance of the compositions of IE1-IE4 is improved, as may be seen in Table 1, presenting hotset elongation of the inventive compositions compared to the composition of RE1. In addition, the cross-linked samples made from the inventive compositions are colourless.

(52) IE14 and IE15 demonstrates that increased polarity of the first olefin polymer (A) improves cross-linking behaviour.

(53) TABLE-US-00001 TABLE 1 RE1 IE1 IE2 IE3 IE4 IE14 IE15 P1 (A, wt %) 96.5 60 33 40 50 — — P2 (B, wt %) — 40 17 30 40 10 10 P3 (C, wt %) — — 50 30 10 — — P4 (A, wt %) — — — — — 90 — P6 (A, wt %) — — — — — — 90 Ad3 (wt %) 3 — — — — — — Ti1 (wt %) 0.5 — — — — — — Cross-linking 180 200 200 200 200 300 300 temperature (° C.) Cross-linking 5  5/10  5/10  5/10  5/10 5 5 time (min) Gel Content (%, 85/— 91/95 >70/— >70/— >80/— — — 5 min/10 min) Hotset 63/— 9/0 50/35 18/14 10/5 >100 <100 elongation (%, 5 min/10 min) Colour yellow colourless colourless colourless colourless

(54) Next, cross-linking behaviour as well as dielectric loss of the compositions according to the present invention were investigated. The results are presented in Table 2.

(55) As may be seen from Table 2, excellent tan δ values can be achieved for peroxide free compositions containing a certain degree of polarity through cross-linking of the epoxy ring through click chemistry-type reactions in the presence of different curing agents (RE2-RE5). Cross-linked compositions showed improved tan δ values compared with thermoplastics. This means that the polarity is locked and fixed into the polymer structure after cross-linking improving tan δ values.

(56) The composition of IE5 is an ethylene polymer composition comprising the first polymer (A) produced in the autoclave reactor and the second polymer (B) comprising acrylic acid. Both IE6 and IE7 comprise compositions wherein the first polymer (A) is produced in a tubular reactor. In IE6, the second polymer (B) comprises acrylic acid functionalities, while in IE7, the second polymer (B) is a terpolymer comprising acrylic acid and tert-butyl acrylate.

(57) Plaques were prepared from the compositions of IE5-IE7 according to the method described above, and cross-linked at 200° C. for 10 min achieving at least 80% gel content. Tan δ values were measured at several temperatures as described above. The compositions of IE5-IE7 exhibited excellent tan δ values especially at elevated temperatures, and also showed excellent cross-linking properties. Further, the composition of IE6, based on the epoxy-containing polymer (A) produced in a tubular reactor and the second polymer (B) comprising only acrylic acid units show exhibited outstanding tan δ values at 90° C., indicating that the first polymer (A) produced in a tubular reactor is preferred.

(58) TABLE-US-00002 TABLE 2 RE2 RE3 RE4 RE5 RE7 IE5 P1 (A, wt %) 98.5 97.5 99 98 99.5 63 P2 (B, wt %) — 37 P3 (C, wt %) P4 (A, wt %) — — — — — — P5 (B, wt %) — — — — — — P9 (C, wt %) Ad1 (wt %) 1 — 1 — — — Ad2 (wt %) — 2 — 2 — — Ti1 (wt %) 0.5 0.5 — — 0.5 — Cross-linking 200 200 200 200 200 200 temperature (° C.) Cross-linking 10 10 10 10 10 10 time (min) Gel Content >80 >80 >50 >50 <50 >80 (%) Tan δ (non- 6.7 .Math. 10.sup.−3 0.02 5.0 .Math. 10.sup.−4 4.4 .Math. 10.sup.−4 1.25 .Math. 10.sup.−4 cross-linked) Tan δ (cross-  1.3 .Math. 10.sup.−4 1.77 .Math. 10.sup.−4 linked, 50° C.) Tan δ (cross- 1.0 .Math. 10.sup.−4 6.9 .Math. 10.sup.−4 1.5 .Math. 10.sup.−4 1.6 .Math. 10.sup.−4 0.42 .Math. 10.sup.−4 0.60 .Math. 10.sup.−4 linked, 70° C.) Tan δ (cross- 0.92 .Math. 10.sup.−4 0.55 .Math. 10.sup.−4 linked, 90° C.) IE6 IE7 IE8 IE9 IE10 IE11 P1 (A, wt %) — — 50 25 25 25 P2 (B, wt %) 30 — 50 25 25 P3 (C, wt %) 50 50 45 P4 (A, wt %) 70 70 — P5 (B, wt %) — 30 — 25 P9 (C, wt %) 5 Ad1 (wt %) Ad2 (wt %) — — — Ti1 (wt %) — — — Cross-linking 200 200 200 200 200 200 temperature (° C.) Cross-linking 10 10 10 10 10 10 time (min) Gel Content >80 >80 >80 >80 >80 >80 (%) Tan δ (non- 0.02  1.5 .Math. 10.sup.−4 cross-linked) Tan δ (cross-   2.11 .Math. 10.sup.−4 1.75 .Math. 10.sup.−4 1.52 .Math. 10.sup.−4 1.52 .Math. 10.sup.−4  1.60 .Math. 10.sup.−4 1.88 .Math. 10.sup.−4 linked, 50° C.) Tan δ (cross-   0.67 .Math. 10.sup.−4 0.68 .Math. 10.sup.−4 0.68 .Math. 10.sup.−4 0.68 .Math. 10.sup.−4 0.068 .Math. 10.sup.−4 1.41 .Math. 10.sup.−4 linked, 70° C.) Tan δ (cross- 0.0067 .Math. 10.sup.−4 0.83 .Math. 10.sup.−4 2.68 .Math. 10.sup.−4 2.67 .Math. 10.sup.−4  0.61 .Math. 10.sup.−4 6.41 .Math. 10.sup.−4 linked, 90° C.)

