Patent Application
20240034692
The present invention is concerned with multilayer plasterboards having enhanced nail pull resistance even in lightweight boards. The present invention is further concerned with methods for the production of corresponding products, an apparatus for the production of such products as well as the use of a synthetic polymer foam for the production of plasterboards with high nail pull resistance.
In a conventional plasterboard production, a calcium sulfate slurry is usually produced using a high-speed rotary mixer. The mixed slurry is subsequently discharged onto a paper or fibrous liner material via a discharging device. The calcium sulfate slurry regularly comprises calcium sulfate as stucco (hemihydrate with possibly minor amounts of anhydrite and/or dihydrate), water, additives and optionally (surfactant) foam.
The additives are auxiliaries, such as liquefiers, accelerators or retarders, which adapt or control the properties of the slurry according to production conditions and modify the plasterboard properties.
The foam additive is the key functional ingredient to control the density of gypsum boards by forming voids. Foam with the desired properties is regularly produced in advance in an appropriate foam generator. The pre-generated foam is then added to the slurry in the mixer along with the other components or it is added to the slurry downstream of the mixer prior to the slurry discharge. To produce the foam, surfactants are typically mixed with water and compressed air is added under high shear. The surfactant ensures that the air is entrapped in sufficiently stable foam bubbles via a surfactant film and the formation of micelles. Depending on the type of surfactant and concentration of the mixture, foams can have varying densities, whereby densities of 70 g/L-250 g/L are preferred for plasterboard production. Typically, plasterboards with final densities in the range of 350-1200 kg/m3 can be produced with surfactant-based foams.
While the incorporation of foam reduces the weight of boards, this is regularly at the cost of a decline in other desired properties of the gypsum board. Most notably, the voids in the board have a negative impact on properties such as surface hardness, compressive strength, nail pull resistance and screwability of the board. Insufficient screwability is a reason for customer complaints. If the plasterboard is not sufficiently hard and stable, screws can easily be driven in too deeply or pull through during or after fixation of the plasterboard to the framing. Nail pull resistance measurements quantify this property.
To counteract these detrimental effects, it is possible to incorporate further chemicals in the board composition, which may again improve the surface hardness and/or the stability and the nail pull. However, depending on the targeted volume weight, these additives have to be used in relatively high amounts and thus frequently increase the cost of the board.
Alternatively, boards can be manufactured with a lightweight core and outer layers that have a higher density, adding unnecessary weight to the board.
Based on this assessment, there is a need for lightweight plasterboards with the desired improved strength and nail pull resistance, but with lower absolute costs.
In the investigations underlying this invention, it has been found that a plasterboard comprising at least two layers A and B of different composition, wherein layer A comprises a calcium sulfate binder and a synthetic polymer foam and the layer B comprises a calcium sulfate binder and optionally a surfactant foam and wherein the at least one layer A is a surface layer that addresses these needs.
The term “plasterboard”, also known as drywall panel or wallboard, according to this invention refers to flat sheets used in construction to assemble walls, floors or ceilings. Plasterboards generally comprise 70-98 wt. % gypsum, i.e. calcium sulfate dihydrate, based on the total weight of the board. A plasterboard is produced by mixing a calcium sulfate binder, i.e. a calcium sulfate hemihydrate (comprising mainly CaSO4×½ H2O) with water and optionally foam and other additives to form a calcium sulfate slurry. After being mixed with water, and optionally foam and other additives, the calcium sulfate binder incorporates water in its crystalline structure and forms gypsum (calcium sulfate dihydrate, CaSO4×2 H2O). In addition to hemihydrate, the calcium sulfate binder regularly contains minor amounts of calcium sulfate anhydrite (CaSO4) and calcium sulfate dihydrate (CaSO4×2 H2O), as well as other impurities. This calcium sulfate binder blend is called stucco. In a finished plasterboard according to the invention, the calcium sulfate in both layers A and B is predominantly present as calcium sulfate dihydrate.
The plasterboard can comprise at least 45 wt.-%, preferably 60 to 99 wt.-%, more preferably 70 to 98 wt.-% and most preferably 80 to 98 wt.-% calcium sulfate dihydrate based on the total weight of the plasterboard. For the production of the plasterboard, alpha- or beta calcium sulfate hemihydrate are suitable, whereas beta hemihydrate is preferred.
