Composite light weight gypsum wallboard

Abstract

The invention provides a light weight composite gypsum board including a foamed low density set gypsum core, a top non-foamed (or reduced-foamed) bonding high density layer and a bottom non-foamed (or reduced-foamed) bonding high density layer, a top cover sheet bonded to the foamed low density set gypsum core by the top non-foamed (or reduced-foamed) bonding high density layer, and a bottom cover sheet bonded to the foamed low density set gypsum core by the bottom non-foamed (or reduced-foamed) bonding high density layer. The foamed low density set gypsum core is prepared having a density of less than about 30 pcf using soap foam in the gypsum-containing slurry. The combination of components provide a composite gypsum board having light weight and high strength.

1. A composite light weight gypsum composite board comprising:
 a foamed low density set gypsum core having a top surface and a bottom surface, the foamed low density set gypsum core made using a gypsum-containing slurry including stucco, from about 0.5% by weight to about 10% by weight pregelatinized starch based on the weight of stucco, and foam, 
 a top non-foamed high density bonding layer having a thickness of about 2 mils to less than about 7 mils covering the top surface of the foamed low density set gypsum core, 
 a bottom non-foamed high density bonding layer having a thickness of about 2 mils to less than about 7 mils covering the bottom surface of the foamed low density set gypsum core, 
 the top and bottom non-foamed high density bonding layers comprising from about 10% by weight to about 16% by weight of the total amount of the gypsum-containing slurry, 
 a top cover sheet, and 
 a bottom cover sheet, 
 
       wherein the top cover sheet is bonded to the foamed low density set gypsum core by the top non-foamed high density bonding layer, and the bottom cover sheet is bonded to the foamed low density set gypsum core by the bottom non-foamed high density bonding layer, the foamed low density set gypsum core has a density from about 10 pcf to about 27 pcf and the top and bottom non-foamed high density bonding layers have a density from about 60 pcf to about 70 pcf, and wherein the composite board has a dry weight of about 1000 lb/msf or less for a ½ inch thick board, a nail pull resistance of at least about 77 lb/msf, and a core hardness of at least about 11 lb/msf. 
     
     
       2. The composite light weight gypsum board of  claim 1  in which the pregelatinized starch is in the form of a pre-dispersion of about 10% by weight in water. 
     
     
       3. The composite light weight gypsum board of  claim 1 , wherein the gypsum-containing slurry further comprises a naphthalenesulfonate dispersant present in an amount from about 0.1% by weight to about 3.0% by weight based on the weight of stucco. 
     
     
       4. The composite light weight gypsum board of  claim 1 , wherein the gypsum-containing slurry further comprises a naphthalenesulfonate dispersant in the form of an aqueous solution containing from about 40% to about 45% by weight naphthalenesulfonate and the aqueous solution is present in the slurry in an amount from about 0.5% to about 2.5% by weight based on the weight of stucco. 
     
     
       5. The composite light weight gypsum board of  claim 1 , wherein the gypsum-containing slurry further comprises sodium trimetaphosphate present in an amount from about 0.12% by weight to about 0.4% by weight based on the weight of stucco. 
     
     
       6. The composite light weight gypsum board of  claim 1 , wherein the gypsum-containing slurry further comprises glass fiber present in an amount up to about 0.5% by weight based on the weight of stucco. 
     
     
       7. The composite light weight gypsum board of  claim 1 , wherein the gypsum-containing slurry further comprises a waterproofing agent. 
     
     
       8. The composite light weight gypsum board of  claim 1 , wherein the foam is soap foam, and the soap is present in an amount from about 0.3 lb/msf to about 0.5 lb/msf. 
     
     
       9. The composite light weight gypsum board of  claim 1 , wherein the top cover sheet is paper having a weight of about 60 lb/msf. 
     
     
       10. The composite light weight gypsum board of  claim 1 , wherein the top cover sheet is a fibrous mat. 
     
     
       11. The composite light weight gypsum board of  claim 10 , wherein the fibrous mat is a nonwoven glass fiber mat. 
     
     
       12. The composite light weight gypsum board of  claim 1 , wherein the gypsum-containing slurry has a water/stucco ratio from about 0.7 to about 1.3. 
     
