Spunbond non-woven fabric for filter and method of manufacturing said fabric

A method of producing a spunbond non-woven fabric for a filter, comprising sequentially carrying out steps (a) to (d):

• (a) a step of spinning, from a spinneret, a composite polyester fiber containing a low melting point polyester arranged in the vicinity of a high melting point polyester, said low melting point polyester having a melting point 10 to 140° C. lower than the melting point of said high melting point polyester;
• (b) a step of subjecting the spun composite polyester fiber to stretch by suction flow with high-speed suction gas, and then capturing the fiber on a moving net conveyor, to obtain a fiber web containing a composite polyester fiber having a single fiber fineness of not less than 1 dtex and less than 3 dtex at the surface layer and a single fiber fineness of not less than 3 dtex and not more than 5 dtex at the back layer;
• (c) a step of passing hot air through the obtained fiber web, said hot air having a temperature higher than the melting point of said low melting point polyester and lower than the melting point of said high melting point polyester, to perform air-through thermal bonding;
• and
• (d) a step of sandwiching the air-through-thermal-bonded fiber web between a pair of flat rolls or two belt conveyors, and performing heat treatment at a temperature 5 to 75° C. lower than the melting point of said low melting point polyester, to obtain a spunbond non-woven fabric having a basis weight of 130 to 300 g/m2.