If foam is used in both layers A and B of the plasterboard, the overall weight of the plasterboard can be adjusted in a wide range. With foam, plasterboards with densities of 450 kg/m3, preferably 350 kg/m3, and lower can be achieved.
By specifying that at least one layer A is a surface layer is meant to denote that at least one layer A forms an outermost calcium sulfate based layer in the plasterboard relative to other calcium sulfate based layers in the product, i.e. at least one layer A may only be further covered by a non-gypsum layer such as a liner.
With regard to the invention, it has unexpectedly been found that plasterboards with at least two layers A and B of a different composition can be prepared, wherein the individual layers strongly adhere to each other and there is no incompatibility of the two. In addition, it has been found that it is effective to concentrate and limit the synthetic polymer foam to the region that is subjected to most external stresses. By limiting the synthetic polymer foam to a surface layer A, external stresses can be absorbed mainly by the outermost part/s of the board. Also, the nail pull resistance can be improved. Thus, by protecting the outermost part/s of the board, a less stress resistant material can be used for the remaining board, thereby limiting the impact on the physical properties, such as the nail pull resistance, of the board.
The synthetic polymer to be used for the production of the synthetic polymer foam in the practice of the present invention is not subject to any relevant restrictions except that the synthetic polymer has to be capable of providing a foam in an aqueous environment upon being admixed with a gas. A synthetic polymer foam can comprise more than 90 wt.-%, preferably more than 95 wt. %, most preferably more than 99 wt.-% synthetic polymers based on all foam forming components aside from water or gas. Particularly suitable synthetic polymers for foam production comprise vinyl acrylic copolymers, polyvinyl acetate, polyvinyl alcohol and/or melamine formaldehyde or mixtures thereof, of which polyvinyl acetate and/or polyvinyl alcohol are preferred.
The amount of the synthetic polymer should on the one hand be thus, that sufficient foam can be produced to adjust the density of the layer A to the desired range, but on the other hand, for cost reasons, the amount of the synthetic polymer should not be more than necessary for this purpose. A suitable amount of a synthetic polymer based on its solids content, relative to the calcium sulfate binder is for example, 0.2 to 5 wt.-%, preferably 0.4 to 3.5 wt.-%, most preferably 0.5 to 2.0 wt.-%.
With regard to the above layer A, it is noted that the main foam forming component therein is the synthetic polymer, so that further foam forming components, such as surfactants are usually not necessary. Preferably, the synthetic polymer is the only foam forming ingredient in layer A and/or layer A is not formulated with a surfactant foam. However, the presence of surfactants in the layer A is not strictly excluded and it is possible that minor amounts thereof are incorporated.
The wording “formulated” in the context of this invention means that the respective ingredient is purposefully added to a composition, which may be used to form a product. In other words, if a composition is not formulated with an ingredient, this only excludes that this ingredient is added intentionally, but does not exclude the presence of trace amounts of this ingredient, which may be contained as impurity of other constituents, which are used to formulate that composition.
In the inventive plasterboards, the thickness of the layer A will regularly be adjusted such, that the intended purpose of increasing the surface strength is achieved best. In most cases, for that purpose it is sufficient that the layer A makes up 40% or less of the thickness of the plasterboard excluding optionally present liners, preferably the layer A makes up 5% to 40% of the thickness of the plasterboard excluding any liners.
In addition, it has been found that the density of the layers A and B does not need to be identical and can vary to some extent, without increasing the risk for deformations of the plasterboard during the drying process. In a preferred embodiment, thus, the density of the layers A and B differs by at most 100 kg/m3. More preferably, the density differs by at most 50 kg/m3. Most preferably, the density differs by at most 10 kg/m3.
Alternatively or in addition thereto, it is preferred that the layer A has a density of 350 to 1200 kg/m3, preferably 350 to 700 kg/m3 and/or the layer B has a density of 350 to 1200 kg/m3, preferably 350 to 700 kg/m3. Further preferably, both layers A and B have a density in the range of 350 to 700 kg/m3, even more preferably both layers A and B have approximately the same density, whereby the same density is desired and the word “approximately” seeks to cover any imprecision attributable to the production process.
