A CONSTRUCTION PANEL HAVING IMPROVED DIMENSIONAL STABILITY

Abstract

Lightweight construction panels, such as gypsum plaster-board, are commonly used to provide internal partitions in buildings It is known to cover, either partially or fully, the panel with an aqueous material such as gypsum plaster or jointing compound. It has been found that known panels expand when they absorb water. This gives rise to several undesirable results such as the gypsum plaster or jointing compound cracking as the panel expands as moisture is absorbed. The present invention provides a panel comprising a gypsum matrix including fibres in an amount of at least 0.8 wt % relative to the gypsum, a polymeric additive in an amount of at least 0.8 wt % relative to the gypsum, and at least one phosphate additive. A panel having such a composition has been found to have desirable characteristics.

Claims

1. A panel comprising: a gypsum matrix; and fibres embedded in the gypsum matrix in an amount of at least 0.8 wt % relative to the gypsum; wherein the gypsum matrix comprises: a polymeric additive in an amount of at least 0.8 wt % relative to the gypsum; and a phosphate additive present in an amount of at least 0.25 wt % relative to the gypsum.

2-3. (canceled)

4. The panel of claim 1, wherein the phosphate additive is present in an amount of at least 0.50 wt % relative to the gypsum.

5. The panel of claim 1, wherein the fibres are present in an amount of at least 1.7 wt % relative to the gypsum, and the polymeric additive is provided in an amount of at least 3.7 wt % relative to the gypsum.

6. The panel of claim 1, wherein the polymeric additive is selected from a group consisting of: polyvinyl acetate, polyvinyl acetate-ethylene co-polymer, polyvinyl pyrrolidone cross-linked with polystyrene sulfonate, polyvinyl alcohol, methyl cellulose, hydroxyethyl methyl cellulose, styrene-butadiene copolymer latex, acrylic ester latex, acrylic copolymer latex, polyester resin, epoxy resin, polymethyl methacrylate, polyacrylic acid, a starch and mixtures thereof.

7. The panel of claim 6, wherein the starch is selected from a group consisting of: cationic starch, ethylated starch, dextrin, pre-gelatinised starch, substituted starch, a migratory starch, an acid-thinned starch, a native starch, a starch having a Brookfield viscosity of less than 60 cps at a temperature below 60° C. and a Brookfield viscosity greater than 10,000 cps at a temperature of 70° C., and mixtures thereof.

8. The panel of claim 6, wherein the polymeric additive comprises polyvinyl acetate in an amount of at least 1.9 wt % relative to the gypsum and starch in an amount of at least 2.5 wt % relative to the gypsum.

9. The panel of claim 6, wherein the polymeric additive comprises polyvinyl acetate in an amount of at least 3.8 wt % relative to the gypsum.

10. The panel of claim 6, wherein the polymeric additive comprises starch in an amount of at least 5.0 wt % relative to the gypsum.

11. The panel of claim 1, wherein the fibres comprise glass fibres, wherein the fibres have a length in the range 4-8 mm and a diameter in the range 5-80 micron.

12. The panel of claim 1, wherein the phosphate additive is selected from a group consisting of: metaphosphates, polyphosphates, trimetaphosphates, sodium trimetaphosphate, tetrasodium pyrophosphate and mixtures thereof.

13. A method of manufacturing the panel according to claim 1, the method comprising the steps: adding the fibres to a stucco slurry; adding the polymeric additive to the stucco slurry; adding the phosphate additive to the stucco slurry; and drying the stucco slurry to form the panel.

14. The method of claim 13, wherein the phosphate additive is added to the stucco slurry as a dry solid or as a solution.

15. The method of claim 13, wherein at least one polymeric additive is added to the stucco slurry as a dry solid or as a solution.

Description

DETAILED DESCRIPTION

[0037] An embodiment of the present invention will now be described by way of example only and with reference to the accompanying drawings, in which:

[0038] FIG. 1 is a schematic graph of percentage change in length against time for Examples 1-3 and Comparative Example 1;

[0039] FIG. 2 is a schematic graph of percentage change in length against time for Examples 4-6 and Comparative Examples 2-4; and

[0040] FIG. 3 is a schematic graph of percentage change in length against time for Examples 5, 7 and 8 and Comparative Example 3.

