Coated gypsum set-stabilized particles having a hydrophobic gypsum core, gypsum boards containing the same, process for producing the particles, and process for producing gypsum boards

Abstract

A plurality of set stabilizer particles, comprising: a particle core comprising 50-98% by weight, preferably 70-98% by weight or 70-95% by weight, calcium sulfate dihydrate; 0.05-10% by weight, preferably 0.5-5% by weight, of a hydrophobic material selected from a wax and / or a siloxane; and a coating on the particle core, the coating comprising a dehydration inhibitor selected from a sugar, a dextrin, and a polyhydroxy alcohol, such as glycerol or a polyglycol, in a ratio of about 5-25 parts by weight of the dehydration inhibitor per 100 parts by weight of calcium sulfate dihydrate. Methods of making and using the set stabilizer particles are also disclosed.

Description

[Technical Field]

[0001] The present disclosure relates to a method for recycling gypsum board waste. The present invention relates to set-stabilized particles comprising a coating and a core of recycled gypsum particles containing a hydrophobic material, such as a siloxane, that are useful for stabilizing the setting time of calcium sulfate hemihydrate cement and plaster against the effects of mixtures of substances that may have an accelerating or retarding effect, as well as against the effects of higher-than-normal temperatures. The present invention also relates to a method for producing the set-stabilized particles, and to gypsum boards comprising the set-stabilized particles. [Background technology]

[0002] In building construction, one of the most common building elements is gypsum board, also known as gypsum paneling, gypsum building panels, gypsum panels, or wallboard, used in the construction of walls and / or ceilings. Walls made from gypsum wallboard are traditionally constructed by fastening the panels to wood studs or metal framing and treating the joints between adjacent panels with a specially formulated adhesive called a jointing compound.

[0003] Gypsum board is made primarily of gypsum, as opposed to cement board, which is primarily made of cement such as Portland cement. Specifically, gypsum board is primarily composed of calcium sulfate dihydrate. Gypsum board is made by reacting water with stucco (calcium sulfate hemihydrate) so that the calcium sulfate hemihydrate sets to form calcium sulfate dihydrate (gypsum). Stucco is made by calcining gypsum and is typically primarily composed of calcium sulfate hemihydrate, although it may also contain calcium sulfate anhydrite. Calcium sulfate hemihydrate is produced by calcining calcium sulfate dihydrate to partially dehydrate it.

[0004] When the stucco is mixed with water, the calcium sulfate hemihydrate particles react and rehydrate to form set gypsum. Methods for manufacturing gypsum panels typically involve depositing an aqueous gypsum slurry (e.g., a mixture containing stucco and water). Optionally, one or more additives may be added to the slurry. Additives may include, for example, retarders, accelerators, foaming agents, wet-strength materials, biocides, sag-resistant components, cellulose fibers, glass fibers, fire-retardant materials, binders, water-repellent components, dust mitigating agents, starches, and other components or enhancing materials known in the art.

[0005] Set retarder approx. 2 lb. / MSF (9.8 g / m 2 ) or drying accelerator (approximately 35 lb. / MSF (170 g / m 2 ) to change the rate at which the hydration reaction occurs.

[0006] A typical set accelerator is freshly ground calcium sulfate dihydrate set stabilizer particles with sugar at a ratio of about 5 to 25 pounds of sugar per 100 pounds of calcium sulfate dihydrate, as further described in U.S. Pat. No. 2,078,199, incorporated herein by reference. Typically, this accelerator may be included in the gypsum slurry used to make gypsum board in an amount of 0.5 to 2 percent by weight of the slurry on a dry (water-free) basis.

[0007] The gypsum slurry is typically deposited onto a moving, continuous facing sheet paper or fiber mat, and then the slurry is covered with another facing sheet paper or fiber mat so that the aqueous gypsum slurry forming the gypsum core is between the two facing materials. To reduce the overall weight of the finished gypsum board, air can be incorporated into the aqueous gypsum slurry as bubbles or air pockets to produce a gypsum board with a foamed or aerated gypsum core with air voids (also called air bubbles). The gypsum slurry is allowed to set to produce a solid product (e.g., to form an interlocking matrix of calcium sulfate dihydrate, called set gypsum) before being cut into panels and sent to a kiln for final drying. The produced gypsum board can be further processed as known in the art, then bundled and ready for shipment.

[0008] Gypsum board can enter the solid waste stream at several different locations. Non-limiting examples include waste from manufacturing facilities, waste from new construction sites, restoration waste, and waste from building demolition or demolition. Generally, waste gypsum materials include a gypsum-containing material, typically a layer or core, and one or more facing sheets. Examples of waste gypsum materials containing calcium sulfate dihydrate include gypsum boards, such as interior drywall, exterior cladding panels, and tile backer boards. Gypsum-containing waste materials also include specialty gypsum board products that contain a fiberglass-reinforced gypsum core or may be externally coated with fiberglass to strengthen the board and increase its moisture resistance. Calcium sulfate dihydrate-containing waste may also contain components such as fibrous woven or nonwoven layers, including paper, glass fiber, mineral fiber, polymers, and the like. In particular, gypsum boards typically have a gypsum core and front and back facing sheets of paper, nonwoven fiber mat, or fiber mesh. The fibers of the nonwoven fiber mat or fiber mesh are typically glass, mineral, or polymeric fibers, most typically glass fibers. Generally, the core layer of the waste gypsum material is greater than 50% by weight gypsum.

[0009] Methods for recovering gypsum from gypsum board are known.

[0010] Methods for producing gypsum board are well known. For example, European Patent Application Publication No. 2 641 886 (A2) describes a gypsum powder containing hemihydrate gypsum powder and type II anhydrite gypsum powder. Type II anhydrite gypsum is obtained by calcining gypsum dihydrate recovered from gypsum board waste. European Patent Application Publication No. 2 641 886 (A2) further describes that a portion of the type II anhydrite gypsum may be replaced with dihydrate. This dihydrate may also be obtained from recycled materials. The powder of gypsum board waste is obtained by crushing the board waste and sieving the crushed material to remove the board paper.

[0011] EP 2 030 693 B1 also describes the recycling of gypsum products, in which a device (such as a sieve) is provided to separate the paper waste from the remainder of the gypsum product waste.

[0012] Published Patent Cooperation Treaty Application WO 2009 / 064602(A1) describes wet-grinding the dihydrate with a specific dispersing agent. This gypsum ground product is used as a filler in cosmetics, paper, paints, etc. However, WO 2009 / 064602(A1) does not relate to the recycling of gypsum product waste.

[0013] Published Patent Cooperation Treaty Application WO 2019 / 001677(A1) (Knauf GIPS KG) discloses a method for producing a gypsum slurry for forming a gypsum product, particularly a gypsum board, preferably a gypsum paperboard, comprising: (a) providing a gypsum paper product, particularly a gypsum paperboard, containing gypsum and a paper component, and / or a broken portion thereof; and (b) wet-grinding the gypsum paper product and / or the broken portion thereof containing at least a portion of the paper component to form a wet-ground gypsum paper component. The method also preferably includes disintegrating (grinding) the gypsum paper product together with the paper component (i.e., without prior removal of the paper component). The method also preferably includes (directly) feeding the (uncalcined) ground material into a gypsum slurry for forming a (new) gypsum product.

[0014] In another method for recovering gypsum from gypsum board, after separating the gypsum core, the board is typically ground to a particle size of about 300 μm or less (e.g., about 10 μm to 200 μm, e.g., a D50 of 10 μm to 60 μm) and then calcined to dehydrate the calcium sulfate dihydrate to calcium sulfate hemihydrate, which can then be reused in new products.

[0015] U.S. Pat. No. 10,570,062 discloses a method for producing gypsum plasterboard in which the bandura dust added to the gypsum slurry is obtained from a plasterboard manufacturing process that has been impregnated with a hydrophobic agent, namely silicone oil.

[0016] Published Patent Cooperation Treaty application WO 2019 / 813144(A1) teaches recycled gypsum having a foaming agent that is at least one α-sulfofatty acid di-salt for reducing the wet density of compositions having a recycled gypsum content of at least 0.5% by weight.

[0017] Japanese Patent Application Publication No. 09165244 discloses a gypsum plasterboard material containing 3% by weight or less of pulverized waste gypsum material. The pulverized waste gypsum material is crushed to a size of 1.0 to 4.0 m with a crushing energy of 3 to 15 kw / glubboard waste. 2 / g BET specific surface area.

[0018] U.S. Patent Application Publication No. 2016 / 0214895 discloses a method and apparatus for recycling gypsum board, which involves crushing the raw material into chunks and further crushing the material in a rolling mill, which reduces the material size and partially knocks the gypsum off its backing. The material is then sieved, and only the gypsum material is placed in a hopper, which then passes it through a mixer assembly, which mixes the various sizes of recycled gypsum into a consistent mixture. The material is then passed through a roll press subsystem to densify the material and produce a material of known uniform composition suitable for cement manufacturing. This particular physical form factor of recycled gypsum can be used to a significant extent as a substitute for virgin gypsum in cement manufacturing. This method and apparatus are applicable to the recycling of both new and repair gypsum-based building materials.

[0019] U.S. Patent Application Publication No. 2021 / 0331978 to Schermann et al. discloses a method for producing gypsum board, the method including combining a first plurality of particles comprising at least about 50% by weight calcium sulfate dihydrate and about 0.05% to about 10% by weight hydrophobic material, the first plurality of particles having a D50 particle size of about 200 μm to about 800 μm, with a second plurality of particles comprising calcium sulfate hemihydrate to form a calcium sulfate combined mixture; adding water to the calcium sulfate combined mixture to form an aqueous gypsum slurry; depositing a core layer comprising the aqueous gypsum slurry on a forming surface; and setting the core layer to thereby form a set gypsum core. Particle size distribution (e.g., D50) can also be determined using means known in the art. For example, one non-limiting example is disclosed in ASTM D6913 / D6913M-17 Method B, Standard Test Method for Particle Size Distribution (Gradation) of Soils Using Sieve Analysis.

