GB1325107A - Polyester filaments and their production - Google Patents

Abstract

1325107 Polyester filaments TEIJIN Ltd 10 Aug 1971 37484/71 Heading B5B A heat-resistant polyester filament is (i) composed of an aromatic polyester in which at least 90 mole per cent of the structural units are ethylene-2,6-naphth.alate units, (ii) has a melting point T m at a constant length of at least 287‹ C. (iii) has a density d of at least 1À370 g/cm<SP>3</SP>, (iv) is insoluble at 160‹C. in a mixed solvent containing 6 parts by weight of phenol and 4 parts by weight of o-dichlorobenzene and (v) meets the requirements expressed by the following formulae where L is a value indicating the crystal size of the aromatic polyester of the filament in the direction almost vertical to the filament axis, said L value being expressed by the equation :- in which B is a (010) diffraction peak width in radian units when the diffraction intensity is (It + Iam)/2 (where It is a diffraction intensity at (010) peak position and Iam is a meridional X-ray diffraction intensity at Bragg's reflection angle 2# = 15À6 degrees), # has the same value as in the above equation for the reflection angle, b is 0À00204 radian, K is 0À94 and # is 1À542; #n denotes the absolute value of the birefringence of the filament determined by the retardation technique using α-bromonaphthalene as a dipping liquid and a Berek compensator; and T m and d are as defined above. Preferably, such a filament has a heat-shrinkage at 255‹ C. for 5 sees. of not more than 5% and a thermal deformation temperature exceeding 260‹ C., a melting point at constant length of at least 288‹ C. is insoluble in 6 : 4 by weight mixture of phenol and o-dichlorobenzene at 170‹ C., has a Young's modulus of more than 1500 Kg/mm<SP>2</SP> at 25‹ C., a denier of 50 or less and a hydrolysis resistance of more than 75%, expressed in terms of the per cent tenacity retention obtained when a sample filament is heated under no tension at 180‹C. and at a relative humidity of 100% for 1 hour. The filament is made by heat-treatment of a melt-spun filament composed of a polyester containing at least 90 mole per cent of ethylene- 2,6-naphthalate units and which has a birefrigence of at least 0À27, wherein the filament generally after preliminary stretching e.g., at 120‹-165‹ C. at a draw ratio of 4 : 1, or at 150‹C. at a draw ratio of 5À8 followed by stretching at 200‹ C. at a draw ratio of 1À25, is heated first at 160‹ to 250‹ C., then at 250‹ to 290‹ C., the time t in hours for which the filament is maintained at any particular temperature T (in ‹C) in the range of 250 to 290‹ C. being such that the sum of all the values E expressed by the equation is at least 1, preferably at least 1À5. Desirably, the filament is heated at 160 to 250‹ C. for 0À5 to 40 sees. In examples, first stage heating is effected for 10 seconds and second stage heating for periods of from 5 mins. to 4 hours. The filament may be heated at at least two different temperatures within the range of 160-250‹ C. and/or within the range of 250- 290‹C. Suitably the filament has a denier of at most 50, a birefringence of at least 0À3 and intrinsic viscosity of 0À35 to 1À0, especially 0À55 to 1À0, determined in a 1% by weight solution of ochlorophenol at 35‹ C., using 120 mg. polymer in 100 ml. of solvent. During the heat-treatment the length of the filament should not change by more than Œ15%, preferably Œ10% and especially Œ5%. In Examples, the first-stage heat-treatment is effected at constant length and the second stage either at constant length, or conditions allowing up to 4À5% shrinkage or up to 4À5% elongation.