Coated gypsum set-stable particles having hydrophobic gypsum core, gypsum board including same, process for preparing particles and process for preparing gypsum board

Abstract

A plurality of set stabilizer particles, the plurality of set stabilizer particles comprising: a particle core comprising from 50% to 98% by weight, preferably from 70% to 98% by weight or from 70% to 95% by weight of calcium sulfate dihydrate and from 0.05% to 10% by weight, preferably from 0.5% to 5% by weight of a hydrophobic material selected from waxes and / or siloxanes; and a coating layer on the particle core, the coating layer comprising an anti-dehydration substance selected from sugars, dextrins, and a polyhydroxy alcohol such as glycerol or polyethylene glycol in a ratio of about 5 to 25 parts by weight of the anti-dehydration substance per 100 parts by weight of calcium sulfate dihydrate. Methods of making and using these coagulation stabilizer particles are also disclosed.

Description

Technical Field

[0001] The present disclosure relates to a method for reusing gypsum board waste. The present invention relates to solidification-stabilized particles comprising a coating and a core of recycled gypsum particles containing a hydrophobic material such as siloxane, which can be used to stabilize the setting time of hemihydrate calcium sulfate cement and gypsum against the influence of mixtures of substances that may have accelerating or delaying effects, and against the effects of temperatures above normal. The present invention also relates to a method for preparing the solidification-stabilized particles and to a gypsum board comprising the solidification-stabilized particles. Background Art

[0002] In the construction of buildings, one of the most common building components is the gypsum board, also known as gypsum panel, gypsum building panel, gypsum wallboard or wall panel, which is used for the construction of walls and / or ceilings. Walls made of gypsum wallboards are traditionally constructed by attaching the panels to wood studs or metal frames and treating the joints between adjacent panels with a specially prepared adhesive called joint compound.

[0003] Gypsum board is mainly made of gypsum, as opposed to cement board, which is mainly cement, such as Portland cement. In particular, gypsum board is mainly composed of calcium sulfate dihydrate. Gypsum board is prepared by reacting water with plaster (hemihydrate calcium sulfate) such that the hemihydrate calcium sulfate solidifies to form calcium sulfate dihydrate (gypsum). Plaster is made by calcining gypsum and typically consists mainly of hemihydrate calcium sulfate and may also contain calcium sulfate anhydrite. Hemihydrate calcium sulfate is produced by calcining calcium sulfate dihydrate to partially dehydrate the calcium sulfate dihydrate.

[0004] When the plaster is mixed with water, the hemihydrate calcium sulfate particles react and rehydrate to become solidified gypsum. The method of manufacturing gypsum panels typically involves depositing an aqueous gypsum slurry (e.g., a mixture containing plaster and water). Optionally, one or more additives may be added to the slurry. Additives may include, for example, retarders, accelerators, foaming agents, wet strength enhancers, biocides, anti-sag components, cellulose fibers, glass fibers, flame retardants, binders, water repellent components, dust suppressants, starch, and other components or reinforcing materials known in the art.

[0005] Adding a retarder (up to about 2 lb. / MSF (9.8 g / m 2 )) or a dry accelerator (up to about 35 lb. / MSF (170 g / m 2 )) to change the rate at which the hydration reaction occurs.

[0006] Typical accelerators are set-stabilizer particles of freshly ground calcium sulfate dihydrate with sugar at a ratio of about 5 pounds to 25 pounds of sugar / 100 pounds of calcium sulfate dihydrate. It is further described in U.S. Patent No. 2,078,199, which is incorporated herein by reference. Generally, the accelerator can be included in the gypsum slurry used to prepare gypsum board in an amount of 0.5 wt% - 2 wt% based on the dry (anhydrous) amount of the slurry.

[0007] The gypsum slurry is typically deposited on a moving continuous facing paper or fiber mat, and then the slurry is covered with another facing paper or fiber mat such that the water-containing gypsum slurry that will form the gypsum core is located between the two facing materials. To reduce the total weight of the finished gypsum board, air can be incorporated into the water-containing gypsum slurry as bubbles or voids, thereby producing a gypsum board having a foamed or bubbly gypsum core with air gaps (also referred to as bubbles). The gypsum slurry is allowed to set (e.g., to form an interlocked matrix of calcium sulfate dihydrate, called set gypsum) to produce a solid article, which is then cut into panels and sent to a kiln for final drying. As is known in the art, the produced gypsum board can be further processed, then bundled, and made ready for shipping.

[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, renovation waste, and waste from building demolition or deconstruction. Generally speaking, waste gypsum materials include gypsum-containing materials, usually a layer or core, and one or more facing sheets. Waste gypsum materials containing calcium sulfate dihydrate include gypsum board, such as interior drywall, exterior cladding panels, and tile backer boards. In addition, waste materials containing gypsum include special gypsum board products, which may contain a glass fiber-reinforced gypsum core or be externally coated with glass fiber to reinforce the board and enhance moisture resistance. Waste materials containing calcium sulfate dihydrate may also contain components such as fibrous woven or non-woven layers, which contain paper, glass fiber, mineral fiber, polymer, etc. In particular, gypsum board typically has a gypsum core and front and back facing sheets of paper, non-woven fiber mat, or fiber mesh. The fibers of the non-woven fiber mat or fiber mesh are typically glass fiber, mineral fiber, or polymer fiber, most commonly glass fiber. Usually, the core layer of the waste gypsum material is more than 50 wt% gypsum.

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

[0010] Methods for producing gypsum boards are well known. For example, the published European patent application EP 2641 886 A2 describes a gypsum powder containing hemihydrate gypsum powder and type II anhydrous gypsum powder. Type II anhydrous gypsum is obtained by calcining dihydrate gypsum recovered from gypsum board waste. EP 2 641 886 A2 further describes that part of the type II anhydrous gypsum can be replaced by dihydrate. In addition, the dihydrate can be obtained from recycled materials. The powder of gypsum board waste is obtained by crushing waste boards and passing the crushed product through a sieve to remove the board paper.

[0011] EP 2 030 693 B1 also describes the recycling of gypsum products, in which devices (such as sieves) are provided to separate paper waste from the rest of the gypsum product waste.

[0012] The published Patent Cooperation Treaty application WO 2009 / 064602 A1 describes wet grinding of dihydrate together with a specific dispersant. The ground gypsum is used as a filler for cosmetics, paper or coatings. However, WO 2009 / 064602 A1 does not relate to the recycling of gypsum product waste.

[0013] The published Patent Cooperation Treaty application WO 2019 / 001677 A1 (Knauf GIPS KG) discloses a method for producing a gypsum slurry for forming gypsum products, in particular gypsum boards, preferably gypsum cardboard, comprising the steps of: a) providing a gypsum paper product, in particular gypsum cardboard, containing gypsum and paper components, and / or its broken parts; b) wet grinding the gypsum paper product containing at least part of the paper components and / or its broken parts to form a wet ground gypsum paper component. The method decomposes (grinds) the gypsum paper product together with the paper components (i.e., without pre-removing the paper components). It also includes feeding the preferably (non-calcined) ground material (directly) into the gypsum slurry to form a (new) gypsum product.

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

[0015] U.S. Patent No. 10,570,062 discloses a method for producing gypsum plasterboard, in which the binder dust added to the gypsum slurry is obtained from the production process of impregnated plasterboard using a hydrophobic agent (i.e., silicone oil).

[0016] Published Patent Cooperation Treaty application WO 2019 / 813144 A1 teaches a recycled gypsum with a blowing agent, which is at least one disalt of α-sulfo fatty acid, for reducing the wet density of the composition, wherein the recycled gypsum content is at least 0.5% by weight.

[0017] Japanese Patent Application Publication No. JP09165244 A discloses a gypsum plasterboard material containing 3% by weight or less of crushed waste gypsum material. The crushed waste gypsum material is ground with a grinding energy of 3 kw - 15 kw / gypsum board waste, so that the BET specific surface area is 1.0 m 2 / g - 4.0 m 2 / g.

[0018] U.S. Patent Application Publication 2016 / 0214895 discloses a method and apparatus for recycling gypsum board, which includes grinding raw materials into pieces and further crushing the materials in a rolling mill, which reduces the material size and partially knocks the gypsum off its backing paper. Then the materials are screened so that only the gypsum materials are subsequently deposited into a hopper and then into a mixer assembly, which mixes recycled gypsum of various sizes into a uniform mixture, and then this material is transferred into a roll compaction subsystem to densify this material, thereby producing a material with a known and uniform composition suitable for cement manufacturing. Then, the recycled gypsum in this specific physical form factor can be used for an important part in cement manufacturing as a substitute for virgin gypsum. The method and apparatus are applicable to the recycling of new and renovated gypsum-based building materials.

