Patent GB-637665-A (GB)
Title: Process for dyeing wool
IPC: D06P3/14
Filed: 1947-06-27
Abstract: Wool fibres impregnated with a dyestuff but having substantially no dyestuff fixed thereon are brought into sudden contact under atmospheric pressure with a heated acidic solution. The fibres are impregnated by immersion or padding with a solution that may be non-acidic, preferably weakly alkaline, at a temperature of 20-95 DEG C., usually around 75 DEG  C.  Wetting agents (except alkyl naphthalene sulphonic acids), solubilizing agents (e.g. tragacanth mucilage, cellulose glycollic acid ether) may be added.  Acid, direct and chrome dyestuffs, and ester salts (e.g. sulphates) of leuco-vat dyestuffs may be used, the usual after-treatment being necessary with the last two.  When using ester salts of leuco compounds, it is desirable to add formaldehyde sulphoxylate to the impregnating bath. The impregnated fibres are then brought into sudden contact with an acidic solution above 80 DEG  C., preferably boiling.  The acid may be sulphuric, formic or oxalic, or a mixture of these, the correct pH for the fixation of the dyestuff being attained by the addition of a buffer, e.g. a monobasic phosphate or sodium sulphate. Non-ionic wetting agents may be present.  The time of treatment in the acidic solution may be 1/2 -10 minutes and the process may be continuous. If the dyestuff does not require after-treatment, the goods are now removed, rinsed and finished in the usual way.  If after-treatment is necessary, this may be combined with the present process.  Thus, when using chrome or vat dyestuffs, the goods are passed directly from the heated acidic bath into a hot bath containing a bichromate with or without an acid such as sulphuric or formic.  They are then rinsed and passed into a weak alkaline neutralizing bath, which may also be heated. Alternatively, the goods may, after leaving the heated acidic solution, be treated with chromate or bichromate solution by padding, spraying or immersion and then passed into a further heated acidic bath.  In the case of vat dyestuffs, this may be sulphuric acid, with or without ammonium thiocyanate, oxalic acid or sulphites.  For chrome dyestuffs, formic or acetic acid is desirable and the excess sulphuric acid from the previous bath may be neutralized by the addition of sodium formate or acetate, with ot without ammonium thiocyanate.  These buffers or thiocyanate may be added to the chromate bath as well as or instead of to the second acid bath.  The duration of treatment in the second acid bath may be 1-7 minutes. When this two-bath chroming process is used, the alkaline neutralizing treatment may be omitted, but such treatment is desirable when the two-bath procedure is used for oxidizing the leuco vat dyestuffs.  These latter may be oxidized by sodium chlorate and ammonium vanadate instead of chromate.  Wetting agents may be present in the rinsing and neutralizing baths.  Examples are given of the process of the invention.  U.S.A.  Specification 2,387,200 is referred to.  According to the Specification as open to inspection under Sect. 91, the process may be applied to other animal fibres, e.g. silk, and to other fibres having similar dyeing properties, e.g. artificial casein fibres and animalized cellulose.  The Specification is not limited to treatment at atmospheric pressure. This subject-matter does not appear in the Specification as accepted.