[0020] While the above process is relatively simple, the regeneration process becomes difficult when recycling gypsum board containing gypsum and hydrophobic material additives. The hydrophobic material additive in the waste gypsum material may be a coating on the outer surface of the gypsum core and / or a component within the gypsum core. Typical hydrophobic materials are siloxanes or waxes. Thus, the hydrophobic additive in the waste gypsum material may be, for example, a siloxane-containing component. Hydrophobic materials tend to repel water, cannot mix with water, and / or have limited wettability with water, as opposed to hydrophilic materials, which tend to mix with, dissolve in, and / or be wetted by water.

[0021] For example, attempts to recycle siloxane-containing gypsum have been unsuccessful because the siloxane-containing gypsum particles interfere with the gypsum setting process, especially when incorporating air bubbles into the gypsum board structure is desirable. Siloxanes are harmful when using such recycled particles to make new gypsum panels because the siloxane-containing gypsum particles prevent the incorporation of air bubbles (foaming) into the gypsum slurry. The incorporation of air bubbles (foaming) into the gypsum slurry is necessary to produce lightweight gypsum board.

[0022] Therefore, these siloxane-containing gypsum board products are typically not recyclable and are either discarded as waste or are best blended in small amounts to have less than 1% by weight of recycled siloxane-containing gypsum in gypsum board made from a mixture of siloxane-containing recycled calcined gypsum and siloxane-free gypsum.

[0023] Therefore, there is a need in the art to develop improved methods of using gypsum particles that contain hydrophobic components. Summary of the Invention

[0024] The present invention relates to a settling stabilizer particle, a particle core comprising 50 to 98% by weight, preferably 70 to 98% by weight or 70 to 95% by weight of calcium sulfate dihydrate and 0.05 to 10% by weight, preferably 0.5 to 5% by weight of a hydrophobic material selected from wax and / or siloxane; a coating on the particle core, the coating comprising a dehydration inhibitor selected from the group consisting of sugars, dextrins, and polyhydroxy alcohols such as glycerol or polyglycols, in a ratio of about 5 to 25 parts by weight of the dehydration inhibitor per 100 parts by weight of calcium sulfate dihydrate.

[0025] The present invention relates to a method for producing the inventive set stabilizer particles from waste gypsum board material. The set stabilizer particles are suitable for use in producing new gypsum board having a foamed core. The method comprises: applying a dehydration inhibitor selected from the group consisting of sugars, dextrins, and polyhydroxy alcohols such as glycerol or polyglycols to a feed particle of waste gypsum board material comprising 50 to 98 weight percent calcium sulfate dihydrate and 0.05 to 10 weight percent hydrophobic material selected from wax and / or siloxane in a ratio of about 5 to 25 weight parts of dehydration inhibitor per 100 weight parts of calcium sulfate dihydrate to produce set stabilizer particles; Application is typically by coating by any suitable mechanical or chemical means, such as by grinding or spray coating feed particles of waste gypsum board material with the dewatering inhibitor.

[0026] The present invention relates to a cement-based powder, stucco particles comprising calcium sulfate hemihydrate, wherein at least 60% by weight of the cementitious powder is calcium sulfate hemihydrate, preferably at least 70% by weight, more preferably at least 80% by weight, typically at least 90% by weight, or typically at least 95% by weight; and 0.5 to 5% by weight, preferably 0.5 to 4% by weight, more preferably 0.5 to 2% by weight or 0.5 to 1.5% by weight of the setting stabilizer particles of the present invention.

[0027] The set stabilizer particles act as seed crystals to accelerate the setting of calcium sulfate hemihydrate, thus acting as a set accelerator.

[0028] The present invention relates to plasters, particles comprising calcium sulfate hemihydrate; A particle of the aggregation stabilizer according to any one of claims 1 to 10, Optionally, a retarder, preferably comprising sodium citrate.

[0029] The present invention also provides a method for producing gypsum board using the set stabilizer particles of the present invention, preparing an aqueous gypsum slurry comprising a mixture of water, stucco, and set stabilizer particles, wherein the stucco comprises calcium sulfate hemihydrate; at least 60% by weight, typically 60 to 98% by weight, preferably at least 70% by weight, more preferably at least 80% by weight, typically at least 90% by weight, or typically at least 95% by weight, of the calcium sulfate hemihydrate on a dry (anhydrous) basis; 0.5 to 5% by weight, preferably 0.5 to 4% by weight, more preferably 0.5 to 2% by weight or 0.5 to 1.5% by weight of setting stabilizer particles; the absence of 0 to 5% by weight on a dry (anhydrous) basis of hydrophobic materials, preferably selected from waxes and / or siloxanes other than those provided by the set stabilizer particles, typically the absence of siloxanes other than those provided by the set stabilizer particles, and the absence of waxes other than those provided by the set stabilizer particles; The calcium sulfate hemihydrate contains a mixture of calcium sulfate hemihydrate and water in a weight ratio of 0.2:1 to 1.2:1; depositing a front cover sheet onto the forming surface; depositing an aqueous gypsum slurry onto a front cover sheet to form a layer of aqueous gypsum slurry, preferably the aqueous gypsum slurry deposited for the core layer being a foamed aqueous gypsum slurry; depositing a back cover sheet onto the aqueous gypsum slurry; setting calcium sulfate hemihydrate to form a panel including a gypsum core comprising calcium sulfate dihydrate; drying the panel and cutting the panel into gypsum boards having one or more predetermined dimensions.

[0030] Gypsum board is a gypsum product that has a board shape (i.e., is particularly at least substantially flat). Gypsum board typically has a rectangular shape.

[0031] The present invention also includes gypsum boards made by the methods of the present invention.

[0032] The present invention also encompasses a gypsum board made by setting a composition comprising a slurry containing a mixture of: Water and particles comprising calcium sulfate hemihydrate; The settling stabilizer particles of the present invention; Optionally, a retarder, preferably comprising sodium citrate. [Brief explanation of the drawings]

[0033] [Figure 1] 1 shows settling stabilizer particles. [Figure 2] 1 shows a process flow diagram for producing settling stabilizer particles by milling. [Figure 3] 1 shows a cross-sectional view of a gypsum board of the present invention, in which the board core (gypsum core) is between the front and back cover sheets. [Figure 4] 4 shows a perspective view of the gypsum board of FIG. 3. [Figure 5] FIG. 1 shows a process flow diagram of one version of a manufacturing production line for making the layered gypsum board of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0034] The present invention includes a method that can be used to recycle waste gypsum materials, such as gypsum board, which may contain hydrophobic materials such as those used in applications to improve the moisture resistance of gypsum board.

[0035] Drywall (wallboard) used in the construction of interior walls and ceilings is exemplified herein as a non-limiting example of a product made from waste gypsum material and recycled gypsum. For purposes of this specification, drywall is defined as a panel (also known as a board) that typically includes a calcium sulfate dihydrate core with additives, typically between a front facer sheet and a back facer sheet. Typically, the facer sheets are made from paper or fiberglass mat, although facers of other fiber sheets may also be used. However, the process disclosed herein can be used to process and reclaim gypsum from any gypsum board having a core layer of gypsum-containing material, as well as to produce any gypsum board building product having a core layer of gypsum-containing material.

[0036] Those skilled in the art will be able to modify the methods described herein to process waste gypsum material from interior wallboard, exterior exterior gypsum panels, gypsum tile backer boards, or other gypsum building panels having a gypsum core between paper facing sheets. For example, a typical gypsum exterior sheathing panel processed according to the present invention may include, from front to back, a first fiber mat, a gypsum core layer having a front surface and a back surface, the gypsum core layer having a thickness of about 0.25 inches to about 1.25 inches, preferably about 0.25 inches to about 1 inch, with the first fiber mat attached to the front surface of the gypsum core layer as a facing cover sheet and the second fiber mat attached to the back surface of the gypsum core layer as a backer cover sheet. The gypsum core layer comprises greater than about 50% by weight calcium sulfate dihydrate, preferably at least about 75% by weight, and more preferably at least about 85% by weight. The first and second fiber mats may comprise paper or fibrous materials (e.g., one or more of polymeric fibers, glass fibers, and mineral fibers).

[0037] Waste gypsum materials can be obtained from a variety of sources. Non-limiting examples include waste from manufacturing facilities, waste from new construction sites, restoration waste, and waste from building demolition or demolition. Generally, waste gypsum materials include a gypsum-containing material, typically a layer or core, and one or more facing sheets. Examples of waste gypsum materials containing calcium sulfate dihydrate include gypsum boards, such as interior drywall, exterior cladding panels, and tile backer boards. Gypsum-containing waste materials also include specialty gypsum board products that contain a fiberglass-reinforced gypsum core or may be externally coated with glass fibers to strengthen the board and increase moisture resistance. Calcium sulfate dihydrate-containing waste may also include components such as fibrous woven or nonwoven layers, including paper, glass fiber, mineral fiber, polymers, and the like. In particular, gypsum boards generally have a gypsum core and front and back facing sheets of paper, nonwoven fiber mat, or fiber mesh. The fibers of the nonwoven fiber mat or fiber mesh are typically glass, mineral, or polymeric fibers, most typically glass fibers. Generally, the core layer of the waste gypsum material is greater than 50% by weight gypsum.

[0038] In one aspect, the present invention comprises a process for converting waste gypsum material containing hydrophobic additives into gypsum suitable for reuse in new gypsum building materials.

[0039] The hydrophobic siloxane material additive in the waste gypsum material may be a coating on the exterior surface of the gypsum core of the waste gypsum board and / or may be a component within the gypsum core of the waste gypsum board. The waste gypsum material may contain up to about 10% by weight of the hydrophobic siloxane material, e.g., about 0.05% to about 10% by weight, or about 0.05% to about 5% by weight, or about 0.1% to about 5% by weight, or about 0.5% to about 2% by weight, e.g., 1% by weight. Thus, by weight, the solid layer of the gypsum core in the waste gypsum material may contain up to about 10% by weight of the hydrophobic siloxane material, e.g., about 0.05% to about 10% by weight, or about 0.1% to about 5% by weight, or about 0.5% to about 2% by weight, e.g., 1% by weight. For example, the lower limit of the hydrophobic siloxane material may be about 0.05%, about 0.1%, about 0.5%, or about 1% by weight of the gypsum-containing material. For example, the upper limit of the hydrophobic siloxane material may be about 2%, about 3%, about 5%, about 7%, or about 10% by weight of the gypsum-containing material. Typical hydrophobic materials are siloxanes and / or waxes, more typically siloxanes. About 1% siloxane in the waste is a typical value.

