Method for producing a wet-laid nonwoven fabric

A method for producing a wet-laid nonwoven fabric for a semipermeable membrane supporting body, the method comprising:

• performing papermaking according to a wet papermaking method by using a fiber slurry containing a synthetic fiber as a main constituent fiber;
• drying the fiber slurry to form a dried sheet;
• subsequently subjecting the dried sheet to hot press processing a first time and a second time by using a heat calender apparatus,
• wherein the hot press processing at the second time is at a temperature that is higher by 10° C. or more than the hot press processing at the first time,
• wherein the heat calender apparatus used for hot press processing during the first time and the second time is a hard nip heat calender apparatus in which the metal rolls are arranged in four or more stages along a height direction of the hard nip heat calender apparatus;
• thereby obtaining a wet-laid nonwoven fabric for a semipermeable membrane supporting body;
• and
• determining whether the wet-laid nonwoven fabric for a semipermeable membrane supporting body satisfies at least one of a first condition or a second condition by extracting one or more samples,
• wherein the first condition is that spots where a printing ink does not easily adhere on a printed surface side are not observed when solid printing is carried out with the printing ink over an entire surface of the one or more samples,
• wherein the second condition is that when the one or more samples have been cut to a size of 210 mm×297 mm and subjected to solid printing over an entire surface with the printing ink, spots where the printing ink does not easily adhere on a printed surface side are not observed in 95% or more of the one or more samples, and
• using the wet-laid nonwoven fabric on a semipermeable membrane supporting body to which a semipermeable membrane liquid is to be applied if at least one of the first condition or the second condition is satisfied.