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 stucco; •the glass fibre is present in the mixture in an amount of over 1 wt % relative to the stucco; •the fluidizer 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. 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.

2. The panel according to claim 1, 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.

3. A panel according to claim 2, wherein the weight ratio of water to stucco in the mixture is less than 0.65.

4. A panel according to claim 2, wherein the weight ratio of water to stucco in the mixture is less than 0.55.

5. A panel according to claim 2, wherein the weight ratio of water to stucco in the mixture is greater than 0.4 and less than 0.65.

6. A panel according to claim 2, wherein the weight ratio of water to stucco in the mixture is greater than 0.4.

7. A panel according to claim 2, wherein the stucco is present in the mixture in an amount of over 70 wt % relative to the total solids content of the mixture.

8. A panel according to claim 2, wherein the stucco is present in the mixture in an amount of over 80 wt % relative to the total solids content of the mixture.

9. A panel according to claim 2, wherein the starch is present in the mixture in an amount of at least 4 wt % relative to the stucco.

10. A panel according to claim 2, wherein the starch is present in the mixture in an amount of at least 5 wt % relative to the stucco.

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

12. A panel according to claim 2, wherein the mixture additionally comprises one or more of a fluidiser and a retarder.

13. A panel according to claim 1, wherein the glass fibres have an average length in the range 3-12 mm and an average diameter in the range 5-50 micron.

14. A panel according to claim 1, wherein the starch is an acid-thinned starch or an oxidised starch.

15. A panel according to claim 1, wherein the density of the gypsum-based panel is greater than 800 kg/m.sup.3.

16. A panel according to claim 1, 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.

17. A panel according to claim 1, 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.

18. 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.

19. The panel according to claim 18, 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.

20. A panel according to claim 19, 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

(1) The invention will now be described by way of example only.

(2) 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.

(3) The gypsum was allowed to set and was cut into sections which were then dried to form gypsum-based boards.

(4) 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.

(5) 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.

(6) The results are set out in Table 1. These are averages, each taken from 16 samples.

(7) 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.

(8) 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