Non-woven fabric for alkali cell separator and process for producing the same

A process for producing an non-woven fabric for an alkali cell separator, comprising the following steps:

• forming a web of fibers comprised of polyolefin, by a wet process, applying a hydroentangling treatment to a surface of said web by use of columnar water stream jet nozzles each in such a shape that an injection outlet opening is broader than a water stream inlet opening, the jet nozzles being provided in an injector of a hydroentangling apparatus, followed by a corona discharge treatment of the entangled web surface and by a calender treatment thereof.

A non-woven fabric for an alkali cell separator, comprising the following:

• fibers comprising polyolefin, wherein the non-woven fabric has a standard deviation of pore diameter distribution of not more than 20 .mu.m, as determined by bubble point method and a percentage of number of pores falling within a range of average pore diameter of .+-.2 .mu.m of not less than 35% of total number of pores in the entire non-woven fabric, the non-woven fabric being subjected to a corona discharge treatment.

A non-woven fabric for an alkali cell separator comprising a non-woven fabric for an alkali cell separator substantially free from perforations therethrough, formed mainly from fibers comprised of polyolefin, partially containing an ethylene/vinyl alcohol copolymer or cross-linked polyethylene oxide and subjected to a corona discharge treatment, where a peak area ratio of oxygen (O) to carbon (C) (C/O ratio) on the surface of the non-woven fabric is 0.50 to 1.85 and at an intermediate position in the thickness direction thereof the C/O ratio is 0.45 to 1.40, as determined by electron spectroscopy (ESCA).

A non-woven fabric for an alkali cell separator, comprising a non-woven fabric substantially free from perforations therethrough, formed mainly from finely creased fibers comprised of polyolefin, partially containing an ethylene/vinyl alcohol polymer and having a large number of fine creases on the surface of fibers and subjected to a corona discharge treatment, where a peas ratio of oxygen elements (O) to carbon elements (C) (O/C ratio) on the surface of the non-woven fabric and that at an intermediate position in the thickness direction thereof are 0.60 to 1.35 and 0.50 to 1.00, respectively, as determined by electron spectroscopy (ESCA).

A process for producing a non-woven fabric for an alkali cell separator, comprising the following steps:

• forming a non-woven fabric substantially from fibers comprised of polyolefin, partially containing an ethylene/vinyl alcohol copolymer or cross-linked polyethylene oxide, and subjecting the non-woven fabric to a corona discharge treatment by use of multi-electrodes having a round electrode tip end at a discharge intensity of not more than 20.0 w/cm.sup.2, thereby making a peak ratio of oxygen elements (O) to carbon elements (C) (O/C ratio) on the surface of the non-woven fabric and that at an intermediate position in the thickness direction thereof 0.05 to 1.85 and 0.45 to 1.40, respectively, as determined by electron spectroscopy (ESCA).