Insulation layer for cables

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 4 to C 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 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):

wherein R 1 and R 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 4 to C 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 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.