WO2022136321A1

WO2022136321A1 - A plasterboard, a stucco slurry, use of a stucco slurry and a partition

Info

Publication number: WO2022136321A1
Application number: PCT/EP2021/086891
Authority: WO
Inventors: Richard Wakefield; Nicholas Jones; Jan Rideout; Laura BROOKS; Maike PARMAR
Original assignee: Saint-Gobain Construction Products Uk Limited
Priority date: 2020-12-21
Filing date: 2021-12-20
Publication date: 2022-06-30
Also published as: GB2602152B; GB2602152A; EP4263464A1; GB202020269D0

Abstract

The present application describes a plasterboard comprising gypsum, sodium trimetaphosphate in an amount from 0.04 wt.% to below 0.17 wt.% relative to the gypsum, and fluidiser in an amount of 0.42 wt.% to 0.76 wt.% inclusive relative to the gypsum. The present application further describes a stucco slurry, use of the stucco slurry and a partition.

Description

A PLASTERBOARD, A STUCCO SLURRY, USE OF A STUCCO SLURRY AND A PARTITION

FIELD OF THE INVENTION

The present invention relates to a plasterboard, more specifically a plasterboard comprising sodium trimetaphosphate (STMP) and a fluidiser. The invention also relates to a stucco slurry, the use of a stucco slurry and a partition.

BACKGROUND TO THE INVENTION

Gypsum construction panels, often referred to as plasterboards, are commonly used in the provision of internal walls and ceilings within buildings. The major component of these plasterboards is typically gypsum, also known as calcium sulphate dihydrate CaSO₄2(H₂O).

Plasterboards are typically formed by mixing stucco, also known as calcium sulphate hemihydrate CaSO₄ 0.5(H₂O), with water. In this scenario, the stucco is hydrated by the water and crystals of gypsum grow and interlink to form the plasterboard. During the hydration process, excess water is driven off by drying the setting plasterboard in an energy intensive process.

Whilst plasterboards comprises significant amounts of gypsum, other components can be incorporated into the plasterboard. Typically, these component are added to the stucco slurry such that they become evenly distributed through the plasterboard during the manufacturing and drying process. One additive that is sometimes added to a stucco slurry is sodium tri metaphosphate (STMP). The addition of sodium trimetaphosphate may be advantageous as it can reduce the deflection seen in the final plasterboard. As low levels of deflection are required in most applications, STMP is usually added to plasterboards in relatively large amounts.

Whilst some additives can be useful in altering the properties of the final plasterboard, other additives may increase the ease with which the plasterboard can be formed. Fluidisers fall into this category of additive, reducing the amount of water required to ensure the slurry is fluid enough for processing. Therefore, incorporating fluidisers into a plasterboard can reduce the cost and timescale for manufacturing a given board.

In view of the above, it is common for plasterboards to include relatively high levels of both STMP and fluidiser. Such boards have many desirable features, especially when used as part of internal partitions in markets where the boards themselves form the face of the partition.

However, the applicant has become aware that such boards may have disadvantages in markets where a partition is typically finished with a thin layer of plaster skim, such as in the UK. Here, cracking of the plaster skim can be observed after drying, especially where the plasterboards abut one another, reducing the aesthetics of the partition. Without wishing to be bound by theory, the applicant believes the observed cracking is due to water being rapidly drawn from the skim layer by the plasterboard during the drying process.

Objects and aspects of the present invention seek to address at least this problem.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provided a plasterboard, the plasterboard comprising gypsum, sodium trimetaphosphate in an amount from 0.04 wt.% to below 0.17 wt.% relative to the gypsum and fluidiser in an amount of 0.42 wt.% to 0.76 wt.% inclusive relative to the gypsum.

The applicant has surprisingly found that reducing the level of sodium trimetaphosphate to these relatively low levels dramatically decreases the surface water absorption of the plasterboard, without increasing the deflection seen in the final plasterboard. As such, the applicant has found that far less cracking is observed in a plaster skim layer over these plasterboards that with previously available plasterboards.

Preferably, the fluidiser is present in an amount of at least 0.46 wt.% relative to the gypsum. Preferably, the fluidiser is present in an amount of at most 0.74 wt.% relative to the gypsum. More preferably, the fluidiser is present in an amount of 0.51 wt.% relative to the gypsum.

Preferably, the sodium trimetaphosphate is present in an amount of at least 0.042 wt.% relative to the gypsum. Preferably, the sodium trimetaphosphate is present in an amount of at most 0.13 wt.% relative to the gypsum. More preferably, sodium trimetaphosphate is present in an amount of at most 0.084 wt.% relative to the gypsum.

Preferably, the fluidiser comprises a polyanion naphthalene sulfonate. More preferably, the fluidiser is Retanal NH35 made by Chromogenia.

