Gypsum boards

Abstract

A gypsum board according to the invention comprises calcium sulphate dihydrate; Tartaric acid in an amount in the range of 0.01 to 0.1% w based on the weight of calcium sulphate hemihydrate; A fluidizer in an amount of 1.0 to 10.0 kg/m.sup.3; Starch in an amount of 3.0 to 12.0 kg/m.sup.3.

Claims

1. A gypsum board comprising calcium sulphate dihydrate; tartaric acid in an amount in the range of 0.01 to 0.1 wt % based on weight of calcium sulphate in hemihydrate form; a fluidizer in an amount of 1.0 to 10.0 kg/m.sup.3; and starch in an amount of 3.0 to 12.0 kg/m.sup.3.

2. A gypsum board according to claim 1, comprising synthetic gypsum.

3. A gypsum board according to claim 1, wherein the fluidizer is a polynaphthalene-based fluidizer.

4. A gypsum board according to claim 1, wherein the starch is fluidified starch, oxidized starch, hydrolysed starch, oxyhydrolysed starch or combinations thereof.

5. A gypsum board according to claim 1, wherein the starch is present in an amount in the range of 4 to 10 kg/m.sup.3.

6. A gypsum board according to claim 1, wherein the tartaric acid is present in an amount in the range of 0.025 to 0.06 wt % based on the weight of the calcium sulphate in hemihydrate form.

7. A gypsum board according to claim 1, wherein the density of the gypsum in the board is more than 0.45 kg/l.

8. A gypsum board according to claim 1, wherein the board further comprises a foaming agent.

9. A gypsum board according to claim 1, wherein the board further comprises glass fibers.

10. A gypsum board according to claim 7, wherein the density of the gypsum in the board is in the range of 0.45 kg/l to 1 kg/l.

11. A method for providing a ceiling, comprising fixing said gypsum board according to claim 1 to two support members, said support members having an axis to axis inter-distance of at least 700 mm.

12. The method according to claim 11, wherein said support members have an axis to axis inter-distance of at least 750 mm.

13. The method according to claim 11, wherein said support members have an axis to axis inter-distance of at least 800 mm.

14. A method for making a gypsum board comprising the steps of providing calcium sulphate hemihydrate; providing tartaric acid in an amount in the range of 0.01 to 0.1 wt % based on the weight of calcium sulphate hemihydrate; providing a fluidizer in an amount of 1.0 to 10 kg per m.sup.3 of slurry; providing starch in an amount of 3.0 to 12.0 kg per m.sup.3 of slurry; providing an aqueous slurry comprising said calcium hemihydrate, fluidizer, tartaric acid, and starch; pasting said slurry; and setting said slurry to provide a gypsum board.

15. A method according to claim 14, wherein the starch is provided in an amount in the range of 4.0 to 10.0 kg per m.sup.3 of slurry.

16. A method according to claim 14, wherein the tartaric acid is present in an amount in the range of 0.025 to 0.06 wt % based on the weight of calcium sulphate hemihydrate.

Description

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

(1) The present invention will be described with respect to particular embodiments.

(2) It is to be noticed that the term comprising, used in the claims, should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. It is thus to be interpreted as specifying the presence of the stated features, steps or components as referred to, but does not preclude the presence or addition of one or more other features, steps or components, or groups thereof. Thus, the scope of the expression a device comprising means A and B should not be limited to devices consisting only of components A and B. It means that with respect to the present invention, the only relevant components of the device are A and B.

(3) Throughout this specification, reference to one embodiment or an embodiment are made. Such references indicate that a particular feature, described in relation to the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases in one embodiment or in an embodiment in various places throughout this specification are not necessarily all referring to the same embodiment, though they could. Furthermore, the particular features or characteristics may be combined in any suitable manner in one or more embodiments, as would be apparent to one of ordinary skill in the art.

(4) Gypsum board according to the invention (ex 1 and ex 2), having a thickness of 12.5 mm, are made by mixing the ingredients as set out in table I into a gypsum slurry. Also a reference gypsum board (ref) of 12.5 mm thickness was made as shown in table I. The FIGURES in table I are expressed as gram per square meter of gypsum board after drying.

(5) TABLE-US-00001 TABLE I board Ex 1 Ex 2 ref Synthetic calcium sulphate hemihydrate 5246 6991 7030 Fluidified starch 100 50 30 Tartaric acid 2 2 0 water 4462 5283 5252 Surfactant (sodium alkylsulphate) 4.6 3.3 3.5 accelerator 30 28 28 retarder 0.25 0.3 0.3 fluidizer 43 40 30

(6) The boards were produced by a standard but identical production process.

(7) This slurry was casted on a standard gypsum board casting machine, using on both sides of the gypsum board a cellulose based or other, non-cellulose based membrane as a facer. The board has a width of about 1250 mm. After curing, this board was tested according to ASTM C473, using an axis to axis inter-distance between the support members of 800 mm. A sagging of only less than 4 mm was measured. This and density property of the boards are set out in table II

(8) TABLE-US-00002 TABLE 11 board Ex 1 Ex 2 ref Sagging 800 mm span - acc. ASTM c437 <3 mm <3.2 mm >6 mm Weight (Kg/m.sup.2) 6.7 8.7 8.7

(9) It is to be understood that although preferred embodiments and/or materials have been discussed for providing embodiments according to the present invention, various modifications or changes may be made without departing from the scope and spirit of this invention.