[0040] Settling-stabilized particles produced from recycled hydrophobic gypsum board waste The present invention relates to a settling stabilizer particle, a particle core comprising 50 to 98% by weight, preferably 70 to 98% by weight or 70 to 95% by weight of calcium sulfate dihydrate and 0.05 to 10% by weight, preferably 0.5 to 5% by weight of a hydrophobic material selected from wax and / or siloxane; a coating on the particle core, the coating comprising a dehydration inhibitor selected from the group consisting of sugars, dextrins, and polyhydroxy alcohols such as glycerol or polyglycols, in a ratio of about 5 to 25 parts by weight of the dehydration inhibitor per 100 parts by weight of calcium sulfate dihydrate.

[0041] The present invention provides settling-stabilized particles having a particulate substrate or core comprising calcium sulfate dihydrate and a hydrophobic material, and an amount of a dehydration-preventing substance. Figure 1 shows a diagram of a typical settling-stabilized particle 1 having a particulate substrate or core 2 comprising calcium sulfate dihydrate and a hydrophobic material, and a full or partial coating 3 comprising a dehydration-preventing substance applied to the substrate or core 2.

[0042] Particle substrates or cores containing calcium sulfate dihydrate are typically seed crystals used to promote the setting of calcium sulfate hemihydrate. The dehydration inhibitor typically has the ability to prevent the calcium sulfate dihydrate seed crystals from losing their water of crystallization. Many substances are suitable as dehydration inhibitors. These can be exemplified by the general group of water-soluble carbohydrates known as sugars, although intermediate substances between starch and sugar, such as more soluble dextrins (e.g., British gum), are also effective for this purpose. Other substances found to be effective in preventing the loss of water of hydration from the seed crystals are polyhydric alcohols such as glycerol, glycols, and polyglycols. Typical dehydration inhibitors are ordinary dextrose or glucose, particularly the commercially available form known as corn sugar.

[0043] The present invention relates to a method for producing the inventive set stabilizer particles from waste gypsum board material. The set stabilizer particles are suitable for use in producing new gypsum board having a foamed core. applying a dehydration inhibitor selected from the group consisting of sugars, dextrins, and polyhydroxy alcohols such as glycerol or polyglycols to a feed particle of waste gypsum board material comprising 50 to 98 weight percent calcium sulfate dihydrate and 0.05 to 10 weight percent hydrophobic material selected from wax and / or siloxane in a ratio of about 5 to 25 weight parts of dehydration inhibitor per 100 weight parts of calcium sulfate dihydrate to produce set stabilizer particles; Here, application is typically coating by any suitable mechanical or chemical means, for example, by grinding or spray coating feed particles of waste gypsum board material with the dewatering inhibitor.

[0044] Typically, the set stabilizer particles are formulated with 100 parts by weight of finely divided calcium sulfate dihydrate crystals as the particle core and 5 to 25 parts by weight of a dehydration inhibitor selected from the group consisting of sugar, dextrin, and polyhydroxy alcohol such as glycerol or polyglycol to coat the particle core. The calcium sulfate dihydrate seed crystals contain 50 to 98% by weight of calcium sulfate dihydrate and 0.05 to 10% by weight of a hydrophobic material selected from wax and / or siloxane, typically siloxane. A gypsum source containing a hydrophobic material is milled to produce the seed crystals that form the cores of the set stabilizer particles of the present invention. Sugar, dextrin, and polyhydroxy alcohol such as glycerol or polyglycol are added to the seed crystals to protect them from high temperatures during the milling process.

[0045] The mixing of the dehydration inhibitor with the calcium sulfate dihydrate seed crystals to produce the set stabilizer particles of the present invention is a separate operation prior to mixing the seed crystals with calcium sulfate hemihydrate to produce gypsum board.

[0046] For example, calcium sulfate dihydrate seed crystals may be thoroughly mixed with a dehydration inhibitor, optionally in the form of an aqueous solution, or directly if glycerol or glycol is used, and the latter is then dried to remove any added solvent, such as water. If the dehydration inhibitor material is soluble in an organic liquid, such as alcohol or ether, such a substance may be used as a diluent or solvent and then evaporated. One way to achieve this result is to take the calcium sulfate dihydrate seed crystal material and, while it is in a powdered state, spray it with a solution or dispersion of a dehydration inhibitor before or simultaneously with its grinding or mixing.

[0047] Preferably, the calcium sulfate dihydrate seed crystals are coated with a dehydration-preventing substance. Therefore, any mechanical or chemical means capable of achieving such coating are considered within the scope and spirit of the present invention. For example, a solution of a dehydration-preventing substance, such as corn sugar, can be sprayed onto 100 parts by weight of powdered calcium sulfate dihydrate in a proportion of 5 to 25 parts by weight, while the latter is vigorously stirred in a mixer until the solvent (water) evaporates, thereby leaving the dehydration-preventing substance attached to or dispersed with the calcium sulfate dihydrate crystals. Alternatively, gypsum particles can be coated with sugar or other dehydration-preventing substance by grinding them in a ball mill or the like. Therefore, the dehydration-preventing substance can be intimately ground together with the settling-stabilized calcium sulfate dihydrate crystal material, for example, in a ball mill or the like, as shown in FIG. 2. As shown in FIG. 2, a flow 4 of particles containing calcium sulfate and a hydrophobic material and a flow 5 of a dehydration-preventing substance are fed to a ball mill 6 and milled together to coat the particles containing calcium sulfate and a hydrophobic material with the dehydration-preventing substance, thereby producing a flow 7 of particles containing calcium sulfate and a hydrophobic material coated with the dehydration-preventing substance.

[0048] When using materials other than corn sugar, it is preferable to use an equivalent amount of the other material. Among the sugars, other than corn sugar, there are sugars having a sweet taste and having the general formula C n H 2n O n or C n H 2n-2 O n-1 In general, any carbohydrate of the general formula CH 12 The hexose sugars O6 are more efficient. However, the invention is not limited to these particular sugars, as it has been found that other sugars, such as maltose, lactose, sucrose, and similar saccharin products, can be used instead. Thus, for example, molasses also exhibits protective properties, although not as efficiently as pure sugar. On the other hand, fully dextrinized starches, such as British gums, can be used, and, as already mentioned, glycerin or glycol can be used as described above.

[0049] The settling stabilizer particles are typically between 5000 and 15000 cm 2 / gm, e.g., 7000-14000 cm 2 / gm, or e.g., 9000-12000 cm 2 / gm. The settling stabilizer particles typically have a particle size distribution with a Dv50 particle size of about 10 μm to about 60 μm, e.g., about 20 μm to about 50 μm. The Dv50 particle size is the largest particle size below which 50% of the sample volume lies, also known as the volume-based median particle size. Particle size can be simply determined by passing the material through an appropriately sized sieve, as is well known in the art. Particle size distribution (e.g., D50) can also be determined using means known in the art. For example, one non-limiting example is disclosed in ASTM D6913 / D6913M-17 Method B, Standard Test Method for Particle Size Distribution (Gradation) of Soils Using Sieve Analysis.

[0050] A mixture of calcium sulfate hemihydrate particles and settling stabilizer particles The present invention relates to a cement-based powder, stucco particles comprising calcium sulfate hemihydrate, wherein at least 60% by weight of the cementitious powder is calcium sulfate hemihydrate, preferably at least 70% by weight, more preferably at least 80% by weight, typically at least 90% by weight, or typically at least 95% by weight; and 0.5 to 5% by weight, preferably 0.5 to 4% by weight, more preferably 0.5 to 2% by weight or 0.5 to 1.5% by weight of the setting stabilizer particles of the present invention.

[0051] Typically, the set stabilizer particles may be included in the slurry used to make the gypsum board in an amount of 0.5 to 5%, preferably 0.5 to 4%, more preferably 0.5 to 2% or 0.5 to 1.5% by weight of the slurry on a dry (water-free) basis. Typical plasters embodying the concepts of the present invention may be combined in the following relative amounts: 1000 parts by weight of calcium sulfate hemihydrate (typically provided by gypsum stucco), 5 to 50 parts by weight, preferably 5 to 40 parts by weight, more preferably 2 to 20 parts by weight or 5 to 15 parts by weight, for example 10 parts by weight of setting stabilizer particles; In this case, the set stabilizer particles themselves are blended in a ratio of 100 parts by weight of finely divided calcium sulfate dihydrate crystals and 5 to 25 parts by weight of a dehydration inhibitor selected from the group consisting of sugars, dextrins, and polyhydroxy alcohols such as glycerol or polyglycols, and the calcium sulfate dihydrate crystals contain 50 to 98% by weight of calcium sulfate dihydrate and 0.05 to 10% by weight of a hydrophobic material selected from waxes and / or siloxanes.

[0052] Gypsum products of the present disclosure can be produced from slurries according to Table 1. The resulting gypsum products can have compositions according to Table 2. In Tables 1 and 2, any range of an ingredient can be substituted for any other range of that ingredient in the respective tables. In Tables 1 and 2, "set stabilizer particles" are set stabilizer particles of the present invention that contain a hydrophobic material. Other set stabilizer particles or accelerators are referred to in this application as "accelerators." For example, the preferred ranges of set stabilizer particles may be used with other ingredients provided in their broad ranges.

[0053] [Table 1]

[0054] [Table 2]

[0055] The present invention relates to plasters, particles comprising calcium sulfate hemihydrate; The settling stabilizer particles of the present invention; Optionally, a retarder, preferably comprising sodium citrate.

