Insulation layer for cables

Abstract

The present invention is directed to a new cable having at least one insulation layer, to a process for producing such cable as well as to the use of a polymeric-nucleating agent for increasing the crystallization temperature of a polymer composition being part of an insulation layer of such a cable and the use of such a cable as communication cable and/or electrical cable.

Claims

1. A cable having a conductor and at least one insulation layer comprising a polymer composition (PC) comprising: (a) at least 98 wt. %, based on the total weight of the polymer composition (PC), of a crystalline polypropylene (PP) homo- or copolymer having a melt flow rate according to ISO 1133 (230° C./2.16 kg) in the range of 1.0 to 10.0 g/10 min, a ratio of the weight and number average molecular weight Mw/Mn as calculated from the molecular weight distribution determined by size exclusion chromatography according to ISO 160140 in the range of from 2.2 to 6.0, and a comonomer content of below 5.0 wt. %, wherein the comonomers are ethylene and/or a C.sub.4 to C.sub.10 α-olefin, (b) 0.5 up to 2.0 wt. %, based on the total weight of the polymer composition (PC), of an adhesion promoter (AP) being a maleic anhydride modified polypropylene homo- or copolymer and/or an acrylic acid modified polypropylene homo- or copolymer having a melt flow rate MFR.sub.2 (230° C./2.16 kg) in the range of from 2 to 500 g/10 min, (c) 0.0001 to 1.0 wt. %, based on the total weight of the polymer composition (PC), of a polymeric a-nucleating agent (pNA), and (d) optionally 0.02 to 1.0 wt. %, based on the total weight of the polymer composition (PC), of a soluble α-nucleating agent (sNA), wherein the crystalline polypropylene (PP) homo- or copolymer, the maleic anhydride modified polypropylene homo- or copolymer and/or an acrylic acid modified polypropylene homo- or copolymer, and the polymeric α-nucleating agent (pNA) are the only polymer components in the polymer composition (PC).

2. The cable according to claim 1, wherein the polymer composition (PC) (a) comprises only the polymeric α-nucleating agent (pNA) and the soluble α-nucleating agent (sNA) as α-nucleating agents; or (b) comprises only the polymeric α-nucleating agent (pNA) as α-nucleating agent.

3. The cable according to claim 1, wherein the polymer composition (PC) and/or the crystalline polypropylene (PP) homo- or copolymer has/have a melting temperature Tm as determined by differential scanning calorimetry (DSC) in the range of 155° C. to 170° C.

4. The cable according to claim 1, wherein the polymer composition (PC) and/or the crystalline polypropylene (PP) homo- or copolymer has a crystallization temperature Tc as determined by differential scanning calorimetry (DSC) in the range of 118° C. to 131° C.

5. The cable according to claim 1, wherein the polymer composition (PC) has a Shore D hardness from 64 to 75.

6. The cable according to claim 1, wherein the polymer composition (PC) and/or the crystalline polypropylene (PP) homo- or copolymer has/have a content of a fraction soluble in xylene at 25° C. from 0.5 wt. % to 8.5 wt. %.

7. The cable according to claim 1, wherein the polymer composition (PC) has a melt flow rate according to ISO 1133 (230° C./2.16 kg) in the range of 1.0 and 8.0 g/10 min.

8. The cable according to claim 1, wherein the polymeric α-nucleating agent (pNA) is a polymerized vinyl compound of formula (IV): ##STR00003## wherein R.sub.1 and R.sub.2 together form a 5 or 6 membered saturated or unsaturated or aromatic ring or they stand independently for a lower alkyl comprising 1 to 4 carbon atoms.

9. The cable according to claim 8, wherein the polymeric α-nucleating agent (pNA) is a polymerized vinyl compound selected from the group consisting of vinyl cycloalkanes.

10. The cable according to claim 1, wherein the soluble α-nucleating agent (sNA) is: (a) selected from the group consisting of sorbitol derivatives, nonitol derivatives, benzene-trisamides and mixtures thereof, and/or (b) present in the polymer composition (PC) in an amount between 0.1 wt. % and 0.8 wt. %, based on the total weight of the polymer composition (PC).