[0019] U.S. Published Patent Application No. 2021 / 0331978 by Schermann et al. discloses a method for preparing gypsum board, the method comprising: combining a first plurality of particles comprising at least about 50% by weight of calcium sulfate dihydrate and from about 0.05% to about 10% by weight of a hydrophobic material and having a D50 particle size of from about 200 μm to about 800 μm with a second plurality of particles comprising calcium sulfate hemihydrate to form a combined calcium sulfate mixture; adding water to the combined calcium sulfate mixture to prepare a hydrated gypsum slurry; depositing a core layer comprising the hydrated gypsum slurry on a forming surface; and solidifying the core layer to form a solidified gypsum core. The particle size distribution (e.g., D50) can also be determined using methods 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] Although the above process is relatively simple, the recycling process becomes difficult when recycling gypsum boards containing gypsum and hydrophobic material additives. The hydrophobic material additives in the waste gypsum material can be coatings on the outer surface of the gypsum core and / or can be components within the gypsum core. Typical hydrophobic materials are siloxanes or waxes. Thus, the hydrophobic additives in the waste gypsum material can be, for example, siloxane-containing components. Hydrophobic materials tend to repel water, cannot be mixed with water, and / or have limited wettability with water. This is contrary to hydrophilic materials that have a tendency to mix with water, dissolve in water, and / or be wetted by water.

[0021] For example, attempts to recycle siloxane-containing gypsum have been unsuccessful because siloxane-containing gypsum particles interfere with the setting process of gypsum, especially when it is necessary to incorporate air bubbles into the gypsum board structure. When using such recycled particles to prepare new gypsum panels, siloxane is harmful because siloxane-containing gypsum particles interfere with the incorporation (foaming) of air bubbles in the gypsum slurry. Incorporating air bubbles (foaming) in the gypsum slurry is for the preparation of lightweight gypsum boards.

[0022] Therefore, these siloxane-containing gypsum board products are generally not recyclable and are discarded as waste or preferably blended in small amounts to have less than 1 wt% of the recycled siloxane-containing gypsum in gypsum boards made from a mixture of recycled calcined gypsum containing siloxane and gypsum not containing siloxane.

[0023] Therefore, there is a need in the art to develop improved methods for using gypsum particles containing hydrophobic components. SUMMARY OF THE INVENTION

[0024] The present invention relates to setting stabilizer particles that comprise

[0025] a particle core that comprises 50 wt% to 98 wt%, preferably 70 wt% to 98 wt% or 70 wt% to 95 wt% of calcium sulfate dihydrate and 0.05 wt% to 10 wt%, preferably 0.5 wt% to 5 wt% of a hydrophobic material selected from wax and / or siloxane, and

[0026] a coating on the particle core, the coating comprising an anti-dehydration substance selected from the group consisting of sugars, dextrins, and polyhydroxy alcohols such as glycerol or polyethylene glycol, in a ratio of about 5 parts to 25 parts of the anti-dehydration substance per 100 parts by weight of calcium sulfate dihydrate.

[0027] The present invention relates to a method for preparing the setting stabilizer particles of the present invention from waste gypsum board materials. The setting stabilizer particles are suitable for the preparation of new gypsum boards with a foamed core. The method comprises:

[0028] An anti-dehydration substance selected from the group consisting of sugars, dextrins, and polyhydric alcohols such as glycerol or polyglycols is applied to the feed particles of waste gypsum board material at a ratio of about 5 to 25 parts by weight of the anti-dehydration substance per 100 parts by weight of calcium sulfate dihydrate to produce solidification stabilizer particles, and these feed particles of waste gypsum board material 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,

[0029] wherein the application is usually carried out by coating by any suitable mechanical or chemical means, such as by grinding or spraying the feed particles of the waste gypsum board material with the anti-dehydration substance.

[0030] The present invention relates to a cementitious powder, which comprises:

[0031] Plaster particles containing calcium sulfate hemihydrate, wherein at least 60% by weight, preferably at least 70% by weight, more preferably at least 80% by weight, usually at least 90% by weight or usually at least 95% by weight of the cementitious powder is calcium sulfate hemihydrate; and

[0032] 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 solidification stabilizer particles of the present invention.

[0033] The solidification stabilizer particles act as crystal seeds to promote the solidification of calcium sulfate hemihydrate. Therefore, they act as accelerators.

[0034] The present invention relates to a gypsum, which comprises:

[0035] Particles containing calcium sulfate hemihydrate;

[0036] The solidification stabilizer particles according to any one of claims 1 to 10;

[0037] Optionally a retarder, preferably the retarder comprises sodium citrate.

[0038] The present invention also provides a method for manufacturing a gypsum board using the solidification stabilizer particles of the present invention, which method comprises:

[0039] Preparing an aqueous gypsum slurry containing a mixture of water, plaster and solidification stabilizer particles, wherein the plaster contains calcium sulfate hemihydrate, and the aqueous gypsum slurry contains a mixture of the following:

[0040] At least 60% by weight, usually 60 to 98% by weight, preferably at least 70% by weight, more preferably at least 80% by weight, usually at least 90% by weight or usually at least 95% by weight of the said calcium sulfate hemihydrate on a dry (anhydrous) basis,

[0041] 0.5 wt% - 5 wt%, preferably 0.5 wt% to 4 wt%, more preferably 0.5 wt% - 2 wt% or 0.5 wt% - 1.5 wt% of solidification stabilizer particles,

[0042] 0 wt% to 5 wt% of a hydrophobic material on a dry (anhydrous) basis, preferably no hydrophobic material is present, the hydrophobic material being selected from wax and / or silicone, rather than the hydrophobic material provided by the solidification stabilizer particles, usually no silicone is present, rather than the silicone provided by the solidification stabilizer particles, and no wax is present, rather than the wax provided by the solidification stabilizer particles, in

[0043] and

[0044] water in a weight ratio of water to hemihydrate calcium sulfate of 0.2:1 to 1.2:1; and

[0045] depositing a front cover sheet on a forming surface;

[0046] depositing an 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 is a foamed aqueous gypsum slurry;

[0047] depositing a back cover sheet on the aqueous gypsum slurry; and solidifying the hemihydrate calcium sulfate to form a panel comprising a gypsum core containing dihydrate calcium sulfate; and

[0048] drying the panel and cutting the panel into gypsum boards having one or more predetermined sizes.

[0049] A gypsum board is a gypsum product having a board shape (i.e., in particular at least substantially flat). Gypsum boards generally have a rectangular shape.

[0050] The present invention also encompasses gypsum boards prepared by the method of the present invention.

[0051] The present invention also encompasses gypsum boards made by solidifying a composition comprising a slurry, the slurry comprising a mixture of:

[0052] water;

[0053] particles comprising hemihydrate calcium sulfate;

[0054] the solidification stabilizer particles of the present invention;

[0055] optionally a retarder, preferably the retarder comprises sodium citrate. Description of the Drawings

[0056] Figure 1 shows the solidification stabilizer particles.

[0057] Figure 2Shows a process flow diagram for preparing solidification stabilizer particles by grinding.

[0058] Figure 3 Shows a cross-sectional view of a gypsum board of the present invention, wherein the board core (gypsum core) is located between a front cover sheet and a rear cover sheet.

[0059] Figure 4 Shows Figure 3 a perspective view of the gypsum board.

[0060] Figure 5 Shows a process flow diagram of one form of a manufacturing production line for producing the laminated gypsum board of the present invention. Detailed Description

[0061] The present invention includes methods that can be used to recycle waste gypsum materials such as gypsum board. The waste gypsum board can contain hydrophobic materials, such as those used in applications to improve the moisture resistance of the gypsum board.

[0062] In this specification, drywall used to construct interior walls and ceilings (interior wall panels) will be exemplified as a non-limiting example of waste gypsum materials and products made from recycled gypsum. Drywall for the purposes of this specification is defined as a panel (also called a board) having a core of calcium sulfate dihydrate, typically having additives, usually between sheets of front and rear facing sheets. Typically, the facing sheets are made of paper or fiberglass mat, but facing sheets of other fibrous sheets can also be used. However, the processes disclosed herein can be used to process and recycle gypsum from any gypsum board having a core layer of gypsum-containing material and produce building products of any gypsum board having a core layer of gypsum-containing material.