[0056] Method for the production of gypsum board The present invention also provides a method for producing gypsum board using the set stabilizer particles of the present invention, preparing an aqueous gypsum slurry comprising a mixture of water, stucco, and set stabilizer particles, wherein the stucco comprises calcium sulfate hemihydrate; at least 60% by weight, typically 60 to 98% by weight, preferably at least 70% by weight, more preferably at least 80% by weight, typically at least 90% by weight, or typically at least 95% by weight, of the calcium sulfate hemihydrate on a dry (anhydrous) basis; 0.5 to 5% by weight, preferably 0.5 to 4% by weight, more preferably 0.5 to 2% by weight or 0.5 to 1.5% by weight of setting stabilizer particles; the absence of 0 to 5% by weight on a dry (anhydrous) basis of hydrophobic materials, preferably selected from waxes and / or siloxanes other than those provided by the set stabilizer particles, typically the absence of siloxanes other than those provided by the set stabilizer particles, and the absence of waxes other than those provided by the set stabilizer particles; The calcium sulfate hemihydrate contains a mixture of calcium sulfate hemihydrate and water in a weight ratio of 0.2:1 to 1.2:1; depositing a front cover sheet onto the forming surface; depositing an aqueous gypsum slurry onto a front cover sheet to form a layer of aqueous gypsum slurry, preferably the aqueous gypsum slurry deposited for the core layer being a foamed aqueous gypsum slurry; depositing a back cover sheet onto the aqueous gypsum slurry; setting calcium sulfate hemihydrate to form a panel including a gypsum core comprising calcium sulfate dihydrate; drying the panel and cutting the panel into gypsum boards having one or more predetermined dimensions.

[0057] All weight percent values ​​herein are by weight unless otherwise indicated. As used herein, "total dry weight" or "on a dry weight basis" refers to the weight of the mixture excluding any water component that may be present. "Water component" excludes water that may be present in the gypsum crystal structure. In contrast, "wet basis" includes water in the weight percent calculation.

[0058] Stucco particles containing calcium sulfate hemihydrate and set stabilizer particles can be fed as separate streams to a slurry mixer to be mixed with water to form an aqueous gypsum slurry. The set stabilizer particles include a particle core containing 50-98% by weight calcium sulfate dihydrate and 0.05-10% by weight of a hydrophobic material selected from wax and / or siloxane, and a coating containing a dehydration inhibitor selected from the group consisting of sugar, dextrin, and polyhydroxy alcohol in a ratio of about 5-25 parts by weight of dehydration inhibitor per 100 parts by weight of calcium sulfate dihydrate. Alternatively, the stucco particles and set stabilizer particles can be combined to form a combined stream of cementitious powder that is fed to a slurry mixer and mixed with water to form an aqueous gypsum slurry. In either case, the aqueous gypsum slurry can be formed into a new gypsum material suitable for use as a building material. For example, new gypsum panels of various widths and thicknesses can be produced by methods known in the art. Water, and optionally one or more additives, are provided to create an aqueous gypsum slurry, either separately or together with the stucco particles and one or more of the set stabilizer particles. The set stabilizer particles are mixed with the stucco to form a powder, and the powder is provided to a mixer.

[0059] Embodiments of the invention may include adding a foaming agent to an aqueous gypsum slurry to form a core layer of a gypsum board. The foaming agent may or may not include an α-sulfofatty acid di-salt.

[0060] Figure 3 shows an embodiment of a wallboard panel 10 of the present invention. Figure 4 shows a perspective top view (axial view) of the wallboard panel 10. The board has a core 28 including a set low-density region (low-density region) 12 as a layer comprising calcium sulfate dihydrate and a set high-density region (also called a densified region or thin high-density gypsum layer) 22 as a layer comprising calcium sulfate dihydrate.

[0061] FIG. 3 shows a wallboard panel 10 of the present invention, in which a core 28 including a gypsum low-density region 12 (e.g., 0.5 inches thick) is between a back cover sheet 14 (also known as a backer cover sheet) and a front cover sheet 16 (also known as a facer cover sheet), each of which can be a single or multiple layer of paper or a fibrous material such as fiberglass mat. The inner surface of the back cover sheet 14 forms a bonding side 24 of the back cover sheet 14 that faces the gypsum core 28. The inner surface of the front cover sheet 16 forms a bonding side 26 of the front cover sheet 16 that faces the gypsum low-density region 12. A high-density region (thin high-density gypsum layer) 22 is located between the gypsum low-density region (low-density region) 12 and the front cover sheet 16, contacting them. Optionally, a second high-density region (also known as a densified region or thin high-density gypsum layer) 20, such as a layer including calcium sulfate dihydrate, is on the bonding side of the back sheet 14. The outer surface of the back cover sheet 14 faces the wall framing (not shown) of a room after the wallboard panel 10 is installed as an interior wall. The outer surface of the front cover sheet 16 faces the interior of the room after the wallboard panel 10 is installed as an interior wall.

[0062] Generally, the relatively low-density regions 12 and the relatively high-density regions 20, 22 have the same composition and are adjacent to each other. However, the low-density regions may be formed from a foamed gypsum slurry, while the high-density regions may be formed from an unfoamed gypsum slurry, resulting in a denser layer. That is, the high-density regions may have less porosity than the low-density regions.

[0063] The combined density of the gypsum low density region 12 and high density regions 20, 22 can be from about 15 lbs / cu ft to about 65 lbs / cu ft, more typically from 25 lbs / cu ft to about 65 lbs / cu ft, for example, from 25 lbs / cu ft to 55 lbs / cu ft.

[0064] The low-density region resulting from the set gypsum low-density region slurry (e.g., low-density region 12 in FIG. 3 ) typically has a thickness of 0.25 inches to 1.5 inches and a density of 15 to 55 pounds per cubic foot. In contrast, the high-density regions (e.g., high-density regions 20, 22 in FIG. 3 ) typically each have a thickness of 5% to 25% of the thickness of the gypsum board 10. Typically, the thickness of the densified layer is about 0.02 inches to about 0.2 inches (about 0.05 to about 0.5 cm), e.g., about 0.0625 inches to about 0.125 inches (about 0.16 to about 0.32 cm). The thickness of the low-density region layer 12 is greater than the thickness of each of the high-density region layers 20, 22. When foamed, the gypsum low-density region layer resulting from the set foamed gypsum slurry has a total void volume of 10 to 92 volume percent, specifically 25 to 90 volume percent, and more specifically 30 to 85 volume percent. In contrast, the densified layer has a total void volume of less than 30 volume percent, such as less than 25 volume percent, and is less than 0.25 inches thick.

[0065] A variety of methods can be used to prepare the gypsum board of the present invention from an aqueous gypsum slurry containing calcium sulfate hemihydrate and the set stabilizer particles of the present invention.

[0066] The base material used in the manufacture of gypsum wallboard and other gypsum products is calcium sulfate hemihydrate (CaSO₄·1 / 2H₂O), commonly called "calcined gypsum" or "stucco," which is produced by the thermal conversion (calcination) of calcium sulfate dihydrate (CaSO₄).

[0067] Exemplary manufacturing techniques and equipment suitable for forming gypsum boards according to the present invention can be found, for example, in U.S. Patent No. 7,364,676 and U.S. Patent Application Publication No. 2010 / 0247937, each of which is incorporated herein by reference in its entirety. To manufacture gypsum boards, stucco is mixed with water, the set stabilizer of the present invention, and optionally other additives to form an aqueous gypsum slurry, which is continuously fed between successive layers of paper on a board machine. One cover sheet is called the front cover sheet, or facer. The other cover sheet is called the back cover sheet, or backer.

[0068] Typically, to manufacture gypsum board with front and back cover sheets, stucco is mixed with water and additives to form an aqueous slurry that is continuously fed between successive sheet layers (e.g., paper sheets) on a board machine. As the board moves down the conveyor line to form panels, the set stabilizer of the present invention helps the calcium sulfate hemihydrate recrystallize or rehydrate back to its original rock state, calcium sulfate dihydrate. As the gypsum sets, the cover sheets are bonded to the core. The panels are then cut to length and conveyed through a dryer to remove free moisture.

[0069] Such a process discharges a first cover sheet onto a moving conveyor. Dry and / or wet components of the aqueous gypsum slurry are fed into a mixer (e.g., a pin mixer or a pinless mixer) where they are agitated to form an aqueous gypsum slurry. The aqueous gypsum slurry can be made with any suitable water / calcium sulfate hemihydrate ratio for placement on the first cover sheet. Because gypsum board is usually formed "face down," this first cover sheet typically corresponds to the facer (front cover sheet) at the completion of the fabrication process. The mixer includes a body and a discharge conduit (e.g., a gate-canister-boot configuration known in the art, or alternative configurations such as those described in U.S. Pat. Nos. 6,494,609 and 6,874,930, which are incorporated herein by reference in their entireties). In some process configurations, the discharge conduit can include a slurry distributor with either a single feed inlet or multiple feed inlets, such as those described in U.S. Patent Application Publication Nos. 2012 / 0168527 and 2012 / 0170403, which are incorporated herein by reference in their entireties. When using a slurry distributor with multiple feed inlets, the discharge conduit can include an appropriate flow splitter, such as that described in U.S. Patent Application Publication Nos. 2012 / 0170403. If desired, a foaming agent (typically soap) can be added to the mixer discharge conduit (e.g., a gate such as those described in U.S. Patent Nos. 5,683,635 and 6,494,609, which are incorporated herein by reference) or to the main body. The slurry discharged from the discharge conduit after all ingredients, including the foaming agent, have been added is the primary gypsum slurry and is used to form the low-density region layer. This gypsum slurry is discharged onto a moving first cover sheet.

[0070] After mixing, air bubbles are optionally added to the aqueous gypsum slurry to reduce the density of the product. The air bubbles are created by combining soap and water. The air bubbles can then be injected into the aqueous gypsum slurry after it exits the mixer through a hose or chute. Air bubbles are typically added to the portion of the aqueous gypsum slurry intended for the low-density layer of the core, but not to the portion of the slurry intended for the densified layer.

[0071] Once the air bubbles and aqueous gypsum slurry are combined, the resulting slurry moves toward and is poured onto a conveyor lined with a first piece of facing material, known as a first cover sheet. Another piece of facing material, known as a second cover sheet, is placed on top of the slurry, forming a sandwich assembly with the slurry between the two facing materials. The sandwich assembly is fed into a forming plate or other forming device, the height of which determines the thickness of the board. Next, continuous sandwich assemblies are cut to the appropriate length (usually 8 to 12 feet) with cutting knives. As the board moves down the conveyor line to form panels, the slurry hardens (sets). The calcium sulfate recrystallizes or rehydrates, returning to its original rock state and forming a board core containing an interlocking crystalline matrix of set gypsum. As the gypsum sets, the cover sheet is bonded to the core. The panels are then cut to length and transported to a kiln or dryer where free moisture is removed. Temperatures in the kiln typically range from 450°F to 500°F.