In the dry state, layer A of the inventive plasterboard is primarily constituted of gypsum, followed by synthetic polymer, and optional additives and is conventionally prepared from stucco, water, synthetic polymer foam and optional additives. Similarly, in the dry state, layer B of this plasterboard is primarily constituted gypsum, followed by a surfactant and optional additives and is conventionally prepared from a stucco, water, a surfactant foam and optional additives. In a preferred embodiment, layer A contains less surfactant foam than the layer B, preferably the layer A does not contain a surfactant foam.
Suitable surfactants for use in the preparation of the surfactant foam in the layer B include e.g. alkali metal and/or ammonium salts of ethoxylated, sulfated alcohols as foaming agents such as those described in U.S. Pat. No. 5,683,635 B. To prepare the foam, the surfactant is admixed with water, wherein the water accounts for the major part of the mixture. For example, the weight ratio of water to soap or surfactant in such mixtures is regularly at least 5:1, preferably at least 9:1 and more preferably at least 15:1. A surfactant foam can comprise at least 60 wt. %, preferably at least 90 wt. %, most preferably more than 98 wt. % surfactant based on all foam forming components aside from water, or other liquids or gas.
The gas in the respective foams can be regular air, but can also be inert gases such as nitrogen, carbon dioxide or argon.
Further additives, which are conventionally used in the production of plasterboards may be added to the compositions used to prepare layer A and/or layer B to adjust or optimize one or more workability properties and final characteristics thereof. For example, an accelerator can be added to speed up the setting of the respective layers, a retardant can be added to delay the setting, and a liquefier/dispersant can be added to improve the flowing and processing properties of the respective composition. Moreover, it is possible to incorporate fibers and in particular glass fibers to improve the strength, dispersing agents to aid in dispersing the dry materials into the aqueous slurry or paper bonding agents and strength enhancers such as e.g. starch. In addition, agents to enhance water resistance of the set gypsum, fillers or fire-resistant additives such as clay, colloidal alumina, muscovite, vermiculite, aluminium hydroxide or water-insoluble calcium sulfate anhydrite whisker fibers can be incorporated. Appropriate additives are well known and available to the skilled practitioner. Accordingly, the layers A and/or B in the inventive plasterboard can comprise one or more of the listed additives.
Although the present description of the inventive plasterboard focused on a board with only one layer A and one layer B, three as well as more than three layers are also encompassed by this invention. In a three-layered board, two layers A can be opposing surface layers. In a board with more than three layers, at least one layer A is not a surface layer. If an inventive plasterboard is used for mounting to e.g. a wall structure, at least one layer A of the plasterboard faces the interior of a room.
Plasterboards generally further comprise a liner or facer covering the surfaces of the board, preferably also covering at least two edges. In plasterboards with liners, the liner is typically the outmost and thus visible component of the board. Consequently, only non-covered edges can expose the gypsum layers in these plasterboards. Preferably, the liner is a paper liner or a fiber mat (e.g. scrim, woven, or non-woven). The fiber mat can be made of glass fibers or a mixture of synthetic, glass/mineral and/or cellulosic fibers. To strengthen and enforce the board, a paper liner with a high grammage (>200 g/m2 and preferably >220 g/m2) is preferred.
The inventive plasterboard preferably has a nail pull resistance of at least 240 N, more preferably at least 250 N and even more preferably at least 270 N. A possible upper limit of the nail pull resistance could be 500 N, preferably 400 N, depending on the overall structure of the product. For the purposes of this invention, the nail pull resistance is determined by ASTM C473:2010.
In a further aspect, the invention is concerned with a wall structure, which comprises at least one plasterboard as described above, wherein the plasterboard is mounted to at least one stud and wherein the plasterboard is positioned within the wall structure such that at least one layer A of the plasterboard faces the interior of a room. This ensures that e.g. a screw head contacts layer A in the mounted state.