[0063] Those skilled in the art will be able to modify the methods described herein to process waste gypsum materials from interior wall panels having a gypsum core between paper facing sheets, exterior clad gypsum panels, gypsum tile backer boards, or other gypsum building panels. For example, a typical gypsum exterior clad panel for processing according to the present invention can include, from front to back, a first fibrous mat, a gypsum core layer having a front surface and a rear 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, wherein the first fibrous mat is attached as a facing cover sheet to the front surface of the gypsum core layer, and a second fibrous mat is attached as a backing cover sheet to the rear surface of the gypsum core layer. The gypsum core layer contains greater than about 50 wt% calcium sulfate dihydrate, preferably at least about 75 wt%, more preferably at least about 85 wt%. The first fibrous mat and the second fibrous mat can include paper or fibrous materials (e.g., one or more of polymer fibers, glass fibers, and mineral fibers).

[0064] Waste gypsum materials can be obtained from a variety of sources. Non-limiting examples include waste from manufacturing facilities, waste from new construction sites, renovation waste, and waste from building demolition or deconstruction. Generally speaking, waste gypsum materials include gypsum-containing materials, usually a layer or core, and one or more facing sheets. Waste gypsum materials containing calcium sulfate dihydrate include gypsum boards, such as interior drywall, exterior cladding panels, and tile backer boards. In addition, waste materials containing gypsum include special gypsum board products, which may include a glass fiber-reinforced gypsum core or an exterior coating of glass fiber to strengthen the board and enhance moisture resistance. Waste materials containing calcium sulfate dihydrate may also contain components such as a fibrous woven or non-woven layer, the fibrous woven or non-woven layer containing paper, glass fiber, mineral fiber, polymer, etc. In particular, gypsum boards typically have a gypsum core and front and back facing sheets of paper, non-woven fiber mats, or fiber meshes. The fibers of the non-woven fiber mat or fiber mesh are typically glass fiber, mineral fiber, or polymer fiber, most typically glass fiber. Usually, the core layer of waste gypsum materials is more than 50% by weight of gypsum.

[0065] In one aspect, the present invention includes a process for converting waste gypsum materials containing a hydrophobic additive into gypsum suitable for reuse in new gypsum building materials.

[0066] The hydrophobic siloxane material additive in the waste gypsum material can be a coating on the outer surface of the gypsum core of the waste gypsum board and / or can be a component within the gypsum core of the waste gypsum board. The waste gypsum material contains up to about 10% by weight, such as 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, such as 1% by weight, of the hydrophobic siloxane material. Thus, by weight, the solid layer of the gypsum core in the waste gypsum material can contain up to about 10% by weight, such as 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, such as 1% by weight, of the hydrophobic siloxane material. For example, the lower limit of the hydrophobic siloxane material can 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 can 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. A typical value for siloxanes in the waste is about 1%.

[0067] Solidified and stabilized particles made from recycled hydrophobic gypsum board waste

[0068] The present invention relates to setting stabilizer particles, which comprise

[0069] A granular core, the granular core comprising 50% to 98% by weight, preferably 70% to 98% 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 silicone, and

[0070] A coating on the granular core, the coating comprising an anti-dehydration substance selected from the group consisting of sugars, dextrins and polyhydric alcohols such as glycerol or polyethylene glycol, in a ratio of about 5 parts to 25 parts by weight of the anti-dehydration substance per 100 parts by weight of calcium sulfate dihydrate.

[0071] The present invention provides solidification-stabilized granules having a granular substrate or core, the granular substrate or core comprising calcium sulfate dihydrate and a hydrophobic material as well as a certain amount of anti-dehydration substance. Figure 1 A diagram showing a typical solidification-stabilized granule 1, the solidification-stabilized granule having a granular substrate or core 2 comprising calcium sulfate dihydrate and a hydrophobic material, and an entire or partial coating 3 comprising an anti-dehydration substance applied to the substrate or core 2.

[0072] The granular substrate or core containing calcium sulfate dihydrate is generally a seed for promoting the solidification of calcium sulfate hemihydrate. The anti-dehydration substance generally has the ability to prevent the loss of the crystallization water of the calcium sulfate dihydrate seed. A large number of substances are suitable for the anti-dehydration substance. They can be exemplified by the general group of water-soluble carbohydrates called sugars, although materials intermediate between starch and sugar, such as the more soluble dextrins, such as British gum, will also operate for the purposes of the present invention. Other materials found to be effective in preventing the loss of water of hydration from the seed are polyhydric alcohols, such as glycerol, ethylene glycol and polyethylene glycol. A typical anti-dehydration substance is ordinary dextrose or glucose, especially in the commercial form called corn sugar.

[0073] The present invention relates to a method for preparing the solidification stabilizer granules of the present invention from waste gypsum board materials. The solidification stabilizer granules are suitable for preparing new gypsum boards with a foamed core. The method comprises:

[0074] Applying an anti-dehydration substance selected from the group consisting of sugars, dextrins and polyhydric alcohols such as glycerol or polyglycol to the feed granules of the waste gypsum board materials at a ratio of about 5 parts to 25 parts by weight of the anti-dehydration substance per 100 parts by weight of calcium sulfate dihydrate to produce solidification stabilizer granules, the feed granules of these waste gypsum board materials comprising 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 silicone,

[0075] wherein the application is generally carried out by coating by any suitable mechanical or chemical means, such as by grinding or spraying the feed granules of these waste gypsum board materials with the anti-dehydration substance.

[0076] Typically, the solidification stabilizer particles are compounded in a ratio of 100 parts by weight of calcium sulfate dihydrate crystals in a finely divided form as the particle core and 5 to 25 parts by weight of a dehydration-preventing substance selected from the group consisting of sugars, dextrins, and polyhydric alcohols such as glycerol or polyethylene glycol to coat the particle core, wherein 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 waxes and / or siloxanes (usually siloxanes). The gypsum source containing the hydrophobic material is ground to prepare the seed crystals that will form the nuclei of the solidification stabilizer particles of the present invention. Sugars, dextrins, and polyhydric alcohols such as glycerol or polyethylene glycol are added to the seed crystals to protect them from high temperatures during the grinding process.

[0077] Combining the dehydration-preventing substance with the calcium sulfate dihydrate seed crystals to prepare the solidification stabilizer particles of the present invention is a separate operation before mixing the seed crystals with hemihydrate calcium sulfate to manufacture gypsum boards.

[0078] For example, the calcium sulfate dihydrate seed crystals can be thoroughly mixed with the dehydration-preventing substance in the form of an aqueous solution, if necessary, or directly mixed in the case of using glycerol or ethylene glycol, and then the latter is dried to remove the added solvent, such as water. If the dehydration-preventing substance material is soluble in an organic liquid such as an alcohol or an ether, this substance can be used as a diluent or solvent and then allowed to evaporate. One way to achieve this result is to take the calcium sulfate dihydrate seed crystal material and, in powder form, spray it with a solution or dispersion of the dehydration-preventing substance before or simultaneously with its grinding or mixing.

[0079] Preferably, the calcium sulfate dihydrate seed crystals are coated with the dehydration-preventing substance, and thus any mechanical or chemical means by which such coating can be achieved are considered to be within the scope and intention of the present inventive concept. For example, a solution of 5 to 25 parts by weight of a dehydration-preventing substance such as corn sugar can be sprayed onto 100 parts by weight of calcium sulfate dihydrate in powder form, while vigorously stirring the calcium sulfate dihydrate in a stirrer until the solvent (water) evaporates, so that the dehydration-preventing substance adheres or spreads on the calcium sulfate dihydrate crystals. Alternatively, it is ground in a ball mill or the like to coat the sugar or other dehydration-preventing substance on the gypsum particles. Thus, as Figure 2 shown, the dehydration-preventing substance can be closely ground together with the solidification-stabilized calcium sulfate dihydrate crystal material, for example, in a ball mill or the like. As Figure 2 shown, a stream 4 of particles containing calcium sulfate and a hydrophobic material and a stream 5 of a dehydration-preventing substance are fed into a ball mill 6 and ground together to coat the dehydration-preventing substance onto the particles containing calcium sulfate and the hydrophobic material, thereby producing a stream 7 of particles containing calcium sulfate and the hydrophobic material coated with the dehydration-preventing substance.

[0080] When using materials other than corn sugar, it is preferred to use an equal amount of other substances. Among sugars, besides corn sugar, it may be mentioned that carbohydrates having a sweet taste and having the general formula C n H 2n O n or C n H 2n-2 O n-1 may be used. Generally speaking, hexoses of the general formula C6H 12 06 are more effective. However, the present invention is not limited to these specific sugars, because it has been found that other sugars such as maltose, lactose, sucrose and similar saccharin products can be used to replace them. Thus, for example, molasses also exhibits protective properties, although it is less effective than pure sugar. On the other hand, fully dextrinized starches such as, for example, gum arabic can be used; and as already mentioned, glycerol or diols can be used in the above-mentioned manner.

