Patent GB-339599-A (GB)
Title: Improvements in or relating to the manufacture of paper
IPC: D21C3/26
Filed: 1929-08-28
Abstract: 339,599. White, A. E., (Mead Pulp & Paper Co.). Aug. 28, 1929. Divided on 339,3:34. Pulp, preparation of. - In the preparation of a free pulp of high strength, colour, and clay carrying quality suitable for paper making from wood, straw, fibrous grasses and the like, the material is first subjected to an incomplete chemical digestion, the condition being controlled to maintain substantial neutrality of the cooking liquor during digestion and to effect only a partial defibering of the fibrous material, after which it is subjected to multi-stage and coordinated chlorination treatment, the first stage being with an insufficient amount of chlorinating agent acting at a limited temperature on a diluted pulp, the second acting on a thickened pulp with a stronger chlorinating agent. The process is particularly applicable to the treatment of hard deciduous or non-resinous broad-leafed wood such as chestnut, oak, walnut, mahogany, gum, and the like, which occur as waste wood in woodworking and furniture factories, and for treating other waste wood supplies such as leached chestnut chips from tannin extract mills, cull lumber, wood shavings, saw mill waste &c. The drawings illustrate suitable apparatus for the process and the treatment of leached chestnut chips as described. These are fed from a chip storage or breaker 10 by a conveyer 11 to the feed hopper 12 of a digester 13 where the material is heated for 1-2 hours at 125 C. with a solution of an alkali metal sulphite such as a sodium sulphite and a salt of a weakly ionized polybasic acid such as sodium bicarbonate, or a tartrate. citrate, borate or oxalate. The excess liquor is then withdrawn and the temperature raised to 160-180 C. for 1-4 hours, carbonic acid gas being supplied at 30 to maintain the liquor approximately neutral. The digested material is washed in the tank 35, then fed by a conveyer 42, bucket elevator 56 and conveyer 57 to a rod mill 60, or other disintegrator such as a Bauer mill, swinghammer mill, edge runner mill, or the like. Further treatment apparatus includes stock chests 68, 102, head boxes 76, 108, mixing box 83, screen 90 and Oliver filter 95. From the head box 108 the material suitably diluted is fed by the pipe 110 together with chlorinating agent from a pipe 111 to a mixer 113, and flows continuously therethrough into a chamber 115 provided with a baffle, the capacity of the chamber and the rate of flow being adjusted to provide the desired reaction time. Suitable chlorinating agents are chlorine, sodium hypochlorite. bromine and the like. After the first chlorination. the material passes to a washing apparatus, a worm-type drum washer 123 being shown. Treatment in a centrifugal thickener 131 follows and the thickened stock passes by an elevator 142 to a chlorinating tower 143 where a strong and drastic chlorination is effected with chlorine gas, or bromine, admitted at 150, out-- lets 151, 152 being provided for the discharge of gas which passes to recovery apparatus. Water or other slushing liquid is introduced at the base and the stock passed to an annular trough 158 and thence to a tank 162, where an alkali such as caustic soda, sodium carbonate or sodium sulphite is supplied to dissolve the reaction products of chlorination. Filtering in an Oliver or like filter 176, bleaching in the tanks 180, 183, 184, and the final filtering at 192 completes the process and the treated material passes to a stock chest 194 for further treatment or for use. The product is easily hydrated and is thus suitable for bonds, writing papers, parchment, glassine, waxpapers, and the like.