To obtain a gypsum board that has a rapid setting and hardening rate, excellent tack adhesion to the facing base board for gypsum board and high strength by adding persulfate salt to the gypsum.
The objective gypsum is prepared by using β-hemihydrate gypsum or a mixture thereof with α-hemihydrate gypsum. As α-hemihydrate gypsum, is used the α-hemihydrate gypsum that is given as a by-product in the production of wet phosphoric acid. The α-hemihydrate gypsum can be used even in the case that alkali is added thereto. The proportion of the α-hemihydrate gypsum as a by-product in the production of wet phosphoric acid can be increased up to 70 wt.%, when it is mixed with β-hemihydrate gypsum. The persulfate salt is, for example, ammonium persulfate, potassium persulfate, sodium persulfate, gallium persulfate or the like. The amount of the persulfate salt to be added is preferably 0.1-5.0 pts.wt. per 100 pts.wt. of the gypsum (on the solid basis). The gypsum slurry including the persulfate salt is cast on the lower facing board, then integrated to the upper facing board to produce the objective gypsum board.
ABE KOJI
YOSHINO TADASHI
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