[0081] The solidification stabilizer particles generally have a particle surface area of 5000 cm 2 / gm to 15000 cm 2 / gm, for example 7000 cm 2 / gm - 14000 cm 2 / gm or for example 9000 cm 2 / gm - 12000 cm 2 / gm. The solidification stabilizer particles generally have a Dv50 particle size of about 10 μm to about 60 μm, for example a particle size distribution of about 20 μm to about 50 μm. The Dv50 particle size will be the maximum particle size below which 50% of the sample volume exists - also known as the median particle size by volume. The particle size can be simply determined by passing the material through a sieve of appropriate size, as is well known in the art. The particle size distribution (e.g., D50) can also be determined using methods known in the art. For example, a non-limiting example is disclosed in ASTM D6913 / D6913M-17 Method B, Standard Test Method for Dirt Particle Size Distribution (Grade) Using Sieve Analysis.

[0082] Mixture of calcium sulfate hemihydrate particles and solidification stabilizer particles

[0083] The present invention relates to a cementitious powder, which comprises:

[0084] Plaster particles containing hemihydrate calcium sulfate, wherein at least 60% by weight, preferably at least 70% by weight, more preferably at least 80% by weight, usually at least 90% by weight or usually at least 95% by weight of the cementitious powder is hemihydrate calcium sulfate; and

[0085] 0.5 wt% - 5 wt%, preferably 0.5 wt% to 4 wt%, more preferably 0.5 wt% - 2 wt% or 0.5 wt% - 1.5 wt% of the setting stabilizer particles of the present invention.

[0086] Typically, the setting stabilizer particles can be included in the slurry for preparing gypsum board in an amount of 0.5 wt% - 5 wt%, preferably 0.5 wt% - 4 wt%, more preferably 0.5 wt% - 2 wt% or 0.5 wt% - 1.5 wt% based on the dry (anhydrous) slurry. A typical gypsum embodying the concept of the present invention can be combined with the following relative amounts:

[0087] 1000 parts by weight of hemihydrate calcium sulfate (usually provided by calcined gypsum plaster),

[0088] 5 parts by weight - 50 parts by weight, preferably 5 parts by weight - 40 parts by weight, more preferably 2 parts by weight - 20 parts by weight or 5 parts by weight - 15 parts by weight, for example 10 parts by weight of the setting stabilizer particles, wherein the setting stabilizer particles themselves are compounded in a ratio of 100 parts by weight of finely divided dihydrate calcium sulfate crystals and 5 parts by weight to 25 parts by weight of a dehydration-preventing substance selected from the group consisting of sugars, dextrins and polyhydric alcohols such as glycerol or polyethylene glycol, wherein the dihydrate calcium sulfate crystals contain 50 wt% to 98 wt% of dihydrate calcium sulfate and 0.05 wt% to 10 wt% of a hydrophobic material selected from waxes and / or siloxanes.

[0089] The gypsum products of the present disclosure can be produced from the slurry according to Table 1. The resulting gypsum products can have the composition according to Table 2. In Tables 1 and 2, any range of components can be replaced by any other range of that component in the corresponding table. In Tables 1 and 2, "setting stabilizer particles" are the setting stabilizer particles of the present invention containing a hydrophobic material. Any other setting stabilizer particles or accelerators are referred to as "accelerators" in this application. For example, the preferred range of the setting stabilizer particles can be used together with other components provided in their broad ranges.

[0090] Table 1: Example slurry compositions (parts by weight, dry basis)

[0091] Component Wide range Preferred range More preferred range Calcium sulfate hemihydrate (plaster) 100 100 100 Catalyst 0.01-5 0.1-5 0.3-3 Siloxane 0.01-2 0.05-1.5 0.1-1.2 Solidification stabilizer particles 0.5-5 0.5-4 0.5-2 Accelerator 0-5 0-3.5 0.5-2 Starch 0-2 0-2 0.5-1.5 Retarder 0-2 0-1 0-1 Dispersant 0.1-2 0.1-1 0.1-0.5 Filler 0-5 0-4 0-3 Other additives (independently) 0-2 0-2 0-2 Water 50-150 75-125 80-110

[0092] Table 2: Example solidified product compositions (parts by weight)

[0093] Component Wide range Preferred range More preferred range Calcium sulfate dihydrate (gypsum) 100 100 100 Catalyst 0.01-5 0.1-5 0.3-3 Siloxane 0.01-2 0.05-1.5 0.1-1.2 Solidification stabilizer particles 0.5-5 0.5-4 0.5-2 Accelerator 0-5 0-3.5 0.5-2 Starch 0-2 0-2 0-1 Retarder 0-2 0-1 0.01-1 Dispersant 0.1-2 0.1-1 0.1-0.5 Filler 0-5 0-4 0-3 Other additives (independently) 0-2 0-2 0-2

[0094] The present invention relates to a gypsum comprising:

[0095] Particles comprising hemihydrate calcium sulfate;

[0096] The setting stabilizer particles of the present invention;

[0097] Optionally, a retarder, preferably the retarder comprises sodium citrate.

[0098] Method for manufacturing gypsum board

[0099] The present invention also provides a method for manufacturing a gypsum board using the setting stabilizer particles of the present invention, the method comprising:

[0100] Preparing an aqueous gypsum slurry comprising a mixture of water, plaster and setting stabilizer particles, wherein the plaster comprises hemihydrate calcium sulfate, and wherein the aqueous gypsum slurry comprises a mixture of the following:

[0101] 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 hemihydrate calcium sulfate on a dry (anhydrous) basis,

[0102] 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,

[0103] 0% to 5% by weight of a hydrophobic material on a dry (anhydrous) basis, preferably no hydrophobic material is present, the hydrophobic material being selected from waxes and / or siloxanes, other than the hydrophobic material provided by the setting stabilizer particles, typically no siloxane is present, other than the siloxane provided by the setting stabilizer particles, and no wax is present, other than the wax provided by the setting stabilizer particles, in order to

[0104] and

[0105] Water in a weight ratio of water to hemihydrate calcium sulfate of 0.2:1 to 1.2:1; and

[0106] Depositing a front cover sheet on a forming surface;

[0107] 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 is a foamed aqueous gypsum slurry;

[0108] Depositing a back cover sheet on the aqueous gypsum slurry; and

[0109] Solidifying the hemihydrate calcium sulfate to form a panel comprising a gypsum core, the gypsum core comprising dihydrate calcium sulfate; and

[0110] Drying the panel and cutting the panel into gypsum boards having one or more predetermined sizes.

[0111] In this specification, unless otherwise indicated, all weight percentage values are by weight. As used herein, "total dry weight" or "dry weight basis" refers to the weight of a 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 % calculation.

[0112] Mortar particles and setting stabilizer particles containing hemihydrate calcium sulfate can be fed as separate streams into a slurry mixer to be mixed with water to form an aqueous gypsum slurry. The setting stabilizer particles comprise a particle core and a coating, the particle core comprising 50 wt% to 98 wt% of dihydrate calcium sulfate and 0.05 wt% to 10 wt% of a hydrophobic material selected from wax and / or silicone, and the coating comprising an anti-dehydration substance selected from the group consisting of sugars, dextrins, and polyhydric alcohols, in a ratio of about 5 parts to 25 parts of anti-dehydration substance per 100 parts by weight of dihydrate calcium sulfate. In an alternative, the mortar particles and the setting stabilizer particles can be combined to form a combined stream of cementitious powder, which is fed into the slurry mixer to be 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 different widths and thicknesses can be manufactured by methods known in the art. Water and optionally one or more additives are fed, either alone or together with one or more of the mortar particles and the setting stabilizer particles, to manufacture the aqueous gypsum slurry. The setting stabilizer particles are mixed with the mortar to form a powder, and the powder is fed into the mixer

[0113] Embodiments of the present invention can include adding a foaming agent to the aqueous gypsum slurry to prepare the core layer of a gypsum board. The foaming agent may or may not include α-sulfofatty acid disalt.

[0114] Figure 3 An example of the wallboard panel 10 of the present invention is depicted. Figure 4 A perspective top (axial) view of the wallboard panel 10 is shown. The board has a core 28, which includes a set low-density region (less dense region) 12 as a layer containing dihydrate calcium sulfate and a set high-density region (also referred to as a dense region or a thin dense gypsum layer) 22 as a layer containing dihydrate calcium sulfate.

