GB1329409A - Method of and apparatus for manufacturing paper or other non- woven fibrous material - Google Patents

Abstract

1329409 Paper making WIGGNS TEAPE RESEARCH & DEVELOPMENT Ltd 6 April 1972 15976/72 Headings D2A and D2B [Also in Division B1] Paper or other non-woven fibrous material is made by producing a foamed liquid medium having a gas dispersed therein as small bubbles and containing a surface active agent, dispersing fibres in the foamed liquid medium and depositing the dispersion on a foraminous support, the percentage volume of gas in the dispersion during its flow to the foraminous support being monitored and the percentage volume of gas in the foamed liquid medium being produced being regulated in dependence upon the results of the monitoring to attain a predetermined percentage volume of gas in the dispersion. To produce the stock, fibres are beaten with water in a Hollander beater 10 and stored in a chest 13 having an agitator 14. From the chest 13 the stock is pumped to a constant-head box 17, circulated through a refiner 19 and passed to a thickener 21 water from which passes to drain or back to the Hollander 10. The thickened stock is mixed with water containing a surface-active agent, in foam producing apparatus 23 comprising vertical mixing cells which foam the liquid by inducting air into vortex produced by each cell. Alternatively, dry fibres may be added to the foamed liquid medium. The percentage volume of air in the dispersion is determined by measuring the electrical conductance of the foam or by a differential pressure cell 100 connected in a vertical conduit 37 leading to a headbox 40, e.g. that described in Specification 1,075,103, the output of the cell being pneumatic or electric and being connected to a gauge or recorder for reading by an operator controlling the apparatus 23 or being used to effect automatic control of the apparatus. The apparatus is controlled by varying the amount of surface-active agent supplied and/or the speed of the mixing cells. The paper-making machine may be of the cylinder type but as shown is a Fourdrinier type having table rolls 41, 44, vacuum boxes 43, 45, 68 and a vacuum couch roll 46. A vacuum pump 47 services the vacuum boxes, the liquid from the first box 43 passing to a separator 49 for removal of air and from there being pumped to a back-water tank 53 by a positive displacement pump 51, Fig. 7 (not shown), the exit of which has a jet for inducing suction in a conduit 56 leading from the second and third boxes 43. Water collected by a collector 57 from the machine wire 91 is also pumped to the tank 53, and the water in the tank 53 is pumped to the foam producing apparatus 23 under the control of a device 90 sensing the liquid level in the apparatus. Make-up surface active agent may be added to the apparatus 23. Liquid from the vacuum boxes 45 and 68 pass to a separator 60 and from there is pumped by a second positive displacement jet pump 61 to a hog pit 64 which also receives surplus trim or broke. An agitator 65 in the hog pit 64 slushes the material therein and a third positive displacement pump 66 pumps it back to the foam producing apparatus 23. Water sprays 71 clean the wire 91 and the water from a collector 72 and a vacuum box 70 goes to drain. A multilayer web may be formed by using several headboxes feeding a single wire. Fillers, e.g. plastics material, may be added to the stock. Foam-producing apparatus The apparatus 23, see also Figs. 2 to 4 (not shown) comprises series connected compartments A, B, C and D, each of the compartments A, C and D containing two vortical foam-producing cells. The stock from the thickener 21 may be fed to the compartment A so that foaming and fibre dispersion occurs simultaneously in that compartment, or it may be fed to the compartment C so that foam is produced in the absence of fibre and the foam production is completed with fibre dispersion in the compartment C. Each foam producing cell comprises a bladed impeller rotated within a stator so that the liquid is subjected to shear and is projected centrifugally at the base of the vortex while air and fibre dispersion, if present, is vertically drawn into the stator. Unfoamed liquid in compartment B is returned to the tops of the cells in compartment A. Back water from tank 53 is pumped to compartment A in dependence upon the level in compartment D sensed by the device 90 controlling the pump. Surface-active agent is metered into compartment A as required. If substantially uniform dispersion of fibres is required the percentage volume of air in the foamed liquid medium is kept between 55% to 75%, the other percentages being used if agglomeration of fibres is required. The surface-active agent may be anionic, cationic or non-ionic. An example of an anionic agent is Ace (Trade Mark), liquid, of a non-ionic agent is a polyoxyalkylene condensate called Texofor (Trade Mank), F.N.15, and of a cationic agent is the proprietary Amine Fb 19. Other agents are octylphenoxypolyethoxy ethanol and commerical grade dodecyl benzene sulfonate. Hot water can be used to form the aqueous solution of surface-active agent. Examples of paper manufacture 1. Filter paper was produced using a furnish of 50% bleached kraft pulp, 25% sulphite pulp and 25% cotton linters. The volume of air in the foam was about 70% and the arithmetical mean diameter of the bubbles was 0.2 m.m. Long fibres forming 10% by weight of the fibres used were added to the apparatus 23, the long fibres being of out, staple nylon of about ¢ inch or 3/4 inch length and 2 denier per fibre. 2. Filter paper furnish was produced by beating cotton linter fibres to 18‹ Sohopper- Riegler, and a wet strength resin of 2% melamine formaldehyde by weight of fibre was added to the furnish. The volume of air was 70%. 3. Filter paper furnish was produced using 67% of free beaten sulphite pulp and 33% antificial latex such as described in Specification 920,848, the latex being added to the fibre dispersion in the apparatus 23. The volume of air was 70%. 4. This example relates to the making of three sheets in a laboratory. The furnish for the first sheet was produced by using 60 gms. of the proprietary Stora 32 softwood pulp disintegrated in 2 litres of water and then diluted by adding 6 litres of water. 6 gms of a particulate clay filler dispersed in 100 ml. of water was then added and the suspension mixed. The furnish for the second sheet was similar but with 20 m.l. of a 33% solution of Nansa (Trade Mark) SL30 surfactant added. The air volume was 64.5%. The furnish for the third sheet was similar but with 50 m.l. of the surfactant added. It was placed in a cylinder and foamed with compressed air until froth overflowed onto a wire, the air volume being 99.4%. 5. This example relates to the making of a sheet in a laboratory and the method was similar to that for making the third sheet in example 4. The furnish was produced using 350 ml. of 0.5% consistency of the proprietary Buckeye H.P.Z. wood pulp beaten to 14‹ S.R. and mixed with 70 m.l. of a 39% solids suspension of the proprietary Primal HA8 acrylic latex which had been partially precipitated to form binder particles. 0.13 gm. of the Nansa S.L. 30 surfactant was added before foaming with compressed air. The sheet had a random net structure with fibre bundles interspersed with holes to give the appearance of fine lace. Reference is also made to the use of short and long crill fibres reinforced with plastics material particles.