11. A process for producing a cable according to claim 1, wherein the process comprises the steps of: (a) forming a polymer composition (PC) comprising: (a1) at least 98.0 wt. %, based on the total weight of the polymer composition (PC), of a crystalline polypropylene (PP) homo- or copolymer having a melt flow rate according to ISO 1133 (230° C./2.16 kg) in the range of 1.0 to 10.0 g/10 min and a comonomer content of below 5.0 wt. %, the comonomers are ethylene and/or a C.sub.4 to C.sub.10 α-olefin, (a2) 0.5 up to 2.0 wt. %, based on the total weight of the polymer composition (PC), of an adhesion promoter (AP) being a maleic anhydride modified polypropylene homo- or copolymer and/or an acrylic acid modified polypropylene homo- or copolymer having a melt flow rate MFR.sub.2 in the range of from 2 to 500 g/10 min, (a3) 0.0001 to 1.0 wt. %, based on the total weight of the polymer composition (PC), of a polymeric α-nucleating agent (pNA), and (a4) optionally 0.02 to 1.0 wt. %, based on the total weight of the polymer composition (PC), of a soluble α-nucleating agent (sNA), wherein the crystalline polypropylene (PP) homo- or copolymer, the maleic anhydride modified polypropylene homo- or copolymer and/or an acrylic acid modified polypropylene homo- or copolymer, and the polymeric α-nucleating agent (pNA) are the only polymer components in the polymer composition (PC), (b) applying the polymer composition (PC) of step a) at a melt temperature of 180° C. to 280° C. on a conductor to form an insulation layer, and (c) producing the cable at a processing speed of 300 m/min to 3000 m/min.

12. The process according to claim 11, wherein the conductor is pre-heated to a temperature of between 50° C. and 150° C.

13. The process of claim 11, wherein the polymeric α-nucleating agent (pNA) is a polymerized vinyl compound and the soluble α-nucleating agent (sNA) is selected from the group consisting of sorbitol derivatives, nonitol derivatives, benzene-trisamides and mixtures thereof.

14. The process according to claim 11, wherein the cable is a communication cable.

Description

EXAMPLES

1. Definitions/Measuring Methods

(1) The following definitions of terms and determination methods apply for the above general description of the invention as well as to the below examples unless otherwise defined.

(2) NMR-Spectroscopy Measurements:

(3) The .sup.13C-NMR spectra of polypropylenes were recorded on Bruker 400 MHz spectrometer at 130° C. from samples dissolved in 1,2,4-trichlorobenzene/benzene-d6 (90/10 w/w). For the triad analysis the assignment is done according to the methods described in literature: (T. Hayashi, Y. Inoue, R. Chüjö, and T. Asakura, Polymer 29 138-43 (1988). and Chujo R, et al, Polymer 35 339 (1994).

(4) The NMR-measurement was used for determining the mm triad concentration in a manner well known in the art.

(5) Melting temperature Tm, crystallization temperature Tc: measured with Mettler TA820 differential scanning calorimetry (DSC) on 5 to 10 mg samples. DSC is run according to ISO 3146/part 3/method C2 in a heat/cool/heat cycle with a scan rate of 10° C./min in the temperature range of +23 to +210° C. Crystallization temperature and enthalpy are determined from the cooling step, while melting temperature and melting enthalpy are determined from the second heating step

(6) Randomness

(7) In the FTIR measurements, films of 250-mm thickness were compression moulded at 225° C. and investigated on a Perkin-Elmer System 2000 FTIR instrument. The ethylene peak area (760-700 cm.sup.−1) was used as a measure of total ethylene content. The absorption band for the structure -P-E-P- (one ethylene unit between propylene units), occurs at 733 cm.sup.−1. This band characterizes the random ethylene content. For longer ethylene sequences (more than two units), an absorption band occurs at 720 cm.sup.−1. Generally, a shoulder corresponding to longer ethylene runs is observed for the random copolymers. The calibration for total ethylene content based on the area and random ethylene (PEP) content based on peak height at 733 cm.sup.−1 was made by .sup.13C NMR. (Thermochimica Acta, 66 (1990) 53-68).
Randomness=random ethylene(-P-E-P-)content/the total ethylene content×100%.

