Gypsum-based panel

Abstract

A panel has a gypsum matrix, in which the following additives are embedded: glass fibre in an amount greater than 1 wt % relative to the gypsum and a synthetic polymeric binder in an amount greater than 2.5 wt % relative to the gypsum. The glass fibre and synthetic polymeric binder are present in a weight ratio of at least 2 parts binder to one part fibre. The amount of sand present in the gypsum matrix lies in the range 0-0.5 wt % relative to the gypsum. The amount of cellulosic fibre present in the gypsum matrix lies in the range 0-2 wt % relative to the gypsum.

Claims

1. A panel having a gypsum matrix, a first facing on a first side of the gypsum matrix, and a second facing on a second opposing side of the gypsum matrix, each of the facings being a paper facing or a fiber mat, the gypsum matrix having the following additives embedded therein: glass fibre in an amount greater than 1 wt % and less than 6 wt % relative to the gypsum, distributed throughout the gypsum matrix; a synthetic polymeric binder in an amount greater than 2.5 wt % and less than 25 wt % relative to the gypsum; the glass fibre and synthetic polymeric binder being present in a weight ratio of at least 2 parts binder to one part fibre; wherein the amount of sand present in the gypsum matrix lies in the range 0-0.5 wt % relative to the gypsum; and further wherein the amount of cellulosic fibre present in the gypsum matrix lies in the range 0-2 wt % relative to the gypsum; and further wherein the gypsum matrix is the set product of a slurry comprising in the range of 79-93 wt % stucco on a solids basis, and further wherein the amount of acrylic resin present in the gypsum matrix lies in the range 0-1 wt % relative to the gypsum.

2. The panel according to claim 1, wherein the polymeric binder is polyvinyl acetate.

3. The panel according to claim 1, wherein the amount of calcium carbonate present in the gypsum matrix lies in the range 0-1 wt % relative to the gypsum.

4. The panel according to claim 1, wherein the total weight of the additives embedded in the gypsum matrix is less than the weight of the gypsum in the gypsum matrix.

5. The panel according to claim 1, wherein the polymeric binder is present in an amount greater than 3.5 wt % relative to the gypsum.

6. The panel according to claim 1, wherein the glass fibres have an average length in the range 3-10 mm.

7. The panel according to claim 1, wherein the glass fibres have an average diameter in the range 5-50 micron.

8. The panel according to claim 1, wherein the glass fibre and polymeric binder are present in a weight ratio of at least 3 parts binder to one part fibre.

9. The panel according to claim 1, wherein a starch content of the panel is less than 5 wt % relative to the amount of synthetic polymer binder.

10. A method of making the panel according to claim 1, comprising providing a stucco slurry comprising glass fibres and a synthetic polymeric binder, and allowing the slurry to set, wherein the amount of lime present in the slurry lies in the range 0-0.5 wt %; and further wherein the step of providing a stucco slurry comprises adding water to stucco in an amount that is less than twice the weight of the stucco.

11. The panel according to claim 1, wherein each facing comprises a paper facing.

12. The panel according to claim 1, wherein each facing comprises a mat partially or fully embedded at the surface of the panel.

13. The panel according to claim 1, wherein the glass fibre is dispersed substantially evenly throughout the gypsum matrix.

14. The panel according to claim 1, wherein the gypsum matrix does not include any fibres other than the glass fibres.

15. The panel according to claim 1, wherein the gypsum matrix is substantially free from acrylic resin.

16. The panel according to claim 2, wherein the polyvinyl acetate is the only synthetic resin present in the gypsum matrix.

Description

DETAILED DESCRIPTION

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

(2) Gypsum plasterboards were prepared from gypsum slurries, according to the following method: 1. Polyvinylacetate (Vinamul 8481 from Celanese Emulsions) is added to water to form an aqueous suspension; 2. Glass fibres are mixed into the aqueous suspension; 3. Stucco is added to the aqueous suspension to form a slurry; 4. The slurry is mixed in a Kenwood Blender® at minimum speed for 10 seconds; 5. The speed in increased and the slurry mixed further for 20 seconds; 6. The slurry is deposited on a forming surface to form a board; 7. The board is dried at a temperature of 160° C. for one hour, and further at a temperature of 40° C. until a constant weight is reached; 8. The board is conditioned at 23° C. and a relative humidity of 50% until a constant weight is achieved.