[0041] FIG. 4 is a schematic graph of percentage change in length against time for Examples 9, 10 and 11 and Comparative Example 5.

[0042] FIG. 1 is a schematic graph of percentage change in length against time. The graph of FIG. 1 includes data collected from tests on Examples 1-3 and Comparative Example 1. The graph shows a plot of percentage change in length against submersion time in hours. Test panels were produced with the compositions as discussed below. The initial length of each test panel was noted. The test panels were then submerged in water. The length of each test panel was measured after 1 hour, 2 hours, 4 hours, 7 hours and 24 hours of submersion in the water.

EXAMPLES 1-3

[0043] Gypsum plasterboards were prepared from the compositions described below.

Example 1

[0044] A gypsum plasterboard was prepared from a slurry containing the following, wherein all percentage values given are relative to the weight of the stucco: [0045] stucco in an amount of 100%; [0046] 6 mm long glass fibres in an amount of 2.4%; [0047] polyvinyl acetate in an amount of 4.5%; [0048] 80% water gauge; and [0049] STMP in an amount of 0.05%.

Example 2

[0050] A gypsum plasterboard was prepared from a slurry containing the following, wherein all percentage values given are relative to the weight of the stucco: [0051] stucco in an amount of 100%; [0052] 6 mm long glass fibres in an amount of 2.4%; [0053] polyvinyl acetate in an amount of 4.5%; [0054] 80% water gauge; and [0055] STMP in an amount of 1%.

Example 3

[0056] A gypsum plasterboard was prepared from a slurry containing the following, wherein all percentage values given are relative to the weight of the stucco: [0057] stucco in an amount of 100%; [0058] 6 mm long glass fibres in an amount of 2.4%; [0059] polyvinyl acetate in an amount of 4.5%; [0060] 80% water gauge; and [0061] STMP in an amount of 3%.

Comparative Example 1

[0062] A comparative gypsum plasterboard was prepared from a slurry containing the following, wherein all percentage values given are relative to the weight of the stucco: [0063] stucco in an amount of 100%; [0064] 6 mm long glass fibres in an amount of 2.4%; [0065] polyvinyl acetate in an amount of 4.5%; and [0066] 80% water gauge.

[0067] As can be seen in the graph of FIG. 1, Example 1, having STMP in an amount of 0.05 wt % relative to the stucco, performs better than Comparative Example 1, which has no STMP. A better performance is to be understood as having a lower percentage change in length. Furthermore, Examples 2 and 3, having STMP in an amount of 1 wt % and 3 wt % relative to the stucco respectively, both perform considerably better than Example 1. Therefore, a first conclusion that can be drawn is that a higher level of STMP reduces dimensional variability due to exposure to moisture.

[0068] However, it can also be seen that Examples 2 and 3 performed similarly. Therefore, a second conclusion that can be drawn is that having 3 wt % STMP relative to the stucco performs similarly to having only 1 wt % relative to the stucco. Accordingly, there may be a saturation point in the range of 0.05 wt % to 1 wt % STMP relative to the stucco, wherein an amount of STMP higher than the saturation point does not provide a significant increase in performance.

[0069] FIG. 2 is a schematic graph of percentage change in length against time. The graph of FIG. 2 includes data collected from tests on Examples 4-6 and Comparative Examples 2-4. The graph shows a plot of percentage change in length against submersion time in hours. Test panels were produced with the compositions as discussed below. The initial length of each test panel was noted. The test panels were then submerged in water. The length of each test panel was measured after 1 hour, 2 hours, 4 hours, 7 hours and 24 hours of submersion in the water.

EXAMPLES 4-6

[0070] Gypsum plasterboards were prepared from the compositions described below.

Example 4

[0071] A gypsum plasterboard was prepared from a slurry containing the following, wherein all percentage values given are relative to the weight of the stucco: [0072] stucco in an amount of 100%; [0073] 6 mm long glass fibres in an amount of 2.4%; [0074] polyvinyl acetate in an amount of 2.25%; [0075] 80% water gauge; and [0076] STMP in an amount of 0.1%.

Example 5

[0077] A gypsum plasterboard was prepared from a slurry containing the following, wherein all percentage values given are relative to the weight of the stucco: [0078] stucco in an amount of 100%; [0079] 6 mm long glass fibres in an amount of 2.4%; [0080] polyvinyl acetate in an amount of 2.25%; [0081] modified starch in an amount of 3%; [0082] 80% water gauge; and [0083] STMP in an amount of 0.1%.