     
       13. A composite light weight gypsum composite board comprising:
 a foamed low density set gypsum core having a top surface and a bottom surface, the foamed low density set gypsum core made using a gypsum-containing slurry including stucco, pregelatinized starch, and foam, 
 a top reduced-foamed high density bonding layer having a thickness of about 2 mils to less than about 7 mils covering the top surface of the foamed low density set gypsum core, 
 a bottom reduced-foamed high density bonding layer having a thickness of about 2 mils to less than about 7 mils covering the bottom surface of the foamed low density set gypsum core, 
 a top cover sheet, and 
 a bottom cover sheet, 
 
       wherein the top cover sheet is bonded to the foamed low density set gypsum core by the top reduced-foamed high density bonding layer, and the bottom cover sheet is bonded to the foamed low density set gypsum core by the bottom reduced-foamed high density bonding layer, the foamed low density set gypsum core has a density from about 10 pcf to about 27 pcf and the top and bottom non-foamed high density bonding layers have a density from about 60 pcf to about 70 pcf, and wherein the composite board has a dry weight of about 1000 lb/msf for a ½ inch thick board, a nail pull resistance of at least about 77 lb/msf, and a core hardness of at least about 11 lb/msf. 
     
     
       14. The composite light weight gypsum board of  claim 13 , wherein the pregelatinized starch is present in an amount from about 0.5% by weight to about 10% by weight based on the weight of stucco. 
     
     
       15. The composite light weight gypsum board of  claim 13  in which the pregelatinized starch is in the form of a pre-dispersion of about 10% by weight in water. 
     
     
       16. The composite light weight gypsum board of  claim 13 , wherein the gypsum-containing slurry further comprises a naphthalenesulfonate dispersant present in an amount from about 0.1% by weight to about 3.0% by weight based on the weight of stucco. 
     
     
       17. The composite light weight gypsum board of  claim 13 , wherein the gypsum-containing slurry further comprises sodium trimetaphosphate present in an amount from about 0.12% by weight to about 0.4% by weight based on the weight of stucco. 
     
     
       18. The composite light weight gypsum board of  claim 13 , wherein the foam is soap foam, and the soap is present in an amount from about 0.2 lb/msf to about 0.7 lb/msf. 
     
     
       19. The composite light weight gypsum board of  claim 18 , wherein the top and bottom reduced-foamed high density bonding layers include about 5% by weight or less of the amount of soap used to make the foamed low density set gypsum core. 
     
     
       20. The composite light weight gypsum board of  claim 13 , wherein the top cover sheet is paper having a weight of about 60 lb/msf. 
     
     
       21. The composite light weight gypsum board of  claim 13 , wherein the foamed low density set gypsum core has a density from about 10 pcf to about 27 pcf. 
     
     
       22. The composite light weight gypsum board of  claim 13 , wherein the top and bottom reduced-foamed high density bonding layers have a density from about 45 pcf to about 60 pcf. 
     
     
       23. A composite light weight gypsum composite board having a dry weight of about 1,000 lb./msf or less for a ½ inch thick board comprising:
 a foamed low density set gypsum core having a top surface and a bottom surface, the foamed low density set gypsum core made using a gypsum-containing slurry including stucco from about 0.5% by weight to about 10% by weight pregelatinized starch based on the weight of stucco, and foam, 
 a top non-foamed high density bonding layer having a thickness of about 2 mils to less than about 7 mils covering the top surface of the foamed low density set gypsum core, 
 a bottom non-foamed high density bonding layer having a thickness of about 2 mils to less than about 7 mils covering the bottom surface of the foamed low density set gypsum core, 
 the top and bottom non-foamed high density bonding layers comprising from about 10% by weight to about 16% by weight of the total amount of the gypsum-containing slurry, 
 a top fibrous mat cover sheet, and 
 a bottom cover sheet, 
 
       wherein the top cover sheet is bonded to the foamed low density set gypsum core by the top non-foamed high density bonding layer, and the bottom cover sheet is bonded to the foamed low density set gypsum core by the bottom non-foamed high density bonding layer, the foamed low density set gypsum core has a density from about 10 pcf to about 30 pcf and the top and bottom non-foamed high density bonding layers have a density from about 60 pcf to about 70 pcf. 
     
     
       24. The composite light weight gypsum board of  claim 23  in which the pregelatinized starch is in the form of a pre-dispersion of about 10% by weight in water. 
     
     
       25. The composite light weight gypsum board of  claim 23 , wherein the gypsum-containing slurry further comprises a naphthalenesulfonate dispersant present in an amount from about 0.1% by weight to about 3.0% by weight based on the weight of stucco. 
     
     
       26. The composite light weight gypsum board of  claim 23 , wherein the gypsum-containing slurry further comprises sodium trimetaphosphate present in an amount from about 0.12% by weight to about 0.4% by weight based on the weight of stucco. 
     