In the following, the invention will be illustrated in detail by aid of non-limiting, exemplary embodiments in
In a further aspect, the invention is concerned with a method for the production of a plasterboard, preferably a plasterboard as described above, comprising the steps:
The substrate in in step (v) can be a liner.
In addition thereto, part of the surfactant foam in step (iii) can be admixed to the mixture to form the first slurry for the layer A. Preferably, the surfactant foam admixed to the first slurry for layer A is smaller than the amount of surfactant foam admixed to the second slurry for layer B. More preferably, the amount of surfactant foam is quantified as 0.01 to 1.0 wt.-% active ingredients, relative to the calcium sulfate binder.
In most cases, the first slurry will be used to form a surface layer (A) and could thus be considered a surface slurry. Similarly, the second slurry will generally be used to produce a core layer (B) and could thus be considered a core slurry. The core layer is considered a core because it generally has the largest thickness (as well as the largest volume), irrespective of whether it is covered by only one or two surface layers.
In this method, the synthetic polymer foam in step (i) preferably has a density of 70 to 250 g/L, more preferably of 100 to 200 g/L.
In a yet further aspect, the invention concerns an apparatus, preferably for implementing a method as described above, wherein said apparatus has the means to apply two mixtures of different composition onto a moving substrate such that one of the mixtures is applied onto the substrate first and the other mixture is subsequently applied onto the first mixture to form a two layered product having at least one surface layer A and a core layer B. The corresponding apparatus comprises a first foaming device 1 for producing a synthetic polymer foam and a second foaming device 2 for producing a surfactant foam. It further comprises at least one mixer 3, 4 for producing a mixture comprising at least stucco and water. The synthetic polymer foam is admixed to the mixture of mixer 3, 4 to form a first slurry and the surfactant foam is admixed to the mixture of mixer 4 to form a second slurry and optionally the first slurry is supplemented with surfactant foam. The apparatus further comprises a first discharging device 5, 5a, 50, 50a for dispensing the first slurry onto a substrate, preferably onto a liner. It also comprises a second discharging device 6 for dispensing the second slurry onto the first slurry. The first foaming device 1 of this apparatus is fluidly interconnected to the first discharging device 5, 5a, 50, 50a, and the second foaming device 2 is fluidly interconnected to the second discharging device 6, optionally the second foaming device is further fluidly interconnected to the first discharging device. Furthermore, the first discharging device 5, 5a, 50, 50a and the second discharging device 6 are spaced apart spatially such that the first slurry from the first discharging device 5, 5a, 50, 50a comprising a synthetic polymer foam 15, 15a is dispensed upstream of the second slurry of the second discharging device 6 comprising the surfactant foam 16.
The term “fluidly interconnected” denotes that a fluid, such as for example a foam, is able to flow from one component to another, but the two components are not necessarily adjacent and/or need not be directly connected to one another. Instead, they may be separated by other components. For example, a conduit (or duct) and/or a first mixer can be situated between the first foaming device and the first discharge device, if these two are fluidly interconnected. Alternatively, or in addition thereto, a conduit (or duct) and/or a second mixer can be situated between the second foaming device and the second mixer. More explicitly, this means that a synthetic polymer foam is created in a first foaming device. From there it travels to a first discharging device via a conduit or it travels to a first discharging device via a conduit and a first mixer. If the synthetic polymer foam does not travel via a first mixer, it is mixed with a slurry received from a second mixer. This mixing can occur in the first discharge device. Alternatively, it could also circumvent a first mixer and be mixed with the slurry of the first mixer in the discharge device. In all alternatives, the first foaming device is fluidly interconnected to the first discharging device. Similarly, the surfactant foam that is created in the second foaming device can travel from there to a second discharge device via a conduit or via a conduit and a second mixer. If the surfactant foam does not enter a mixer, the mixing of the surfactant foam with a slurry can take place in the second discharge device. Again, the second foaming device is fluidly interconnected to the second discharging device in both alternatives. The term “directly connected” denotes that the two components are adjacent to one another. It further denotes that the two components may only be separated by minor components that are not explicitly mentioned in this disclosure such as e.g. connecting pieces, valves etc.
