Biodegradable filament nonwoven fabric and method of producing the same

A nonwoven fabric comprising modified cross-section monocomponent filaments of a polylactic acid based copolymer, wherein

• the copolymer comprises a copolymer of D-lactic acid and L-lactic acid, having a melting point of not lower than 100° C., in which the copolymerization molar ratio of one of the D-lactic acid and L-lactic acid is not lower than 90% and that of the other is not more than 10%, or a blend of copolymers of D-lactic acid and L-lactic acid, having a melting point of not lower than 100° C., in which each of the copolymers has a different copolymerization molar ratio of the D-lactic acid and L-lactic acid within the range that the copolymerization molar ratio of one of the D-lactic acid L-lactic acid is not lower than 90% and that of the other is not more than 10%,
• the filaments have a degree of crystallinity of 12 to 30 wt % and a crystal size of not greater than 80 Å as measured axially of the filaments, and
• the nonwoven fabric comprises filaments partially bonded to each other with heat and pressure to create fusion-bonded spots in a partially bonded area of the fabric, the nonwoven fabric having a boiling water shrinkage percentage of not higher than 15% and a compressive resilience of not more than 150 g for each weight per unit area of 100 g/m2,
• wherein the partial bonding with heat and pressure is effected so that each fusion-bonded spot has an area of 0.2 to 15 mm2, a distribution density of the fusion-bonded spots in the partially bonded area is 4 to 100 spots/cm2, and a percentage of the fusion-bonded spot area to the partially fusion-bonded area is 3 to 50%.

A method of producing a nonwoven fabric composed of polylactic acid based monocomponent filaments, the method comprising the steps of:

• melting a polylactic acid based copolymer, which has a melt flow rate of 10 to 100 g/10 min as measured at 210° C. in conformity with ASTM-D-1238, at a temperature of (Tm+20)° C. to (Tm+80)° C. (wherein Tm is the melting point of the polylactic acid based copolymer), the polylactic acid based polymer being a copolymer of D-lactic acid and L-lactic acid, having a melting point of not lower than 100° C., in which copolymerization molar ratio of one of the D-lactic acid and L-lactic acid is not lower than 90% and that of the other is not more than 10%, or a blend of copolymers of D-lactic acid and L-lactic acid, having a melting point of not lower than 100° C., in which each of the copolymers has a different copolymerization molar ratio of the ID-lactic acid and L-lactic acid within the range that the copolymerization molar ratio of one of the D-lactic acid and L-lactic acid is not lower than 90% and that of the other Is not more than 10%;
• extruding the resulting melt through a spinneret into monocomponent filaments;
• drafting the resulting monocomponent filaments at a drafting speed of 3,000 to 6,500 m/min by means of a suction device;
• and then spreading open each other and accumulating the drafted monocomponent filaments on a movable collector surface thereby to form a web;
• and
• partially bonding the web with heat and pressure at a temperature lower than the melting point of the copolymer to form fusion-bonded spots, whereby each fusion-bonded spot has an area of 0.2 to 15 mm2, a distribution density of the fusion-bonded spots in the web is 4 to 100 spots/cm2, and a percentage of the fusion-bonded spot area to the total web area is 3 to 50%.