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 calcium sulphate-based product formed by drying an aqueous slurry comprising:
gypsum that is calcined and a shrinkage resistance additive, wherein:
the shrinkage resistance additive is melamine polyphosphate or melamine pyrophosphate, and
the calcium sulphate-based product has an area shrinkage of between 8-14% after heating to a temperature of 1000° C. over 120 minutes.
2. The product according to claim 1 , wherein the shrinkage resistance additive is provided in an amount from 0.1 to 20 wt %.
3. The product according to claim 2 , wherein the shrinkage resistance additive is provided in an amount from 2 to 5 wt %.
4. The product according to claim 1 , wherein the product is a wallboard, panel, tile, joint filler material or mould for metal casting.
5. The product according to claim 4 , wherein the product is a composite wallboard comprising a core of the gypsum and shrinkage resistance additive sandwiched between two liners.
6. The product according to claim 1 , wherein the shrinkage resistance additive is melamine polyphosphate.
7. A method for manufacturing the calcium sulphate-based product according to claim 1 , the method comprising:
mixing the gypsum that is calcined and the shrinkage resistance additive with water to provide an aqueous slurry; and
drying the aqueous slurry.
8. The calcium sulphate-based product comprising:
gypsum and a shrinkage resistance additive, wherein:
the shrinkage resistance additive is melamine polyphosphate or melamine pyrophosphate, and
the calcium sulphate-based product has a linear shrinkage between 5% and 10% at a temperature of 1000° C.
9. The product according to claim 8 , wherein the shrinkage resistance additive is provided in an amount from 0.1 to 20 wt %.
10. The product according to claim 9 , wherein the shrinkage resistance additive is provided in an amount from 2 to 5 wt %.
11. The product according to claim 8 , wherein the product is a wallboard, panel, tile, joint filler material or mould for metal casting.
12. The product according to claim 11 , wherein the product is a composite wallboard comprising a core of the gypsum and shrinkage resistance additive sandwiched between two liners.
13. The product according to claim 8 , wherein the shrinkage resistance additive is melamine polyphosphate.
14. A method for manufacturing the calcium sulphate-based product according to claim 8 , the method comprising:
mixing the gypsum that is calcined and the shrinkage resistance additive with water to provide an aqueous slurry; and
drying the aqueous slurry.