Method and device changing the vapour pressure inside the paper web in calendering
AssigneeMetso Paper, Inc.
InventorsKoivukunnas Pekka, Hannamari Harkonen, Risto Talja
Life of this patent
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Abstract
In the method for calendering a paper or paperboard web, the properties of a paper or paperboard web (W) are modified by changing the vapour pressure inside a moist paper or paperboard web. The device for calendering a paper or paperboard web comprises means for changing the vapour pressure inside the moist paper or paperboard web (W).
Claims8
A method for calendering a moist paper or paperboard web (W) travelling 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, the first counter surface having a first temperature (T1) of at least 100° C. and the second counter surface having a second temperature (T2) of at least 160° C., in such a way that the second surface of the web is calendered during travelling between the counter surfaces by the contact with the second counter surface and that the inner vapour pressure inside the moist paper or paperboard web is increased due to the heating of the web and the restriction of the evaporation of moisture from the web by means of the counter surfaces, said inner vapour pressure resisting the slight pressing pressure between the smooth counter surfaces thus counteracting reduction of the thickness of the web during calendering.
The method according to any preceding claims, characterized in that the first surface of the web is calendered in a similar way.
A device (F, S) for calendering a moist paper or paperboard web (W) comprising two smooth moisture impermeable counter surfaces forming a long nip through which the web (W) to be calendered is arranged to travel under a slight external pressing pressure, and of which counter surfaces at least one is arranged to be heated, and a first surface of the web is arranged to be in contact with the first counter surface and a second surface of the web is arranged to be in contact with the second counter surface, the first counter surface having a first temperature (T1) of at least 100° C. and the second counter surface having a second temperature (T2) of at least 160° C., in such a way that the second surface of the web is calendered during travel between the counter surfaces by the contact with the second counter surface and that the inner vapour pressure inside the moist paper or paperboard web is increased due to the heating of the web and the restriction of the evaporation of moisture from the web by means of the counter surfaces, said inner vapour pressure resisting the slight pressing pressure between the smooth counter surfaces thus counteracting reduction of the thickness of the web during calendering.
Dependencies are inferred from the claim text.