[0072] As described above, the front cover sheet is in interfacial contact with the high-density region, also known as the densified layer. The densified layer typically adjoins the low-density region layer after setting. If air bubbles are inserted into the discharge conduit, a secondary gypsum slurry stream can be removed from the mixer body before foaming to provide the slurry for forming the densified layer. The densified layer can be deposited on the first cover sheet, along with the moving gypsum slurry, before the main portion of the gypsum slurry is deposited to form the low-density region layer. After the gypsum slurry for the low-density region is discharged from the discharge conduit, it is optionally spread on the first cover sheet and the densified layer. At this point, a second cover sheet is placed on top of the spread gypsum low-density region slurry. If no second high-density region is present, the spread gypsum low-density region slurry is contacted with the second cover sheet on which the first densified layer has already been deposited. The resulting wet assembly takes the form of a multi-layer assembly and serves as a precursor to the final gypsum board product. The densified layer can be formed from the same or a different gypsum slurry as the low-density region layer.

[0073] In particular, Figure 5 illustrates an embodiment of the wet end 80 of a manufacturing production line for producing a layered gypsum board of the present invention having a gypsum layer between two cover sheets, which are provided with a densified layer. The cover sheets are made of paper, such as manila paper or kraft paper.

[0074] Wetting end 80 includes gypsum slurry mixing and distribution assembly 82, forming station 86. Figure 5 shows that the stucco particles and set stabilizer particles of the present invention can be fed together as stream 74 to gypsum slurry mixing and distribution assembly 82. However, alternatively, the stucco particles and set stabilizer particles of the present invention can be fed separately to gypsum slurry mixing and distribution assembly 82.

[0075] A first moving web 90 of first cover sheet material (face sheet) moves in a longitudinal motion "T" along a forming table 92. A gypsum low density region slurry 94 is mixed in a gypsum slurry mixing and distribution assembly 82, where additives are added and foaming of the slurry occurs for the low density region layer (e.g., layer 12 in FIG. 3). Although the gypsum slurry mixing and distribution assembly 82 is illustrated as a single component of the wet end 80, there can be multiple components comprising the gypsum slurry mixing and distribution assembly 82.

[0076] The densified layer slurry 70 from the gypsum slurry mixing and distribution assembly 82 is applied to a first cover sheet material 90 to form a densified layer (e.g., densified region 22 in FIG. 3 ) on the first cover sheet material 90, which passes under the first gypsum densified layer roller 72 before depositing a gypsum central low-density region layer slurry 94. The densified layer slurry 76 is applied to a second cover sheet material (back sheet material) 96 to form a second high-density region layer (e.g., layer 20 in FIG. 3 ). The second cover sheet material (back sheet material) 96 is then applied over the deposited low-density region layer slurry 94 to form a multi-layer structure. The multi-layer structure then passes through a forming station 86 to compress the layers to the desired total thickness. The resulting structure is a gypsum board preform 98.

[0077] The cover sheet material may be uncoated or may be coated, for example, with a previously applied exterior polymeric coating and hydrophobic finish. Typically, the exterior surfaces of the applied moving webs 90 and 96 and the resulting exterior surfaces of the gypsum board front and back cover sheets are uncoated and not in contact with additional layers.

[0078] Additional components may be included at the wet end 80 of the production line.

[0079] The gypsum densified layer is thinner and denser than the low-density region layer. Therefore, the gypsum densified layer slurry is relatively denser than the gypsum low-density region layer slurry, which may be a foamed gypsum slurry. Typically, the calcined gypsum (calcium sulfate hemihydrate) slurry 94 for the low-density region layer is foamed to be less dense than the densified layer slurries 70 and 76. Therefore, if desired, the calcined gypsum low-density region layer slurry stream 94 may pass through a foaming device (not shown) that mixes the calcined gypsum low-density region layer slurry stream 94 with bubbles and / or air, for example, before deposition on the first cover sheet material 90. Alternatively, the densified layer may be achieved by directing a portion of the gypsum slurry from a mixer to a densified layer mixer or by knocking bubbles out of the gypsum densified layer slurry before introducing bubbles into the gypsum slurry. Thus, a gypsum low-density region layer slurry 94 for the low-density region layer of the board is deposited on the gypsum densified layer slurry 70. Typically, the gypsum low-density region layer slurry stream 94 and the gypsum densified layer slurry streams 70, 76 have the same composition and density. However, if desired, the gypsum low-density region layer slurry stream 94 and the slurry streams for the gypsum densified layers 70, 76 can have different compositions and / or densities. FIG. 5 shows all gypsum slurries 70, 76, 94 supplied from the same calcined gypsum slurry mixing and distribution assembly 82. However, the calcined gypsum slurries 70, 76, 94 can be obtained from different mixing and distribution assemblies so as to have different properties, such as different densities.

[0080] The gypsum densifying layer roller 72, forming table 92, and forming station 86 can all include conventional equipment suitable for their respective purposes, as known in the art. The wet end 80 can be equipped with other conventional equipment, as known in the art.

[0081] The calcined gypsum in the gypsum slurries 70, 76, 94 reacts with water and sets as the conveyor moves the gypsum board preform 98 down the production line. The gypsum board preform 98 is dried and cut into segments of predetermined dimensions at points along the line where the gypsum board preform 98 has sufficiently set. The segments can be dried (e.g., in a kiln) to drive off excess water and processed to provide the final layered wallboard of the desired dimensions.

[0082] The forming station 86 is the location at the board line where the wet board precursor is sized to a predetermined width and thickness, and optionally, length. Thus, the forming station can include or be any apparatus capable of performing the final mechanical spreading and / or shaping of the slurry across the width of the backing layer, many of which are known in the art. The forming station includes means for adjusting the thickness and width of the slurry to the final desired thickness and width of the wet board precursor that will produce the cementitious board product upon setting. The final desired thickness and width of the slurry produced at the forming station may, of course, differ from the final thickness and width of the finished board product. For example, the thickness and / or width of the slurry may expand and / or contract during crystallization (i.e., setting) and drying of the slurry. Typically, the desired slurry thickness is substantially equal to the desired board thickness (e.g., about 0.375 inches (about 0.95 cm), about 0.5 inches (about 1.27 cm), about 0.625 inches (about 1.59 cm), about 0.75 inches (about 1.90 cm), or about 1 inch (about 2.54 cm). By way of example only, the final board thickness is typically within about + or - 1 / 8 inch (about 0.32 cm) or less of the final slurry thickness.

[0083] The forming station includes any equipment capable of producing the desired slurry thickness and width of the wet board precursor. Suitable equipment includes, for example, a forming plate, forming rollers, forming press, screed, etc. The specific equipment used will depend in part on the type of cementitious board being produced. In a preferred embodiment, for example, when the board forming system is a gypsum board or acoustic panel forming system, the board forming station comprises a forming plate as known in the art. The board forming system of any of the above embodiments optionally further comprises a blade for cutting the wet board precursor or dry cementitious board product to a desired length and / or a drying area capable of removing water from the set cementitious board.

[0084] Plaster and stucco (plaster of Paris) The calcium sulfate hemihydrate component used to form the crystalline matrix of the gypsum panel core typically includes beta calcium sulfate hemihydrate, water-soluble calcium sulfate anhydrous, alpha calcium sulfate hemihydrate, or a mixture of any or all of these, and is obtained from natural or synthetic sources. Calcium sulfate hemihydrate is typically provided in a raw material known as stucco or calcined gypsum. In some aspects, the stucco may contain small amounts of non-gypsum minerals, such as clay or other ingredients, associated with the gypsum source or added during the stucco's calcination, processing, and / or delivery to the mixer. Stucco can be fibrous or non-fibrous. Typically, raw stucco has at least 70% by weight calcium sulfate hemihydrate, preferably at least 80% by weight calcium sulfate hemihydrate, more preferably at least 85% by weight calcium sulfate hemihydrate, and even more preferably at least 90% by weight calcium sulfate hemihydrate.

[0085] additives In addition to the set stabilizer particles of the present invention, other additives may be present in the gypsum slurry used to form the board core. Such additives may include, but are not limited to, reinforcing agents, foam (prepared from a suitable foaming agent), dispersants, polyphosphates (e.g., sodium trimetaphosphate), starches, retarders, accelerators, reburn inhibitors, binders, adhesives, secondary dispersion aids, leveling or non-leveling agents, thickeners, bactericides, fungicides, pH adjusters, buffers, colorants, reinforcing materials, flame retardants, water repellents (e.g., siloxanes), fillers, and mixtures thereof.

[0086] The additives and other components of the gypsum slurry can be added to the mixer in a variety of ways. For example, various combinations of components can be premixed before entering the mixer, either as one or more dry components and / or one or more wet components. Similarly, a single component can be introduced to the mixer in wet or dry form. When introduced in wet form, the component can be included in a carrier fluid, such as water, at any suitable concentration.

[0087] Fibers may optionally be used in the methods and compositions of the present invention. Fibers may include mineral fibers (also known as mineral wool), glass fibers, carbon fibers, and mixtures of such fibers, as well as other equivalent fibers that provide similar benefits to wallboard. For example, glass fibers may be incorporated into the gypsum low-density region slurry and / or the high-density region layer slurry and the resulting crystalline core structure. In such embodiments, the glass fibers may have an average length of about 0.5 to about 0.75 inches and a diameter of about 11 to about 17 microns. In other embodiments, such glass fibers may have an average length of about 0.5 to about 0.675 inches and a diameter of about 13 to about 16 microns. In still other embodiments, E-glass fibers having a softening point above about 800°C or at least above about 900°C are utilized. Mineral wool or carbon fibers, as known to those skilled in the art, may be used in place of or in combination with the glass fibers.

[0088] When included, the fibers can be present in the gypsum low-density layer slurry and / or the gypsum densified layer slurry in an amount of about 0.5 to about 10 pbw, preferably about 1 to about 8 pbw, more preferably about 2 to about 7 pbw, and most preferably about 3 to about 6 pbw, on a dry basis per 100 pbw of calcium sulfate hemihydrate. Alternatively, the fibers may be absent.

