Recombinant battery separator

DETAILED DESCRIPTION The substrate of the recombinant battery separator of the present invention is formed using a conventional melt blowing apparatus.
Such an apparatus typically includes pressurized, heated die through which a plurality of filaments of molten thermoplastic polymer are extruded.
The die also uses heated and pressurized air flowing in the direction of extrusion to attenuate the molten polymer upon exit from the orifices.
The fibers are continuously deposited on a moving conveyor to form a consolidated flat web of desired thickness, which may be cut into the desired shape.
The construction and operation of a melt blowing apparatus for forming a coherent mat are considered conventional, and the design and operation are well within the ability of those skilled in the art.
Suitable apparatus and methods are described in U.
S.
Pat.
No.
3,849,241 and U.
S.
Pat.
No.
3,972,759, incorporated herein by reference.
The polymers used to make the substrate include thermoplastic polymers capable of being melt extruded into a submicron size diameter, and resistant to strong acids.
Potential candidates include polystyrene, polyamides, polyesters and polyolefins, but polypropylene is preferred.
Several approaches are available in the selection of a suitable resin.
So-called metallocene polypropylene resins, produced by single-site catalysis, have a narrow distribution of molecular weight.
A conventional polypropylene resin may be treated with known viscosity reducing agents such as peroxides.
Also, untreated resins having melt flow rates greater than 1000 and preferably greater than 1200 may be employed.
In order to achieve submicron diameters and high surface area, the processing conditions must be optimized for the particular resin employed.
For conventional polypropylene resins having a high MFR, the temperature of the attenuating air must be greater than the temperature of the polymer melt, and preferably at least 15.
degree.
C.
higher.
The rate of flow of the attenuating air may be increased from normal levels until ultrafine fibers are produced