Patent ID: 6758135
Filing Date: 2004-07-06
Classification: D21G

Abstract:
A method for calendering a paper or board web in a multinip calendar, having at least two hot thermo rolls between 100 and 350 degrees C. and at least four polymer covered rolls in the multinip calender,the calender being arranged to form an upper set of rolls having at least a first polymer covered roll followed by a first hot thermo roll, followed by a second polymer covered roll; and a lower set of rolls having a third polymer covered roll followed by a second hot thermo roll, followed by a fourth polymer covered roll; wherein calendering nips are formed between the first polymer covered roll and the first hot thermo roll, between the first hot thermo roll and the second polymer covered roll, and between the third polymer covered roll and the second hot thermo roll, and between the second hot thermo roll and the fourth polymer covered roll; wherein a web is calendered in said calendering nips; and wherein the web is moisturized a first time, on a first side of the web before passing through at least one nip in the upper set of rolls by a first liquid moisturizing device producing a drop size of less than 20 &mgr;m on average so that the moisture content of the web is raised to a moisture content of between 8 and 12 percent, the time between when the web is moisturized the first time and the web passes through said at least one nip in the upper set of rolls is such that the moisture is concentrated in a first surface layer so that the first surface layer has a moisture content of 20 percent to 40 percent while passing through said at least one nip in the upper set of rolls; and wherein the web is moisturized a second time, on a second side of the web before passing through at least one nip in the lower set of rolls by a second liquid moisturizing device producing a drop size of less than 20 &mgr;m on average, the time between when the web is moisturized the second time and the web passes through said at least one nip in the lower set of rolls is such that the moisture is concentrated in a second surface layer so that the second surface layer has a moisture content of 15 percent to 40 percent while passing through said at least one nip in the lower set of rolls.