(8) Number average molecular weight (M.sub.n), weight average molecular weight (M.sub.w) and molecular weight distribution (MWD) are determined by size exclusion chromatography (SEC) using Waters Alliance GPCV 2000 instrument with online viscometer. The oven temperature is 140° C. Trichlorobenzene is used as a solvent (ISO 16014).

(9) MFR.sub.2 (230° C.) is measured according to ISO 1133 (230° C., 2.16 kg load).

(10) MFR.sub.2 (190° C.) is measured according to ISO 1133 (190° C., 2.16 kg load).

(11) Ethylene content is measured with Fourier transform infrared spectroscopy (FTIR) calibrated with .sup.13C-NMR. When measuring the ethylene content in polypropylene, a thin film of the sample (thickness about 250 mm) was prepared by hot-pressing. The area of absorption peaks 720 and 733 cm.sup.−1 was measured with Perkin Elmer FTIR 1600 spectrometer. The method was calibrated by ethylene content data measured by .sup.13C-NMR. Content of any one of the C4 to C10 α-olefins is determined with .sup.13C-NMR; literature: “IR-Spektroskopie für Anwender”; WILEY-VCH, 1997 and “Validierung in der Analytik”, WILEY-VCH, 1997.

(12) The xylene cold solubles (XCS, wt.-%): Content of xylene cold solubles (XCS) is determined at 23° C. according ISO 6427.

(13) Shore D hardness is measured at 3 and 15 seconds according to ASTM D2240-05.

(14) REact parameter: The materials were pressed into films and circular samples were punched out of the films with weight of ca. 2 mg. DSC runs were performed with heating rate of 20° C./min to the temperature of 210° C. which was kept constant for 10 minutes. The samples were then cooled with different cooling rates (3, 10, 30, 100° C./min) and the crystallization temperature at each cooling rate was recorded. The quenching resistance was evaluated with a phenomenological dimensionless parameter “REact” often related to activation energy, E.sub.act, for various phenomena. This approach was first described by H. E. Kissinger in Journal of Research of the National Bureau of Standards 1956, volume 57, issue 4, page 217, equation 7, for the differential thermal analysis of kaolinite clays, and afterwards used also for polymer crystallization.

(15) $\mathrm{\text{'}\text{'}}\mathrm{REact}\mathrm{\text{'}\text{'}}=-R^{-1}{E}_{\mathrm{act}}=\frac{d\left[\ln \left(\frac{T^{\prime }}{T_{\mathrm{cr}}^2}\right)\right]}{d\left(\frac{1}{T_{\mathrm{cr}}}\right)}$
where T′ is the cooling rate from the melt, T.sub.cr is the crystallization temperature, R is the gas constant. This “REact” parameter was found to correlate well with the crystallization temperature at cooling rates in the order of 30° C./s, from DSC plots of crystallization temperature vs. cooling rate, as well as with the α phase crystalline content of cables as measured with the deconvolution of Wide Angle X-Ray Scattering patterns.

(16) Surface quality: The final cable was assessed optically by an experienced person and ranked on a relative scale from 1 to 10, on which “1” stands for massive roughness going to the point of defects in the insulation layer while “10” stands for a perfectly smooth and homogeneous surface.

(17) Strip force: ASTM D 4565, part 19 is used to measure insulation adhesion to the conductor. The samples are prepared according to the standard, cutting out a 130 mm long section of the insulated cable and removing the insulation until only a 25 mm long insulated section remains. The sample is conditioned for 16 h at ambient temperature at 50% relative atmospheric humidity. The bared conductor is then passed through a die plate or orifice having an aperture measuring 0.07 to 0.13 mm larger than the conductor until the shoulder of insulation rests on the die plate. Using a tensile testing setup with a load cell tension between the conductor and the die plate is applied and the force required to strip the remaining insulation from the wire is recorded. The maximal force is registered.