[0115] Figure 3Depicts the wallboard panel 10 of the present invention, which includes a core 28 of a gypsum low-density region 12 (e.g., 0.5 inches thick) between a rear cover sheet 14 (also referred to as a backing cover sheet) and a front cover sheet 16 (also referred to as a finish cover sheet), where the rear cover sheet and the front cover sheet can each be a single layer or multiple layers of paper or fiber material, such as a fiberglass mat. The inner surface of the rear cover sheet 14 creates an adhesive side 24 of the rear cover sheet 14 facing the gypsum core 28. The inner surface of the front cover sheet 16 creates an adhesive side 26 of the front cover sheet 16 facing the gypsum low-density region 12. A high-density region (a thin dense gypsum layer) 22 is located between the gypsum low-density region (a less dense region) 12 and the front cover sheet 16, in contact with the gypsum low-density region 12 and the front cover sheet 16. Optionally, a second set of high-density regions (also referred to as dense regions or thin dense gypsum layers) 20, which are layers containing calcium sulfate dihydrate, are located on the adhesive side of the rear sheet 14. After the wallboard panel 10 is installed as an interior wall, the outer surface of the rear cover sheet 14 faces the wall framing of the room (not shown). 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.

[0116] Typically, the relatively low-density region 12 and the relatively high-density regions 20, 22 have the same composition and are adjacent to each other. However, the low-density region can be formed from a foamed state of gypsum slurry, while the high-density regions can be formed from an unfoamed gypsum slurry, thus forming a denser layer. That is, the high-density regions can have a lower porosity associated with them than the low-density region.

[0117] The combined density of the gypsum low-density region 12 and the high-density regions 20, 22 can be from about 15 pounds per cubic foot to about 65 pounds per cubic foot, more typically from 25 pounds per cubic foot to about 65 pounds per cubic foot, such as from 25 pounds per cubic foot to 55 pounds per cubic foot.

[0118] The low-density region (e.g., Figure 3 the low-density region 12) produced from the solidified gypsum low-density region slurry typically has a thickness of 0.25 inches to 1.5 inches and a density of 15 pounds per cubic foot to 55 pounds per cubic foot. In contrast, typically the high-density regions (e.g., Figure 3The high-density regions 20, 22) each have a thickness of 5% to 25% of the thickness of the gypsum board 10. Generally, the thickness of the dense layer is from about 0.02 inches to about 0.2 inches (about 0.05 cm to about 0.5 cm), for example from about 0.0625 inches to about 0.125 inches (about 0.16 cm to about 0.32 cm). The thickness of the low-density region layer 12 is greater than the thickness of the high-density region layers 20, 22. When foamed, the gypsum low-density region layer produced from the solidified foamed gypsum slurry has a total void volume of 10% to 92% by volume, particularly 25% to 90% by volume, and more particularly 30% to 85% by volume. In contrast, the dense layer has a total void volume of less than 30% by volume, for example less than 25% by volume, and is less than 0.25 inches thick.

[0119] The gypsum board of the present invention can be prepared from an aqueous gypsum slurry containing hemihydrate calcium sulfate and the setting stabilizer particles of the present invention by various methods.

[0120] The base material for manufacturing gypsum wallboards and other gypsum products is calcium sulfate in hemihydrate form (CaSO4·1 / 2H2O), commonly known as "calcined gypsum" or "plaster", which is produced by the thermal conversion (calcination) of calcium sulfate in dihydrate form (CaSO4).

[0121] Exemplary manufacturing techniques and equipment suitable for forming the gypsum board according to the present invention can be found, for example, in U.S. Patent 7,364,676 and U.S. Patent Application Publication 2010 / 0247937, each of which is incorporated herein by reference in its entirety. To produce a gypsum board, the plaster is mixed with water, the setting stabilizer of the present invention, and other additives if desired to form an aqueous gypsum slurry, which is continuously fed between successive paper layers on a board machine. One cover sheet is referred to as a face cover sheet or a front cover sheet or a finish. The other cover sheet is referred to as a back cover sheet or a backing.

[0122] Generally, to produce a gypsum board having a front cover sheet and a back cover sheet, the plaster is mixed with water and additives to form an aqueous slurry, which is continuously fed between successive sheets (such as paper sheets) on a board machine. As the board moves down the conveyor line to form a panel, the setting stabilizer of the present invention helps to recrystallize or rehydrate the hemihydrate calcium sulfate to revert to calcium sulfate in its original rock state of dihydrate. When the gypsum sets, the cover sheets become bonded to the core. The panel is then cut to a certain length and conveyed through a dryer to remove any free moisture.

[0123] Such a process discharges a first cover sheet onto a moving conveyor. The dry and / or wet components of the aqueous gypsum slurry are fed into a mixer (e.g., a pin or pinless mixer), where they are agitated to form an aqueous gypsum slurry. The aqueous gypsum slurry can be made at any suitable water / calcium sulfate hemihydrate ratio for application to the first cover sheet. Since the gypsum board is typically formed "face down", this first cover sheet generally corresponds to the finish (front cover sheet) at the end of the manufacturing process. The mixer includes a body and a discharge conduit (e.g., a gate-tank-shroud arrangement as known in the art, or an alternative arrangement such as those described in U.S. Pat. Nos. 6,494,609 and 6,874,930, which are incorporated herein by reference in their entirety). In some process configurations, the discharge conduit can include a slurry distributor having a single feed inlet or multiple feed inlets, such as those described in U.S. Patent Application Publications 2012 / 0168527 and 2012 / 0170403, which are incorporated herein by reference in their entirety. When a slurry distributor with multiple feed inlets is used, the discharge conduit can include a suitable diverter, such as those described in U.S. Patent Application Publication 2012 / 0170403. If desired, a foaming agent (typically a soap) can be added to the discharge conduit of the mixer (e.g., added to a gate as described in U.S. Pat. Nos. 5,683,635 and 6,494,609, which are incorporated herein by reference) or to the body. The slurry discharged from the discharge conduit after all ingredients including the foaming agent have been added is a primary gypsum slurry and is used to form a low-density region layer. This gypsum slurry is discharged onto the moving first cover sheet.

[0124] After mixing, foam is optionally added to the aqueous gypsum slurry to reduce the product density. The foam is created by combining soap and water. Then, the foam can be injected into the aqueous gypsum slurry after the aqueous gypsum slurry has been discharged from the mixer through a hose or chute. The foam is typically added to the portion of the aqueous gypsum slurry that is used for the less dense layer of the core, but not to the portion of the slurry that is used for the dense layer.

[0125] When the foam and the aqueous gypsum slurry have been brought together, the resulting slurry is moved to a conveyor and poured onto the conveyor, which is lined with a first facing material (which is a first cover sheet). Another facing material (which is a second cover sheet) is placed on top of the slurry, thereby forming a sandwich assembly, where the slurry is located 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 plate. Next, the continuous sandwich assembly is cut into appropriate lengths at a cutter, typically eight feet to twelve feet. As the plate moves down the conveyor line to form a panel, the slurry is allowed to harden (set). The calcium sulfate recrystallizes or rehydrates, returning to its original rock state to form a board core that contains an interlocking crystalline matrix of solidified gypsum. As the gypsum sets, the cover sheets become bonded to the core. The panel is then cut to length and conveyed through a kiln or dryer to remove any free moisture. The temperature in the kiln is typically in the range of 450°F to 500°F maximum.

[0126] As described above, the front cover sheet interfaces with the high-density region (also known as the dense layer). The dense layer is typically adjacent to the low-density region layer after setting. In the case of inserting foam into the discharge conduit, a secondary gypsum slurry stream can be removed from the agitator body prior to foaming to provide a slurry for forming the dense layer. The dense layer can be deposited onto the moving first cover sheet before depositing the major portion of the gypsum slurry to form the low-density region layer. The gypsum slurry for the low-density region, after being discharged from the discharge conduit, is spread over the first cover sheet and the dense layer as needed. At this time, the second cover sheet is placed on the spread gypsum low-density region slurry. If there is no optional second high-density region, the spread gypsum low-density region slurry is brought into contact with the second cover sheet on which the first dense layer has been deposited. The resulting wet assembly is in the form of a multi-layer assembly, which is a precursor of the final gypsum board product. The dense layer can be formed from the same or a different gypsum slurry as the low-density region layer.

[0127] Figure 5 An example of the wet end 80 (upstream portion) of a manufacturing production line for a laminated gypsum board of the present invention having a gypsum layer between two cover sheets and provided with a dense layer is illustrated. The cover sheets are made of paper, such as manila paper or Kraft paper, for example.

