Patent Application
20230043281
The present invention relates to panels for use in building construction, and in particular, to a panel having improved dimensional stability.
Lightweight construction panels, such as plasterboard, (e.g. gypsum plasterboard) are commonly used to provide internal partitions in buildings. To provide a partition, it is typical to first construct a framework from wood, metal, or another suitable material, and affix sheets of plasterboard to the frame with screws or other fixings to provide a continuous partition surface. It is also known to affix said panels to solid walls, such as brick walls, to provide a more desirable finished surface. Said panels are typically used to construct walls and ceilings. Once the panels are affixed to the framework or wall, it is known to finish the partition by either filling the joints and screw head depressions or covering the entire panel with a finishing material, such as cement plaster or gypsum plaster. It is also known to paint such panels.
Typical finishing materials are aqueous. Due to the composition of said panels, they are known to absorb water. Accordingly, when the finishing material is applied to the panel, it is known that the panel will absorb water from the finishing material.
Furthermore, it has been found that known panels expand when they absorb water. In certain circumstances, such as extreme conditions of high humidity, this gives rise to several undesirable results. A first result is that the finishing material may be cracked or damaged as the panel expands as moisture is absorbed, and also as the panel dries out and returns to its original size and shape. A second result is that the panels themselves, or the framework to which they are affixed, may be damaged. This is particularly relevant in partitions which use a framework with a relatively low strength.
Objects and aspects of the present invention seek to alleviate at least these problems with prior known construction panels.
According to a first aspect of the present invention, there is provided 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.
A key advantage of the present invention is that a panel having the composition as described above has a greater dimensional stability when wetted, when compared to prior known panels. The applicant has surprisingly discovered that it is especially important for panels including relatively large amounts of fibres and polymeric additive to have good dimensional stability. Panels including large amounts of polymeric additive and fibre have increased stiffness. As such, when these panels are installed within a constrained system, such as a partition wall, any change in dimension can result in significant bowing, bending or cracking, when compared to panels without large amounts of polymeric additive and fibre.
The panel may be used in construction. For example, the panel may be used, along with a supporting frame, to provide an internal partition in a building. The panel may be plasterboard, drywall, sheetrock, gyp board, wallboard or any other known construction panel. The panel may be any construction panel which expands when wetted.
Once in position, the panel may be jointed, wherein the joints between adjacent panels are filled such that a continuous outer surface is provided. Depressions due to screw heads may also be filled in this way. Alternatively, the entire panel may be covered once in position. The panel may be jointed or entirely covered in a gypsum plaster, a cement plaster, a jointing compound or other material configured to set and/or dry.
The panel may comprise backing paper on one or more surfaces. The backing paper may allow moisture to pass therethrough.
In the production of plasterboards, it is typical that a slurry comprising calcium sulphate hemihydrate (stucco) with the chemical formula CaSO4 ½.(H2O) is converted to calcium sulphate dihydrate (gypsum) with the chemical formula CaSO4 2.(H2O) during a drying step. Due to the hydration of the stucco during the process, the weight of the calcium sulphate based component is higher in the plasterboard than in the slurry. The molar mass of stucco is 0.84 that of calcium sulphate dihydrate. As such, the weight of an additive relative to the stucco in the slurry is higher than the weight of the additive relative to the gypsum in the final plasterboard product.
The gypsum matrix may be friable. The gypsum matrix may be cast from a stucco slurry and/or pressed into a panel.
The fibres being embedded in the gypsum matrix may mean that the fibres are set in the gypsum matrix. Each fibre, or cluster of fibres, may be surrounded by the gypsum matrix. The fibres may be distributed evenly throughout the gypsum matrix. Alternatively, the fibres may be unevenly distributed throughout the gypsum matrix. For example, the density of fibres may be greater adjacent a first surface of the panel when compared to a second, opposite, surface of the panel.
The fibres may be provided in an amount in the range 0.8-7 wt % relative to the gypsum. Alternatively, the fibres may be provided in an amount in the range 1.6-5 wt % relative to the gypsum. For example, the fibres may be provided in an amount of approximately 1.6 wt %, 1.7 wt %, 1.9 wt %, 2.5 wt %, 3.0 wt %, 4.0 wt %, 4.5 wt % or 5 wt % relative to the gypsum. The fibres may be provided in a maximum amount of 7 wt % relative to the gypsum.
