Filtration media made from melt-blown fibers with improved filtration properties
AssigneeBorealis AG
InventorsJingbo Wang, Markus Gahleitner, Klaus Bernreitner, Joachim Fiebig, Henk Van Paridon, Wilhelmus Sars, Gustaf Tobieson
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Abstract
The present invention relates to filtration media made from melt-blown fibers having improved barrier properties. The melt-blown fibers in the filtration media of the invention are made of a visbroken metallocene-catalyzed propylene homopolymer composition with specified melting temperature Tm and molecular weight distribution (MWD).
Claims16
A filtration medium made of melt-blown fibers comprising a polypropylene composition, wherein:
- (i) the polypropylene composition comprises a propylene homopolymer (HPP) polymerized in the presence of a metallocene catalyst,
- (ii) the polypropylene composition has been visbroken,
- (iii) the polypropylene composition has a melting temperature (Tm) measured by differential scanning calorimetry (DSC) according to ISO 11357 in the range from 152 to 160° C., and
- (iv) the polypropylene composition has a molecular weight Mw (measured with GPC on the filtration medium) of between 20000-200000 g/mol, and a molecular weight distribution (MWD) of between 1.5-5.0.
A process for preparing a filtration medium comprising the steps of:
- (i) polymerizing a propylene homopolymer (HPP) in the presence of a metallocene catalyst system,
- (ii) mixing 90.000 to 99.999 wt % of the propylene homopolymer (HPP) obtained in step (i) together with 0.001-10.000 wt % of a hydroxylamine ester compound for visbreaking,
- (iii) pelletizing the mixture obtained in step (ii) in a pelletizer, and
- (iv) melt-blowing the blend pellets obtained in step (iii) and forming into a filtration medium.
A method of increasing the quality factor of a filtration medium to at least 0.7 when the weight per unit area of the filtration medium is 9.5±1.0 g/m2, the method comprising using a polypropylene composition to prepare the filtration medium, wherein
- (i) the polypropylene composition comprises a propylene homopolymer (HPP) polymerized in the presence of a metallocene catalyst,
- (ii) the polypropylene composition has been visbroken,
- (iii) the polypropylene composition has a melting temperature (Tm) measured by differential scanning calorimetry (DSC) according to ISO 11357 in the range from 152 to 160° C., and
- (iv) the polypropylene composition has a molecular weight Mw (measured with GPC on the filtration medium) of between 20000-200000 g/mol, and a molecular weight distribution (MWD) of between 1.5-5.0.
Dependencies are inferred from the claim text.