[0128] The wet end 80 includes a gypsum slurry mixing and dispensing assembly 82 and a forming station 86. Figure 5 It is shown that the plaster aggregate and the setting stabilizer aggregate of the present invention can be fed into the gypsum slurry mixing and dispensing assembly 82 together as stream 74. However, in an alternative, the plaster aggregate and the setting stabilizer aggregate of the present invention can be fed into the gypsum slurry mixing and dispensing assembly 82 separately.

[0129] The first moving web 90 of the first cover sheet material (face sheet) moves along the forming table 92 in the longitudinal travel direction "T". The plaster low-density region slurry 94 is mixed in the plaster slurry mixing and dispensing assembly 82, additives are added therein, and foaming of the slurry for the low-density region layer (e.g., layer 12, Figure 3 ) occurs. Although the plaster slurry mixing and dispensing assembly 82 is illustrated as a single component of the wet end 80, there may be multiple components including the plaster slurry mixing and dispensing assembly 82.

[0130] The dense layer slurry 70 from the plaster slurry mixing and dispensing assembly 82 is applied to the first cover sheet material 90 to form a dense layer (e.g., high-density region 22, Figure 3 ) on the first cover sheet material 90 and passes under the first plaster dense layer roller 72 before depositing the plaster central low-density region layer slurry 94. The dense layer slurry 76 is applied to the second cover sheet material (back sheet material) 96 to form a second high-density region layer (e.g., layer 20, Figure 3 ). Then the second cover sheet material (back sheet material) 96 is applied over the deposited low-density region layer slurry 94 to form a multi-layer structure. Then, the multi-layer structure is passed through the forming station 86 to compress the layers to the desired total thickness. The resulting structure is a gypsum board preform 98.

[0131] The cover sheet material can be uncoated or coated with, for example, a pre-applied outer surface polymer coating and a hydrophobic finish. Generally, the outer surfaces of the applied webs 90 and 96 and the resulting outer surfaces of the front and back cover sheets of the gypsum board are uncoated and do not contact additional layers.

[0132] Additional components may be included in the wet end 80 of the production line.

[0133] The gypsum dense layer will be thinner and denser than the low-density region layer. Thus, the gypsum dense layer slurry is relatively denser compared to the gypsum low-density region layer slurry which is 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 slurries 70 and 76 of the dense layer. Thus, if desired, the calcined gypsum low-density region layer slurry stream 94 can pass through a foaming device (not shown) that, for example, mixes the calcined gypsum low-density region layer slurry stream 94 with foam and / or air before depositing it on the first cover sheet material 90. As is known in the art, the dense layer can be achieved by diverting a portion of the gypsum slurry out of the agitator and into a dense layer agitator before introducing the foam into the gypsum slurry, or by knocking the foam out of the gypsum dense layer slurry. Thus, the gypsum low-density region layer slurry 94 for the low-density region of the board is deposited on the gypsum dense layer slurry 70. Typically, the gypsum low-density region layer slurry stream 94 and the slurry streams 70, 76 for the gypsum dense layer 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 dense layer 70, 76 can have different compositions and / or densities. Figure 5 All of the gypsum slurries 70, 76, 94 are shown as coming from the same calcined gypsum slurry mixing and dispensing assembly 82. However, the calcined gypsum slurries 70, 76, 94 can come from different mixing and dispensing assemblies to have different properties, such as different densities.

[0134] The gypsum dense layer rollers 72, the forming table 92, and the forming station 86 can each include conventional equipment suitable for the intended purposes known in the art. The wet end 80 can be equipped with other conventional equipment known in the art.

[0135] The calcined gypsum in the gypsum slurries 70, 76, 94 reacts with water and solidifies 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 a predetermined size at a point along the line where the gypsum board preform 98 has sufficiently solidified. These segments can be dried (e.g., in a kiln) to drive off excess water and processed to provide the final laminated wallboard of the desired dimensions.

[0136] The forming station 86 is the location in the board line where the wet board precursor is sized to a predetermined width and thickness and optionally length. Thus, the forming station includes or can be any device capable of performing the final mechanical spreading and / or forming of the slurry across the width of the backing layer, many of which are known in the art. The forming station includes means for bringing the slurry thickness and width into conformance with the final desired thickness and width of the wet board precursor, which when solidified will produce the cementitious board product. Of course, the final desired slurry thickness and width produced at the forming station can be different from the final thickness and width of the finished board product. For example, the slurry thickness and / or width can expand and / or contract during crystallization (i.e., solidification) and drying of the slurry. Generally, the desired slurry thickness is substantially equal to the desired board thickness (e.g., about 0.375” (about 0.95 cm), about 0.5” (about 1.27 cm), about 0.625” (about 1.59 cm), about 0.75” (about 1.90 cm) or about 1” (about 2.54 cm)). By way of illustration only, the final board thickness is typically in the range of about + or - 1 / 8” (about 0.32 cm) or less of the final slurry thickness.

[0137] The forming station includes any device capable of producing the desired slurry thickness and width of the wet board precursor. Suitable devices include, for example, forming plates, forming rolls, forming presses, doctor blades, etc. The specific device 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 sound deadening panel forming system, the board forming station includes a forming plate as known in the art. The board forming system of any of the above embodiments optionally further includes a blade for cutting the wet board precursor or the dry cementitious board product into the desired length, and / or a drying zone capable of removing water from the solidified cementitious board.

[0138] Gypsum and plaster (calcined gypsum)

[0139] The hemihydrate calcium sulfate component for forming the crystalline matrix of the gypsum panel core generally comprises β-hemihydrate calcium sulfate, water-soluble anhydrous calcium sulfate, α-hemihydrate calcium sulfate, or a mixture of any one or all of these, and is obtained from natural or synthetic sources. The hemihydrate calcium sulfate is typically provided as a raw material called plaster of Paris or calcined gypsum. In some aspects, the plaster of Paris can include non-gypsum minerals, such as small amounts of clay or other components associated with the gypsum source or added during the calcination, processing, and / or delivery of the plaster of Paris to the mixer. The plaster of Paris can be fibrous or non-fibrous. Generally, the raw plaster of Paris has at least 70 wt% hemihydrate calcium sulfate, preferably at least 80 wt% hemihydrate calcium sulfate, more preferably at least 85 wt% hemihydrate calcium sulfate, and still more preferably at least 90 wt% hemihydrate calcium sulfate.

[0140] Additive

[0141] In addition to the setting 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, foams (prepared from suitable foaming agents), dispersants, polyphosphates (such as sodium metaphosphate), starches, retarders, accelerators, re-calcination inhibitors, binders, adhesives, secondary dispersion aids, leveling agents or non-leveling agents, thickeners, bactericides, fungicides, pH regulators, buffers, colorants, reinforcing materials, flame retardants, water repellents (such as siloxanes), fillers, and mixtures thereof.

[0142] The additives and other components of the gypsum slurry can be added to the mixer in various ways. For example, various combinations of the components can be premixed before entering the mixer, either as one or more dry components and / or as one or more wet components. A single component can be similarly introduced into the mixer in wet or dry form. If introduced in wet form, the component can be included in a carrier liquid (such as water) at any suitable concentration.

[0143] Fibers can optionally be used in the methods and compositions of the present invention. Fibers can include mineral fibers (also known as mineral wool), glass fibers, carbon fibers, and mixtures of such fibers, as well as other comparable fibers that provide comparable benefits to the wallboard. For example, glass fibers can be incorporated into the gypsum low-density region slurry and / or the gypsum high-density region layer slurry and the resulting crystalline core structure. Glass fibers in such aspects can have an average length of about 0.5 inches to about 0.75 inches and a diameter of about 11 microns to about 17 microns. In other aspects, such glass fibers can have an average length of about 0.5 inches to about 0.675 inches and a diameter of about 13 microns to about 16 microns. In still other aspects, E-glass fibers with a softening point higher than about 800 °C or higher than at least about 900 °C are used. Mineral wool or carbon fibers such as those known to those of ordinary skill in the art can be used in place of or in combination with glass fibers.

[0144] When fibers are included, they can be present in the gypsum low-density layer slurry and / or the gypsum high-density layer slurry in an amount of about 0.5 pbw to about 10 pbw per 100 pbw of hemihydrate calcium sulfate on a dry basis; preferably about 1 pbw to about 8 pbw; more preferably about 2 pbw to about 7 pbw; and most preferably about 3 pbw to about 6 pbw. Fibers may also be absent.

[0145] Optionally, if desired, the slurry may further contain one or more phosphate-containing compounds. For example, these phosphate-containing components may include water-soluble components and may be in the form of ions, salts or acids, namely condensed phosphoric acids, each of which contains two or more phosphoric acid units; salts or ions of condensed phosphates, each of which contains two or more phosphate units; and monovalent salts or monovalent ions of orthophosphates and water-soluble acyclic polyphosphates. Exemplary examples are described in U.S. Pat. Nos. 6,342,284; 6,632,550; 6,815,049; and 6,822,033, which are incorporated herein by reference in their entirety.

