High salt gypsum wallboard containing salt absorbents and methods of making same

A gypsum board comprising:

• a core comprising a central core layer and a first densified layer, the core having opposed first and second faces, the core comprising set gypsum, the set gypsum comprising calcium sulfate dihydrate;
• a first cover sheet having an outer surface and an inner surface, the first cover sheet inner surface facing the first face of the core, wherein the first cover sheet comprises a first paper cover sheet or a first fiber glass mat;
• a second cover sheet having an outer surface and an inner surface, the second cover sheet inner surface facing the second face of the core, wherein the second cover sheet comprises a second paper cover sheet or a second fiber glass mat;
• wherein the core is between the first cover sheet and the second cover sheet;
• the first densified layer comprising the set gypsum and salt absorbent particles (preferably said salt absorbent particles are uniformly distributed throughout the first densified layer), said salt absorbent particles comprising salt absorbent material, wherein said salt absorbent material comprises zeolite, or hydrotalcite, or a blend of zeolite and hydrotalcite, wherein the first densified layer is between the central core layer and the second cover sheet, wherein opposing sides of the first densified layer respectively contact the central core layer and the second cover sheet;
• wherein the central core layer results from setting of an aqueous central core layer slurry comprising a mixture of stucco and water between the first cover sheet and the second cover sheet, wherein the stucco comprises calcium sulfate hemihydrate and one or more chloride salts;
• wherein the aqueous central core layer slurry is made from:
• at least 60 wt.%, preferably at least 70 wt.%, more preferably at least 80 wt.%, typically at least 90 wt.% or typically at least 95 wt.% said calcium sulfate hemihydrate on a dry (water free) basis,
• 150 to 4000 parts by weight chloride anion, typically about 300 to about 3000 parts by weight, more typically from about 400 to about 2000 parts by weight, and further typically from about 600 to about 1000 parts by weight, per 1,000,000 parts by weight said calcium sulfate hemihydrate, and
• the water at a weight ratio of the water to the calcium sulfate hemihydrate of 0.2:1 to 1.2:1;
• wherein the first densified layer results from setting of an aqueous first densified layer slurry made from the stucco, the salt absorbent particles, and water, wherein the stucco comprises calcium sulfate hemihydrate and one or more chloride salts, and
• wherein the aqueous first densified layer slurry is made from:
• at least 60 wt.%, preferably at least 70 wt.%, more preferably at least 80 wt.%, typically at least 90 wt.% or typically at least 95 wt.% said calcium sulfate hemihydrate on a dry (water free) basis,
• 150 to 4000 parts by weight chloride anion, typically about 300 to about 3000 parts by weight, more typically from about 400 to about 2000 parts by weight, and further typically from about 600 to about 1000 parts by weight, per 1,000,000 parts by weight said calcium sulfate hemihydrate,
• the salt absorbent material in an amount of 0.5 to 10 parts by weight, preferably 1 to 5 parts by weight, more preferably 1 to 3 parts by weight, per 100 parts by weight of the stucco for the first densified layer slurry;
• and
• the water at a weight ratio of water to the calcium sulfate hemihydrate of 0.2:1 to 1.2:1;
• wherein parts by weight of said salt absorbent material per 100 parts by weight stucco in the aqueous central core layer slurry is relatively less than parts by weight of said salt absorbent material per 100 parts by weight stucco in the aqueous first densified layer slurry,
• wherein parts by weight of said salt absorbent material per 100 parts by weight set gypsum in the central core layer is relatively less than parts by weight of said salt absorbent material per 100 parts by weight set gypsum in the first densified layer;
• wherein the core has a density of about 15 to 55, preferably about 15 to 40, pounds per cubic foot,
• wherein the first densified layer has a density at least 1.1 times a density of the central core layer,
• wherein the first densified layer is thinner than the central core layer, and
• wherein thickness of the first densified layer is 5% to 25% of thickness of the gypsum board.