Patent ID: 6706128
Filing Date: 2004-03-16
Classification: C04B

Abstract:
A method of providing void spaces in a gypsum wallboard, the method comprising:adding air bubbles to a gypsum slurry; mixing the air bubble-containing gypsum slurry to distribute the air bubbles throughout the gypsum slurry, the gypsum slurry forming a core composition of the gypsum wallboard; depositing the core composition on a first cover sheet; and applying a second cover sheet over the core composition to form a gypsum wallboard; wherein: the slurry comprises calcium sulfate hemihydrate and sufficient water to hydrate the calcium sulfate hemihydrate; the air bubbles are formed by separately foaming a first foaming agent in water and a second foaming agent in water; the first foaming agent has a chemical formula R(OCH2CH2)aOSO3M1 wherein R represents linear and branched hydrocarbons having a maximum molecular weight of about 169, and mixtures thereof; the average value of a is 0.4 to 1.3; and M1 is selected from the group consisting of sodium, potassium, magnesium, ammonium, quatemary ammonium, and mixtures thereof; the second foaming agent has a chemical formula CH3(CH2)bCH2(OCH2CH2)cOSO3M2 wherein the average value of b is 6.5 to 7.5; the average value of c is 1.5 to 2.5; and M2 is selected from the group consisting of sodium, potassium, magnesium, ammonium, quatemary ammonium, and mixtures thereof; the air bubbles formed by foaming the first foaming agent are added to the gypsum slurry separately from the air bubbles formed by foaming the second foaming agent; the first foaming agent and second foaming agent produce air bubbles that differ in stability; the air bubbles produced by foaming the first foaming agent are less stable air bubbles; the air bubbles produced by foaming the second foaming agent are more stable air bubbles; the weight ratio of the first foaming agent to the second foaming agent is 75:25 to 95:5; and the presence of said more stable air bubbles in said slurry increases the residence time of said less stable bubbles in said slurry, thereby preventing premature rupture of said less stable bubbles before the gypsum slurry sets sufficiently, and thereby preventing said slurry from filling the void spaces formed by the ruptured air bubbles.