[0089] Optionally, if desired, one or more phosphate-containing compounds can also be included in the slurry.For example, these phosphate-containing components can include water-soluble components, and can be in the form of ions, salts, or acids, i.e., condensed phosphoric acids, each of which contains two or more phosphate units, condensed phosphate salts or ions, each of which contains two or more phosphate units, and monobasic salts or monovalent ions of orthophosphates, and water-soluble acyclic polyphosphates.Illustrative examples are described in U.S. Patent Nos. 6,342,284, 6,632,550, 6,815,049, and 6,822,033, the entire contents of which are incorporated herein by reference.

[0090] The phosphate-containing component can enhance green strength, resistance to permanent deformation (e.g., deflection), dimensional stability, etc. For example, trimetaphosphate compounds including sodium trimetaphosphate, potassium trimetaphosphate, lithium trimetaphosphate, and ammonium trimetaphosphate can be used. Sodium trimetaphosphate (STMP) is commonly used, but other compounds, such as sodium tetrametaphosphate, have from about 6 to about 27 repeating phosphate units and have the molecular formula Na n+2 P n O 3n+1 where n=6-27; sodium hexametaphosphate having the molecular formula KPO; tetrapotassium pyrophosphate having the molecular formula NaKPO; 10 Trisodium tripolyphosphate, with the molecular formula Na5P3O 10sodium tripolyphosphate having the molecular formula Na4P2O7, tetrasodium pyrophosphate having the molecular formula Na4P2O7, aluminum trimetaphosphate having the molecular formula Al(PO3)3, sodium pyrophosphate having the molecular formula Na2H2P2O7, sodium pyrophosphate having 1000-3000 repeating phosphate units and the molecular formula (NH4 n+2 P n O 3n+1 (wherein n=1000 to 3000), or ammonium polyphosphate having two or more repeating phosphate units and having the molecular formula H n+2 P n O 3n+1 Other phosphate salts may also be suitable, including polyphosphates having the formula: where n is 2 or greater.

[0091] The phosphate salt is typically added in dry form and / or in aqueous liquid form, with the dry ingredients being added to a slurry mixer and the liquid ingredients being added to a mixer or at another stage or procedure.

[0092] If present, the phosphate can be included in the gypsum slurry in dry form or in aqueous form (e.g., about 5% to about 20% phosphate solution, such as about a 10% solution). If included, the phosphate can be present in any suitable amount (solids / solids basis), such as about 0.01% to about 0.5% by weight of the stucco (e.g., about 0.03% to about 0.4%, about 0.1% to about 0.3%, or about 0.12% to about 0.4% by weight of the stucco). Phosphate may also be absent.

[0093] The gypsum slurry may optionally contain at least one dispersant to enhance fluidity. The dispersant may be introduced into the gypsum slurry in dry form, optionally with other additives, and / or in liquid form, optionally with other liquid components. Examples of suitable dispersants include naphthalene sulfonates, such as polynaphthalene sulfonic acid and its salts (polynaphthalene sulfonates), and derivatives that are condensation products of naphthalene sulfonic acid with formaldehyde, as well as polycarboxylate dispersants, such as polycarboxylic acid ethers. Other examples of suitable dispersants include lignosulfonates or sulfonated lignin. Lignosulfonates are water-soluble anionic polyelectrolyte polymers that are by-products from the production of wood pulp using sulfite pulp.

[0094] Lower molecular weight dispersants may be desirable. Lower molecular weight naphthalene sulfonate dispersants may be preferred because they tend to have higher viscosities and lower water demands than higher molecular weight dispersants. Thus, a molecular weight of about 3,000 to about 10,000 (e.g., about 8,000 to about 10,000) may be desirable for dispersants. If desired, the molecular weight of a polycarboxylate dispersant may be about 20,000 to about 60,000, which may exhibit less retardation than dispersants with molecular weights greater than about 60,000.

[0095] A typical naphthalene sulfonate is an aqueous naphthalene sulfonate solution having a naphthalene sulfonate solids content ranging from about 35% to about 55% by weight, however, if desired, the naphthalene sulfonate can be used in dry solid or powder form.

[0096] When present, the dispersant can be included in the gypsum slurry in any suitable (solids / solids) amount, such as, for example, about 0.1% to about 5% by weight of the stucco, e.g., about 0.1% to about 4%, about 0.1% to about 3%, about 0.2% to about 3%, about 0.5% to about 3%, about 0.5% to about 2.5%, about 0.5% to about 2%, about 0.5% to about 1.5%, etc. Any one or more of the polynaphthalenesulfonate, polycarboxylic acid ether, or lignosulfonate may be absent.

[0097] In addition to the set stabilized particles of the present invention, additional accelerators may be added to the gypsum thin layer slurry and / or the dense layer slurry.

[0098] An accelerator can be added to the gypsum low-density layer slurry and / or the high-density layer slurry to modify the rate at which the hydration reaction of calcium sulfate hemihydrate occurs. When present, the accelerator can be incorporated into the gypsum slurry in an amount, for example, from about 0% to about 10% (e.g., from about 0.1% to about 10%) of the weight of the stucco on a solids basis, for example, from about 0% to about 5% (e.g., from about 0.1% to about 5%) of the weight of the stucco. Suitable accelerators can include, for example, potassium sulfate, calcium sulfate dihydrate, carbohydrate-coated calcium sulfate, calcium sulfate dihydrate / organic phosphonate, and calcium sulfate dihydrate / organic phosphate.

[0099] Another accelerator can be used to stabilize the particles, having an absence of siloxanes and an absence of waxes and other hydrophobic materials. A typical such accelerator is calcium sulfate dihydrate set stabilizer particles freshly ground with sugar at a ratio of about 5 to 25 pounds of sugar per 100 pounds of calcium sulfate dihydrate. This is further described in U.S. Pat. No. 2,078,199, which is incorporated herein by reference.

[0100] Another accelerator includes 95% calcium sulfate dihydrate co-ground with 5% sugar and heated to 250°F (121°C) to caramelize the sugar, as done in accordance with U.S. Patent No. 3,573,947, which is incorporated herein by reference.

[0101] A description of the use of other accelerators and their methods of manufacture is disclosed in U.S. Patent No. 6,409,825, which is incorporated herein by reference. The wet gypsum accelerator is applied in an amount of from about 5 to about 80 pounds per 1000 square feet (24.3 to 390 g / m) of board product. 2 ) is used in amounts ranging from 100mg to 150mg.

[0102] A retarder can be added to the gypsum low-density layer slurry and / or the high-density layer slurry to modify the rate at which the hydration reaction of calcium sulfate hemihydrate occurs. If present, the retarder can be incorporated into the gypsum slurry in an amount, on a solids basis, of, for example, about 0% to about 10% (e.g., about 0.1% to about 10%) of the weight of the stucco, for example, about 0% to about 5% (e.g., about 0.1% to about 5%) of the weight of the stucco.

[0103] There may be no accelerators and / or retarders other than the set stabilized particles of the present invention.

[0104] Air bubbles (also known as aerated water) can optionally be introduced into the gypsum low-density region slurry and / or the high-density region slurry (preferably the gypsum low-density region slurry) in an amount that provides the reduced low-density region density and panel weight described above. The foaming agent for generating the air bubbles is typically a soap or other suitable surfactant. Introducing the bubbles into the gypsum low-density region slurry in the appropriate amount, formulation, and process will create a desired network and void distribution within the low-density region of the final dry wallboard. This void structure allows for reduction of the gypsum and other low-density region components and the low-density region density and weight while maintaining the desired panel structure and strength properties. When present, the foaming agent can comprise a major weight portion of an unstable component and a minor weight portion of a stable component (e.g., when unstable and stable / unstable blends are combined). The weight ratio of unstable to stable components is effective to form a void distribution within the set gypsum low-density region, as described in U.S. Patent Nos. 5,643,510, 6,342,284, and 6,632,550, the entire contents of which are incorporated herein by reference. Approaches for adding foam to gypsum low-density region slurries are known in the art; one example of such an approach is discussed in U.S. Patent No. 5,683,635, the disclosure of which is incorporated herein by reference. Evaporated water voids, generally having voids with a diameter of about 5 μm or less, also contribute to the total void distribution along with the aforementioned air (bubble) voids. The volume ratio of voids with a pore size greater than about 5 microns to voids with a pore size of about 5 microns or less is about 0.5:1 to about 9:1, e.g., about 0.7:1 to about 9:1, about 1.8:1 to about 2.3:1, etc. The foaming agent is present in the gypsum slurry in an amount, for example, less than about 0.5% by weight of the stucco, such as from about 0.01% to about 0.5%, from about 0.01% to about 0.2%, from about 0.02% to about 0.4%, from about 0.02% to about 0.2%, from about 0.01% to about 0.1%, etc. In some cases, no foaming agent is present.

[0105] Ingredients for fire resistance and / or water resistance may also be included in the gypsum slurry. Examples include, for example, siloxanes (water resistant), fibers, heat sink additives such as aluminum trihydrite (ATH), magnesium hydroxide, and / or high expansion particles (e.g., capable of expanding to greater than about 300% of their original volume when heated at 1560°F for about 1 hour). Further disclosure of such additives can be found in U.S. Pat. No. 8,323,785, which is incorporated by reference in its entirety. High expansion vermiculite may be included, although other fire-resistant materials may be included. When present, the fire-resistant or water-resistant additive may be included in any suitable amount desired, depending, for example, on fire rating and similar performance parameters. For example, if included, the fire-resistant or water-resistant additive may be individually present in an amount of from about 0.5% to about 10% by weight of the stucco, e.g., from about 1% to about 10% by weight, from about 1% to about 8% by weight, from about 2% to about 10% by weight, from about 2% to about 8% by weight, etc.

[0106] If included, the siloxane may be introduced desirably in the form of an emulsion. The slurry may then be shaped and dried under conditions that promote polymerization of the siloxane to form a highly crosslinked silicone resin. A catalyst may be added to the gypsum slurry to promote polymerization of the siloxane to form a highly crosslinked silicone resin. A solvent-free methylhydrogen siloxane fluid may be used as the siloxane. This product is a siloxane fluid that does not contain water or solvent. It is contemplated that, if desired, about 0.3% to about 1.0% siloxane may be used, based on the weight of the dry ingredients. For example, if desired, about 0.4% to about 0.8% siloxane, based on the weight of the dry stucco, may be present in the gypsum slurry.

