Steam drawing of polyester monofilament to improve loop strength and resistance to fibrillation

The method of improving the loop strength and resistance to fibrillation of a high denier polyethylene terephthalate monofilament which comprises the sequential steps of:

• (a) passing, prior to any previous orientation drawing thereof, a spun linear polyethylene terephthalate monofilament having an intrinsic viscosity of at least 0.6 and having a denier in the range of from 500 to 50,000 through a vapor medium containing entrained water in droplet form at an elevated temperature;
• (b) impinging said vapor medium onto the surface of said monofilament at substantially right angles to the longitudinal axis of the monofilament whereby the temperature of said monofilament is raised above the apparent second order transition temperature, but below the apparent melt temperature of the particular polyethylene terephthalate;
• (c) drawing the monofilament in a first drawing operation by gradually tapering and deforming said monofilament from its undrawn dimensions to its drawn dimensions in a draw ratio of from 1.5:1 to 4:1 while exposed to said vapor medium at a predetermined pressure to optimize loop strength;
• and
• (d) further drawing the monofilament in a subsequent drawing operation to an aggregate draw ratio of from 4:1 to 10:1, and thereby increasing the loop strength of the monofilament to at least 2.5 grams/denier.

The method of improving the loop strength and resistance to fibrillation of a polyethylene terephthalate monofilament which comprises the sequential steps of:

• (a) passing, prior to any previous orientation drawing thereof, an extensible spun linear polyethylene terephthalate monofilament having an intrinsic viscosity of at least 0.6 and having a denier in the range of from 500 to 50,000 through an elongated chamber;
• (b) exposing the monofilament to a steam medium at an elevated temperature and pressure within said chamber whereby the temperature of said monofilament is raised above the apparent second order transition temperature, but below the apparent melt temperature of the particular polyethylene terephthalate;
• (c) drawing the monofilament in a first drawing operation while exposed to said steam medium at a draw ratio of from 1.5:1 to 4:1 and at a predetermined steam pressure to optimize loop strength;
• and
• (d) further drawing of the monofilament in a subsequent drawing operation at a draw ratio of at least 1.5:1 and to an aggregate draw ratio of from 4:1 to 10:1 to enable the monofilament to be provided with a loop strength of at least 2.5 grams/denier.