Bopp film for use in capacitor

Polypropylene homopolymer having

• a content of isotactic pentad fraction of from 93.0 to 99.6%
• a melt flow rate MFR2 according to ISO 1133 from 0.4 to 10.0 g/10 min,
• an aluminium content of more than 0.0 ppm and
• a titanium content of more than 0.0 ppm and
• an ash content of 0.0 - 50.0 ppm, all based on the total amount of the polypropylene composition,
• characterized in that the ash contains more than 0.0 up to at most 25.0 wt.-%, based on the total amount of the ash content, of metals (summed up) selected from elements in IUPAC groups 4 up to and including 13 of the periodic table.

A process for producing a biaxially oriented polypropylene film comprising the steps of:

• (A) providing a polypropylene composition comprising of
• a homopolymer of propylene (A) having a content of isotactic pentad fraction of from 93.0 to 98.0 % and a melt flow rate MFR2 of from 0.4 to 10.0 g/10.0 min, and having
• an aluminium content of more than 0.0 ppm, optionally up to 1.50 ppm and
• a titanium content of more than 0.0 ppm, optionally up to 1.00 pppm, and
• an ash content of 0.0 - 50.0 ppm, all based on the total amount of the polypropylene composition,
• characterized in that the ash contains more than 0.0 up to at most 25.0 wt.-%, based on the total amount of the ash content, of metals (summed up) selected from elements in IUPAC groups 4 up to and including 13 of the periodic table, the metals preferably being aluminium and titan,
• (B) extruding the polypropylene composition to a flat film,
• (C) orienting the flat film simultaneously in the machine direction and in the transverse direction to obtain the biaxially oriented polypropylene film, and
• (D) recovering the biaxially oriented polypropylene film having a dielectric breakdown field strength Eb63.2 of between 550 kV/mm and 630 kV/mm, which is obtained as the Scale parameter α of a fitted two-parameter Weibull distribution based on 50 results, measured with active electrode area of 2.84 cm2 using 250 V/s DC voltage ramp rate on films with a thickness of 3.8-4.2 µm.

A slurry polymerisation process for the preparation of a polypropylene homopolymer having a decaline soluble content in the range of 0.0 to 3.5 wt.-%, wherein the catalyst system comprises:

• a) a Ziegler-Natta catalyst,
• b) Organoaluminum cocatalyst,
• c) External donor of the formula (I)
• wherein
• R1 and R2 are independently H or C1-C3 saturated or unsaturated hydrocarbyl, optionally linked together to give one or more cyclic structures;
• R3 and R4 are independently H or C1-C4 hydrocarbyl, optionally linked together to give one or more cyclic structures;
• R5 is H or C1-C12 hydrocarbyl,
• with the provision that a least one radical of R3-R5 is not a hydrogen.