| abstract |
The invention relates to a method and apparatus for the surface treatment of paper/board. The method comprises treating a fibrous web with a drying- shrinkage achieving chemical, such that the chemical penetrates substantially throughout the fibrous web thickness, and thereafter the fibrous web is set to proceed to a treatment zone (N) between two heated metal surfaces (12, 15) with a result that moisture within the fibrous web migrates into a middle portion, whereby the middle portion swells as a result of increased moisture and the surface portion is subjected to a high drying stress as the surface portion is prevented from shrinking. As the fibrous web exits from the treatment zone, the vaporized water escapes rapidly through surface pores without substantial condensation in the surface layers, resulting in an increased elastic modulus for the surfaces and at the same time a low density for the middle portion. |