Preferably, the plasterboard comprises a gypsum matrix. Preferably, the majority component of the plasterboard is gypsum.

According to a second aspect of the present invention, there is provided a stucco slurry comprising stucco, water, sodium trimetaphosphate in an amount from 0.047wt.% to below 0.2 wt.% relative to the stucco and fluidiser in an amount of 0.5 wt.% to 0.9 wt.% inclusive relative to the stucco.

Such a stucco slurry may be used to provide a plasterboard with the advantages already described. The relative amounts of the sodium tri metaphosphate and the fluidiser between the first and second aspects of the invention are equivalent, with the variance due to the difference in molecular weight between gypsum (calcium sulphate dihydrate) and stucco (calcium sulphate hemihydrate).

Preferably, the fluidiser is present in an amount of at least 0.55 wt.% relative to the stucco. Preferably, the fluidiser is present in an amount of at most 0.88 wt.% relative to the stucco. More preferably, the fluidiser is present in an amount of 0.6 wt.% relative to the stucco. Such levels of fluidiser may be preferable as they ensure the slurry is fluid enough for processing without negatively influencing the chemistry of the production process.

Preferably, the sodium trimetaphosphate is present in an amount of at least 0.05 wt.% relative to the stucco. Preferably, the sodium trimetaphosphate is present in an amount of at most 0.15 wt.% relative to the stucco. More preferably, the sodium trimetaphosphate is present in an amount of at most 0.1 wt.% relative to the stucco.

Preferably, the fluidiser comprises a polyanion naphthalene sulfonate. Polyanion naphthalene sulfonate may also be known as polynaphthalene sulfonate. More preferably, the fluidiser is Retanal NH35.

Preferably, the water is present in an amount of 75 wt.% or less relative to the stucco. More preferably, the water is present in an amount of 70 wt.% or less relative to the stucco. Reducing the water content of the slurry may be preferable as it may reduce the time needed for any plasterboard produced from the stucco slurry to dry.

Preferably, the slurry is a plasterboard precursor slurry. A plasterboard precursor slurry is a slurry that is used in the manufacture of a plasterboard.

According to a third aspect of the present invention, there is provided the use of the slurry as hereinbefore described in the formation of a gypsum product. Preferably, the gypsum product is a plasterboard.

According to a fourth aspect of the present invention, there is provided a partition comprising at least one plasterboard as previously described, wherein the at least one plasterboard is fixed to at least one frame member.

In this way, there is provided a partition that may be coated with a plaster skim and exhibit reduced cracking.

Preferably, the partition comprises a plaster skim layer across at least a portion of the surface of said at least one plasterboard. More preferably, the partition comprises a plaster skim layer substantially across at least one face of the partition. DETAILED DESCRIPTION

Embodiments of the present invention will now be described by way of example only and with reference to the accompanying figures, in which:

Figure 1 is a graph depicting the measured deflection in a variety of plasterboards both within and outside the scope of the present invention:

Figure 2 is a graph illustrating the water adsorption of a variety of plasterboards both within and outside the scope of the present invention;

Figure 3 is a partition according to the present invention;

Figure 4 is a comparison of cracking seen in a partition including a plasterboard according to the present invention and a comparative example; and

Figure 5 is a further graph illustrating the water adsorption of a variety of plasterboards both within and outside the scope of the present invention.

Figure 1 is a graph illustrating the measured deflection of a number of plasterboards. Here, plasterboards comprising 0.51 wt.% relative to the gypsum Retanal NH35 fluidiser were manufactured using standard manufacturing techniques, each plasterboard also containing STMP between 0.0 wt.% and 0.84 wt.% relative to the gypsum. Each plasterboard had a width of 2.4 m, a thickness of 12.5 mm and paper facings extending across both major faces (12.5 mm Gyproc Wallboard).

After manufacture, the deflection of each plasterboard was measured by incorporating the plasterboard sheet into a partition, placing a straight edge across the width of the plasterboard and measuring the maximum distance between the straight edge and the face of the plasterboard.

The results of these experiments are detailed below.

As can be seen from the above data and Figure 1 , the measured deflection of the plasterboard was far higher where no STMP was present in the board, whereas even small amounts of STMP were sufficient to significantly improve the plasterboard’s deflection performance. Deflection of the plasterboard is undesirable, as it can lead to a partition formed by the plasterboards appearing to undulate along its length. Additionally, the measured defection where STMP is not present can lead to cracks appearing in the locations of the joints between plasterboards, these cracks usually extending along the length of the joints where the plasterboards abut one another.

Figure 2 is a graph illustrating the surface water adsorption of a number of plasterboards. Again, plasterboards comprising 0.51 wt.% relative to the gypsum Retanal NH35 fluidiser were manufactured as outlined in relation to Figure 1 , each plasterboard also containing STMP between 0.0 wt.% and 0.84 wt.% relative to the gypsum.

