To obtain an ultrafine polyester multifilament yarn excellent in a soft feeling and color developing properties when formed into a woven or a knitted fabric and further having biodegradability by providing the specific ultrafine multifilament yarn with a single filament fineness within a prescribed range.
This ultrafine polyester multifilament yarn is obtained by directly spinning an aliphatic polyester consisting essentially of poly-L-lactic acid, a polyhydroxybutyrate, etc., having ≥130°C melting point and has -5 to +15% shrinkage percentage in boiling water (SWA) and a dry shrinkage percentage (SD) satisfying the following formula: SWA≤SD≤SWA+10(%). The single filament fineness is 0.1-1 dtex. The woven or knitted fabric is preferably produced by a filament combining treatment of a multifilament yarn having 2-6 dtex single filament fineness and comprising a thermoplastic polymer with the ultrafine polyester multifilament yarn, producing a combined filament yarn and using the resultant combined filament yarn or the ultrafine polyester multifilament yarn as a part thereof.
ARANISHI YOSHITAKA
TAKAHASHI HIROSHI
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