     
       27. The composite light weight gypsum board of  claim 23 , wherein the foam is soap foam, and the soap is present in an amount from about 0.2 lb/msf to about 0.7 lb/msf. 
     
     
       28. The composite light weight gypsum board of  claim 23 , wherein the board has a dry weight from about 900 lb/msf to about 1100 lb/msf. 
     
     
       29. The composite light weight gypsum board of  claim 23 , wherein the fibrous mat cover sheet is a nonwoven glass fiber mat. 
     
     
       30. A method of making composite light weight gypsum board having a dry weight from about 900 lbs./msf to about 1,100 lbs./msf, comprising the steps of:
 (a) mixing a non-foamed gypsum-containing slurry having a density from about 80 pcf to about 85 pcf comprising 
 water, stucco, pregelatinized starch, and a naphthalenesulfonate dispersant, 
 
       wherein the pregelatinized starch is present in an amount from about 0.5% by weight to about 10% by weight based on the weight of stucco, and wherein the naphthalenesulfonate dispersant is present in an amount from about 0.1% to about 3.0% by weight based on the weight of stucco;
 (b) depositing from about 6% to about 9% by weight of the total amount of the non-foamed gypsum-containing slurry on a first cover sheet; 
 (c) adding soap foam to from about 84% to about 90% by weight of the total amount of the non-foamed gypsum-containing slurry to form a foamed gypsum-containing slurry; 
 (d) depositing the foamed gypsum-containing slurry onto the non-foamed gypsum-containing slurry on the first cover sheet; 
 (e) depositing from about 4% to about 7% by weight of the total amount of the non-foamed gypsum-containing slurry on a second cover sheet; 
 (f) placing the non-foamed gypsum-containing slurry-covered surface of the second cover sheet over the deposited foamed gypsum-containing slurry to form a composite light weight gypsum board; 
 (g) cutting the composite light weight gypsum board after the foamed gypsum-containing slurry has hardened sufficiently for cutting; and 
 (h) drying the composite light weight gypsum board to provide a foamed low density set gypsum core in the finished composite light weight gypsum board. 
 
     
     
       31. The method of  claim 30  in which the pregelatinized starch is in the form of a pre-dispersion of about 10% by weight in water. 
     
     
       32. The method of  claim 30 , wherein the non-foamed gypsum-containing slurry further comprises sodium trimetaphosphate present in an amount from about 0.12% by weight to about 0.4% by weight based on the weight of stucco. 
     
     
       33. The method of  claim 30 , wherein the non-foamed gypsum-containing slurry further comprises glass fiber present in an amount up to about 0.5% by weight based on the weight of stucco. 
     
     
       34. The method of  claim 30 , wherein the non-foamed gypsum-containing slurry further comprises paper fiber present in an amount up to about 1.0% by weight based on the weight of stucco. 
     
     
       35. The method of  claim 30 , wherein the soap foam includes soap present in an amount from about 0.3 lb/msf to about 0.5 lb/msf. 
     
     
       36. The method of  claim 30 , wherein the first cover sheet and the second cover sheet are made of paper. 
     
     
       37. The method of  claim 30 , wherein the first cover sheet is paper having a weight of about 60 lb/msf. 
     
     
       38. The method of  claim 30 , wherein the first cover sheet is a fibrous mat. 
     
     
       39. The method of  claim 38 , wherein the fibrous mat is a nonwoven glass fiber mat. 
     
     
       40. The method of  claim 30 , wherein the foamed gypsum-containing slurry has a water/stucco ratio from about 0.7 to about 1.3. 
     
     
       41. The method of  claim 30 , wherein the pregelatinized starch is corn starch. 
     
     
       42. A composite light weight gypsum board, comprising:
 a foamed low density set gypsum core having a top surface and a bottom surface, the foamed low density set gypsum core made using a gypsum-containing slurry comprising water, stucco, pregelatinized corn starch present in an amount of about 6% by weight based on the weight of stucco, a 45% by weight aqueous solution of a naphthalenesulfonate dispersant present in an amount of about 1.2% by weight based on the weight of stucco, sodium trimetaphosphate present in an amount of about 0.3% by weight based on the weight of stucco, paper fiber present in an amount of about 1% based on the weight of stucco, and glass fiber present in an amount of about 0.5% based on the weight of stucco, and soap foam, 
 a top non-foamed high density bonding layer having a thickness of about 2 mils to less than about 7 mils covering the top surface of the foamed low density set gypsum core, 
 a bottom non-foamed high density bonding layer having a thickness of about 2 mils to less than about 7 mils covering the bottom surface of the foamed low density set gypsum core, 
 the top and bottom non-foamed high density bonding layers comprising from about 10% by weight to about 16% by weight of the total amount of the gypsum-containing slurry, 
 a top paper cover sheet having a weight of about 60 lb/msf, and 
 a bottom paper cover sheet, 
 
