Patent GB-380488-A (GB)
Title: Improvements in and relating to bleaching
IPC: D06L4/24
Filed: 1931-03-18
Abstract: Cellulosic materials, such as wood pulp, kraft pulp, soda pulp, sulphite pulp, rag pulp, cotton textiles, artificial silks, wood surfaces, ground wood or ground wood pulp are bleached by treatment with an aqueous solution containing a chlorite of an alkali or alkaline-earth metal such as sodium or calcium chlorine the solution being acid, neutral or alkaline as desired.  The treatment may be carried out in one or more steps combined, if desired, with other bleaching treatments such as a treatment with an aqueous solution of an alkaline hydroxide such as sodium hydroxide, a peroxide such as hydrogen peroxide or sodium peroxide, an acid or acid salt such as hydrochloric acid or sodium sulphite or sulphate or with chlorine or a hypochlorite.  Wood pulps, soda pulps, and rag pulps are advantageously bleached in acid solution whilst cotton textiles are with advantage bleached in a non-acid solution preferably in conjunction with kier boiling.  Artificial silks such as cellulose acetate or nitrate, viscose or cuprammonium silks are with advantage impregnated with an alkaline or neutral solution of a chlorite and then treated with an acid substance such as hydrochloric acid or if an alkali metal chlorite has been used with sodium acid sulphite. Wood surfaces such as veneers are bleached with an acid solution such as sodium chlorite and acetic acid.  For laundry purposes the goods may be treated as usual up to the sour excluding the bleaching treatment and a chlorite is added to the sour usually employed such as acetic acid.  It is preferable to avoid undesired reactions such as the precipitation of calcium sulphate through using calcium chlorite in solutions containing a sulphate.  In examples (1) a heated mixture of disintegrated kraft pulp and water is treated with an aqueous solution of acetic acid and caustic soda and then with a solution of calcium chlorite.  The pulp is separated and washed, treated secondly with caustic soda, again separated and washed, and finally the first step is repeated the bleaching solution being added to the cold pulp and water mixture.  (2) A mixture of disintegrated kraft pulp and water is treated with a solution of caldium chlorite and, after heating, the pulp is separated and washed and further treated with hydrochloric acid and calcium chlorite.  (3) A heated mixture of disintegrated kraft pulp and water is treated with hydrochloric acid and calcium chlorite and the washed, separated pulp is treated as in the second step of example (1) the pulp separated therefrom being further treated with hydrochloric acid and calcium chlorite.  (5) Pulp, treated as in the first stage of example (1) is treated with sodium acid sulphite and the washed, separated pulp treated with a mixture of caustic soda, acetic acid, and calcium chlorite separated and washed.  (6) Separated and washed kraft pulp that has been treated with acetic acid and calcium chlorite is treated as in the second stage of example (5) and finally the first step of the treatment is repeated.  (7) The intermediate step of example (1) is replaced by a treatment with sodium acid sulphite the first step being conducted at a lower temperature.  (8) Disintegrated kraft pulp is treated with a mixture of calcium hydroxide and chlorite.  (9) Disintegrated soda pulp is treated with a mixture of hydrochloric acid and calcium chlorite, the separated washed pulp is then treated with acid sodium sulphite and the first step then repeated.  (10) Disintegrated sulphite pulp or blue rag pulp is treated with a mixture of hydrochloric acid and calcium chlorite. (12) Cotton towelling is treated with sodium chlorite and carbonate. (13) Artificial silk threads are immersed in a solution of sodium chlorite and hydrochloric acid, allowed to drain and then washed. (14) Artificial silk skeins are treated with sodium chlorite and phosphoric acid.  (15) Artificial silk threads which have been immersed in a solution of sodium chlorite and hydroxide are treated, after draining, with hydrochloric acid and then drained and washed.