The phosphate additive may be selected from a group consisting of: metaphosphates, polyphosphates, trimetaphosphates, sodium trimetaphosphate (STMP) tetrasodium pyrophosphate (TSPP) and mixtures thereof.
The phosphate additive may be present in an amount of at least 0.04 wt %, 0.08 wt %, 0.21 wt %, 0.25 wt %, 0.42 wt %, 0.5 wt %, 0.84 wt % or 2.5 wt % relative to the gypsum. The addition of a phosphate additive may act to improve the dimensional stability of the panel. In particular, the phosphate additive may reduce the expansion of the panel when the panel is moistened.
The phosphate additive may be provided in a minimum amount required to provide preferable panel characteristics. For example, the phosphate additive may be STMP and may be provided in an amount of 0.08 wt % relative to the gypsum. This particular phosphate additive, and said amount, have been found to provide preferable panel characteristics. A lesser amount of STMP may not provide preferable panel characteristics. A greater amount of STMP may provide more preferable panel characteristics, but the increase in performance from that seen in a panel including 0.08 wt % STMP relative to the gypsum may not justify the addition of STMP in the greater amount.
The fibres may be present in an amount of at least 1.7 wt % relative to the gypsum. The polymeric additive may be provided in an amount of at least 3.7 wt % relative to the gypsum.
A polymeric additive may be a polymer which is added to the gypsum matrix.
The polymeric additive may combine with the gypsum matrix. Alternatively, the polymeric additive may remain distinct within the gypsum matrix. The polymeric additive may be 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.
The starch may be selected from a group consisting of: cationic starch, ethylated starch, dextrin, pre-gelatinised starch, substituted starch, a migratory starch, a non-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.
Said Brookfield viscosity may be measured by creating a solution by dissolving 100 g of starch on 600 ml of water at a temperature of 20° C., wherein the solution is brought to 60° C. and then heated at a rate of 1° C./min up to 90° C., using a Brookfield viscometer adapted for measuring viscosities from 1 to 100,000 cps with the number 6 spindle at a speed of 10 rpm, allowing the maximum result to be directly read off the Brookfield viscometer between 50% and 80% of the range on the scale, whereas another spindle may be selected outside said range on the scale.
The polymeric additive may be provided in an amount in the range 0.8-9 wt % relative to the gypsum. Accordingly, the polymeric additive may be provided in a maximum amount of 9 wt % relative to the gypsum. Alternatively, the polymeric additive may be provided in an amount in the range 0.8-7 wt % relative to the gypsum. Alternatively, the polymeric additive may be provided in an amount in the range 2.1-5 wt % relative to the gypsum. For example, the polymeric additive may be provided in an amount of approximately 1.6 wt %, 2.1 wt %, 2.9 wt %, 3.8 wt %, 4.2 wt %, 4.4 wt % or 5 wt % relative to the gypsum. The polymeric additive may be provided in a maximum amount of 7 wt % relative to the gypsum.
The polymeric additive may comprise polyvinyl acetate in an amount of at least 1.9 wt % relative to the gypsum. Alternatively, the polymeric additive may comprise polyvinyl acetate in an amount of at least 3.8 wt % relative to the gypsum.
The polymeric additive may comprise starch in an amount of at least 2.5 wt % relative to the gypsum. Alternatively, the polymeric additive may comprise starch in an amount of at least 5.0 wt % relative to the gypsum.
The values of additives disclosed above have been found to provide preferably dimensional stability characteristics.
The fibres may comprise glass fibres. Alternatively, or additionally, the fibres may comprise wood fibres, fibres derived from wood, regenerated cellulose fibres and/or synthetic polymer fibres. Each fibre may be elongate. The inclusion of fibres may reduce the friability of the gypsum matrix and/or improve a nail pull-out strength of the panel.
The fibres may have a length in the range 4-8 mm. Alternatively, the fibres may have a length on the range 2-10 mm. For example, the fibres may have a length of approximately 6 mm. The fibres may have a diameter in the range 5-80 micron. Alternatively, the fibres may have a diameter in the range 2-150 micron. It is to be understood that the lengths and diameters referred to herein may be a mean, median or modal length or diameter. Furthermore, the lengths and diameters referred to herein may be the length or diameter of the fibres as present in the panel. It is to be understood that a portion of the fibres may be damaged and reduced in length or diameter during the manufacture and subsequent use of the panel.
