3. January 2010
Editor: Jukka Laitinen
Companies: Kemi Oy, Metsä-Botnia
4.17. Mottled liner in Kemi Oy
Background:
A new kraftliner machine, ”Polar Queen”, nominal capacity 180 000 ton/a brown kraftliner, was started in the year 1971. Polar Queen was equipped by a secondary head box for the top layer formation. The investment did include also one of the first Kamyr digesters of a new generation equipped by a separate pre impregnation tower. The Kamyr digester was designed to produce the bottom layer for the kraftliner. Quite soon it did turn out that also the top layer could be possible to produce by the same digester by switching the kappa number. In the year 1975 the first bleach plant investment was completed. It was the first five stage kraft pulp bleach plant in Finland.
Mottled kraftliner:
After the start up of the bleach plant, it was started also trials to feed a thin layer, approximately 45 g/m2, bleached pulp to the secondary head box and so the new board grade, mottled liner was developed. The mottling pattern is specific for every board machine depending of technical concept and raw material. Basis weight area was 125 – 250 g/m2 and brightness 73 -74 ºISO. The printing properties of mottled liner were significantly better compared to the brown liner and Kemi mottled was very much liked by the customers and did have a quite stabile market, in the beginning about 30 000 ton/a and later on the level of about 60 - 70 000 ton/a. The product was suitable especially for the fruit and vegetable packages. In the middle of 80’s the whole wet end was rebuild, and secondary head box was replaced by a secondary wire section, which did open the road to the white top grades. The strength properties of mottled liner did also improve and the appearance of surface was immediately accepted by the customers. In the beginning of 2000’s the coated liners did replace mottled kraftliner at Kemi Mill. During the time period of 25 years mottled liner has been one important step in the development path of Kemi liner grades from brown liner to the white top grades and has to some extend also softened the volatility of the brown liner market.
Note! Kemi Oy as a part of Oy Metsä-Botnia Ab since 1991.