The surface water adsorption of each plasterboard was measured using Cobb rings according to EN520:2009 5.9.1.

As can be seen in the table above and Figure 2, the surface water absorption of the plasterboards increased significantly when STMP was present in an amount of 0.17 wt.% relative to the gypsum and above. The applicant considers that this increased water absorption increases the cracking seen in any skim layer applied to the surface of the plasterboard, as water is rapidly removed from the skim by the plasterboard, resulting in undesirably rapid drying times and stresses accumulating in the skim layer.

From Figures 1 and 2 in combination it can be seen that plasterboards of the invention exhibit both reduced water absorption and good deflection characteristics. Turning to Figure, 3, there is depicted a partition according to the present invention.

Figure 3(a) illustrates the framework within the partition 300. The partition 300 comprises metal studs 310 running vertically with centres at 600mm, the metal studs 310 mounted in channels 320 running perpendicular to the studs 310, the channels 320 located at the top and bottom of the studs 310. Turning to Figure 3(b), plasterboards 330 of 12.5mm thickness and 2.4 m width are mounted to the metal studs 310 and channels 320 using standard drywall screws 340 at 300 mm vertical centres. Each plasterboard comprises gypsum, with STMP at 0.084 wt.% relative to the gypsum and fluidiser in the form of Retanal NH35 at 0.51 wt.% relative to the gypsum.

In substantial constructions, it is envisaged that the joints between plasterboards 330 could be staggered to improve the performance of the partition 300. Additionally, it is envisaged that the joints between the plasterboards 330 may be covered by scrim tape before the partition 300 is substantially covered with a plaster layer, for example with Thistle multifinish.

Turning to Figure 4, two partitions are depicted, the first partition as illustrated in Figure 4(a) not according to the present invention, and the second partition as illustrated in Figure 4(b) according to the present invention. In both cases, the illustrated partition has been skimmed with an approximately 2mm layer of Thistle multifinish plaster and allowed to dry to provide a plaster skim layer.

Figure 4(a) depicts a section of a partition constructed as outlined in Figure 3, where the plasterboards used within the partition have the composition of Comparative Example 1. Figure 4(a) focuses on an area where two plasterboards within the partition abut, with the line of abutment between the plasterboards extending substantially vertically though the centre of the figure. As can be seen in Figure 4(a), a crack is present in the plaster layer used to skim the partition, this crack found in the region where the plasterboards abut. The region of abutment is highlighted by a rectangle drawn on to the surface of the partition. Such cracks are undesirable, as they reduce the aesthetic appeal of the partition.

Figure 4(b) again depicts a section of a partition constructed as outlined in Figure 3, in this case where the plasterboards used within the partition have the composition of Example 2. Figure 4(b) again focuses on an area where two plasterboards within the partition abut, with the line of abutment between the plasterboards extending substantially vertically though the centre of the figure. In contrast to Figure 4(a), no cracking is seen in the region where the plasterboards abut when plasterboards according to the present invention are used in the partition. Again, the region of abutment is highlighted by a rectangle drawn on to the surface of the partition.

Figure 5 is a graph illustrating the surface water adsorption of a number of plasterboards. Plasterboards comprising Retanal NH35 fluidiser in amounts of 0.3 wt.%, 0.55 wt.% and 1.0 wt.% relative to the gypsum were manufactured using standard manufacturing techniques. Each plasterboard also contained STMP between 0.02 wt.% and 0.20 wt.% relative to the gypsum. As above, the surface water adsorption of each plasterboard was measured using Cobb rings according to EN520:2009 5.9.1.

As can be seen in the table above and Figure 5, the surface water absorption of the plasterboards began to increase when STMP was present in an amount of 0.13 wt.% relative to the gypsum, and increased rapidly where the amount of STMP was above this level. Again, the applicant considers that this increased water absorption increases the cracking seen in any skim layer applied to the surface of the plasterboard. It is the Applicant’s belief that as water is rapidly removed from the skim by the plasterboard, this results in undesirably rapid drying times and stresses accumulating in the skim layer.

Turning to the table below, expansion data for a variety of plasterboards is illustrated. Similar to the plasterboards of Figure 5, plasterboards comprising Retanal NH35 fluidiser in an amount of 0.55 wt.% relative to the gypsum were manufactured using standard manufacturing techniques, each plasterboard also containing STMP between 0 wt.% and 0.13 wt.% relative to the gypsum.

The percentage expansion of the plasterboard samples was measured by cutting samples 200mm by 50mm of each plasterboard perpendicular to the machine direction, and subsequently fixing a small brass knob to each end of the sample. The samples were then immersed in water. A reference Perspex sample was also tested in the same manner and the percentage dimensional expansion of each sample relative to the Perspex reference sample expansion was calculated. Dimensional measurements of each sample were taken at intervals of 1 , 2, 6 and 24 hours to determine the percentage expansion at each of these time points.