       wherein the top cover sheet is bonded to the foamed low density set gypsum core by the top non-foamed high density bonding layer, and the bottom cover sheet is bonded to the foamed low density set gypsum core by the bottom non-foamed high density bonding layer, wherein the foamed low density set gypsum core has a density of about 25 pcf, the top and bottom non-foamed high density bonding layers have a density from about 60 pcf to about 70 pcf and wherein the composite board has a dry weight of about 1000 lb/msf for a ½ inch thick board, a nail pull resistance of at least about 77 lb/msf, and a core hardness of at least about 11 lb/msf. 
     
     
       43. The composite light weight gypsum board of  claim 42  in which the pregelatinized corn starch is in the form of a pre-dispersion of about 10% by weight in water. 
     
     
       44. A composite gypsum board comprising:
 a set gypsum core having a top surface and a bottom surface, the set gypsum core formed from at least stucco, starch, and foam,   a top bonding layer having a thickness of about 2 mils to less than about 7 mils adjacent the top surface of the set gypsum core,   a bottom bonding layer having a thickness of about 2 mils to less than about 7 mils covering the bottom surface of the set gypsum core,   a top cover sheet, and   a bottom cover sheet,   wherein the top cover sheet is bonded to the set gypsum core by the top bonding layer, and the bottom cover sheet is bonded to the set gypsum core by the bottom bonding layer, the set gypsum core has a density from about 10 pcf to about 27 pcf and less than the density of either the top or bottom bonding layer, and wherein the board, when at a thickness of about ½ inch, has a dry weight of about 1100 lbs/MSF or less and a core hardness of at least about 11 lb as determined in accordance with ASTM C473.   
     
     
       45. The composite gypsum board of claim 44, wherein the starch is present in an amount from about 0.5% by weight to about 10% by weight based on the weight of the stucco. 
     
     
       46. The composite gypsum board of claim 44, wherein the set gypsum core further comprises dispersant present in an amount from about 0.1% bv weight to about 3.0% by weight based on the weight of the stucco. 
     
     
       47. The composite gypsum board of claim 44, wherein the set gypsum core further comprises a trimetaphosphate salt present in an amount from about 0.12% by weight to about 0.4% by weight based on the weight of the stucco. 
     
     
       48. The composite gypsum board of claim 44, wherein the top and bottom bonding layers have a density from about 45 pcf to about 70 pcf. 
     
     
       49. A composite gypsum board comprising:
 a set gypsum core having a dry density;   the set gypsum core adjacent to a first and a second bonding layer each having a dry density, the set gypsum core dry density being less than each of the first and second bonding layer dry densities by a differential of at least about 10 pcf;   the first and second bonding layers each having a thickness of about 2 mils to less than about 7 mils;   the board, when at a thickness of about ½ inch, having a dry weight of about 1100 lbs/MSF or less; and   the set gypsum core has an average core hardness of at least about 11 pounds as determined in accordance with ASTM C473.   
     
     
       50. The composite gypsum board of claim 49, wherein the first and second bonding layers are formed from one or more slurries, the amount of slurry used to form the first and second bonding layers comprising from about 10% to about 16% by weight of the total amount of slurry used to form the set gypsum core and the first and second bonding layers. 
     
     
       51. The composite gypsum board of claim 49, the set gypsum core formed from a slurry comprising water, stucco, foam, and starch present in an amount from about 0.5% to about 10% by weight based on the weight of the stucco, the starch effective to increase the core hardness of the gypsum board relative to the core hardness of the gypsum board without the starch. 
     
     
       52. The composite gypsum board of claim 49, the set gypsum core formed from a slurry comprising water, stucco, foam, and dispersant present in an amount from about 0.1% to about 3.0% by weight based on the weight of the stucco. 
     
     
       53. The composite gypsum board of claim 49, the set gypsum core formed from a slurry comprising water, stucco, foam, and a trimetaphosphate salt present in an amount from about 0.12% by weight to about 0.4% by weight based on the weight of the stucco. 
     
     
       54. The composite gypsum board of claim 49, the set gypsum core having a density from about 10 pcf to about 27 pcf and the top and bottom bonding layers having a density from about 45 pcf to about 70 pcf. 
     
