Patent ID: 7691467

Claim:
A plaster board comprising: a plaster core having a front surface, a back surface, a first side surface, and a second side surface opposite the first side surface, and two opposite end surfaces, and a covering base paper covering the front surface, the back surface, the first side surface, and the second side surface of the plaster core, the plaster core comprising: a first high-density hard edge part comprising the first side surface and a second high-density hard edge part comprising the second side surface, the first and second high-density hard edge parts being covered with the covering base paper; at least one high-density layer comprising the front surface or back surface of the plaster core and being covered with the covering base paper, the at least one high-density layer being continuous with and extending between the first high-density hard edge part and the second high-density hard edge part and having a density substantially equal to densities of the first and second high-density hard edge parts; and a central low-density part having a density less than the densities of the first and second high-density hard edge parts and the high-density layer and being inscribed in the first and second high-density hard edge parts and the high-density layer, wherein each of the first and second high-density hard edge parts has a minimum thickness of about 2.0 mm and a maximum thickness of about 10.0 mm in directions perpendicular to one of the first or second side surfaces of the plaster core.