To increase the strength of board ends and improve the handling for transport or the like and improve the water-resistant property, by adding an alkali into α-hemihydrate gypsum slurry and applying it to a board base paper and further, pouring β-hemihydrate gypsum slurry into the middle part.
After α-hemihydrate gypsum produced as a byproduct on producing phosphoric acid by a wet phosphoric acid production method has been dried and an alkali has been added thereto, the α-hemihydrate gypsum slurry is applied on the upper and lower board base papers. The β-hemihydrate gypsum slurry is poured in the lower board base paper and integrally formed and cured and dried with the upper board base paper. It is preferable that the slurry of 100-200g/m2 in α-hemihydrate gypsum base is applied on the board base paper. As an applying method, it is preferable that the slurry is applied on respective one side faces of the upper and lower board base papers by use of a roll but the method is not necessarily limitted as long as there is no special trouble in the workability.
DOI KIYOTO
YOSHINO TADASHI
ABE KOJI
