SPUNBONDED NONWOVEN FABRIC AND PRODUCTION METHOD THEREFOR

The present invention provides a spunbonded nonwoven fabric which has a smooth surface, is highly unlikely to cause a widthwise curl due to a difference between the states of front and back surfaces, has a superior membrane formability of not allowing, at the time of casting of a resin solution, a bleed-through of the resin solution due to excessive permeation, a peel-off of a membrane substance, or any other defect such as nonuniform membrane or pin hole due to fluffing of the support, and further exhibits membrane bondability that is strong enough to prevent the membrane substance from peeling off after membrane formation.The spunbonded nonwoven fabric of the present invention is a spunbonded nonwoven fabric composed of thermoplastic fibers. In this spunbonded nonwoven fabric, the thermoplastic fiber is a conjugate fiber in which a low-melting polymer having a melting point lower by 10 to 140°C than that of a high-melting polymer is provided around the high-melting polymer, an apparent single fiber fineness of the conjugate fiber as viewed from the surface of the spunbonded nonwoven fabric is 0.5 dtex or more and 10 dtex or less. When the apparent single fiber fineness of the conjugate fiber is 0.5 dtex or more and less than 2 dtex, an apparent density is 0.50 to 0.70 g/cm, and air permeability satisfies the following [formula 1]. When the apparent single fiber fineness of the conjugate fiber is 2 dtex or more and 10 dtex or less, the apparent density is 0.50 to 0.80 g/cm, and the air permeability satisfies the following [formula 2]...