A typical plasterboard manufacture involves mixing the solid components including calcium sulfate hemihydrate (stucco) with water in a mixer to form a slurry. Liquid additives are generally introduced into this mixer. Foam can be introduced into the mixer or after leaving the mixer, sometimes even both in the mixer and after leaving the mixer. As the action of a mixer can destroy some of the foam, foam is frequently incorporated downstream of the mixer.
A plasterboard according to the invention can be two-layered, three-layered or comprise more than three layers. Apparatus embodiments for two- and three-layered plasterboards are presented.
In a preferred embodiment, the first foaming device 1 of the apparatus described above is fluidly interconnected to the first discharging device 5, 5a via a first mixer 3 and/or the second foaming device is fluidly interconnected to the second discharging device via a second mixer 4. Alternatively, or in addition thereto, the first foaming device 1 can be connected directly to the first discharging device 50, 50a and/or the second foaming device can be connected directly to the second discharging device. Foam can be added to the slurry in a mixer or admixed in one of the discharging devices. If foam is added to the slurry in a discharging device, the discharging device generally comprises a device or structure that will promote the mixing of the foam with the slurry.
Preferably, at least one of the foaming devices 1 and 2 is a stick mixer.
Further, it is possible that the inventive apparatus can have a levelling means such as a rotating roll 8, by which the thickness of a first slurry 15, 15a for layer A on a substrate, can be spread and adjusted before the second slurry 16 for layer B is applied onto the layer A 15 or the layer A 15a is applied onto the second slurry 16.
After the plasterboard ribbon has been formed and separated into individual boards, the boards are dried in a dryer (not shown).
In the following, the inventive apparatus and process will be illustrated in more detail with reference to
The apparatus in
Various combinations of individual features of the embodiments described in the figures are also possible. For example, part of the synthetic polymer foam can enter a mixer 3 and the other part can be introduced into the first discharging device 5, 5a. Similarly, part of the surfactant foam can be introduced into a mixer 4, while the other part of the surfactant foam can be introduced into the second discharging device 6.
In yet another not explicitly depicted combination, the synthetic polymer foam can be produced in the first foaming device 1, guided to the first mixer 3 via a first conduit 13 and exit the first mixer 3 into a first discharging device. At the same time, the surfactant foam can be routed from the second foaming device 2 to the second conduit 14 and directly to the second discharging device 6, without entering the second mixer. Vice versa, the synthetic polymer foam can circumvent the first mixer 3 and be guided directly to the first discharging device 5, 5a, while the surfactant foam or at least part of the surfactant foam enters the second mixer 4 before exiting into the second discharging device 6. If, as e.g. in
In a final aspect, the invention concerns the use of a synthetic polymer foam for the preparation of at least one surface layer A of a plasterboard to obtain a nail pull resistance of at least 240 N, as determined by ASTM C473:2010. Preferably, the synthetic polymer foam is not used in layer B.
In the above, any preferred or particularly suitable embodiments, which have been described in connection with one aspect, are also applicable to all other aspects of the invention, unless that combination is in clear contradiction to that aspect. Thus, all such combinations are encompassed by and deemed as described in invention, even if this is not explicitly indicated.
Test prisms with dimensions of 4×4×16 cm, were produced by formulating and mixing the compositions as shown in Table 1, pouring them into respective molds and allowing them to set and drying them to a constant weight. The respective characteristics of flexural strength, compressive strength and surface hardness were assessed according to DIN EN 13279-2:2004.
1=synthetic polymer solid matter based on the weight of the stucco;
2 = the synthetic polymer emulsion has a solids content of 37%, with the remaining 63% being water; by adding the water content of the emulsion to the total water content, all samples were prepared with 440 g water;
3= the surfactant in Sample 2 contained 35% active ingredients;
4= determined according to DIN EN 13279-2: 2004
As is apparent from the above table, a compact plasterboard has the best surface hardness and compressive strength, but also the highest volumetric weight (Sample 1). If the product is formulated with a foam, the volumetric weight can significantly be reduced, but this is at the expense of a significantly decline in physical characteristics (Sample 2). Incorporating a synthetic polymer (Sample 3) provides a similar volumetric weight and improves the flexural strength, while ensuring a compressive strength and surface hardness that lie in between those of Samples 1 and 2. If the synthetic polymer is foamed, the flexural strength is not significantly affected, while the volumetric weight can be reduced significantly. Surprisingly, the compressive strength and surface hardness of Sample 4 are equivalent or even somewhat higher to those of Sample 3 with the same amount of non-foamed synthetic polymer.