[0107] water Water is added to the slurry in any amount that will produce a flowable slurry. The amount of water used will vary greatly depending on the application for which it is being used, the exact dispersant used, the properties of the calcium sulfate hemihydrate, and any additives used.

[0108] The water used to make the slurry should be as pure as possible to best control the properties of both the slurry and the set gypsum. Salts and organic compounds are well known to alter the setting time of the slurry, ranging from accelerators to set inhibitors. Some impurities cause structural irregularities as the interlocking matrix of dihydrate crystals forms, reducing the strength of the set product. Therefore, product strength and consistency are enhanced by using water that is as free of contaminants as practical.

[0109] Water can be present in the gypsum low density zone slurry and / or high density zone layer slurry of the present invention in a weight ratio of water to calcium sulfate hemihydrate of about 0.2:1 to about 1.2:1, preferably about 0.3:1 to about 1.1:1, more preferably about 0.6:1 to about 1:1, most preferably 0.7:1 to 0.95:1, and typically about 0.85:1.

[0110] Back cover sheet and front cover sheet The front and back cover sheets may be made of paper or other fibrous materials such as glass fiber mats. The back and front cover sheets may be made of any suitable paper material having any suitable basis weight.

[0111] The back cover sheet and the front cover sheet may be made of paper, but the paper material of each cover sheet may be the same or different.

[0112] Various grades of paper may be used for gypsum panels, including smooth-calendared Manila-grade paper, often used as the facer paper cover sheet, and rougher-finished Newsline paper, often used as the backer paper cover sheet. Typically, both paper grades are multi-ply, with at least one liner ply and several filler plies. However, if desired, at least one or both paper cover sheets can be made of single-ply paper.

[0113] Typically, the back cover sheet covers only the back surface, in contrast to the front cover sheet which covers the front surface of the board and also wraps around the edges of the board to meet the back cover sheet.

[0114] If desired, to increase the strength (e.g., nail pull strength) of particularly low density gypsum boards, one or both of the cover sheets can be formed from paper having a basis weight of, for example, at least about 45 lbs / MSF (e.g., from about 45 lbs / MSF to about 65 lbs / MSF, from about 45 lbs / MSF to about 60 lbs / MSF, from about 45 lbs / MSF to about 55 lbs / MSF, from about 50 lbs / MSF to about 65 lbs / MSF, from about 50 lbs / MSF to about 60 lbs / MSF, etc.). If desired, the front paper cover sheet can have a higher basis weight than the back cover sheet, which can provide improved nail pull resistance and handling. The back paper cover sheet can have a somewhat lower basis weight, if desired (e.g., less than 45 lbs / MSF, e.g., from about 33 lbs / MSF to 45 lbs / MSF (e.g., from about 33 lbs / MSF to about 40 lbs / MSF)).

[0115] Invention clause The following sections disclose various aspects of the present invention.

[0116] Clause 1. A plurality of particles of a settling stabilizer, a particle core comprising 50 to 98% by weight, preferably 70 to 98% by weight or 70 to 95% by weight of calcium sulfate dihydrate and 0.05 to 10% by weight, preferably 0.5 to 5% by weight of a hydrophobic material selected from wax and / or siloxane; a coating on a particle core, the coating comprising a dehydration inhibitor selected from the group consisting of sugars, dextrins, and polyhydroxy alcohols such as glycerol or polyglycols, in a ratio of about 5 to 25 parts by weight of the dehydration inhibitor per 100 parts by weight of calcium sulfate dihydrate.

[0117] Clause 2. The settling stabilizer particles of clause 1, wherein the dehydration inhibitor comprises a hexose sugar.

[0118] Clause 3. The settling stabilizer particles of clause 1, wherein the dehydration inhibitor comprises corn sugar.

[0119] Clause 4. The settling stabilizer particles of clause 1, wherein the dehydration prevention substance comprises glycerol.

[0120] Clause 5. The settling stabilizer particles of clause 1, wherein the dehydration-preventing substance comprises a substance selected from the group consisting of sugar, dextrin, and polyhydroxy alcohol.

[0121] Clause 6. The set stabilizer particles of clause 1, comprising sugar-coated calcium sulfate dihydrate particles.

[0122] Clause 7. The set stabilizer particles of clause 1, wherein the hydrophobic material comprises a siloxane.

[0123] Clause 8. The set stabilizer particles of clause 1, wherein the hydrophobic material comprises a siloxane, and the set stabilizer particles comprise from about 0.05% to about 5% by weight, typically from 0.1% to about 3% by weight, of said siloxane.

[0124] Clause 9. The set stabilizer particles of clause 1, wherein the hydrophobic material comprises a wax.

[0125] Clause 10. The set stabilizer particles of clause 1, wherein the hydrophobic material comprises a wax and the set stabilizer particles comprise from about 0.5% to about 10% by weight, typically from 1% to about 7% by weight, for example from about 3% to about 7% by weight of said wax.

[0126] Clause 11. A method for producing the settling stabilizer particles according to any one of clauses 1 to 10, comprising: applying a dehydration inhibitor selected from the group consisting of sugars, dextrins, and polyhydroxy alcohols such as glycerol or polyglycols to a feed particle of waste gypsum board material comprising 50 to 98 weight percent calcium sulfate dihydrate and 0.05 to 10 weight percent hydrophobic material selected from wax and / or siloxane in a ratio of about 5 to 25 weight parts of dehydration inhibitor per 100 weight parts of calcium sulfate dihydrate to produce set stabilizer particles; Here, application is typically coating by any suitable mechanical or chemical means, for example, by grinding or spray coating feed particles of waste gypsum board material with the dewatering inhibitor.

[0127] Clause 12. Cementitious powders, stucco particles comprising calcium sulfate hemihydrate, wherein at least 60% by weight of the cementitious powder is calcium sulfate hemihydrate, preferably at least 70% by weight, more preferably at least 80% by weight, typically at least 90% by weight, or typically at least 95% by weight; 0.5 to 5 wt. %, preferably 0.5 to 4 wt. %, more preferably 0.5 to 2 wt. % or 0.5 to 1.5 wt. % of the set stabilizer particles according to any one of clauses 1 to 10.

[0128] Clause 13. The cementitious powder of clause 12, further comprising a retarder.

[0129] Clause 14. The cementitious powder according to clause 13, wherein the retarder comprises a keratin-based material treated with caustic soda and quicklime, which is a nitrogen-containing product that has a retarding effect on the setting time of plaster of Paris, powdered adhesive, citrate, acetate, timothy hay extract, or proteinaceous retarder, preferably sodium citrate or proteinaceous retarder, due to its colloidal properties.

[0130] Clause 15. A set-stabilized calcium sulfate hemihydrate plaster comprising stucco particles comprising calcium sulfate hemihydrate, a retarder, and set stabilizer particles, wherein the particle cores of the set stabilizer particles comprising calcium sulfate dihydrate are seed crystals, and the dehydration inhibitor comprises a water-soluble, relatively non-volatile polyhydroxy alcohol material that coats the dihydrate and protects the dihydrate from losing its water of crystallization.

[0131] Clause 16. Plasters, particles comprising calcium sulfate hemihydrate; Clauses 1 to 10, wherein the particles of the settling stabilizer are Optionally, a retarder, preferably comprising sodium citrate.

[0132] Clause 17. A method for using the set stabilizer particles according to any one of clauses 1 to 10 for producing gypsum board, comprising: preparing an aqueous gypsum slurry comprising a mixture of water, stucco, and set stabilizer particles, wherein the stucco comprises calcium sulfate hemihydrate; at least 60% by weight, typically 60 to 98% by weight, preferably at least 70% by weight, more preferably at least 80% by weight, typically at least 90% by weight, or typically at least 95% by weight, of the calcium sulfate hemihydrate on a dry (anhydrous) basis; 0.5 to 5% by weight, preferably 0.5 to 4% by weight, more preferably 0.5 to 2% by weight or 0.5 to 1.5% by weight of setting stabilizer particles; the absence of 0 to 5% by weight on a dry (anhydrous) basis of hydrophobic materials, preferably selected from waxes and / or siloxanes other than those provided by the set stabilizer particles, typically the absence of siloxanes other than those provided by the set stabilizer particles, and the absence of waxes other than those provided by the set stabilizer particles; The calcium sulfate hemihydrate contains a mixture of calcium sulfate hemihydrate and water in a weight ratio of 0.2:1 to 1.2:1; depositing a front cover sheet onto the forming surface; depositing an aqueous gypsum slurry onto a front cover sheet to form a layer of aqueous gypsum slurry, preferably the aqueous gypsum slurry deposited for the core layer being a foamed aqueous gypsum slurry; depositing a back cover sheet over the aqueous gypsum slurry; setting calcium sulfate hemihydrate to form a panel including a gypsum core comprising calcium sulfate dihydrate; drying the panel and cutting the panel into gypsum boards having one or more predetermined dimensions.

[0133] Clause 18. A first portion of the gypsum slurry is disposed in an unfoamed state as a high density region in the form of a layer contacting the front cover sheet, and a second portion of the gypsum slurry is disposed in a foamed state as a low density region contacting the high density region, the high density region having a higher density than the low density region; 18. The method of claim 17, wherein the board core comprises an aggregated low density region comprising calcium sulfate dihydrate and an aggregated high density region comprising calcium sulfate dihydrate, the aggregated high density region being interposed as a layer between the aggregated low density region and the front cover sheet.

[0134] Clause 19. The method of clause 17, wherein at least one of the front cover sheet and the back cover sheet comprises a glass mat facer sheet or a paper facer sheet.

[0135] Clause 20. The method of clause 17, wherein the low density region has a total void volume of about 45% to about 80% by volume.

[0136] Clause 21. The method of clause 17, wherein the densified region has a total void volume of less than about 30% by volume.

[0137] Clause 22. The method of clause 17, wherein the densified region has a total void volume of less than about 10% by volume.

[0138] Clause 23. Gypsum board manufactured by the method described in clause 17.

[0139] Clause 24. A gypsum board made by setting a composition comprising a slurry, the slurry comprising: Water and particles comprising calcium sulfate hemihydrate; Clauses 1 to 10, wherein the particles of the settling stabilizer are Optionally, a retarder, preferably comprising sodium citrate.

