Light weight gypsum board

1. A light weight gypsum board comprising:

a set gypsum core disposed between two cover sheets;

the set gypsum core comprising a gypsum crystal matrix having a pore size distribution comprising (i) water voids having a pore size less than about 5 microns in diameter, (ii) air voids having a pore size of at least about 5 microns and less than about 50 microns in diameter, (iii) air voids having a pore size from about 50 microns to about 100 microns in diameter, and (iv) air voids having a pore size greater than about 100 microns in diameter, the air voids having a pore size greater than about 100 microns in diameter comprising at least about 20% of the total void volume of the set gypsum core, the voids measured using scanning electron photomicrograph imaging;

the air void pore size having greatest frequency is a diameter of about 100 microns or less;

the gypsum crystal matrix disposed such that the set gypsum core has an average core hardness of at least about 11 pounds as determined in accordance with ASTM C-473; and

the board having a density of 33 pcf or less.

2. The light weight gypsum board of claim 1 , wherein at least about 50% of the total void volume are air voids having a pore size greater than about 50 microns in diameter.

3. The light weight gypsum board of claim 1 , wherein the board density is from about 24 pcf to 33 pcf or less.

4. The light weight gypsum board of claim 1 , the set gypsum core formed from a slurry comprising water, foam, stucco, naphthalenesulfonate dispersant, and pregelatinized starch.

5. The light weight gypsum board of claim 3 , the set gypsum core formed from a slurry comprising water, foam, stucco, and a pregelatinized starch, the pregelatinized starch in an amount from about 0.5% to about 10% by weight based on the weight of the stucco.

6. The light weight gypsum board of claim 3 , the set gypsum core formed from a slurry comprising water, foam, stucco, and trimetaphosphate compound chosen from the group consisting of sodium trimetaphosphate, potassium trimetaphosphate, lithium trimetaphosphate, and ammonium trimetaphosphate, the trimetaphosphate compound being in an amount from about 0.12% to about 0.4% by weight based on the weight of the stucco.

7. The light weight gypsum board of claim 5 , wherein the slurry includes naphthalenesulfonate dispersant in an amount from about 0.1% to about 3.0% by weight based on the weight of the stucco.

8. A light weight gypsum board comprising a set gypsum core disposed between two cover sheets, wherein the set gypsum core comprises (a) a gypsum crystal matrix with a distribution of air voids and water voids disposed therein, the air voids with a pore size of about 5 microns or greater and water voids with a pore size less than about 5 microns, in a volume ratio of air voids to water voids from about 1.8 to 1 to about 9 to 1, (b) a distribution of air voids having pore sizes of at least about 5 microns to less than about 100 microns, (c) a distribution of air voids further having pore sizes greater than about 100 microns in diameter such that the air voids having a pore size greater than about 100 microns in diameter comprise at least about 20% of the total void volume of the set gypsum core, the voids measured using scanning electron photomicrograph imaging, the air void pore size having greatest frequency is a diameter of about 100 microns or less, and (d) the board has a density from about 24 pcf to 33 pcf, and a ratio of density (pcf) to average core hardness (lb) of less than about 3.2, wherein the core hardness is determined in accordance with ASTM C473.

9. The light weight gypsum board of claim 8 , wherein the volume ratio of air voids to water voids is from about 2.3 to 1 to about 9 to 1.

10. The light weight gypsum board of claim 8 , wherein the board, when at a thickness of about ½ inch, has a dry weight from about 1000 lb/MSF to about 1300 lb/MSF.

11. The light weight gypsum board of claim 8 , wherein at least about 50% of the total void volume comprises air voids having a pore size greater than about 50 microns in diameter.

12. The light weight gypsum board of claim 8 , the set gypsum core formed from a slurry comprising water, foam, stucco, naphthalenesulfonate dispersant, and a pregelatinized starch, wherein the naphthalenesulfonate dispersant is in an amount from about 0.1% to about 3.0% by weight based on the weight of the stucco, and the pregelatinized starch is in an amount from about 0.5% to about 10% by weight based on the weight of the stucco.

13. The light weight gypsum board of claim 12 , wherein the slurry further comprises trimetaphosphate compound chosen from the group consisting of sodium trimetaphosphate, potassium trimetaphosphate, lithium trimetaphosphate, and ammonium trimetaphosphate, the trimetaphosphate compound being in an amount from about 0.12% to about 0.4% by weight based on the weight of the stucco.

14. The light weight gypsum board of claim 1 , wherein the air voids having a pore size of about 5 microns or greater and water voids having a pore size of less than about 5 microns are in a volume ratio from about 1.4:1 to about 2.3:1.

15. The light weight gypsum board of claim 1 , wherein the air voids having a pore size of about 5 microns or greater and water voids having a pore size of less than about 5 microns are in a volume ratio from about 2.3:1 to about 9:1.

16. The light weight gypsum board of claim 1 , wherein air voids having a pore size from about 50 microns to about 100 microns in diameter comprise at least about 30% of the total void volume of the set gypsum core.

17. The light weight gypsum board of claim 6 , wherein the trimetaphosphate compound is sodium trimetaphosphate, and the slurry further comprises pregelatinized starch in an amount from about 0.5% to about 10% by weight based on the weight of the stucco and naphthalenesulfonate dispersant in an amount from about 0.1% to about 3.0% by weight based on the weight of the stucco.