[0146] The phosphate-containing components can enhance green strength, resistance to permanent deformation (such as sag), dimensional stability, etc. Tripolyphosphate compounds can be used, including, for example, sodium tripolyphosphate, potassium tripolyphosphate, lithium tripolyphosphate, and ammonium tripolyphosphate. Sodium tripolyphosphate (STMP) is commonly used, although other phosphates may be suitable, including, for example, sodium tetrapolyphosphate, hexametaphosphates having from about 6 to about 27 repeating phosphate units and having the formula Na n+2 P n O 3n+1 (where n = 6-27), potassium pyrophosphate having the formula K4P2O7, dipotassium trisodium tripolyphosphate having the formula Na3K2P3O 10 (where n = 6-27), potassium pyrophosphate having the formula K4P2O7, dipotassium trisodium tripolyphosphate having the formula Na3K2P3O 10 (where n = 6-27), potassium pyrophosphate having the formula K4P2O7, dipotassium trisodium tripolyphosphate having the formula Na3K2P3O n+ 2P n O 3n+1 (where n = 6-27), potassium pyrophosphate having the formula K4P2O7, dipotassium trisodium tripolyphosphate having the formula Na3K2P3O n+2 P n O 3n+1 (where n = 6-27), potassium pyrophosphate having the formula K4P2O7, dipotassium trisodium tripolyphosphate having the formula Na3K2P3O

[0147] Phosphates are usually added in dry form and / or in the form of aqueous liquid, where the dry components are added to the slurry agitator, the liquid components are added to the agitator, or added at other stages or procedures.

[0148] When present, the phosphate can be included in the gypsum slurry in dry form or in aqueous form (e.g., a phosphate solution of about 5% to about 20%, such as a about 10% solution). If included, the phosphate can be present in any suitable amount (solid / solid basis), such as about 0.01 wt% to about 0.5 wt% of the stucco, e.g., about 0.03 wt% to about 0.4 wt%, about 0.1 wt% to about 0.3 wt% or about 0.12 wt% to about 0.4 wt% of the stucco. The phosphate may also be absent.

[0149] The gypsum slurry can optionally include at least one dispersant to enhance fluidity. The dispersant can optionally be introduced into the gypsum slurry in dry form together with other additives and / or optionally in liquid form together with other liquid components. Examples of suitable dispersants include naphthalenesulfonates, such as polynaphthalenesulfonic acid and its salts (polynaphthalenesulfonates) and derivatives, which are condensation products of naphthalenesulfonic acid and formaldehyde, and polycarboxylate dispersants, such as polycarboxylic acid ethers for example. Other examples of suitable dispersants include lignosulfonates or sulfonated lignin. Lignosulfonates are water-soluble anionic polyelectrolyte polymers that are by-products of the production of wood pulp using the sulfite pulping process.

[0150] Lower molecular weight dispersants may be desirable. Lower molecular weight naphthalenesulfonate dispersants may be advantageous because they tend to have a lower water demand compared to higher viscosity, 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) can be a desirable molecular weight for the dispersant. If desired, the molecular weight of the polycarboxylate dispersant can be about 20,000 to about 60,000, which may exhibit less retardation compared to dispersants having a molecular weight higher than about 60,000.

[0151] Typical naphthalenesulfonates are aqueous solutions of naphthalenesulfonates having a naphthalenesulfonate solids content of about 35 wt% to about 55 wt%. However, if desired, the naphthalenesulfonate can be used in dry solid or powder form.

[0152] When present, the dispersant can be included in the gypsum slurry in any suitable (solid / solid) amount, such as, for example, about 0.1 wt% to about 5 wt% of the stucco, e.g., about 0.1 wt% to about 4 wt%, about 0.1 wt% to about 3 wt%, about 0.2 wt% to about 3 wt%, about 0.5 wt% to about 3 wt%, about 0.5 wt% to about 2.5 wt%, about 0.5 wt% to about 2 wt%, about 0.5 wt% to about 1.5 wt%, etc. Any one or more of the polynaphthalenesulfonate, polycarboxylic acid ether or lignosulfonate may also be absent.

[0153] In addition to the setting-stabilizing particles of the present invention, additional accelerators can be added to the low-density layer gypsum slurry and / or the high-density layer gypsum slurry.

[0154] Accelerators can be added to the gypsum low-density layer slurry and / or the high-density layer slurry to change the rate at which the hemihydrate calcium sulfate hydration reaction occurs. When present, the accelerator can be incorporated into the gypsum slurry in an amount, by solids, of, for example, from about 0 wt% to about 10 wt% (e.g., from about 0.1% to about 10%) of the plaster, such as, for example, from about 0 wt% to about 5 wt% (e.g., from about 0.1% to about 5%) of the plaster. Suitable accelerators can include, for example, potassium sulfate, calcium sulfate dihydrate, carbohydrate-coated calcium sulfate, calcium sulfate dihydrate / organophosphonate, and calcium sulfate dihydrate / organophosphate.

[0155] Another accelerator can be a setting stabilizer particle that does not contain hydrophobic materials (such as no siloxane and no wax). This typical coagulant is a setting stabilizer particle of calcium sulfate dihydrate freshly ground with sugar at a ratio of about 5 pounds of sugar / 100 pounds of calcium sulfate dihydrate to 25 pounds of sugar / 100 pounds of calcium sulfate dihydrate. It is further described in U.S. Patent No. 2,078,199, which is incorporated herein by reference.

[0156] Another accelerator comprises 95% calcium sulfate dihydrate, which is co-ground with 5% sugar and heated to 250°F (121°C) to caramelize the sugar. This is carried out according to U.S. Patent No. 3,573,947, which is incorporated herein by reference.

[0157] A description of the use and manufacturing method of another accelerator is disclosed in U.S. Patent No. 6,409,825, which is incorporated herein by reference. The amount of the wet gypsum accelerator is in the range of about 5 pounds per thousand square feet to about 80 pounds per thousand square feet (24.3 g / m 2 to 390 g / m 2 ) of the board product.

[0158] Retarders can be added to the gypsum low-density layer slurry and / or the high-density layer slurry to change the rate at which the hemihydrate calcium sulfate hydration reaction occurs. When present, the retarder can be incorporated into the gypsum slurry in an amount, by solids, of, for example, from about 0 wt% to about 10 wt% (e.g., from about 0.1% to about 10%) of the plaster, such as, for example, from about 0 wt% to about 5 wt% (e.g., from about 0.1% to about 5%) of the plaster.

[0159] In addition to the setting stabilizer particles of the present invention, accelerators and / or retarders may also be absent.

[0160] Foam (also referred to as foam water) may 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 to provide the above-described reduced low-density region density and panel weight. The foaming agent that produces the foam is typically a soap or other suitable surfactant. Introducing foam into the gypsum low-density region slurry in an appropriate amount, formulation, and process will create the desired void network and distribution within the low-density region of the final dried wallboard. This void structure allows for a reduction in the gypsum and other low-density region components, as well as the low-density region density and weight, while maintaining the desired panel structural and strength properties. If present, the foaming agent may comprise a major weight fraction of an unstable component and a minor weight fraction of a stabilizing component (e.g., an unstable and stable / unstable blend combination). The weight ratio of the unstable component to the stabilizing component is effective for forming an air-gap distribution within the set gypsum low-density region, as described in U.S. Patents 5,643,510; 6,342,284; and 6,632,550, which are incorporated herein by reference in their entirety. Methods for adding foam to the gypsum low-density region slurry are known in the art, and an example of such a method is discussed in U.S. Patent No. 5,683,635, the disclosure of which is incorporated herein by reference. Evaporated water voids, typically having voids with a diameter of about 5 μm or less, also contribute to the total void distribution along with the above-described air (foam) voids. The volume ratio of voids having a pore diameter greater than about 5 microns to voids having a pore diameter of about 5 μm or less is from about 0.5:1 to about 9:1, such as for example 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 weight % of the plaster, such as about 0.01 weight % to about 0.5 weight %, about 0.01 weight % to about 0.2 weight %, about 0.02 weight % to about 0.4 weight %, about 0.02 weight % to about 0.2 weight %, about 0.01 weight % to about 0.1 weight %, etc. The foaming agent may also be absent.

