Process for producing a highly bulky nonwoven fabric

Claim 1

A process for producing a highly bulky nonwoven fabric which comprises: (a) melt-spinning a first component consisting of a crystalline propylene polymer and a second component consisting of an ethylene polymer into composite fibers having a side-by-side or sheath-core configuration so that the second component can occupy at least a portion of the fiber surface continuously in the lengthwise direction of the fibers, the Q value, ratio of the weight average molecular weight to the number average molecular weight of said first component after melt-spinning being 3.5 or greater, to prepare unstretched fibers; (b) collecting said unstretched fibers into the form of a continuous tow; (c) preheating the resultant tow to a temperature of 80° C. or higher but lower than the melting point of said second component in advance of stretching, (d) successively stretching said tow in a stretch ratio of three times or more the original length thereof, in which ratio neither of said composite components break; (e) cooling the resulting stretched tow down to a temperature below the preheating temperature, at and after the point where the stretching has been finished, (f) cooling the stretched tow down to 50° C. or lower and then drawing it by means of a pair of nip rolls, at least one of which is of a non-metal, to obtain heat-adhesive composite fibers having apparent crimps, the number of which is 4 to 12 per inch and the percentage crimp modulus of which is 75% or higher, and having substantially no latent crimpability; and (g) subjecting a web consisting only of said heat-adhesive composite fibers or containing at least 20% by weight of said heat-adhesive composite fibers to heat treatment at a temperature equal to or higher than the melting point of said second component of the composite fibers, but lower than the melting point of said first component thereof, to obtain a highly bulky nonwoven fabric stabilized in structure mainly by the melt-adhesion of the second component of said heat-adhesive composite fibers.