초록 ▼

An improved water resistant gypsum board is made by adding an aqueous wax emulsion containing a cationic surfactant to an aqueous slurry containing calcium sulfate and host particles at a slurry temperature which maintains calcium sulfate hemihydrate crystals. The wax emulsion is stable at the tempe

An improved water resistant gypsum board is made by adding an aqueous wax emulsion containing a cationic surfactant to an aqueous slurry containing calcium sulfate and host particles at a slurry temperature which maintains calcium sulfate hemihydrate crystals. The wax emulsion is stable at the temperature of slurry which maintains the calcium sulfate hemihydrate. The slurry is then dewatered and rehydrated to form a gypsum board and dried at a temperature to melt the wax.

대표청구항 ▼

[ I claim:] [1.] A process for making a gypsum board product having improved water resistance which comprises:forming an aqueous slurry of a calcium sulfate material selected from the group consisting of calcium sulfate hemihydrate, calcium sulfate anhydrite and mixtures thereof, and host particles

[ I claim:] [1.] A process for making a gypsum board product having improved water resistance which comprises:forming an aqueous slurry of a calcium sulfate material selected from the group consisting of calcium sulfate hemihydrate, calcium sulfate anhydrite and mixtures thereof, and host particles each having voids penetratable by the slurry menstruum over a substantial portion of their bodies, said slurry containing at least about 70% by weight of water;forming an aqueous emulsion of wax with a cationic surfactant, said emulsion being stable under the conditions in which calcium sulfate hemihydrate crystals are maintained;adding said wax emulsion to said aqueous slurry, while said slurry is at a temperature at which calcium sulfate hemihydrate crystals are maintained;passing said wax-containing slurry onto a flat porous forming surface to form a filter cake before the temperature of said filter cake falls below the temperature at which the calcium sulfate hemihydrate rapidly rehydrates to calcium sulfate dihydrate;removing a substantial portion of the water from said filter cake through said porous forming surface and cooling said filter cake to a temperature at which rehydration begins,pressing said filter cake to form a board and remove additional water whereby calcium sulfate hemihydrate crystals about said host particles rehydrate in situ to calcium sulfate dihydrate crystals; anddrying said board to remove the remaining free water and to cause the core of said board to reach a temperature sufficient to melt said wax.