The fibres may be present in the panel in the form of particles of agglomerated fibres, for example, paper particles and/or wood particles such as fine sawdust particles. Typically, said particles are irregular in shape.
The composition may have a water gauge in the range 60-90%, preferably 60-80%, more preferably 60-70%. For example, the composition may have a water gauge of approximately 65%.
According to a second aspect of the present invention, there is provided a method of manufacturing the panel according to the first aspect, 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. Typically, the slurry comprises mainly calcium sulphate hemihydrate (stucco), which is converted to calcium sulphate dihydrate during the drying step. The molar mass of calcium sulphate hemihydrate is 0.84 that of calcium sulphate dihydrate.
The step of adding the phosphate additive to the stucco slurry may comprise adding the phosphate additive as a dry solid. Alternatively, or additionally, the step of adding the phosphate additive to the stucco slurry may comprise adding the phosphate additive as a solution. The solution may be a water based solution. The percentages referred to above may be the relative percentage of the solids content of the solution, when compared to the gypsum.
The step of adding the polymeric additive to the stucco slurry may comprise adding polymeric additive as a dry solid. Alternatively, or additionally, the step of adding the polymeric additive to the stucco slurry may comprise adding the polymeric additive as a solution. The solution may be a water based solution. The percentages referred to above may be the relative percentage of the solids content of the solution, when compared to the gypsum.
The method may further comprise the step of drying the stucco slurry at a temperature in the range 100-250° C. The step of drying the stucco slurry may comprise a plurality of drying stages. Each drying stage may be carried out at a different temperature to at least one other drying stage. For example, the step of drying the stucco slurry may comprise a first drying step at approximately 250° C. and a second drying step at approximately 100° C.
The method may further comprise the step of agitating or mixing the stucco slurry to evenly distribute the fibres and/or additives.
The method may further comprise the step of placing the stucco slurry into a form. The form may determine the shape of the panel produced via the method.
An embodiment of the present invention will now be described by way of example only and with reference to the accompanying drawings, in which:
Gypsum plasterboards were prepared from the compositions described below.
A gypsum plasterboard was prepared from a slurry containing the following, wherein all percentage values given are relative to the weight of the stucco:
A gypsum plasterboard was prepared from a slurry containing the following, wherein all percentage values given are relative to the weight of the stucco:
A gypsum plasterboard was prepared from a slurry containing the following, wherein all percentage values given are relative to the weight of the stucco:
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:
As can be seen in the graph of
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.
Gypsum plasterboards were prepared from the compositions described below.
A gypsum plasterboard was prepared from a slurry containing the following, wherein all percentage values given are relative to the weight of the stucco:
A gypsum plasterboard was prepared from a slurry containing the following, wherein all percentage values given are relative to the weight of the stucco:
A gypsum plasterboard was prepared from a slurry containing the following, wherein all percentage values given are relative to the weight of the stucco:
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:
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:
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:
As can be seen in the graph of
Furthermore, as can be seen in the graph of
Also, as can be seen in the graph of
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.
The compositions of Example 5 and Comparative Example 3 are discussed above with reference to
Gypsum plasterboards were prepared from the compositions described below.
A gypsum plasterboard was prepared from a slurry containing the following, wherein all percentage values given are relative to the weight of the stucco:
A gypsum plasterboard was prepared from a slurry containing the following, wherein all percentage values given are relative to the weight of the stucco:
As can be seen in the graph of
Furthermore, as can be seen in the graph of
Gypsum plasterboards were prepared from the compositions described below.
A gypsum plasterboard was prepared from a slurry containing the following, wherein all percentage values given are relative to the weight of the stucco:
A gypsum plasterboard was prepared from a slurry containing the following, wherein all percentage values given are relative to the weight of the stucco:
A gypsum plasterboard was prepared from a slurry containing the following, wherein all percentage values given are relative to the weight of the stucco:
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:
As can be seen in the graph of
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| FR2001386 | Feb 2020 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2021/051886 | 1/27/2021 | WO |