(3) The composition of the slurries and the densities of the boards are detailed in Table 1.

(4) Polyvinylacetate is added to the slurry in the form of an aqueous suspension. The amount of polyvinylacetate set out in Table 1 refers to the amount of polyvinylacetate contained within the aqueous suspension, rather than the total mass of the suspension added to the slurry.

(5) TABLE-US-00001 TABLE 1 Slurry composition (g) Board Glass density Stucco fibre Polymer Water (kg/m.sup.3) Example 1 1050 21 52.5 poly- 787.5 951.1 vinyl- acetate Example 2 1050 21 157.5 poly- 682.5 953.9 vinyl- acetate Example 3 1050 21 262.5 poly- 577.5 959.7 vinyl- acetate Compar- 1050 21 52.5 starch 840 965.7 ative example 1 Compar- 1050 21 52.5 starch 840 929.62 ative example 2 Compar- 1050 52.5 52.5 starch 840 975.76 ative example 3 Compar- 1050 21 0 840 980.04 ative example 4 Example 4 1050 21 52.5 poly- 787.5 970.12 vinyl- acetate Example 5 1050 21 105 poly- 735 953.68 vinyl- acetate Example 6 1050 21 157.5 poly- 682.5 960.53 vinyl- acetate Example 7 1050 21 210 poly- 630 946.44 vinyl- acetate Example 8 1050 21 262.5 poly- 577.5 954.24 vinyl- acetate Compar- 1050 21 52.5 starch 945 886.0 ative example 5
Screw Pull-Out Tests

(6) 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 using a torque screwdriver, the screw 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.

(7) 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.

(8) Refix Pull-Out Tests

(9) Refix pull-out tests were carried out using the same protocol as the screw pull-out tests, with the additional step, immediately after the step of inserting the screw into the sample using a torque screwdriver, of removing the screw and reinserting it in the same position using the torque screwdriver.

(10) Fatigue Tests

(11) Fatigue tests were carried out using the same protocol as the screw pull-out tests, with the additional step, between the steps of applying a 10N pre-load to the screw and setting a cross-head speed of 10 mm/minute, of applying 100 loading cycles between 10N and 300N at a cross-head speed of 10 mm/minute.

(12) Hand Torque Tests

(13) Hand torque 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 using a screw gun, the screw passing through a steel washer positioned on the surface of the sample.

(14) The screw gun was configured to cut out when the screw had been inserted into the sample to such a depth that the head protruded by 10 mm from the sample. The screw was then turned using a torque-controlled manual screwdriver until a sharp increase in the torque reading was observed, as the screw head came into contact with the sample. Using the manual screwdriver, the screw was then turned further in increments of ⅛th of a turn, the torque reading being recorded after each increment and then being re-set to zero. This process was continued until at least 1.5 turns after a maximum torque had been achieved. The maximum torque was then recorded.

(15) The results of mechanical testing are set out in Table 2. The number in brackets indicates the number of samples tested.

(16) TABLE-US-00002 TABLE 2 Pull out Refix pull out strength (N) strength (N) Fatigue (N) Hand torque (Nm) Example 1   772 ± 36 (3)  650 ± 28 (3)  681 ± 26 (3) 2.03 ± 0.15 (3) Example 2   1231 ± 82 (3) 1117 ± 76 (3) 1237 ± 78 (3) 2.73 ± 0.46 (3) Example 3   1460 ± 19 (3) 1493 ± 63 (3) 1490 ± 80 (3) 3.93 ± 1.1 (3)  Comparative  614.9 ± 14 (3) 418.2 ± 74 (3)   575 ± 69 (3) 2.47 ± 0.21 (3) example 1 Comparative 631.30 ± 59 (8) example 2 Comparative   705 ± 92 (8) example 3 Comparative  342.5 ± 83 (8) example 4 Example 4  832.6 ± 69 (8) Example 5 1018.4 ± 41 (8) Example 6 1239.7 ± 67 (8) Example 7  1439.1 ± 123 (8)  Example 8 1592.6 ± 90 (8) Comparative  531.8 ± 75 (8) example 5