(59) The tan delta values reported above, especially those of IE6 are low. Without wishing to be limited by theory, it is envisaged that the absence of a curing agent helps reduce tan delta. Curing agents can often contain metals or highly polar substances that negatively affect the electrical properties of a material.

(60) TABLE-US-00003 TABLE 3 IE5 IE12 IE6 IE7 P1 (A, wt %) 63 60 — — P2 (B, wt %) 37 — 30 — P4 (A, wt %) — — 70 70 P5 (B, wt %) — 40 — 30 Cross-linking 200 220 240 240 temperature (° C.) Cross-linking 5 5 5 5 time (min) Gel Content 80 90 72 77 (%) Pre-cross- Yes, Yes, No No linking during above above extrusion 150° C. 150° C.

(61) Further, the effect of the manufacturing method of the first olefin polymer (A) on cross-linking properties of the ethylene polymer composition has been studied. The results are summarized in Table 3. The ethylene polymer composition of IE5 comprises the first olefin polymer (A) being produced in an autoclave. From the composition of IE5, tapes were extruded at 150° C. Extrusion temperature above 150° C. resulted in pre-cross-linking during extrusion. Precross-linking was assessed by visual inspection of plaques. If dips, spots, bumps or other surface imperfections were observed, the sample was considered precross-linked. From the tapes extruded without precross-linking, plaques were made by compression moulding and cross-linked under the conditions specified in Table 3.

(62) The ethylene polymer composition of IE12 comprises the first olefin polymer (A) being produced in an autoclave. Although the gel content for the cross-linked composition of IE12 was higher compared to IE5, indicating better cross-linking performance, the composition of IE12 exhibited pre-cross-linking during extrusion at temperatures above 150° C.

(63) IE6 and IE7 comprises ethylene polymer compositions comprising the first olefin polymer (A) produced in a tubular reactor. No pre-cross-linking was observed in either case at temperatures higher than 150° C. under tape extrusion, and both compositions exhibited good cross-linking performance, indicated by gel content of 72 and 77% respectively. Without wishing to be bound by any theory, the more blocky nature of first olefin polymer (A) produced in tubular reactor slows down cross-linking speed thus resulting in absence of precross-linking.

(64) Finally, studies were performed in order to investigate DC conductivity of the polymer composition according to the present invention. The results are shown in Table 4.

(65) TABLE-US-00004 TABLE 4 RE7 IE5 IE6 IE7 IE13 P1 (A, wt %) 99.5 63 — — 30 P2 (B, wt %) — 37 30 — 30 P3 (C, wt %) 40 P4 (A, wt %) 70 70 P5 (B, wt %) — — — 30 Ti1 (wt %) 0.5 — — — Cross- 200 200 200 200 200 linking temperature (° C.) Cross- 10 10 10 10 10 linking time (min) Gel Content <50 >80 >80 >80 >80 (%) δ (S/cm, 6.9 .Math. 10.sup.−16 1.8 .Math. 10.sup.−16 4.0 .Math. 10.sup.−17 6.6 .Math. 10.sup.−17 2.8 .Math. 10.sup.−16 70° C.) δ (S/cm, 4.1 .Math. 10.sup.−15 1.6 .Math. 10.sup.−15 3.6 .Math. 10.sup.−16 3.4 .Math. 10.sup.−16  16 .Math. 10.sup.−16 90° C.) δ (S/cm, 2.2 .Math. 10.sup.−14 1.2 .Math. 10.sup.−14 7.0 .Math. 10.sup.−15 6.3 .Math. 10.sup.−15 — 110° C.) δ (S/cm, 5.7 .Math. 10.sup.−14 3.9 .Math. 10.sup.−14 3.3 .Math. 10.sup.−14 2.4 .Math. 10.sup.−14 — 130° C.)

(66) As may be seen in Table 4, the compositions of the IE5-IE7 exhibit lower DC conductivities compared to the compositions of RE7. In particular, the composition of IE7, wherein the polymers produced in tubular reactor are used, shows the lowest DC conductivity values.

(67) 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.