GB545124A - Improvements in or relating to the manufacture of paper - Google Patents

Abstract

545,124. Coated paper. K. C. M. CO. Aug. 21, 1940, No. 13305. Convention date, Sept. 26, 1939. [Class 96] Paper, e.g. for high grade printing and made from a furnish including soda, sulphite, ground wood, broke and kraft pulps, and after preliminary drying to 3 to 8 per cent. moisture content and calendering, is coated under adjustable pressure by rolls 35, 36 carrying sufficient mixture to coat the paper and to leave a thin film on the roll surfaces so that further coating. mixture spreads uniformly over the roll surfaces, the mixture having, e.g. 40-56 per cent. of solids as a uniform suspension and having thixotropic characteristics such that by stirring the viscosity 'is reduced and on application to the paper does not exceed 50 poises whereafter it reverts to its normally high viscosity. The web 25 may pass through a 2-roll calender at 10 to 40 per cent. moisture content and 135 lbs. per inch pressure and through a calender 31 at 3 to 8 per cent. moisture content and 350 lbs. per inch, the rolls of either calender being separable so that the calender may be non-operative. The web 25 from the calender 31 preferably passes over a cooled guide roll 110 with a spring suspension 111, between the rolls 35, 36 which may be preceded by a guide roll 112 preferably crowned substantialy and such that the paper first contacts the harder roll 35. The web is preferably subjected to air-blast from slotted or apertured pipes 180 to prevent it adhering to either roll, and at high speed such air may be heated to aid in drying and setting the coating, whereupon the web passes about a roll 171 preferably cooled sufficiently for moisture to condense upon it to further drying rolls 27 and a further calender stack. The roll 35 is carried by arms 50 pivoted at 49 to a fixed framework and at 60a to rods 60 &c. attached to springs 65, 66 &c. such that rotation of a motor 67 &c. causes the roll 35 to be raised or lowered against spring action to control the pressure at the nip of the rolls 35, 36 the pressure being indicated on scales 75, 78, a similar spring system being provided to control the pressure of rolls 37, 37<SP>1</SP> and 140 against the rolls 35, 36 and 37<SP>1</SP> respectively, the arms 50 allowing the roll 35 to be moved away from the roll 36 without disturbing the setting of the roll 37, arms 142 pivoted at 141 allowing the rolls 37<SP>1</SP> and 140 to be moved away from the roll 36 without altering the setting of the roll 37<SP>1</SP> with respect to the roll 140. The coating mixture which may include oxidized starch, casein, clay, ammonium oleate, sodium metaphosphate &c: is supplied through manifolds 115, 115<SP>1</SP> connected by flexible pipes to reciprocated nozzles discharging into nip-troughs with dams 160 at each end. There may be two coating presses and an additional drying unit, the second coating being of,lighter weight and having a smaller proportion of mineral to adhesive than the first.