Gypsum products utilizing a two-repeating unit dispersant and a method for making them

Abstract

A gypsum slurry includes water, a hydraulic component including stucco and a polycarboxylate dispersant. The dispersant has two repeating units wherein the first repeating unit is an olefinic unsaturated mono-carboxylic acid repeating unit or an ester or salt, and the second repeating unit is a vinyl or allyl group bound to a polyether by an ether linkage. The slurry can be made into a gypsum panel.

1 . A gypsum slurry comprising: 
 water;    a hydraulic component comprising at least 50% calcium sulfate hemihydrate by weight based on the dry weight of the hydraulic component; and    a polycarboxylate dispersant consisting essentially of a first and a second repeating unit, wherein said first repeating unit is an olefinic unsaturated mono-carboxylic acid repeating unit or an ester or salt thereof, or an olefinic unsaturated sulphuric acid repeating unit or a salt thereof, and said second repeating unit is of the general formula (I)                          and wherein R 3  is hydrogen or an aliphatic C 1  to C 5  hydrocarbon group, R 4  is hydrogen or an aliphatic C 1  to C 20  hydrocarbon group, a cycloaliphatic C 5  to C 8  hydrocarbon group, a substituted C 6  to C 14  aryl group or a group conforming to the formula                          wherein R 5  and R 7  independently of each other represent an alkyl, aryl, aralkyl or alkylaryl group and R 6  is a divalent alkyl, aryl, aralkyl or alkaryl group, p is 0 to 3, inclusive, m and n are, independently, an integer from 2 to 4, inclusive and x and y are integers from 55 to 350, inclusive.    
     
     
         2 . The gypsum slurry of  claim 1  wherein at least one of m and n is 2.  
     
     
         3 . The gypsum slurry of  claim 1  wherein p is 0 or 1.  
     
     
         4 . The gypsum slurry of  claim 1  further comprising a modifier chemically configured to increase the efficacy of said polycarboxylate dispersant.  
     
     
         5 . The gypsum slurry of  claim 4  wherein said modifier is selected from the group consisting of lime, soda ash, carbonates, silicates, phosphates, phosphonates, cement and combinations thereof.  
     
     
         6 . The gypsum slurry of  claim 1  further comprising at least one additive selected from the group consisting of set retarders, set accelerators, foaming agents, trimetaphosphates, biocides, starches, sugars, siloxanes and wax emulsions.  
     
     
         7 . The gypsum slurry of  claim 6  wherein said set accelerator comprises at least one of wet gypsum accelerator, HRA and CSA.  
     
     
         8 . The gypsum slurry of  claim 1  wherein said first repeating unit comprises at least one of the group consisting of acrylic acid and methacrylic acid.  
     
     
         9 . The gypsum slurry of  claim 1  wherein said hydraulic component comprises at least 80% calcium sulfate hemihydrate by weight.  
     
     
         10 . The gypsum slurry of  claim 1  wherein said calcium sulfate hemihydrate comprises less than 600 ppm of soluble salt.  
     
     
         11 . The gypsum slurry of  claim 1  wherein the charge density of said dispersant is in the range of about 600 to about 2000 μequiv. charges/g co-polymer.  
     
     
         12 . The gypsum slurry of  claim 1  wherein said dispersant is present in said slurry in amounts from about 0.01% to about 2% by weight of the dry dispersant calculated as a percentage of the dry gypsum.  
     
     
         13 . The gypsum slurry of  claim 12  wherein said dispersant is present in amounts from about 0.05% to about 0.3% by weight of the dry dispersant calculated as a percentage of the dry gypsum.  
     
     
         14 . A gypsum board comprising: 
 at least one facing material; and    a core material bound to the facing material comprising calcium sulfate dihydrate and a dispersant consisting essentially of a first and a second repeating unit, wherein said first repeating unit is an olephinic unsaturated mono-carboxylic acid repeating unit or an ester or salt thereof, or an olephinic unsaturated sulphuric acid repeating unit or a salt thereof, and said second repeating unit is of the general formula (I)                          and wherein R 3  is hydrogen or an aliphatic C 1  to C 5  hydrocarbon group, R 4  is hydrogen or an aliphatic C 1  to C 20  hydrocarbon group, a cycloaliphatic C 5  to C 8  hydrocarbon group, a substituted C 6  to C 14  aryl group or a group conforming to the formula                          wherein R 5  and R 7  independently of each other represent an alkyl, aryl, aralkyl or alkylaryl group and R 6  is a divalent alkyl, aryl, aralkyl or alkaryl group, p is 0 to 3, inclusive, m and n are, independently, an integer from 2 to 4, inclusive and x and y are an integer from 55 to 350, inclusive.    
     
     
         15 . The gypsum board of  claim 14  wherein said core material further comprises at least one of the group consisting of a set accelerator, foaming agent, set retarders, strengthening agent, starch, trimetaphosphate and a modifier.  
     
     
         16 . The gypsum board of  claim 14  wherein said board is at least 50% set within 5 minutes.  
     
     
         17 . The gypsum board of  claim 14  further comprising voids formed by foam.  
     
     
         18 . The gypsum board of  claim 14  wherein said board is at least 50% set in 10 minutes in the absence of accelerators.  
     
     
         19 . The gypsum board of  claim 14  wherein the water to calcined gypsum weight ratio is less than 0.6.  
     
     
         20 . The gypsum board of  claim 19  wherein the water to calcined gypsum weight ratio is less than 0.5.