[0140] The following examples further illustrate the present invention but, of course, should not be construed as in any way limiting its scope. [Example]

[0141] In the following examples, gypsum slurries were made by mixing 400 g of calcium sulfate hemihydrate, 400 g of water, and 20 g of set accelerator (set stabilizer particles). The slurry density was controlled by adding air bubbles to the mixer. The air bubbles were created with a foam generator and added at a constant flow rate for exactly 7 seconds. After mixing the hemihydrate, set accelerator, water, and air bubbles in a mixer equipped with a paddle for a total of 20 seconds, the slurry was poured into 1 / 2-inch thick, 4-inch diameter disks. Four disks were cast for each condition. The disks were dried overnight at 110°F to a constant weight. The amount of air bubbles added within 7 seconds, taking into account that all bubbles remained while mixed with the slurry, resulted in a density of 28 lb / ft when the slurry set and dried. 3 This gives a dry density of 1000 sq ft. If some of the bubbles burst during mixing, the dry density will be higher. The disks were weighed to determine the average dry density.

[0142] Example 1 As comparative examples, three different types of calcium sulfate hemihydrate were made in the laboratory by calcining calcium sulfate dihydrate from different sources (Types A, B, and C) at 350°F for 40 minutes. Type A: Calcium sulfate dihydrate was a dry synthetic gypsum containing a hydrophobic agent (siloxane) and no recycled waste (control sample). Type B: Calcium sulfate dihydrate was obtained by grinding pieces of drywall that did not contain a hydrophobic agent. Type C: Calcium sulfate dihydrate was obtained by grinding pieces of drywall containing about 0.7% by weight of a siloxane-based hydrophobic agent.

[0143] Table 3 shows the densities of Type A, Type B, and Type C blends containing calcium sulfate hemihydrate obtained by calcining Type A, Type B, and Type C sources of calcium sulfate dihydrate, respectively.

[0144] [Table 3]

[0145] The results show the effect of using waste board containing a hydrophobic agent (siloxane in the examples) on air bubbles and final density. The addition of siloxane-containing waste increased density by partially destroying air bubbles during mixing. The set accelerator used in the experiments described above for the comparative examples was a control set accelerator made by grinding gypsum (containing no siloxane-containing waste) and 5% by weight dextrose.

[0146] Example 2 The set accelerator (set stabilizer particles) of the present invention was prepared by grinding a board containing 0.7% by weight of a siloxane hydrophobic agent together with 5% by weight of dextrose in a ball mill for 10 minutes. When the set accelerator of the comparative example was replaced with the set accelerator (set stabilizer particles) of the present invention, the dry density was 27.9 lb / ft. 3 was found to be approximately the same as the control sample made without the siloxane-containing waste material, and also achieved a target density of 28 lb / ft 3This proves that when siloxane-containing waste is ground with an appropriate grinding aid (dextrose in this example) to produce a set accelerator used to make gypsum board, the siloxane-containing waste does not affect the air bubbles.

[0147] The present invention provides and uses a set-stabilized calcium sulfate hemihydrate cement or plaster containing calcium sulfate dihydrate seed crystals protected against loss of water of hydration as a result of heating, and an equivalent amount of retarder, to produce a plaster whose setting time does not change upon storage in the presence of heat or upon accidental mixing for accelerating or retarding effects, as claimed by the inventors.

[0148] Advantageously, the method described herein allows for the regeneration of otherwise unsuitable gypsum materials for reuse in new products.In particular, even when gypsum particles are reduced in size, they may still contain and be coated with one or more hydrophobic additives present in the solid layer from which the particles are formed, which has previously been described herein as being incompatible with incorporation into aqueous gypsum slurries for drywall production, especially for drywall containing cellular components.Previous attempts have revealed that gypsum particles containing hydrophobic substances destroy the walls of the cellular components and impair the stability of the slurry.

[0149] In particular, gypsum drywall containing hydrophobic components that would otherwise be discarded can be recycled into new drywall having properties that meet ASTM Standard C1396 / C1396M-17. Various properties, such as flexural strength, hardness (core, end, and edge), nail pull resistance, humid deflection, end squareness, nominal thickness, concave or tapered edge depth, width, length, water resistance of core-treated water-repellent gypsum panel products, and surface water resistance of gypsum panel products having a water-repellent surface, can be determined as described in ASTM C473-19.

[0150] All documents described herein, including any priority documents and / or testing procedures, to the extent not inconsistent herewith, are incorporated by reference for purposes in all jurisdictions where such practice is permitted. While forms of the disclosure have been illustrated and described, as is apparent from the foregoing general description and specific embodiments, various modifications can be made without departing from the spirit and scope of the disclosure. Accordingly, no limitation of the disclosure is intended. For example, the compositions described herein may not include any component or composition not expressly enumerated or disclosed herein. Any method may lack any step not described or disclosed herein. Similarly, the term "comprising" is considered synonymous with the term "including." Whenever a method, composition, element, or group of elements is preceded by the transitional phrase "comprising," it is understood that the same composition or group of elements having the transitional phrase "consisting essentially of," "consisting of," "selected from the group consisting of," or "is" preceding the composition, element, or list of elements is also contemplated, and vice versa.

[0151] Unless otherwise indicated, all numbers expressing quantities of ingredients, properties such as molecular weight, reaction conditions, and the like used in the specification and related claims are to be understood as being modified in all instances by the term "about." Accordingly, unless otherwise indicated, the numerical parameters set forth in the following specification and appended claims are approximations that may vary depending upon the desired properties sought to be obtained by embodiments of the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should, at the very least, be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

[0152] Whenever a numerical range with a lower and upper limit is disclosed, any number falling within that range and any included range is specifically disclosed. In particular, any range of values ​​disclosed herein (in the form of "about a to about b," or, equivalently, "approximately a to b," or, equivalently, "approximately a to b") should be understood to describe any number or range encompassed within that broader range of values. Furthermore, terms in the claims have their plain and ordinary meaning unless expressly and unambiguously defined otherwise by the patent owner. Furthermore, the indefinite article "a" or "an," as used in the claims, is defined herein to mean one or more of the element it introduces.

Claims

1. a plurality of set stabilizer particles, a particle core comprising 50 to 98% by weight, preferably 70 to 98% by weight or 70 to 95% by weight of calcium sulfate dihydrate and 0.05 to 10% by weight, preferably 0.5 to 5% by weight of a hydrophobic material selected from waxes and / or siloxanes; a coating on a particle core, the coating comprising a dehydration inhibitor selected from the group consisting of sugars, dextrins, and polyhydroxy alcohols such as glycerol or polyglycols, in a ratio of about 5 to 25 parts by weight of the dehydration inhibitor per 100 parts by weight of calcium sulfate dihydrate.

2. 10. The settling stabilizer particles of claim 1, wherein the dehydration inhibitor comprises at least one of a hexose sugar or a corn sugar.

3. 2. The settling stabilizer particles of claim 1, wherein the dehydration-inhibiting substance comprises a material selected from the group consisting of dextrin and polyhydroxy alcohol.

4. 10. The set stabilizer particles of claim 1, comprising sugar-coated calcium sulfate dihydrate particles.

5. A method for making the settling stabilizer particles of any one of claims 1 to 4, comprising: applying a dehydration inhibitor selected from the group consisting of sugars, dextrins, and polyhydroxy alcohols such as glycerol or polyglycols to a feed particle of waste gypsum board material comprising 50 to 98% by weight calcium sulfate dihydrate and 0.05 to 10% by weight hydrophobic material selected from wax and / or siloxane in a ratio of about 5 to 25 parts by weight of the dehydration inhibitor per 100 parts by weight of calcium sulfate dihydrate to produce set stabilizer particles; The method wherein the application is typically by any suitable mechanical or chemical means, for example by grinding or spray coating the feed particles of waste gypsum board material with the dewatering prevention substance.

6. A cement-based powder comprising: stucco particles comprising calcium sulfate hemihydrate, wherein at least 60% by weight of the cementitious powder is calcium sulfate hemihydrate, preferably at least 70% by weight, more preferably at least 80% by weight, typically at least 90% by weight, or typically at least 95% by weight; 0.5 to 5% by weight, preferably 0.5 to 4% by weight, more preferably 0.5 to 2% by weight or 0.5 to 1.5% by weight of the set stabilizer particles according to any one of claims 1 to 4.

7. A plaster, particles comprising calcium sulfate hemihydrate; A settling stabilizer particle according to any one of claims 1 to 4; and optionally a retarder, preferably a retarder comprising sodium citrate.

8. A method for producing a gypsum board using the set stabilizer particles according to any one of claims 1 to 4, preparing an aqueous gypsum slurry comprising a mixture of water, stucco, and the set stabilizer particles, wherein the stucco comprises calcium sulfate hemihydrate; at least 60% by weight, typically 60 to 98% by weight, preferably at least 70% by weight, more preferably at least 80% by weight, typically at least 90% by weight, or typically at least 95% by weight, of said calcium sulfate hemihydrate on a dry anhydrous basis; 0.5 to 5 wt. %, preferably 0.5 to 4 wt. %, more preferably 0.5 to 2 wt. % or 0.5 to 1.5 wt. % of the settling stabilizer particles; preferably in the absence of 0-5% by weight on a dry anhydrous basis of hydrophobic materials selected from waxes and / or siloxanes other than those provided by the set stabilizer particles, typically in the absence of siloxanes other than those provided by the set stabilizer particles, and in the absence of waxes other than those provided by the set stabilizer particles; a mixture of calcium sulfate hemihydrate and water in a weight ratio of 0.2:1 to 1.2:1; depositing a front cover sheet onto the forming surface; depositing the aqueous gypsum slurry on the front cover sheet to form a layer of the aqueous gypsum slurry, preferably the aqueous gypsum slurry deposited for the core layer being a foamed aqueous gypsum slurry; depositing a back cover sheet over the aqueous gypsum slurry; allowing the calcium sulfate hemihydrate to set to form a panel comprising a gypsum core comprising calcium sulfate dihydrate; drying the panel and cutting the panel into gypsum boards having one or more predetermined dimensions.

9. A gypsum board manufactured by the method of claim 8.

10. A gypsum board made by setting a composition comprising a slurry, the slurry comprising: Water and particles comprising calcium sulfate hemihydrate; A settling stabilizer particle according to any one of claims 1 to 4; and optionally a retarder, preferably a retarder comprising sodium citrate.

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