Method for the Production of Gypsum-Based Boards and Stucco Slurry Comprising Non-Pregelatinized Migratory Starch for Use Therewith

Abstract

A method for continuously forming gypsum-based panels of high fixing strength comprises the steps of: forming a mixture comprising stucco, non-pregelatinized migratory starch, glass fibre, fluidizer and water; casting the mixture in a continuous band; maintaining the band under conditions sufficient for the stucco to form an interlocking matrix of set gypsum; cutting the band to form one or more wet panel precursors; and drying the wet panel precursor to form one or more gypsum-based panels. The weight ratio of water to stucco in the mixture is less than 0.7; the stucco is present in the mixture in an amount of over 60 wt % relative to the total solids content of the mixture; the starch is present in the mixture in an amount of over 3 wt % relative to the the stucco; the glass fibre is present in the mixture in an amount of over 1 wt % relative to the stucco; the fluidizer is is present in the mixture in an amount of at least 0.1 wt % relative to the stucco; and the density of the gypsum-based panel is greater than 700 kg/m.

Claims

1-12. (canceled)

13. A panel having a gypsum-based core that comprises a gypsum matrix having embedded therein a migratory starch in an amount of at least 3 wt % relative to the gypsum and glass fibre in an amount of at least 1 wt % relative to the gypsum, the panel having a maximum dimension greater than 1 m, wherein the density of the gypsum-based core is greater than 700 kg/m.sup.3, and the amount of gypsum in the gypsum-based core is greater than 60 wt %, and further wherein the total volume of water voids in the gypsum-based core is less than the total volume of the gypsum in the panel core.

14. The panel according to claim 13, formed by a continuous method comprising: forming a mixture comprising stucco, migratory starch, glass fibre and water; casting the mixture in a continuous band; maintaining the band under conditions sufficient for the stucco to form an interlocking matrix of set gypsum; cutting the band to form one or more wet panel precursors; and drying the wet panel precursor to form one or more gypsum-based panels; wherein the weight ratio of water to stucco in the mixture is less than 0.7; the stucco is present in the mixture in an amount of over 60 wt % relative to the total solids content of the mixture.

15. A panel according to claim 14, wherein the weight ratio of water to stucco in the mixture is less than 0.65.

16. A panel according to claim 14, wherein the weight ratio of water to stucco in the mixture is less than 0.55.

17. A panel according to claim 14, wherein the weight ratio of water to stucco in the mixture is greater than 0.4 and less than 0.65

18. A panel according to claim 14, wherein the weight ratio of water to stucco in the mixture is greater than 0.4.

19. A panel according to claim 14, wherein the stucco is present in the mixture in an amount of over 70 wt % relative to the total solids content of the mixture.

20. A panel according to claim 14, wherein the stucco is present in the mixture in an amount of over 80 wt % relative to the total solids content of the mixture.

21. A panel according to claim 14, wherein the starch is present in the mixture in an amount of at least 4 wt % relative to the stucco.

22. A panel according to claim 14, wherein the starch is present in the mixture in an amount of at least 5 wt % relative to the stucco.

23. A panel according to claim 14, wherein the glass fibre is present in the mixture in an amount of over 2 wt % relative to the stucco.

24. A panel according to claim 14, wherein the mixture additionally comprises one or more of a fluidiser and a retarder.

25. A panel according to claim 13, wherein the glass fibres have an average length in the range 3-12 mm and an average diameter in the range 5-50 micron.

26. A panel according to claim 13, wherein the starch is an acid-thinned starch or an oxidised starch.

27. A panel according to claim 13, wherein the density of the gypsum-based panel is greater than 800 kg/m.sup.3.

28. A panel according to claim 13, wherein the total volume of water voids in the gypsum-based core is less than 90% of the total volume of gypsum in the panel core.

29. A panel according to claim 13, wherein the total volume of water voids in the gypsum-based core is less than 80% of the total volume of gypsum in the panel core.

30. A panel having a gypsum-based core that comprises a gypsum matrix having embedded therein a migratory starch in an amount of at least 2.5 wt % relative to the gypsum and glass fibre in an amount of at least 0.8 wt % relative to the gypsum, the panel having a maximum dimension greater than 1 m, wherein the density of the gypsum-based core is greater than 700 kg/m.sup.3, and the amount of gypsum in the gypsum-based core is greater than 60 wt %, and further wherein the total volume of water voids in the gypsum-based core is less than the total volume of the gypsum in the panel core.