Example 6

[0084] A gypsum plasterboard was prepared from a slurry containing the following, wherein all percentage values given are relative to the weight of the stucco: [0085] stucco in an amount of 100%; [0086] 6 mm long glass fibres in an amount of 2.4%; [0087] modified starch in an amount of 3%; [0088] 80% water gauge; and [0089] STMP in an amount of 0.1%.

Comparative Example 2

[0090] A comparative gypsum plasterboard was prepared from a slurry containing the following, wherein all percentage values given are relative to the weight of the stucco: [0091] stucco in an amount of 100%; [0092] 6 mm long glass fibres in an amount of 2.4%; [0093] polyvinyl acetate in an amount of 2.25%; and [0094] 80% water gauge.

Comparative Example 3

[0095] A comparative gypsum plasterboard was prepared from a slurry containing the following, wherein all percentage values given are relative to the weight of the stucco: [0096] stucco in an amount of 100%; [0097] 6 mm long glass fibres in an amount of 2.4%; [0098] polyvinyl acetate in an amount of 2.25%; [0099] modified starch in an amount of 3%; and [0100] 80% water gauge.

Comparative Example 4

[0101] A comparative gypsum plasterboard was prepared from a slurry containing the following, wherein all percentage values given are relative to the weight of the stucco: [0102] stucco in an amount of 100%; [0103] 6 mm long glass fibres in an amount of 2.4%; [0104] modified starch in an amount of 3%; and [0105] 80% water gauge.

[0106] As can be seen in the graph of FIG. 2, Example 4, having polyvinyl acetate in an amount of 2.25 wt % relative to the stucco and STMP in an amount of 0.1 wt % relative to the stucco, performs better than Comparative Example 2, which has polyvinyl acetate in an amount of 2.25 wt % relative to the stucco and no STMP. A better performance is to be understood as having a lower percentage change in length.

[0107] Furthermore, as can be seen in the graph of FIG. 2, Example 5, having polyvinyl acetate in an amount of 2.25 wt % relative to the stucco, modified starch in an amount of 3 wt % relative to the stucco and STMP in an amount of 0.1 wt % relative to the stucco, performs better than Comparative Example 3, which has polyvinyl acetate in an amount of 2.25 wt % relative to the stucco, modified starch in an amount of 3 wt % relative to the stucco and no STMP. A better performance is to be understood as having a lower percentage change in length.

[0108] Also, as can be seen in the graph of FIG. 2, Example 5, having modified starch in an amount of 3 wt % relative to the stucco and STMP in an amount of 0.1 wt % relative to the stucco, performs better than Comparative Example 4, which has modified starch in an amount of 3 wt % relative to the stucco and no STMP. A better performance is to be understood as having a lower percentage change in length.

[0109] Therefore, a conclusion that can be drawn is that the addition of STMP in an amount of 0.1 wt % relative to the stucco improves the performance of panels having polyvinyl acetate, modified starch and a combination thereof as an additive.

[0110] FIG. 3 is a schematic graph of percentage change in length against time. The graph of FIG. 3 includes data collected from tests on Examples 5, 7 and 8 and Comparative Example 3. The graph shows a plot of percentage change in length against submersion time in hours. Test panels were produced with the compositions as discussed below. The initial length of each test panel was noted. The test panels were then submerged in water. The length of each test panel was measured after 1 hour, 2 hours, 4 hours, 7 hours and 24 hours of submersion in the water.

[0111] The compositions of Example 5 and Comparative Example 3 are discussed above with reference to FIG. 2.

EXAMPLES 7 AND 8

[0112] Gypsum plasterboards were prepared from the compositions described below.

Example 7

[0113] A gypsum plasterboard was prepared from a slurry containing the following, wherein all percentage values given are relative to the weight of the stucco: [0114] stucco in an amount of 100%; [0115] 6 mm long glass fibres in an amount of 2.4%; [0116] polyvinyl acetate in an amount of 2.25%; [0117] modified starch in an amount of 3%; [0118] 80% water gauge; and [0119] STMP in an amount of 0.25%.

