Naphthalate polyester filaments

Abstract

Naphthalate polyester filaments, yarns or fibers consisting essentially of a naphthalate polyester which has an intrinsic viscosity of 0.3 to 3.5 and a softening point of at least 200.degree. C, and in which at least 85 mol% of the total recurring units consist of units of the formula ##STR1## wherein n is 4 or 6, and having at least one diffraction peak at a Bragg scattering angle 2.theta. = 16.3.degree. -- 16.7.degree. and/or 2.theta. = 25.3.degree. - 25.8.degree. in their X-ray diffraction. These filaments, yarns or fibers are useful especially as an electrically insulating material, an elastomeric reinforcing material, a fluid filter material, a paper-making canvas and a fastener component material. Of these, filaments, yarns or fibers of poly(tetramethylene 2,6-naphthalate) are prepared by melt-spinning the polymer thereby to form undrawn filaments having a birefringence of at lest 0.01 and a density of not more than 1.300, drawing the undrawn filaments in at least one step at a temperature of at least 60.degree. C. at a total draw ratio of at least 1.8, and then heat-treating the drawn filaments at a temperature higher than the temperature employed in the drawing step and within a range of 100.degree. to 240.degree. C. at constant length, under a restricted shrinkage of not more than 15%, or under a stretch of not more than 15%.

Dependencies are inferred from the claim text.