Patent ID: 6779440
Filing Date: 2004-08-24
Classification: D21G

Abstract:
A method for calendaring a moist paper or paperboard web made with pulp, comprising the steps of:moving the moist paper or paperboard web under a slight external pressing pressure through a long nip formed between two smooth, moisture impermeable counter surfaces from which at least one is heated, and a first surface of the web is in contact with the first counter surface and a second surface of the web is in contact with the second counter surface, wherein the first counter surface has a first temperature of at least 100Â° C. and the second counter surface has a second temperature which is higher than the first temperature and at least 160Â° C., the web being moved in such a way that the second surface of the web is calendered during traveling between the first counter suface and the second counter suface by the contact with the second counter surface; and wherein the web is calendered during traveling between the first counter surface and the second counter surface such that the web has an inner vapour pressure inside the moist paper or paperboard web which is increased due to the heating of the web and the restriction of the evaporation of moisture from the web by means of the first counter suface and the second counter suface, said inner vapour pressure acting to resist resisting the slight pressing pressure between the the first counter surface and the second counter surfaces, thus counteracting reduction of the thickness of the paper or paperboard web during calendering.