Semi-conductive polymer composition

Abstract

The present invention relates to a semi-conductive polymer composition, the present invention provides a semi-conductive polymer composition comprising an ethylene copolymer comprising polar co-monomer units; an olefin homo- or copolymer; and a conductive filler; wherein the olefin homo- or copolymer has a degree of crystallinity below 20%. The invention also relates to a wire or cable comprising said semi-conductive polymer composition, and to the use of said composition for the production of a layer, preferably a semi-conducting shield layer of a wire or cable.

Claims

1. A semi-conductive polymer composition consisting of: (A) an ethylene-methyl acrylate (EMA) copolymer, present in an amount from 45 to 65 wt % of the total polymer composition; (B) an atactic polypropylene homopolymer, present in an amount from 1 to 10 wt % of the total polymer composition; (C) carbon black, present in an amount from 20 to 37 wt % of the total polymer composition; (D) optionally a cross-linking agent; and (E) optionally at least one further additive selected from the group consisting of antioxidants, scorch retarders, cross-linking boosters, stabilizers, processing aids, flame retardant additives, acid scavengers, inorganic fillers, voltage stabilizers, and additives for improving water tree resistance; wherein the atactic polypropylene homopolymer (B) has a degree of crystallinity below 20%; and wherein the atactic polypropylene homopolymer (B) has a Mw below 50,000.

2. The composition according to claim 1 wherein the atactic polypropylene homopolymer (B) has a degree of crystallinity below 12%.

3. The composition according to claim 1 satisfying the following relationship: MFR(21.6 Kg 130° C.)≥11.5× log (VR), or MFR(21.6 Kg 130° C.)≥19.5*VR+3.

4. The composition according to claim 1 having a MFR(21.6 Kg 130° C.) higher than 15 g/10 min.

5. A wire or cable having a coating thereon which comprises the composition of claim 1.

6. A process for forming a semi-conductive layer on a wire or cable comprising extruding the composition of claim 1 on a metallic conductor or on at least one coating layer thereof.

7. The composition according to claim 1, wherein the Mw of the atactic polypropylene homopolymer (B) is below 35,000.

8. The composition according to claim 1, wherein the amount of the atactic polypropylene homopolymer (B) is from 5 to 10 wt % of the total polymer composition.

9. The composition according to claim 1, wherein the degree of crystallinity of the atactic polypropylene homopolymer (B) is below 0.8%.

10. The composition according to claim 1, wherein the degree of crystallinity of the atactic polypropylene homopolymer (B) is below 0.5%.

11. The composition according to claim 1, wherein the carbon black is a furnace carbon black having an ash-content of less than 0.05 wt % measured according to ASTM-1506, a 325 mesh sieve residue of less than 15 ppm measured according to ASTM D-1514, and less than 0.05 wt % total sulfur measured according to ASTM 1619.

12. The composition according to claim 1, wherein the carbon black is present in an amount of at least 30 wt % and less than 33 wt % of the total polymer composition.

13. The composition according to claim 1, wherein the carbon black is present in an amount of 30 wt % to 36 wt % of the total polymer composition; and wherein the EMA copolymer is present in an amount of 47.2 wt % to 53.2 wt % of the total polymer composition.

14. The composition according to claim 1, wherein a majority of the carbon black (C) is located in the EMA copolymer (A).

15. The composition of claim 1, wherein the atactic polypropylene homopolymer has at least 70% of an atactic component.

16. A semi-conductive polymer composition consisting of: (A) an ethylene-methyl acrylate (EMA) copolymer, present in an amount from 45 to 65 wt % of the total polymer composition; (B) an atactic polypropylene homopolymer, present in an amount from 1 to 10 wt % of the total polymer composition; (C) carbon black, present in an amount from 30 wt % to 36 wt % of the total polymer composition; (D) optionally a cross-linking agent; and (E) optionally at least one further additive selected from the group consisting of antioxidants, scorch retarders, cross-linking boosters, stabilizers, processing aids, flame retardant additives, acid scavengers, inorganic fillers, voltage stabilizers, and additives for improving water tree resistance; wherein the atactic polypropylene homopolymer (B) has a degree of crystallinity below 0.5%; and wherein the atactic polypropylene homopolymer (B) has a Mw below 35,000.

17. The semi-conductive composition of claim 16, wherein the atactic polypropylene homopolymer has at least 70% of an atactic component.