The table below illustrates the percentage expansion for each plasterboard relative to the reference sample at each time point measured.

As can be seen in the table above, the expansion of the plasterboards increased significantly when STMP was present in an amount of 0.02 wt.% relative to the gypsum and below. Low STMP concentrations are unsuitable due to high expansion of the plasterboard and consequently the increased likelihood of cracking of the skim layer. In particular, Comparative Examples 12 and 18 are unsuitable due to high expansion and risk of cracks forming in the skim layer.

From Figure 5 and the table of the expansion data, it can be seen that plasterboards of the invention exhibit both reduced surface water absorption and good expansion characteristics.

An amount below 0.04 wt.% STMP relative to the gypsum leads to high expansion of the plasterboard and consequently the increased likelihood of cracking of the skim layer. But an amount over 0.17 wt.% STMP relative to the gypsum causes increased surface water absorption, leading to increased risk of cracking seen in any skim layer applied to the surface of the plasterboard. Therefore, an advantageous range of STMP relative to the gypsum is from 0.04 wt.% to below 0.17 wt.% relative to the gypsum.

The selected range of fluidiser is preferred for improved ease of manufacture. It is challenging to provide an adequately fluid slurry using fluidiser in an amount of less than 0.42 wt.% relative to the gypsum. In addition, it is desirable to reduce resource cost and so it is advantageous to minimise the quantity of fluidiser added to the slurry, while maintaining the fluidising properties. As such, it is preferable to incorporate fluidiser in an amount of less than 0.76 wt.% inclusive relative to the gypsum.

Claims

1. A plasterboard, said plasterboard comprising: gypsum; sodium tri metaphosphate in an amount from 0.04 wt.% to below 0.17 wt.% relative to the gypsum; and fluidiser in an amount of 0.42 wt.% to 0.76 wt.% inclusive relative to the gypsum.

2. The plasterboard of claim 1 , wherein said fluidiser is present in an amount of at least 0.46 wt.% relative to the gypsum.

3. The plasterboard of claim 1 or claim 2, wherein said fluidiser is present in an amount of at most 0.74 wt.% relative to the gypsum.

4. The plasterboard of any one preceding claim, wherein said sodium trimetaphosphate is present in an amount of at least 0.042 wt.% relative to the gypsum.

5. The plasterboard of any one preceding claim, wherein said sodium trimetaphosphate is present in an amount of at most 0.13 wt.% relative to the gypsum.

6. The plasterboard of any one preceding claim, wherein said sodium trimetaphosphate is present in an amount of at most 0.084 wt.% relative to the gypsum.

7. The plasterboard of any one preceding claim, wherein said fluidiser comprises a polyanion naphthalene sulfonate.

8. The plasterboard of claim 7, wherein said fluidiser is Retanal NH35.

9. A stucco slurry, said stucco slurry comprising: stucco; water; sodium trimetaphosphate in an amount of 0.047 wt.% to below 0.2 wt.% relative to the stucco; and fluidiser in an amount of 0.5 wt.% to 0.9 wt.% inclusive relative to the stucco.

10. The stucco slurry of claim 9, wherein said fluidiser is present in an amount of at least 0.55 wt.% relative to the stucco.

11. The stucco slurry of claim 9 or claim 10, wherein said fluidiser is present in an amount of at most 0.88 wt.% relative to the stucco.

12. The stucco slurry of any one of claims 9 to 11 , wherein said sodium trimetaphosphate is present in an amount of at least 0.05 wt.% relative to the stucco.

13. The stucco slurry of any one of claims 9 to 12, wherein said sodium trimetaphosphate is present in an amount of at most 0.15 wt.% relative to the stucco.

14. The stucco slurry of any one of claims 9 to 13, wherein said sodium trimetaphosphate is present in an amount of at most 0.1 wt.% relative to the stucco.

15. The stucco slurry of any one of claims 9 to 14, wherein said fluidiser comprises a polyanion naphthalene sulfonate.

16. The stucco slurry of claim 15, wherein said fluidiser is Retanal NH35.

17. The stucco slurry of any one of claims 9 to 16, wherein said water is present in an amount of 75 wt.% or less relative to the stucco.

18. The stucco of claim 17, wherein said water is present in an amount of 70 wt.% or less relative to the stucco.

19. Use of the slurry of any one of claims 9 to 18 in the formation of a gypsum product. 14 A partition, said partition comprising at least one plasterboard according to any one of claims 1 to 8, wherein said at least one plasterboard is fixed to at least one frame member. The partition of claim 20, wherein said partition comprises a skim layer across at least a portion of the surface of said at least one plasterboard.