18. The light weight gypsum board of claim 1 , wherein the board density is from about 24 pcf to about 32 pcf or less.

19. The light weight gypsum board of claim 1 , wherein the board density is from about 24 pcf to about 31 pcf or less.

20. The light weight gypsum board of claim 8 , wherein the board density is from about 24 pcf to about 32 pcf or less.

21. The light weight gypsum board of claim 8 , wherein the board density is from about 24 pcf to about 31 pcf or less.

22. The light weight gypsum board of claim 1 , wherein the average air void pore size is less than about 100 microns in diameter.

23. The light weight gypsum board of claim 8 , wherein the average air void pore size is less than about 100 microns in diameter.

24. A light weight gypsum board comprising:

a set gypsum core disposed between two cover sheets;

the set gypsum core comprising a gypsum crystal matrix having a pore size distribution comprising (i) water voids having a pore size less than about 5 microns in diameter, (ii) air voids having a pore size of at least about 5 microns and less than about 50 microns in diameter, (iii) air voids having a pore size from about 50 microns to about 100 microns in diameter, and (iv) air voids having a pore size greater than about 100 microns in diameter, the air voids having a pore size greater than about 100 microns in diameter comprising at least about 20% of the total void volume of the set gypsum core, the voids measured using three-dimensional imaging acquired by X-ray CT-scanning analysis (XMT);

the air void pore size having greatest frequency is a diameter of about 100 microns or less;

the gypsum crystal matrix disposed such that the set gypsum core has an average core hardness of at least about 11 pounds as determined in accordance with ASTM C-473; and

the board having a density of about 33 pcf or less.

25. The light weight gypsum board of claim 24 , wherein the board density is from about 24 pcf to about 33 pcf or less.

26. The light weight gypsum board of claim 24 , wherein the board density is from about 24 pcf to about 32 pcf or less.

27. The light weight gypsum board of claim 24 , wherein the board density is from about 24 pcf to about 31 pcf or less.

28. The light weight gypsum board of claim 24 , the set gypsum core formed from a slurry comprising water, foam, stucco, naphthalenesulfonate dispersant, and a pregelatinized starch.

29. The light weight gypsum board of claim 28 , wherein the pregelatinized starch is in an amount from about 0.5% to about 10% by weight based on the weight of the stucco.

30. The light weight gypsum board of claim 28 , wherein the slurry further comprises trimetaphosphate compound chosen from the group consisting of sodium trimetaphosphate, potassium trimetaphosphate, lithium trimetaphosphate, and ammonium trimetaphosphate, the trimetaphosphate compound being in an amount from about 0.12% to about 0.4% by weight based on the weight of the stucco.

31. The light weight gypsum board of claim 28 , wherein the naphthalenesulfonate dispersant is in an amount from about 0.1% to about 3.0% by weight based on the weight of the stucco.

32. The light weight gypsum board of claim 30 , wherein the trimetaphosphate compound is sodium trimetaphosphate, the pregelatinized starch is in an amount from about 0.5% to about 10% by weight based on the weight of the stucco, and the naphthalenesulfonate dispersant is in an amount from about 0.1% to about 3.0% by weight based on the weight of the stucco.

33. A light weight gypsum board comprising a set gypsum core disposed between two cover sheets, wherein the set gypsum core comprises (a) a gypsum crystal matrix with a distribution of air voids and water voids disposed therein, the air voids with a pore size of about 5 microns or greater and water voids with a pore size less than about 5 microns, in a volume ratio of air voids to water voids from about 1.8 to 1 to about 9 to 1, (b) a distribution of air voids having pore sizes of at least about 5 microns to less than about 100 microns, (c) a distribution of air voids further having pore sizes greater than about 100 microns in diameter such that the air voids having a pore size greater than about 100 microns in diameter comprise at least about 20% of the total void volume of the set gypsum core, the voids measured using three-dimensional imaging acquired by X-ray CT-scanning analysis (XMT), the air void pore size having greatest frequency is a diameter of about 100 microns or less, and (d) the board has a density from about 24 pcf to 33 pcf, and a ratio of density (pcf) to average core hardness (lb) of less than about 3.2, wherein the core hardness is determined in accordance with ASTM C473.

34. The light weight gypsum board of claim 33 , wherein the volume ratio of air voids to water voids is from about 2.3 to 1 to about 9 to 1.

35. The light weight gypsum board of claim 33 , wherein the board, when at a thickness of about inch, has a dry weight from about 1000 lb/MSF to about 1300 lb/MSF.

36. The light weight gypsum board of claim 33 , wherein at least about 50% of the total void volume comprises air voids having a pore size greater than about 50 microns in diameter.

37. The light weight gypsum board of claim 33 , the set gypsum core formed from a slurry comprising water, foam, stucco, naphthalenesulfonate dispersant, and a pregelatinized starch, wherein the naphthalenesulfonate dispersant is in an amount from about 0.1% to about 3.0% by weight based on the weight of the stucco, and the pregelatinized starch is in an amount from about 0.5% to about 10% by weight based on the weight of the stucco.

38. The light weight gypsum board of claim 37 , wherein the slurry further comprises trimetaphosphate compound chosen from the group consisting of sodium trimetaphosphate, potassium trimetaphosphate, lithium trimetaphosphate, and ammonium trimetaphosphate, the trimetaphosphate compound being in an amount from about 0.12% to about 0.4% by weight based on the weight of the stucco.