18. The composition of claim 17, wherein the atactic polypropylene homopolymer has at least 70% of an atactic component.

Description

(1) FIG. 1 reports graphically the VR and MFR results of Table 1.

(2) FIG. 2 reports graphically the VR versus CB of the samples in Table 1.

(3) Table 1 and FIG. 1 also show that the VR increases slightly in the blends containing aPP, but it is still comparable and within the predefined limit of approximately 100 Ω/cm.

(4) It should be noted that in the reference samples #1 to #6, the CB loading is 38 or 40 wt %, and by adding EPP or aPP, it is possible to lower it to approximately 30-36 wt % without significantly sacrificing electrical performance.

(5) In fact, when the amount of CB is decreased but no EPP or aPP is added to the composition as in samples #15 to #21 the volume resistivity increases to an unacceptable level well above 100 Ωcm.

(6) The big change with respect to performances can be seen in the MFR measurements. When using the EPP or aPP, the MFR values dramatically increase. The increase is seen for all types of EVAs and EBAs. In FIG. 1 the MFR values of samples containing EVA, EBA, aPP or EPP are graphically reported.

(7) In summary, the semi-conductive polymer compositions of EVA, EBA, aPP and CB have the following advantageous feature: Similar volume resistivity despite lower CB concentration; Better processability as seen by higher melt flow index; Lower material cost;

(8) when compared with the basic EVA-based semiconducting solutions.

(9) The semi-conductive polymer compositions of EVA, EBA, EPP and CB have the following advantageous feature: Identical electrical performances despite lower CB concentration; Better processability as seen by higher melt flow index; Similar cost;

(10) when compared with the basic EVA/EBA-based semiconducting solutions.

Samples #22 and #23

(11) EMA in Table 2 stands for a conventional copolymer of ethylene with methyl acrylate polymer produced in a tabular reactor of a high pressure polymerization process. It has a MFR (2.16 Kg, 190° C.) of 4 g/10 min and a melting temperature of 105° C. Methyl Acrylate content is of 8 wt %.

(12) CB in Table 2 stands for “Denka Black” carbon black. It is a commercially available granulated acetylene carbon black of carbon black used as conductive filler (C). It has a mean particle size of 35 nm (ASTM D3849-95a procedure D). The iodine number is 93 mg/g (ASTM D1510-07). The DBP absorption number is of 200 ml/100 g (ASTM D2414-06a).

(13) The ethylene-propylene copolymer (EPP) used has a polyethylene content of 8.6 wt % and a polypropylene content of 91.4 wt %. It has a 21.78% of atactic component and 78.22% isotactic component. It has M.sub.w of 17000 and M.sub.n of 8000. It features a degree of crystallinity of 10% and a melting temperature of 80.1° C. The trade name for the ethylene-propylene copolymer (EPP) used is Licocene™ PP 1502 from Clariant, made by a metallocene type catalyst.

(14) The formulations as described in Table 2 have been compounded using a BUSS kneader L603 at 170° C. for approximately 2 minutes at a screw speed of 210 rpm. Mixing of the polymers with CB is done at the same time ensuring proper mixing and allowing the filler particles enough mobility for adequate localization in the preferential phase. Final blends are cooled down with water at room temperature and pelletized for easier use.

(15) Sample #22 is used as reference as it does not include EPP. Sample #17 contains EPP. Both samples include 0.8 wt % of antioxidant (polymerized 2,2,4-trimethyl-1,2-dihydroquinoline, having a melting point of 80-135° C. (CAS:26780-96-1).

(16) TABLE-US-00002 TABLE 2 EMA EPP CB VR25 MFR.sub.21.6 Kg 130° C. Sample wt % wt % wt % Ohm/cm g/10 min NOP 0 NOP 1 NOP 2 NOP 3 NOP 4 #22 69.2 30 45.9 24.8 28 9 3 2 2 #23 65.2 4.0 30 63.9 70.0 48 15 0 0 0

(17) As seen in Table 2 the MFR of the sample containing EPP is dramatically increased while the VR is only marginally affected by the inclusion of EPP. The higher MFR results in a lower compounding pressure. Concerning surface smoothness, the data show that the inclusion of EPP gives smaller protuberances and the number of large surface irregularities is significantly decreased, resulting in an improved surface smoothness.