Continuous prodn. of white viscose yarn - by two-stage coagulation, and washing with water of acid pH (PT 26.2.82)

In continuous prepn. of very white viscose rayon yarns, a viscose soln. is extruded into a coagulation bath, giving an extruded fibre with coagulation index 15-25. The extruded fibre, moving in a spiral path, is drawn, and coagulation is completed to a coagulation index not greater than 1, followed by washing with non-alkaline water until the max. contents in the fibre are: total S 0.2%, sulphide S 0.02%, elemental S 0.06%, Fe 40 ppm, Zn 700 ppm, and Pb 30 ppm. The partly coagulated fibre is drawn in a ratio of 1-1.57. Completion of coagulation may be by (a) extension of the time, without use of reagents other than that entrained on the yarn, and/or (b) treatment with acid, e.g. H2SO4 contg. ZnSO4 and/or Na2SO4, e.g. at 50-100 deg.C. Opt., the fibres may be treated in baths of varying acidity. Water treatment is esp. at 20-30 deg.C for 25-40 secs., using water with pH 4-5.5 (4-4.7) and contg., per 1 not more than 1.5 mg Ca(2+) and 1 mg Me(2+). The water may be purified with a weakly acid ion-exchange resin. The max. metal contents of the yarn are pref.: 20 ppm Fe, 500 ppm Zn, and 10 ppm Pb. The rate of spinning is pref. at least 90 m/min. White yarns are obtd. by a simpler method. L'INVENTION A POUR OBJET UN PROCEDE DE PRODUCTION CONTINUE DE FILS DE RAYONNE VISCOSE A DEGRE ELEVE DE BLANC. CE PROCEDE COMPREND L'EXTRUSION D'UNE SOLUTION DE VISCOSE DANS UN BAIN DE COAGULATION, L'ETIRAGE ET LA COAGULATION DES FILAMENTS OBTENUS, LA MISE EN CIRCULATION DESDITS FILAMENTS SELON UN PARCOURS SENSIBLEMENT HELICOIDAL ALORS QU'ILS SONT SOUMIS A TOUS LES TRAITEMENTS NECESSAIRES A LA PRODUCTION DU FIL TERMINE ET QUI COMPRENNENT, APRES LA SORTIE DES FILAMENTS DU BAIN DE FILAGE, L'ACHEVEMENT DE LA COAGULATION SELON UN INDICE DE COAGULATION QUI N'EST PAS SUPERIEUR A 1 ET UN TRAITEMENT AVEC L'EAU, A UN PH NON ALCALIN.