Separator for lead acid storage battery
[Problem] A separator for a lead acid storage battery that is prevented from suffering the puncture of a separator formed of a microporous film is to be provided. [Solution] The separator includes: a microporous film having a thickness of from 0.1 to 0.3 mm as a base portion 3 ; plural main ribs 2 a that are provided on one surface 3 a of the base portion 3 ; and plural miniature ribs 2 b that have a lower height than a height of the main ribs 2 a and are provided on the other surface 3 b of the base portion 3 , and the plural miniature ribs 2 b are provided in a linear form with an inter-rib distance P, which is a distance between facing surfaces of the adjacent miniature ribs 2 b , of less than 1.9 mm.
1. A separator for a lead acid storage battery, comprising:
a microporous film having a thickness of from 0.1 to 0.3 mm as a base portion;
plural main ribs that are provided on one surface of the base portion; and
plural miniature ribs that have a lower height than a height of the main ribs and are provided on the other surface of the base portion for contacting a lead portion of an electrode plate,
the plural miniature ribs being provided in a linear form with an inter-rib distance, which is a distance between facing surfaces of the adjacent miniature ribs, of less than 1.9 mm,
wherein the miniature ribs have an inclination to the flow direction of the sheet, the inclination angle being 30° or less.
2. The separator for a lead acid storage battery according to claim 1 , wherein in a case where a contact width of a tip surface having a diameter of 1.9 mm of a needle to the miniature rib in a cross section perpendicular to the linear direction of the miniature rib is changed while repeatedly increasing and decreasing at a constant cycle by perpendicularly touching the miniature rib of the other surface with the tip surface of the needle and moving the needle along a direction of the inter-rib distance, a probability of contacting the tip surface of the needle with the miniature rib is 10% or more and 30% or less, and
the probability is determined from a ratio of a width of the miniature rib that is brought into contact with the needle to a width of the tip surface of the needle while the needle moves for one cycle of the cycle.
3. The separator for a lead acid storage battery according to claim 1 , wherein the miniature ribs have a miniature rib height of from 0.05 to 0.20 mm.
4. The separator for a lead acid storage battery according to claim 1 , wherein the base portion has a thickness of from 0.15 to 0.25 mm.
5. The separator for a lead acid storage battery according to claim 1 , wherein the miniature ribs are provided in a linear form in a direction in parallel to a flow direction of a sheet in compression molding in production of the microporous film.