2. Polymers

(18) XPP1 is an experimental polypropylene random copolymer containing small amounts of etylene (0.65 wt.-%) and 50 ppm of polymerized vinyl cyclohexane (pVCH), produced in a Borstar PP pilot unit with one loop and one gas phase reactor. A catalyst prepolymerized with pVCH as described in example 1 of EP 1183307 A1 was used in combination with triethylaluminium as cocatalyst and dicyclopentyl dimethoxy silane as external donor with an aluminium to donor ratio of 10 mol/mol. This polymer was mixed with 0.1 wt.-% of Irganox B225 (1:1-blend of Irganox 1010 (Pentaerythrityl-tetrakis(3-(3′,5′-di-tert.butyl-4-hydroxytoluyl)-propionate and tris(2,4-di-t-butylphenyl)phosphate)phosphite) of BASF AG, Germany) and 0.05 wt % calcium stearate in a co-rotating twin-screw extruder (type: Coperion ZSK 57). Details of the polymerization as well as characteristics of the polymer can be taken from Table 1.

(19) TABLE-US-00001 TABLE 1 Polymerization and characzeristics of XPP1 XPP1 Loop Temperature [° C.] 70 MFR.sub.2 [g/10 min] 3.9 C2 content [wt-%] 0.65 H.sub.2/C3 ratio [mol/kmol] 2.0 C2/C3 ratio [mol/kmol] 1.1 amount [wt.-%] 55 1 GPR Temperature [° C.] 85 MFR.sub.2 [g/10 min] 3.9 C2 content [wt-%] 0.65 H.sub.2/C3 ratio [mol/kmol] 19.0 C2/C3 ratio [mol/kmol] 1.2 amount [wt.-%] 45 Final MFR.sub.2 [g/10 min] 3.9 C2 content [wt.-%] 0.65 XCS [wt.-%] 2.0 Tm [° C.] 161 Tc [° C.] 124 Mw [kg/mol] 430 Mw/Mn [—] 3.9

(20) DM55pharm is a polypropylene homopolymer having a melting temperature of 164° C., an XCS content of 2.0 wt % and an MFR.sub.2 (230° C.) of 2.8 g/10 min, commercially available from Borealis Polyolefine GmbH, Austria. It has a weight average molecular weight (Mw) of 480 kg/mol and a broadness of the molecular weight distribution expressed as Mw/Mn of 4.7. “PP-R” is an experimental propylene-ethylene random copolymer which was produced based on the commercial Avant ZN M1 catalyst supplied by LyondellBasell, USA in combination with triethylaluminium as cocatalyst and cyclohexyl trimethoxy silane as external donor with an aluminium to donor ratio of 5 mol/mol. The polymerization was performed in a Borstar PP plant using one liquid-phase loop rector and two gas phase reactors. The resulting copolymer had an ethylene content of 2.0 wt %, an MFR.sub.2 (230° C./2.16 kg) of 1.9 g/10 min, a melting temperature of 149° C. and an xylene cold soluble (XCS) content of 4.5 wt.-%. This polymer was mixed with 0.1 wt % of Irganox B225 (1:1-blend of Irganox 1010 (Pentaerythrityl-tetrakis(3-(3′,5′-di-tert.butyl-4-hydroxytoluyl)-propionate and tris(2,4-di-t-butylphenyl)phosphate)phosphite) of BASF AG, Germany) and 0.04 wt % synthetic hydrotalcite (DHT-4A supplied by Kisuma Chemicals, Netherlands) in a co-rotating twin-screw extruder (type: Coperion ZSK 57).

(21) HE3366 is a high-density polyethylene polymer designed for data cable insulation having an MFR.sub.2 (190° C.) of 0.8 g/10 min commercially available from Borealis Polyolefine GmbH, Austria.

(22) HE4872 is a high-density polyethylene polymer composition comprising an adhesion promoter designed for data cable insulation having an MFR.sub.2 (190° C.) of 0.9 g/10 min commercially available from Borealis Polyolefine GmbH, Austria.

3. Nucleating Agent (sNA)

(23) Millad NX8000 is the soluble α-crystal nucleating agent (NA) 1,2,3-trideoxy-4,6:5,7-bis-O-[(4-propylphenyl)methylene]-nonitol (CAS No. 882073-43-0) commercially available from Miliken Co., USA. Millad NX8000 is used in an amount of 0.25 wt.-%, based on the total weight of the polymer composition (PC).

