Process for producing high knot strength polyamide monofilaments

DETAILED DESCRIPTION OF THE INVENTION The process of the present invention basically comprises at least three steps including drawing undrawn monofilament (M.
sub.
1) to thereby make it partially oriented monofilament (M.
sub.
2), heating the monofilament (M.
sub.
2) in steam and relaxing its length to some extent to produce a relaxed monofilament (M.
sub.
3), and imparting second-stage drawing to the monofilament (M.
sub.
3) to produce a completely drawn monofilament (M.
sub.
4).
Further, as occasion demands, a fourth step may be added which comprises passing the monofilament (M.
sub.
4) through a hot water zone, thereby relaxing and heatsetting the monofilament to about 0.
9-1.
0 times its length.
The steps of this invention will now be discussed in detail, one by one.
The designation of steps by number is not intended to mean that these are the only steps to be practiced since many other procedures may be used before, after, between, or during the practice of the numbered steps explained in detail hereinafter.
First Step: This step comprises drawing undrawn polyamide monofilament (M.
sub.
1) melt spun through an inlet (a spinneret) to about 3-5.
5 times its length, to provide a partially oriented monofilament (M.
sub.
2) having a diameter of about 0.
05-2 mm.
The polyamide is melt spun using any of a variety of known processes, is passed through a short cooling zone and thereafter the spun monofilament is quenched by a refrigerant of water, trichlorethylene or n-hexane to produce an undrawn monofilament (M.
sub.
1).
Any of the known polyamides may be used in the practice of the present invention.
These include, but are not limited to homopolymers such as polyhexamethylene adipamide (nylon 66), polyhexamethylene sebacamide (nylon 610), polycapramide (nylon 6), polydodecanamide (nylon 12) and polyhexamethylene isophthalamide (nylon 6I) and the like.
Also included are copolymers thereof and blended polymers thereof.
However, nylon 6 and copolymers thereof are considered to be optimum polyamides for use as fishing nets and fishing lines for which monofilaments of the present invention are typically used