METHOD OF PREPARING SYNTHETIC TANNER Russian patent published in 2001 - IPC

FIELD: leather industry. SUBSTANCE: invention relates to technology of production of synthetic tanners used in leather industry when manufacturing sole leather for and when filling chrome- tannage leather for uppers in mixture with other synthetic tanners and vegetable extracts in retannage stage. Synthetic tanner is prepared by sulfonation of beta-naphthol at 115-120 C and continuous stirring followed by condensation of resultant beta-naphtholsulfonic acid with dihydroxydiphenyl sulfone employed in the form of aqueous suspension prepared by mixing crushed dihydroxydiphenyl sulfone with water at 40-50 C to homogeneous state. Condensation is carried out in presence of formalin which is added for 1-1.25 h while raising temperature to 80-85 C. Reaction in the whole is continued for 4- 5 h until free formaldehyde is no longer present. Condensation mixture is cooled to 70 C and neutralized by ammonia solution at 70-80 C with velocity 12- 15 l/min to attain pH 3.5-4.3. Product is dried and ground. Such procedure allows adding formalin at lower temperature and eliminating use of ethylenediaminetetraacetic acid, mixture of chlorinated phenols. Excluded is also acidification step involving formic and acetic acids. Duration of formalin-addition stage is considerably reduced (4-5 h instead of 8 h). Tanned leather is characterized by bright coloration. EFFECT: simplified process.