Calcium sulphate-based products
This invention relates to improved high temperature resistant calcium sulphate-based products e.g. gypsum wallboard products and, in particular, to products having reduced shrinkage at high temperatures. The invention provides calcium sulphate-based product comprising gypsum and a shrinkage resistance additive. The shrinkage resistance additive is melamine polyphosphate or melamine pyrophosphate.
1. A gypsum product in the form of a composite wallboard comprising:
a first liner and a second liner; and
a core sandwiched between the first liner and the second liner, the core comprising a set gypsum composition comprising gypsum and a shrinkage resistance additive, wherein the shrinkage resistance additive is melamine polyphosphate, melamine pyrophosphate or a combination thereof, the shrinkage-resistant additive being present in an amount such that the gypsum product has an area shrinkage of between 8-14% after heating to a temperature of 1000° C. over 120 minutes.
2. The gypsum product according to claim 1 , wherein the shrinkage resistance additive is melamine polyphosphate.
3. The gypsum product according to claim 1 , wherein the shrinkage resistance additive is melamine pyrophosphate.
4. The gypsum product according to claim 1 , wherein the shrinkage resistance additive is present in the set gypsum composition in an amount from 0.1-20 wt %.
5. The gypsum product according to claim 1 , wherein the shrinkage resistance additive is present in the set gypsum composition an amount from 1-10 wt %.
6. The gypsum product according to claim 1 , wherein the shrinkage resistance additive is present in the set gypsum composition an amount from 1-5 wt %.
7. The gypsum product according to claim 1 , wherein the shrinkage resistance additive is present in the set gypsum composition an amount from 2-5 wt %.
8. The gypsum product according to claim 1 , wherein the core does not include inorganic fibers.
9. The gypsum product according to claim 1 , wherein the core does not include glass fibers.
10. The gypsum product according to claim 1 , made by a process comprising:
forming an aqueous slurry comprising stucco and the shrinkage resistance additive in water; allowing the aqueous slurry to set via hydration of the stucco to gypsum; and drying the set slurry to form the set gypsum composition.
11. The gypsum product according to claim 10 , wherein the slurry further comprises an accelerator.
12. The gypsum product according to claim 11 , wherein the accelerator includes one or more of ground gypsum including sugar or a surfactant; aluminium sulphate, zinc sulphate and potassium sulphate.
13. A gypsum product in the form of a composite wallboard comprising:
a first liner and a second liner; and
a core sandwiched between the first liner and the second liner, the core comprising a set gypsum composition comprising gypsum and a shrinkage resistance additive, wherein the shrinkage resistance additive is melamine polyphosphate, melamine pyrophosphate or a combination thereof, wherein the shrinkage resistance additive is present in the range of 1-2.5 wt %.