Improvements in the bleaching of paper

Paper is bleached by treating it with an aqueous solution of peracetic acid or a salt thereof, e.g. the sodium salt, heating it, e.g. at about 100 DEG C for up to 60 seconds, treating it with an aqueous solution of a hydrosulphite e.g. sodium or zinc hydrosulphite, and drying it. The solutions may be applied by immersing the paper in the solutions, by spraying or by transfer rolls. The peracetic acid or its salt may be present in the solution in a concentration of 0.1 - 2% by weight, the solution optionally being buffered to a pH of 6-9 and being stabilised by the addition of about 1% by weight of a phosphate, e.g. tetrasodium pyrophosphate. After the heating step and prior to treatment with the hydrosulphite solution the peracetic acid on the paper may be neutralized with an SO2 sulphite, bisulphite or metabisulphite solution. The hydrosulphite solution which may have a pH of 4 - 7, may contain 0.1 - 2% by weight of the hydrosulphite and may be stabilised by the addition of 1-3% by weight of a phosphate, e.g. KH2 PO4. After treatment with the hydrosulphite solution the paper may be heated at a temperature of about 100 DEG C for up to 120 seconds. The bleaching may be effected before the final drying step in the paper making process.