Organic anti-shrinking agent for lead storage battery and manufacturing method thereof

The organic shrink-proof agent for a lead storage battery according to the present invention comprises lignosulfonic acid, and is characterized in that the content of reducing saccharides per unit of solid content is 5% by mass or less relative to the total, and the content of the reducing saccharides per unit of solid content is 5% by mass or less relative to the total content of lignosulfonic acid. The content of substances having a molecular weight of 5000 or less per unit solid content is 30% by mass or less of the whole; and a method for producing an organic anti-shrinking agent for a lead-acid battery, the method being characterized by comprising a step for subjecting a black liquor obtained by digesting sulphurous acid/sulfite to ultrafiltration treatment using an ultrafiltration membrane and recovering a concentrated liquor of the black liquor obtained by digesting sulphurous acid/sulfite, and a method for producing an organic anti-shrinking agent for a lead-acid battery, the method being characterize