Patent GB-519865-A (GB)
Title: Improvements in or relating to a process for the treatment of lac or shellac
IPC: C09F1/00
Filed: 1938-10-05
Abstract: 519,865. Treating lac. SUTER, A. F., JANSER, A., and SUTER, W. E. Oct. 5,1938, No. 28925. [Class 95] Solid lac or shellac is subjected to the action of an aqueous solution of an alkali hypochlorite and of an aqueous solution of an alkali, in such a manner that the lac or shellac is dissolved and that the chlorination thereof,is the predominating reaction at first. The lac used should not have been subjected to any preliminary dissolution in alkalies. The alkali used in the process may be added after the reaction between the lac and the hypochlorite has taken place, or may be used, wholly or in part, at the same time as the hypochlorite is used. Treatment may take place in the presence of a free-oxygenyielding substance, such as hydrogen peroxide, potassium permanganate, sodium chlorate, sodium perchlorate, sodium peroxide or sodium perborate, and when the oxygen-yielding substance is alkaline, it may provide some or all of the alkali required for the treatment. The process achieves a superior bleaching effect upon the lac, without breaking down the lac matter. According to examples : (1) orange shellac is finely ground and treated with sodium hypochlorite solution at 35‹C. The liquor is removed, and the remaining lac is treated with more hypochlorite solution. This is repeated until all of the lac is dissolved. The extracts are mixed, and hydrogen peroxide solution is added. When frothing has subsided, an aqueous solution of caustic soda is added. The solution is cooled and precipitated with dilute sulphuric acid ; (2) ground seed lac is stirred into sodium hypochlorite solution at 30‹C., and while the reaction is vigorously proceeding, hydrogen peroxide solution is added. When the reaction has abated, a solution of sodium carbonate at 95‹C. is added, followed by the addition of cold water, cooling, filtration and precipitation with hydrochloric acid ; (3) washed and ground stick lac is made into a slurry with water at 20‹C., and there is added an aqueous solution of sodium hypochlorite and sodium carbonate. A vigorous reaction takes place, the temperature rising to 45‹C. A solution of sodium carbonate and sodium peroxide is run in, with stirring. Finally, cold water is added, and the solution is filtered and precipitated with dilute acetic acid, the precipitate being washed, and dried in vacuo ; (4) ground seed lac is stirred to a slurry with a solution consisting of water, sodium hypochlorite and sodium carbonate. While the reaction is still vigorously proceeding, an aqueous solution of sodium carbonate is stirred in. Cold water is finally added and the treated lac then precipitated ; (5) seed lac is ground to a paste-like slurry with an aqueous solution of sodium hypochlorite and sodium hydroxide. When the reaction has subsided. cold water is added, the.liquor is separated, and the dissolved lac matter is precipitated therefrom. To the drained undissolved lac is then simultaneously added an aqueous solution of sodium carbonate and sodium chlorate, at 85‹C., and a solution of sodium hypochlorite and sodium carbonate. When solution is complete and the reaction has subsided, the lac is recovered. Specification 496,124 is referred to.