4. Further Additives

(24) All polypropylene types were specifically modified for cable insulation purposes by adding 0.1 wt.-% of the metal deactivator Lowinox MD 24 (N,N′-bis(3(3′,5′-di-tert. butyl-4′-hydroxyphenyl)propionyl) hydrazine, CAS No. 32687-78-8, supplied by Chemtura Europe GmbH, CH) and 0.1 wt % of the sulfur stabilizer Lowinox DSTDP (Di-stearyl-thio-di-propionate, CAS No. 693-36-7, supplied by Chemtura Europe GmbH, CH).

5. Adhesion Promoter

(25) The adhesion promoter (AP) is the maleic anhydride modified polypropylene homopolymer (PP-g-MAH) Exxelor PO1050 having an MFR2 (230° C.) of 430 g/10 min and a maleic anhydride content of 0.75 wt % supplied by ExxonMobil Chemical, USA.

6. Polymer Composition (PC)s

(26) All polymer composition (PC)s as listed in table 1 (for inventive and comparative polymer composition (PC)s based on propylene-ethylene random copolymers and polypropylene homopolymers) were prepared by melt compounding in a Coperion ZSK 57 twin screw extruder (screw diameter 57 mm, L/D ratio 40) at temperatures between 190° C. and 240° C.

7. Cable Processing

(27) The polymer compositions of table 1 were extruded as insulation layer onto a copper wire conductor having a diameter of 0.53 mm with a single screw extruder and a standard wire coating extrusion head with die dimensions, extruder pressures and speeds as indicated in table 2. The conductor was pre-heated to a temperature of 100° C., the melt temperature was set to 220° C. and a final cable diameter of 0.93 mm was adjusted in all cases. Cooling of the cable was performed first with water of 25° C. in a spray-cooling setup having a length of 2 m and then with water of 15° C. in an immersion-cooling setup.

(28) TABLE-US-00002 TABLE 1a Polymer compositions (n.a.—not applicable) AP MFR 2.16 kg Polymer AP amount 190*/230° C. type Nucleant type [wt.-%] [g/10 min] IE1 XPP1 pVCH PP-g-MAH 1.5 4.1 IE2 XPP1 pVCH + PP-g-MAH 1.5 4.2 NX8000 CE1 XPP1 pVCH — — 3.9 CE2 DM55pharm NX8000 PP-g-MAH 1.5 2.8 CE3 DM55pharm — — — 2.8 CE4 PP-R NX8000 PP-g-MAH 1.5 2.0 CE5 HE4872 — EMAA  0.85 0.9* CE6 HE3366 — — — 0.8* AP adhesion promoter

(29) TABLE-US-00003 TABLE 1b Polymer compositions (n.a.—not analyzed) DSC 10K/min REact Tm Tc parameter C2 total Shore D [° C.] [° C.] — [wt.-%] — IE1 160 124 6791 0.65 70 IE2 161 127 6808 0.65 70 CE1 160 124 6872 0.65 70 CE2 164 128 6169 0 71 CE3 164 120 3963 0 70 CE4 153 126 4806 2.0 67 CE5 127 117 n.a. n.a. 58 CE6 127 116 n.a. n.a. 58

(30) TABLE-US-00004 TABLE 2 Processing and cable characteristics Die geometry body length/ Extruder Line Screw Surface Strip Polymer type diameter pressure speed speed quality force (base) [mm] [bar] [m/min] [rpm] (1-10) [N] IE1 XPP1 30/1.00 255  977 57 10 10.4 IE2 XPP1 30/1.00 260  995 58 10  8.4 CE1 XPP1 30/1.00 270  994 58  9  7.0 CE2 DM55pharm 30/1.00 317 1006 71 10  9.2 CE3 DM55pharm 25/0.94 360 1100 96  7  6.2 CE4 PP-R 25/0.94 323 1031 61 10  9.8 CE5 HE4872 25/0.94 460 1025 54 10  9.0 CE6 HE3366 25/0.94 460 1010 49  9  5.5