31. The panel according to claim 30, formed by a continuous method comprising: forming a mixture comprising stucco, migratory starch, glass fibre and water; casting the mixture in a continuous band; maintaining the band under conditions sufficient for the stucco to form an interlocking matrix of set gypsum; cutting the band to form one or more wet panel precursors; and drying the wet panel precursor to form one or more gypsum-based panels; wherein the weight ratio of water to stucco in the mixture is less than 0.7; the stucco is present in the mixture in an amount of over 60 wt % relative to the total solids content of the mixture; and the starch is present in the mixture in an amount of at least 3 wt % relative to the stucco the glass fibre is present in the mixture in an amount of over 1 wt % relative to the stucco.

32. A panel according to claim 31, wherein the total volume of water voids in the gypsum-based core is less than 80% of the total volume of gypsum in the panel core.

Description

DETAILED DESCRIPTION

[0053] The invention will now be described by way of example only.

[0054] Gypsum-based boards having a weight of 12 kg/m.sup.2 were prepared from stucco slurries according to the recipes set out in Table 1. The amounts of the ingredients are given as a percentage relative to the stucco amount. The slurry was cast as a continuous band overlaying a first paper liner. A second paper liner was overlaid on the deposited slurry.

[0055] The gypsum was allowed to set and was cut into sections which were then dried to form gypsum-based boards.

[0056] Screw pull-out tests were carried out on samples measuring 100 mm by 100 mm that had been conditioned at a temperature of 23 C. and a relative humidity of 50%. A 50 mm single thread wood screw was inserted into the sample, passing through a metal load transfer element positioned on the surface of the sample. The load transfer element has a first portion that is configured to lie between the screw head and the surface of the sample, and a second portion that is configured to engage with a testing machine so as to allow a load to be applied to the screw along the axis of the screw.

[0057] The specimen was then mounted in a Zwick Universal Testing Machine and a 10N pre-load applied to the screw along the axis of the screw. Subsequently, the load was increased by setting a constant cross-head speed of 10 mm/minute until pull out was achieved.

[0058] The results are set out in Table 1. These are averages, each taken from 16 samples.

[0059] It can be seen that screw pull-out strength increases with decreasing water gauge. This is thought to be due to the fact that starch is more evenly distributed in boards prepared at a lower water gauge, that is, the starch has a lower tendency to migrate to the board surface.

TABLE-US-00001 TABLE 1 Comparative Examples Examples 1 2 3 4 5 6 7 8 1 2 3 Water gauge (%) 61 61 55 61 61 58 64 60 72 76 76 Glass fibre, 6 mm 2 2 2 2 2 2 2 2 2 2 2.5 length (%) Acid modified 5.sup.1 5.5.sup.2 5.sup.1 5.sup.2 6.sup.2 6.sup.2 6.sup.2 6.sup.2 5.sup.1 6.sup.2 6.sup.2 starch (%) Retarder .sup.3 (%) 0 0 0 0.01 0.01 0.01 0.02 0.02 0 0.02 0.02 Fluidizer (%) 0.2.sup.4 0.2.sup.4 0.2.sup.4 0.2.sup.4 0.2.sup.4 0.3.sup.4 1.sup.5 1.3.sup.5 0.2.sup.4 0.8.sup.6 0.8.sup.6 Setting accelerator (%) 0.1 0.1 0.1 0.3 0.3 0.3 0.2 0.2 0.1 0.1 0.1 Stucco 100.sup.7 100.sup.7 100.sup.7 100.sup.7 100.sup.7 100.sup.7 100.sup.8 100.sup.8 100.sup.7 100.sup.8 100.sup.8 Line speed 27 27 27 22 22 22 22 22 27 22 22 (M/min) Screw Pull (N) 729 735 793 627 666 734 617 701 495 572 600 .sup.1Merifilm 102 corn starch from Tate & Lyle .sup.2Fluitex MB065 corn starch from Roquette .sup.3 PlastRetard from Sicit 2000 .sup.4Ethacryl M copolymer fluid iser comprising side chains from BASF .sup.5Phosphated polycondensate fluidiser .sup.6Bozzeto CA40 .sup.7Desulphogypsum .sup.8Natural gypsum