     
       55. The composite gypsum board of claim 54, wherein the board, when at a thickness of about ½ inch, has (a) a nail pull resistance of at least 65 lb and (b) an average flexural strength of at least 36 lb in a machine direction and/or 107 lb in a cross-machine direction, as determined in accordance with ASTM C473. 
     
     
       56. The composite gypsum board of claim 54, the set gypsum core formed from a slurry comprising water, stucco, foam, dispersant, a trimetaphosphate salt and starch present in an amount from about 0.5% to about 10% by weight based on the weight of the stucco, the starch effective to increase the core hardness of the gypsum board relative to the core hardness of the gypsum board without the starch and dispersant present in an amount from about 0.1% to about 3.0% by weight based on the weight of the stucco and a trimetaphosphate salt present in an amount from about 0.12% by weight to about 0.4% by weight based on the weight of the stucco. 
     
     
       57. A composite gypsum board comprising:
 the set gypsum core adjacent to a first and a second bonding layer, the dry density of the gypsum core being less than each of the dry densities of first and second bonding layer by a differential of at least about 10 pcf;   the first and second bonding layers each having a thickness of about 2 mils to less than about 7 mils;   the board, when at a thickness of about ½ inch, having a dry weight of about 1100 lbs/MSF or less; and   the board has a ratio of dry density (pcf) to average core hardness (lb) of less than about 3.2, wherein the core hardness is determined in accordance with ASTM C473.   
     
     
       58. The composite gypsum board of claim 57, wherein the first and second bonding layers are formed from one or more slurries, the amount of slurry used to form the first and second bonding layers comprising from about 10% to about 16% by weight of the total amount of slurry used to form the set gypsum core and the first and second bonding layers. 
     
     
       59. The composite gypsum board of claim 57, the set gypsum core formed from a slurry comprising water, stucco, foam, and starch present in an amount from about 0.5% to about 10% by weight based on the weight of the stucco, the starch effective to increase the core hardness of the gypsum board relative to the core hardness of the gypsum board without the starch. 
     
     
       60. The composite gypsum board of claim 57, the set gypsum core formed from a slurry comprising water, stucco, foam, and a trimetaphosphate salt present in an amount from about 0.12% by weight to about 0.4% by weight based on the weight of the stucco. 
     
     
       61. The composite gypsum board of claim 57, the set gypsum core having a density from about 10 pcf to about 27 pcf and the top and bottom bonding layers having a density from about 45 pcf to about 70 pcf. 
     
     
       62. A composite gypsum board comprising:
 a set gypsum core having a dry density;   the set gypsum core adjacent to a first and a second bonding layer each having a dry density, the set gypsum core dry density being less than each of the first and second bonding layer dry densities by a differential of at least about 10 pcf;   the first and second bonding layers each having a thickness of about 2 mils to less than about 7 mils;   the board, when at a thickness of about ½ inch, having a dry weight of about 1100 lbs/MSF or less; and   the board, when at a thickness of about ½ inch (about 1.3 cm), has a nail pull resistance to average core hardness ratio from about 4 to about 8, each as determined in accordance with ASTM C473.   
     
     
       63. The composite gypsum board of claim 62, the set gypsum core formed from a slurry comprising water, stucco, foam, and starch present in an amount from about 0.5% to about 10% by weight based on the weight of the stucco, the starch effective to increase the core hardness of the gypsum board relative to the core hardness of the gypsum board without the starch. 
     
     
       64. The composite gypsum board of claim 62, the set gypsum core formed from a slurry comprising water, stucco, foam, and a trimetaphosphate salt present in an amount from about 0.12% by weight to about 0.4% by weight based on the weight of the stucco. 
     
     
       65. The composite gypsum board of claim 62, the set gypsum core having a density from about 10 pcf to about 27 pcf and the top and bottom bonding layers having a density from about 45 pcf to about 70 pcf. 
     
     
       66. The composite gypsum board of claim 65, the set gypsum core has an average core hardness of at least about 11 pounds as determined in accordance with ASTM C473. 
     
     
       67. The composite gypsum board of claim 65, the set gypsum core formed from a slurry comprising water, stucco, foam, and starch present in an amount from about 0.5% to about 10% by weight based on the weight of the stucco, the starch effective to increase the core hardness of the gypsum board relative to the core hardness of the gypsum board without the starch and dispersant present in an amount from about 0.1% to about 3.0% by weight based on the weight of the stucco and a trimetaphosphate salt present in an amount from about 0.12% by weight to about 0.4% by weight based on the weight of the stucco.