Heat-bonding conjugated fibers and highly elastic fiber balls comprising the same

Highly elastic fiber balls comprising a crystalline thermoplastic elastomer E and a nonelastic polyester P having a higher melting point than that of said elastomer E arranged at an area ratio E:P of 20:80 to 80:20 in the circular fiber cross section;

• said fiber balls being composed of a staple fiber group containing a blend of heat-bonding conjugated fibers having the cross section and surface thereof specified by the following requirements (1) to (5) in an amount of 5 to 49% by weight based on the total fiber weight with nonelastic crimped polyester staple fibers;
• flexible heat-bonded spots being formed in at least a part of the fiber crossover points of the mutual heat-bonding conjugated fibers or the heat-bonding conjugated fibers with the nonelastic crimped polyester staple fibers:
• (1) said elastomer E is arranged in a crescent shape formed by two circular arcs having different curvature radii and a curve having a larger curvature radius r.sub.1 forms a part of the outer circumference line in the fiber cross section;
• (2) said polyester P is joined to said elastomer along a curve having a smaller curvature radius r.sub.2 in the two curves forming the crescent shape and, on the other hand, the curve having the larger curvature radius r.sub.1 forms a part of the fiber surface in a circular arc form so as to provide the outer circumference line within the range of the circumference ratio R of 25 to 49% in the fiber cross section, with the proviso that the circumference ratio R is defined by the ratio of the outer circumference line L.sub.3 to the whole circumference L.sub.1 +L.sub.3 in the circle having the radius r.sub.1 in FIG. 1 and calculated by an equation R={(L.sub.3)/(L.sub.1 +L.sub.3).times.100 (%)};
• (3) the curvature radius ratio Cr which is the ratio r.sub.1 /r.sub.2 of the curvature radius r.sub.1 to the curvature radius r.sub.2 is higher than 1 but not exceeding 2;
• (4) the bending coefficient C of the curve having the curvature radius r.sub.2 is within the range of 1.1 to 2.5 with the proviso that the bending coefficient C is defined by the ratio of the length of the circular arc L.sub.2 having the radius r.sub.2 to the length L between contact points P.sub.1 -P.sub.2 formed by the circumference of the circle having the radius r.sub.1 and the circular arc (L.sub.2) in FIG. 1 and calculated by an equation C=(L.sub.2)/(L) and
• (5) the wall thickness ratio D of said elastomer E to said polyester (P) is within the range of 1.2 to 3 with the proviso that the wall thickness ratio D is defined by a ratio of the length LP of a polyester component P in the direction of a straight line passing through the center of the circle having the radius r.sub.1 and the center of the circle containing the circular arc having the radius r.sub.2 as a part thereof to the length LE of the elastomer component E in FIG. 1 and calculated by an equation D=(L.sub.P)/(L.sub.E).