The company said it plans to use the cash released by the sale, valued at 350 million euros ($420 million), to develop investments in paperboard.
"This provides an excellent platform to grow our core business - sustainable and high-quality fresh fibre paperboard," said chief executive Mika Joukio.
($1 = 0.8351 euros)
(Reporting by Boleslaw Lasocki in Gdansk. Editing by Jane Merriman)