Modifiers for gypsum slurries and method of using them

Abstract

An improved gypsum slurry that includes water, calcium sulfate hemihydrate, a polycarboxylate dispersant and a modifier. The modifier is chemically configured to improve the efficacy of the polycarboxylate dispersant. Preferred modifiers include cement, lime, slaked lime, soda ash, carbonates, silicates and phosphates.

1 . A gypsum slurry comprising: 
 water;    calcined gypsum;    a polycarboxylate dispersant; and    at least one modifier chemically configured to increase the efficacy of said polycarboxylate dispersant.    
   
   
       2 . The gypsum slurry of  claim 1  wherein said modifier is selected from the group consisting of lime, soda ash, carbonates, silicates, phosphates, phosphonates and combinations thereof.  
   
   
       3 . The gypsum slurry of  claim 2  wherein said modifier is soda ash.  
   
   
       4 . The gypsum slurry of  claim 1  wherein said modifier is present in concentrations of about 0.15% to about 0.25% by weight based on the dry weight of said calcined gypsum.  
   
   
       5 . The gypsum slurry of  claim 1  wherein said polycarboxylate dispersant comprises a vinyl repeating unit and a repeating unit comprising at least one of the group consisting of acrylic acid, methacrylic acid, maleic acid, their salts or esters.  
   
   
       6 . The gypsum slurry of  claim 1  wherein said polycarboxylate dispersant has a charge density ratio of about 5 to about 8.  
   
   
       7 . The gypsum slurry of  claim 1  wherein said polycarboxylate dispersant is present in amounts of about 0.05% to about 0.5 % based on the dry weight of said calcined gypsum.  
   
   
       8 . The gypsum slurry of  claim 1  wherein said water is present in amounts of about 0.4 to about 0.8 based on the dry weight of said calcined gypsum.  
   
   
       9 . A gypsum panel comprising 
 at least one facing material;    a gypsum core comprising the hydrated gypsum slurry of  claim 1 .    
   
   
       10 . The gypsum panel of  claim 9  wherein said modifier is selected from the group consisting of lime, soda ash, carbonates, silicates, phosphates, cement and combinations thereof.  
   
   
       11 . The gypsum panel of  claim 10  wherein said modifier is soda ash.  
   
   
       12 . The gypsum panel of  claim 9  wherein said modifier is present in concentrations of about 0.05% to about 0.25% by weight based on the dry weight of said calcined gypsum.  
   
   
       13 . The gypsum panel of  claim 9  wherein said polycarboxylate dispersant comprises a polyether repeating unit and at least one of acrylic acid, methacrylic acid and maleic acid repeating units.  
   
   
       14 . The gypsum panel of  claim 9  wherein said polycarboxylate dispersant has a charge density ratio of about 5 to about 8.  
   
   
       15 . The gypsum panel of  claim 9  wherein said polycarboxylate dispersant is present in amounts of about 0.05 % to about 0.5 % based on the dry weight of said calcined gypsum.  
   
   
       16 . The gypsum panel of  claim 9  wherein said water is present in amounts of about 0.5 to about 0.6 based on the dry weight of said calcined gypsum.  
   
   
       17 . A method of making a gypsum slurry comprising a polycarboxylate dispersant comprising: 
 selecting a modifier chemically configured to increase the efficacy of the polycarboxylate dispersant;    combining the modifier, dispersant, water and calcined gypsum to form a gypsum slurry.    
   
   
       18 . The method of  claim 17  wherein the modifier is selected from the group consisting of lime, soda ash, carbonates, silicates, phosphates and cement.