Polyethylene membrane and method of its production
AssigneeLydall Solutech B.V.
InventorsGijsbertus Hendrikus Maria Calis, Hendrik Derk Hoving
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Abstract
The invention relates to a porous membrane having a particle filtration value of at least 10 under U.S. Military Standard MIL-STD-282 (1956), where the porous membrane is a polyethylene membrane. The membranes according to the invention are particularly useful for filters such as ASHRAE filters, HEPA filters and ULPA filters for example in heating, ventilating, respirators and air conditioning applications.
Claims17
A gas filtration media, comprising a multilayered polyethylene membrane having a particle filtration, PF, value calculated according to the formula:
- PF=(-log(Penetration (%)/100)/Pressure loss (mm H2O))×100 in which the Penetration (%)=100-Collection efficiency at a Pressure loss (unit:
- mm H2O) measured when air is flowing through the membrane at a flow velocity of 5.3 cm/second and a collection efficiency (unit:
- %) measured using dioctyl phthalate having a particle size of 0.3 μm (U.S. Military Standard MIL-STD-282 (1956)), the PF value of the membrane is at least 20, and wherein the membrane has a porosity of at least 88 vol-%, a thickness of greater than 10 μm to less than 200 μm, and an average pore size of at least 0.5 μm, wherein the polyethylene is stretched in a transverse directions by a factor of at least 10 times the area and in the machine direction alone is stretched by a factor of at least 2.5 times the area.
A method of preparing a gas filtration membrane comprising the steps of:
- providing a mixture of a solvent and a polyethylene optionally with a further component, wherein the polyethylene optionally with the further component is about 5 to 30 weight percent of the total weight of the solvent, extruding a membrane from the mixture, removing the solvent to form a base member, and stretching the membrane by a factor of at least 2.5 to 10 times the original length in a machine direction at a deformation speed of less than 30 mm/s and by a factor of 3 to 10 times the original length in a transverse direction at a speed that provides the membrane for use as a gas filtration media having a PF value of more than 20, a porosity of at least 88 vol-% and an average pore size of at least 0.5 μm.
Gas filtration membrane prepared by a process comprising:
- extruding a solution comprising a polyethylene polymer having a solids content of 10 to 25 weight percent to form a porous multilayered structure;
- stretching the porous polyethylene multilayered structure in a transverse direction by a factor of at least 10 times the extruded width and in the machine direction by a factor of at least 2.5 times the extruded length to form a membrane, wherein the membrane has a particle filtration, PF, value calculated according to the formula:
- PF=(-log(Penetration (%)/100)/Pressure loss (mm H2O))×100 in which the Penetration (%)=100-Collection efficiency at a Pressure loss (unit:
- mm H2O) measured when air is flowing through the membrane at a flow velocity of 5.3 cm/second and a collection efficiency (unit:
- %) measured using dioctyl phthalate having a particle size of 0.3 μm (U.S. Military Standard MIL-STD-282 (1956)), the PF value of the membrane is at least 20, and wherein the membrane has a porosity of at least 88 vol-%, a thickness of greater than 10 μm to less than 200 μm and an average pore size of at least 0.5 μm.
Dependencies are inferred from the claim text.