High temperature sag resistant lightweight gypsum board

1 . A gypsum board comprising:

a gypsum core layer comprising

at least 70 wt. % calcium sulfate dihydrate,

and

0.2-0.5 wt. % urea distributed uniformly throughout the gypsum core,

0.1 to 1.0 wt. % glass fiber or 0.5 to 10 wt. % mineral wool as reinforcing material,

0.5 to 3 wt. % pregelatinized, partially hydrolyzed starch,

0 to 0.4 wt. % phosphate,

0 to 1.0 wt. % dispersant,

optionally vermiculite,

optionally an accelerator,

optionally a retarder,

and an absence of clay additive,

wherein the gypsum core layer results from setting of a mixture comprising an addition of urea provided in dry form or an aqueous solution admixed to an aqueous slurry comprising calcium sulfate hemihydrate and water,

wherein the gypsum core has air voids,

wherein the gypsum core layer has a density of 30-40 pounds per cubic foot, and

wherein the gypsum board has a mass of pounds per area 1600 to 1886 lbs/msf, wherein the mass of pounds per area lbs/msf values are for a ⅝ inch thick board and subject to proportional adjustment for thicker or thinner boards,

wherein the board has a thickness of ⅜″-1″,

wherein the gypsum core layer has opposed front and back outer surfaces, further comprising a front cover sheet on the gypsum core front surface and a back cover sheet on the gypsum core back surface, and

wherein the front and/or back cover sheets are made of paper or fiberglass.

2 . The gypsum board of claim 1 , wherein the gypsum board has a mass of pounds per area 1600 to 1856 lbs/msf, wherein the mass of pounds per area lbs/msf values are for a ⅝ inch thick board and subject to proportional adjustment for thicker or thinner boards.

3 . The gypsum board of claim 2 , wherein the gypsum core layer further comprises 0-0.1% sodium trimetaphosphate.

4 . The gypsum board of claim 1 , further comprising less than 120 parts by weight chloride per 1,000,000 parts by weight of said calcium sulfate dihydrate.

5 . The gypsum board of claim 1 , further comprising about 120 parts by weight to about 3000 parts by weight chloride per 1,000,000 parts by weight of said calcium sulfate dihydrate.

6 . The gypsum board of claim 1 , wherein the front and/or back cover sheets are made of paper, wherein the gypsum core layer has mass of pounds per area 1600 to 1856 lbs/msf, wherein the mass of pounds per area lbs/msf values are for a ⅝ inch thick board and subject to proportional adjustment for thicker or thinner boards.

7 . The gypsum board of claim 1 , wherein the gypsum core layer has mass of pounds per area 1809 to 1856 lbs/msf, wherein the mass of pounds per area lbs/msf values are for a ⅝ inch thick board and subject to proportional adjustment for thicker or thinner boards.

8 . The gypsum board of claim 1 , further comprising a skim layer that has a thickness (“T1”) of from about 0.02 inches (about 0.05 cm) to about 0.2 inches (about 0.5 cm) comprising at least 60 wt. % calcium sulfate dihydrate on at least one side of the gypsum core layer, said skim layer having a density at least 1.1 times higher than the density of the core layer.

9 . The gypsum board of claim 8 , wherein the skim layer further comprises 0.05-0.5 wt. % urea.

10 . The gypsum board of claim 9 ,

wherein the board has a thickness of ⅜″-0.75″,

and

wherein the board mass of pounds per area is 1600 to 1856 lbs/msf, wherein the mass of pounds per area lbs/msf values are for a ⅝ inch thick board and subject to proportional adjustment for thicker or thinner boards.

11 . The gypsum board of claim 10 , wherein the gypsum board has a mass of pounds per area 1809 to 1856 lbs/msf, wherein the mass of pounds per area lbs/msf values are for a ⅝ inch thick board and subject to proportional adjustment for thicker or thinner boards.

12 . The gypsum board of claim 1 ,

wherein a thermal sag is measured according to a thermal sag test that is 10-30%, of the thermal sag observed in a control boards of the same gypsum board composition without the urea, wherein the thermal sag test is conducted on 10″×1.5″×⅝″ strips were cut from the cast boards, placed horizontally in a furnace on bricks (2.5″ high) spaced 8″ apart in the middle of the heated space, the furnace heated from ambient temperature to 1600° F. (870° C.) in about 75 minutes, and then maintained at 1600° F. (870° C.) for 15 minutes for a total heating time was 90 minutes.

13 . The gypsum board of claim 1 , wherein the gypsum core layer provides a High Temperature Shrinkage (S) of about 10% or less, the gypsum board has High Temperature Shrinkage (S) measured at about 1560° F. (850° C.) according to ASTM Pub. WK25392 of 10% or less,

wherein the board has a thickness of ⅜″-0.75″, and

wherein the board mass of pounds per area is 1809 to less than 1886 lbs/msf.