Table 2 below shows the composition of plasterboard test samples (12.5 mm×40 cm×30 cm):
1= water-to-stucco-ratio;
2= 35% active ingredients;
3= 37% solids content
The plasterboard test boards were covered by two non-woven fiber mat liners instead of the typically used high grammage paper liners. The thus prepared test boards were subjected to the nail pull test according to ASTM C473 (2010). The nail pull test is a measure of the force required to pull a plasterboard off a wall by forcing a fastening nail through the panel. The reported value for Nail Pull Resistance is the maximum stress achieved while the head penetrates through the board surface and core. The characteristics of the test samples and results of these investigations, which included three measurements each, are shown in Table 3 below:
As is apparent from Table 3, the boards prepared with synthetic polymer instead of surfactant foam had about the same dry weight. However, the boards prepared using a synthetic polymer foam showed a significantly higher nail pull resistance. An increase in the amount of synthetic polymer from about 0.7 wt.-% to about 1.5 wt.-% of synthetic polymer solid matter based on the weight of the stucco further improved the nail pull resistance.
The results in both Examples 1 and 2 show that a synthetic polymer foam plasterboard has improved nail pull resistance relative to plasterboards prepared with surfactant foams. If the synthetic polymer foam based gypsum composition is used to prepare only the surface layer of a gypsum board, the amount of synthetic polymer necessary to prepare corresponding boards can be significantly decreased (e.g. to 30%, if the thickness of the synthetic polymer foam based gypsum layer is about 30% of the whole thickness of the board), without significant loss in the nail pull resistance performance.
Further nail pull resistance measurements according to ASTM C473:2010 were carried out for 20 cm×20 cm×1.2 cm test specimen. The results are shown in Tables 5 to 7. Analogous to Samples 5 to 7, these plasterboard test specimen were covered by two non-woven fiber mat liners instead of the typically used high grammage paper liners. Samples 8 and also layers B (8 mm to 10 mm thick) of Samples 10 were production castings. The stucco slurry containing the synthetic polymer foam was prepared analogously on the laboratory scale. Different volumetric weights originated from different mixing times, where foam could be partially destructed by extending the mixing time. The target thickness for all test specimen was 12.5 mm. Layer A of Samples 10 was 2.5 mm to 4.5 mm thick. The main components of all stucco slurries used in Samples 8 to 10 are listed in Table 4.
1= water-to-stucco-ratio;
2based on weight of calcium sulfate binder;
3relative amounts for boards with a density of <800 kg/m3;
4relative amounts for boards with a density >800 kg/m3;
5relative amounts of layer A correspond Sample 9 and relative amounts of layer B correspond to Sample 8. Polyvinyl acetate was used as synthetic polymer foam for the test specimen of Samples 9 and 10;
6This corresponds to 0.3 wt.-% synthetic polymer solid matter based on the calcium sulfate binder of the entire test specimen.
Tables 5 to 7 list the nail pull measurements of test specimen containing a surfactant foam (Table 5), test specimen containing a synthetic polymer foam (Table 6) and two-layered specimen (Table 7) for a representative range of volumetric weight. The comparison shows that a layer of only 2.5 mm to 4.5 mm of synthetic polymer foam is sufficient to achieve the nail pull results in the range of test specimen prepared entirely with synthetic polymer foam. The two-layered samples fall within or slightly above the correlation curve of the samples made with only synthetic polymer foam.
| Number | Date | Country | Kind |
|---|---|---|---|
| 20000482.8 | Dec 2020 | EP | regional |
This application is the United States national phase of International Application No. PCT/EP2021/000158 filed Dec. 22, 2021, and claims priority to European Patent Application No. 20000482.8 filed Dec. 22, 2020, the disclosures of which are hereby incorporated by reference in their entireties.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2021/000158 | 12/22/2021 | WO |
