Synthetic polymer multifilament yarn useful for bulky yarn and process for producing the same

A synthetic polymer multifilament yarn capable of being converted to a bulky yarn, consisting of a plurality of irregular individual filaments, each of which individual filaments comprises a filament-forming synthetic polymer and is composed of:

• (A) at least two belt-shaped filamentary constituents each extending along the longitudinal axis of the filament;
• (B) at least one core filamentary constituent sinuously extending in wave form along the longitudinal axis of the filament, having a thickness thereof varying alternately between thick and thin and arranged between the belt-shaped filamentary constituents;
• and
• (C) at least two middle filamentary constituents each extending along the longitudinal axis of the filament and located between the core constituent and the belt-shaped constituents to connect the core constituent to the belt-shaped constituents therethrough, and in each of which individual filaments:
• (a) the core constituent has a cross-sectional profile having an inscribed circle thereof having a diameter (lB);
• (b) the belt-shaped constituents have a substantially I-shaped cross-sectional profile;
• (c) the middle constituents have a waist-formed cross-sectional profile having a narrowest portion thereof;
• and
• (d) cross-sectional regions consisting of the I-shaped cross-section segments and half portions of the middle cross-section segments located between the I-shaped segments and lines drawn along the narrowest portions of the middle segments have inscribed circles having diameters (lC) smaller than the diameter (lB) of the inscribed circle of the core segment.