Example 8

[0120] A gypsum plasterboard was prepared from a slurry containing the following, wherein all percentage values given are relative to the weight of the stucco: [0121] stucco in an amount of 100%; [0122] 6 mm long glass fibres in an amount of 2.4%; [0123] polyvinyl acetate in an amount of 2.25%; [0124] modified starch in an amount of 3%; [0125] 80% water gauge; and [0126] STMP in an amount of 0.5%.

[0127] As can be seen in the graph of FIG. 3, Examples 5 and 7, having STMP in an amount of 0.1 wt % relative to the stucco and 0.25 wt % relative to the stucco respectively, perform similarly and better than Comparative Example 3, which has no STMP. A better performance is to be understood as having a lower percentage change in length. Accordingly, a conclusion that may be drawn is that STMP in an amount in the range 0.1-0.25 wt % relative to the stucco performs similarly.

[0128] Furthermore, as can be seen in the graph of FIG. 3, Example 8, having STMP in an amount of 0.5 wt % relative to the stucco, performs better than Comparative Example 3, which has no STMP, and Examples 5 and 7 which have STMP in an amount of 0.1 wt % relative to the stucco and 0.25 wt % relative to the stucco respectively. A better performance is to be understood as having a lower percentage change in length. Accordingly, another conclusion that may be drawn is that STMP in an amount of 0.5 wt % relative to the stucco performs better than lower levels of STMP, such as in the range 0.1-0.25 wt % relative to the stucco. Accordingly providing STMP in an amount greater than 0.25 wt % may provide better performance.

[0129] FIG. 4 is a schematic graph of percentage change in length against time. The graph of FIG. 4 includes data collected from tests on Examples 9 to 11 and Comparative Example 5. The graph shows a plot of percentage change in length against submersion time in hours. Test panels at full commercial scale were produced with the compositions as discussed below. The initial length of each test panel was noted. The test panels were then submerged in water. The length of each test panel was measured after 1 hour, 2 hours, 4 hours, 7 hours and 24 hours of submersion in the water.

EXAMPLES 9-11

[0130] Gypsum plasterboards were prepared from the compositions described below.

Example 9

[0131] A gypsum plasterboard was prepared from a slurry containing the following, wherein all percentage values given are relative to the weight of the stucco: [0132] stucco in an amount of 100%; [0133] 6 mm long glass fibres in an amount of 2.4%; [0134] polyvinyl acetate in an amount of 4.5%; [0135] 80% water gauge; and [0136] STMP in an amount of 1%.

Example 10

[0137] A gypsum plasterboard was prepared from a slurry containing the following, wherein all percentage values given are relative to the weight of the stucco: [0138] stucco in an amount of 100%; [0139] 6 mm long glass fibres in an amount of 2.4%; [0140] polyvinyl acetate in an amount of 4.5%; [0141] 80% water gauge; and [0142] TSPP in an amount of 1%.

Example 11

[0143] A gypsum plasterboard was prepared from a slurry containing the following, wherein all percentage values given are relative to the weight of the stucco: [0144] stucco in an amount of 100%; [0145] 6 mm long glass fibres in an amount of 2.4%; [0146] polyvinyl acetate in an amount of 4.5%; [0147] 80% water gauge; and [0148] TSPP in an amount of 0.1%.

Comparative Example 5

[0149] A comparative gypsum plasterboard was prepared from a slurry containing the following, wherein all percentage values given are relative to the weight of the stucco: [0150] stucco in an amount of 100%; [0151] 6 mm long glass fibres in an amount of 2.4%; [0152] polyvinyl acetate in an amount of 4.5%; and [0153] 80% water gauge.

[0154] As can be seen in the graph of FIG. 4, Examples 9 to 11, comprising STMP and TSPP perform better than Comparative Example 5, which has no phosphate additive. A better performance is to be understood as having a lower percentage change in length. Therefore, a first conclusion that can be drawn is that the inclusion of a phosphate additive in a plasterboard reduces dimensional variability due to exposure to moisture.

[0155] Furthermore, Example 9, having STMP in an amount of 1 wt % relative to the stucco, performs better than Examples 10 and 11 comprising TSPP in amounts of 1 wt % and 0.1 wt % TSPP relative to the stucco respectively. Therefore, a second conclusion that can be drawn is that, in plasterboards, STMP is more effective than TSPP in reducing dimensional variability due to exposure to moisture.