| 摘要 |
At least one polyamine of the formula NH2(CH2CHR.NH)nH in which R is hydrogen or a methyl group and n is 1-4 is added to an aqueous bleaching bath containing a water-soluble metal chlorite, and having a pH of 2-7, in an amount sufficient to prevent the evolution of chlorine dioxide from the bath but insufficient to destroy the bleaching power of the chlorite. Alkali or alkaline-earth metal chlorites, e.g. sodium, lithium, potassium and calcium chlorites, are preferably used and the concentration, in the case of sodium chlorite is preferably 0.1 to 20 grams per litre. The polyamines, which may be in the form of their hydrochloride or phosphate salts, may be used at concentrations within the range of 10 to 500 parts per million by weight in a bleaching bath containing about 1,000 to 2,000 parts per million by weight of sodium chlorite or p equivalent amounts of other water-soluble metal chlorites. The bath may also contain buffers, e.g. Na2HPO4, NaH2PO4, polyphosphates, NH4HF2, sodium acetate and acetic acid, to maintain a constant pH, wetting agents, e.g. the salts of acylalkyl taurides, up to 0.50 moles of ammonium nitrate or alkali or alkaline-earth metal nitrate per mole of chlorite, to reduce corrosion of stainless apparatus, and 5 to 50 parts per million by weight, based on the solution of a chelating agent, e.g. ethylene diamine tetra-acetic acid, hydroxyethyl-ethylene diamine triacetic acid, imino diacetic acid, nitrilo-triacetic acid and symmetrical ethylene diamine diacetic acid and their salts, and citric, maleic, lactic and tartaric acids and salts of citric and tartaric acids, to minimize the action of iron and other metal ions, e.g. nickel and cobalt, in engendering the formation of chlorine dioxide. The polyamine may be added to the bleaching bath as an aqueous concentrate containing the polyamine and an alkali or alkalineearth metal nitrate, a suitable concentrate having the composition: nitrate 20%-32% by weight, polyamine 5%-12% by weight and chelating agent 3%-10% by weight, the balance being water. Alternatively, the polyamine may be added to the bleaching bath as a solid composition containing the polyamine, preferably in the form of a hydrochloride or phosphate, an alkali-metal nitrate and a buffering agent, a suitable solid composition being: nitrate 30%-55% by weight, buffer 25%-50% by weight, polyamine (or salt) 8%-12% by weight and chelating agent 3%-20% by weight. The bleaching of cotton, polyacrylonitrile and polyethylene terephthalate fibres is described. U.S.A. Specifications 2,358,866 and 2,526,839 are referred to. |