14 . The gypsum board of claim 1 , made by a method of making the gypsum board, comprising:

preparing an aqueous gypsum slurry comprising a mixture of water and stucco, wherein the stucco comprises calcium sulfate hemihydrate, and

wherein the aqueous gypsum slurry comprises a mixture of:

at least 70 weight percent of said calcium sulfate hemihydrate on a dry basis,

0.2-0.5 wt. %-urea on a dry basis,

0.1 to 1.0 wt. % glass fiber or 0.5 to 10 wt. % mineral wool as reinforcing material,

0.5 to 3 wt. % pregelatinized, partially hydrolyzed starch,

0 to 0.4 wt. % phosphate,

0 to 1.0 wt. % dispersant,

optionally vermiculite,

an accelerator,

optionally a retarder, and

water at a weight ratio of water to the calcium sulfate hemihydrate of 0.2:1 to 1.2:1;

disposing the aqueous gypsum slurry onto a surface and allowing the aqueous gypsum slurry to set to form a set gypsum core layer comprising calcium sulfate dihydrate;

wherein the aqueous slurry is disposed between a front cover sheet and a back cover sheet, each cover sheet having an inner surface and an outer surface;

wherein the aqueous slurry contacts the inner surface of the front cover sheet and the back cover sheet, and

at least a portion of the aqueous slurry is in a foamed state while being disposed between the front cover sheet and the back cover sheet;

cutting the set gypsum core layer into a panel of predetermined dimensions; and

drying the panel,

wherein the set gypsum core layer has a density of 30-40 pounds per cubic foot or less,

wherein the gypsum board has a mass of pounds per area less than 2100 lbs/msf, wherein the mass of pounds per area lbs/msf values are for a ⅝ inch thick board and subject to proportional adjustment for thicker or thinner boards,

wherein the board has a thickness of ⅜″-1″,

wherein the gypsum core layer has opposed front and back outer surfaces, further comprising a front cover sheet on the gypsum core front surface and a back cover sheet on the gypsum core back surface, and

wherein the front and/or back cover sheets are made of paper or fiberglass.

15 . The gypsum board of claim 14 , wherein the gypsum board has a mass of pounds per area 1600-1856 lbs/msf, wherein the mass of pounds per area lbs/msf values are for a ⅝ inch thick board and subject to proportional adjustment for thicker or thinner boards.

16 . A gypsum board having a gypsum core layer between front and back cover sheets, the gypsum core layer made from a mixture of:

an aqueous slurry comprising water and at least 70 wt. % on a dry basis calcium sulfate hemihydrate,

0.03-1 wt. % on a dry basis urea in dry form or an aqueous solution,

0.1 to 1.0 wt. % glass fiber or 0.5 to 10 wt. % mineral wool,

0.5 to 3 wt. % pregelatinized, partially hydrolyzed starch,

0 to 0.4 wt. % phosphate,

0 to 1.0 wt. % dispersant,

0 to 1.0 wt. % dispersant,

optionally an accelerator,

optionally a retarder,

optionally sodium trimetaphosphate,

an absence of clay additive,

optionally vermiculite,

water, and

air,

wherein the mixture results from a process comprising an addition of urea admixed to the aqueous slurry comprising the calcium sulfate hemihydrate and the water,

wherein the gypsum core layer has a density of 30-40 pounds per cubic foot or less,

wherein the gypsum board has a mass of pounds per area 1600 to 1886 lbs/msf, wherein the mass of pounds per area lbs/msf values are for a ⅝ inch thick board and subject to proportional adjustment for thicker or thinner boards,

wherein the gypsum board has a thickness of ⅜″-1″,

wherein the gypsum core layer has opposed front and back outer surfaces, the front cover sheet on the gypsum core front surface and the back cover sheet on the gypsum core back surface, and

wherein the front and/or back cover sheets are made of paper or fiberglass.

17 . A method of making a gypsum board of claim 1 , comprising:

preparing an aqueous gypsum slurry comprising a mixture of water and stucco, wherein the stucco comprises calcium sulfate hemihydrate, and

wherein the aqueous gypsum slurry comprises a mixture of:

at least 70 weight percent of said calcium sulfate hemihydrate on a dry basis,

0.2-0.5 wt. % urea on a dry basis,

0.1 to 1.0 wt. % glass fiber or 0.5 to 10 wt. % mineral wool as reinforcing material,

0.5 to 3 wt. % pregelatinized, partially hydrolyzed starch,

0 to 0.4 wt. % phosphate,

0 to 1.0 wt. % dispersant,

optionally vermiculite,

optionally an accelerator,

optionally a retarder,

an absence of clay additive,

and

the water at a weight ratio of water to the calcium sulfate hemihydrate of 0.2:1 to 1.2:1;

disposing the aqueous gypsum slurry onto a surface and allowing the aqueous gypsum slurry to set to form a set gypsum core layer comprising calcium sulfate dihydrate;

wherein the aqueous slurry is disposed between a front cover sheet and a back cover sheet, each cover sheet having an inner surface and an outer surface;

wherein the aqueous slurry contacts the inner surface of the front cover sheet and the back cover sheet, and

at least a portion of the aqueous slurry is in a foamed state while being disposed between the front cover sheet and the back cover sheet;

cutting the set gypsum core layer into a panel of predetermined dimensions; and

drying the panel,

wherein the set gypsum core layer has a density of 30-40 pounds per cubic foot or less,

wherein the gypsum board has a mass of pounds per area less than 2100 lbs/msf, wherein the mass of pounds per area lbs/msf values are for a ⅝ inch thick board and subject to proportional adjustment for thicker or thinner boards,

wherein the board has a thickness of ⅜″-1″,

wherein the gypsum core layer has opposed front and back outer surfaces, further comprising a front cover sheet on the gypsum core front surface and a back cover sheet on the gypsum core back surface, and

wherein the front and/or back cover sheets are made of paper or fiberglass.

18 . The gypsum board of claim 16 , wherein the gypsum board has a mass of pounds per area 1600 to 1856 lbs/msf, wherein the mass of pounds per area lbs/msf values are for a ⅝ inch thick board and subject to proportional adjustment for thicker or thinner boards.

19 . The gypsum board of claim 16 , wherein the gypsum board has a mass of pounds per area 1809 to less than 1856 lbs/msf, wherein the mass of pounds per area lbs/msf values are for a ⅝ inch thick board and subject to proportional adjustment for thicker or thinner boards.