[0161] The gypsum slurry may also include components for fire resistance and / or water resistance. Examples include, for example, siloxanes (water resistance); fibers; heat dissipating additives such as aluminum trihydrate (ATH), magnesium hydroxide, etc.; and / or high expansion particles (e.g., when heated at 1560°F for about one hour, can expand to about 300% or more of the original volume). Further disclosure regarding such additives can be found in U.S. Patent 8,323,785, which is incorporated herein by reference in its entirety. High expansion vermiculite may be included, although other refractory materials may be included. If present, the fire resistance or water resistance additives may be included in any suitable amount as needed, for example, according to the fire rating and similar performance parameters. For example, if included, the fire resistance or water resistance additives may be present individually in an amount of about 0.5 wt% to about 10 wt% of the mortar, such as about 1 wt% to about 10 wt%, about 1 wt% to about 8 wt%, about 2 wt% to about 10 wt%, about 2 wt% to about 8 wt%, etc.

[0162] If included, the siloxane can be advantageously introduced in the form of an emulsion. The slurry can then be shaped and dried under conditions that promote the polymerization of the siloxane to form a highly cross-linked silicone resin. A catalyst that promotes the polymerization of the siloxane to form a highly cross-linked silicone resin can be added to the gypsum slurry. A solvent-free methylhydrogen siloxane fluid can be used as the siloxane. The product is a siloxane fluid that is free of water or solvent. It is expected that if needed, based on the weight of the dry ingredients, about 0.3% to about 1.0% of the siloxane can be used. For example, if needed, about 0.4% to about 0.8% of the siloxane, based on the dry mortar weight, can be present in the gypsum slurry.

[0163] Water

[0164] Water is added to the slurry in any amount that forms a flowable slurry. The amount of water used varies widely depending on the application for which it is used, the exact dispersant used, the nature of the hemihydrate calcium sulfate, and the additives used.

[0165] The water used to prepare the slurry should be as pure as possible to optimize control of the properties of the slurry and the set gypsum. It is well known that salts and organic compounds can change the setting time of the slurry, varying widely from accelerators to setting inhibitors. Some impurities cause irregular structures because of the interlocking matrix formation of the dihydrate crystals, reducing the strength of the set product. Therefore, the strength and consistency of the product are enhanced by using water that is as free of contaminants as possible.

[0166] Water can be present in the gypsum low density region slurry and / or high density region layer slurry of the present invention in a weight ratio of water to hemihydrate calcium sulfate 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.

[0167] Rear cover sheet and front cover sheet

[0168] The front cover sheet and the back cover sheet can be made of paper or other fibrous materials, such as fiberglass mats. The back paper cover sheet and the front cover sheet can be made of any suitable paper material with any suitable basis weight.

[0169] The back cover sheet and the front cover sheet can be made of paper. However, the paper materials used for each cover sheet can be the same or different.

[0170] Various paper grades can be used in gypsum panels. Manila grade paper with a smooth calendered finish material is usually used as the finish paper cover sheet, and newspaper (Newsline paper) with a rougher finish material is usually used as the backing paper cover sheet. Generally, both paper grades are multi - layer with at least one liner layer and several filler layers. However, if desired, at least one paper cover sheet or both paper cover sheets are made of single - layer paper.

[0171] Generally, the back cover sheet only covers the back surface. In contrast, the front cover sheet covers the front surface of the board and also wraps around the board edge to contact the back cover sheet.

[0172] If desired, to increase strength (e.g., nail - pull - out strength), especially for low - density gypsum boards, one or both of the cover sheets can be made of paper with a basis weight of, for example, at least about 45 lbs / MSF (e.g., about 45 lbs / MSF to about 65 lbs / MSF, about 45 lbs / MSF to about 60 lbs / MSF, about 45 lbs / MSF to about 55 lbs / MSF, about 50 lbs / MSF to about 65 lbs / MSF, 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 enhanced nail - pull - out resistance and handleability. If desired, the back paper cover sheet can have a slightly lower basis weight (e.g., a basis weight less than 45 lbs / MSF, e.g., about 33 lbs / MSF to 45 lbs / MSF (e.g., about 33 lbs / MSF to about 40 lbs / MSF)).

[0173] Terms of the present invention

[0174] The following clauses disclose various aspects of the present invention.

[0175] Clause 1. A plurality of setting stabilizer particles, the plurality of setting stabilizer particles comprising

[0176] A granular core, the granular core comprising 50% to 98% by weight, preferably 70% to 98% 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 silicone, and

[0177] A coating on the granular core, the coating comprising an anti-dehydration substance selected from the group consisting of sugars, dextrins, and polyhydric alcohols such as glycerol or polyethylene glycol, in a ratio of about 5 to 25 parts by weight of the anti-dehydration substance per 100 parts by weight of calcium sulfate dihydrate.

[0178] Clause 2. The solidification stabilizer particles according to clause 1, wherein the anti-dehydration substance comprises hexose.

[0179] Clause 3. The solidification stabilizer particles according to clause 1, wherein the anti-dehydration substance comprises corn sugar.

[0180] Clause 4. The solidification stabilizer particles according to clause 1, wherein the anti-dehydration substance comprises glycerol.

[0181] Clause 5. The solidification stabilizer particles according to clause 1, wherein the anti-dehydration substance comprises a substance selected from the group consisting of sugars, dextrins, and polyhydric alcohols.

[0182] Clause 6. The solidification stabilizer particles according to clause 1, the solidification stabilizer particles comprising sugar-coated calcium sulfate dihydrate particles.

[0183] Clause 7. The solidification stabilizer particles according to clause 1, wherein the hydrophobic material comprises silicone.

[0184] Clause 8. The solidification stabilizer particles according to clause 1, wherein the hydrophobic material comprises silicone, and wherein the solidification stabilizer particles comprise about 0.05% to about 5% by weight, typically 0.1% to about 3% by weight of the silicone.

[0185] Clause 9. The solidification stabilizer particles according to clause 1, wherein the hydrophobic material comprises wax.

[0186] Clause 10. The solidification stabilizer particles according to clause 1, wherein the hydrophobic material comprises wax, and wherein the solidification stabilizer particles comprise about 0.5% to about 10% by weight, typically 1% to about 7% by weight, such as about 3% to about 7% by weight of the wax.

[0187] Clause 11. A method for preparing the solidification stabilizer particles according to any one of clauses 1 to 10, the method comprising:

[0188] An anti-dehydration substance selected from the group consisting of sugars, dextrins, and polyhydric alcohols such as glycerol or polyglycols is applied to the feed particles of the waste gypsum board material at a ratio of about 5 to 25 parts by weight of the anti-dehydration substance per 100 parts by weight of calcium sulfate dihydrate to produce solidification stabilizer particles. These feed particles of the waste gypsum board material 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.

[0189] The application is generally carried out by coating by any suitable mechanical or chemical means, such as by grinding or spraying the feed particles of the waste gypsum board material with the anti-dehydration substance.

[0190] Clause 12. A cementitious powder, the cementitious powder comprising:

[0191] Plaster particles containing calcium sulfate hemihydrate, wherein at least 60% by weight, preferably at least 70% by weight, more preferably at least 80% by weight, generally at least 90% by weight or generally at least 95% by weight of the cementitious powder is calcium sulfate hemihydrate; and

[0192] 0.5% - 5% by weight, preferably 0.5% to 4% by weight, more preferably 0.5% - 2% by weight or 0.5% - 1.5% by weight of the solidification stabilizer particles according to any one of Clauses 1 to 10.

[0193] Clause 13. The cementitious powder according to Clause 12, the cementitious powder further comprising a retarder.

[0194] Clause 14. The cementitious powder according to Clause 13, wherein the retarder comprises a keratin material that has been treated with caustic soda and quicklime, and the quicklime is a nitrogen-containing product. Due to its colloidal properties, the quicklime has a retarding effect on the setting time of calcined gypsum, powdered glue, citrate, acetate, timothy hay extract, or protein retarder, preferably sodium citrate or protein retarder.

[0195] Clause 15. The cementitious powder according to Clause 12, the cementitious powder being a solidification-stabilized calcium sulfate hemihydrate gypsum, the solidification-stabilized calcium sulfate hemihydrate gypsum comprising: these plaster particles containing the calcium sulfate hemihydrate, a retarder, these solidification stabilizer particles, wherein the particle core of these solidification stabilizer particles containing the calcium sulfate dihydrate is a seed crystal, and wherein the anti-dehydration substance comprises a water-soluble and relatively non-volatile polyhydric alcohol material, and the anti-dehydration substance coats the dihydrate and protects the dihydrate from loss of its water of crystallization.

[0196] Clause 16. A gypsum, the gypsum comprising:

[0197] Particles containing calcium sulfate hemihydrate;

[0198] The setting stabilizer particles according to any one of clauses 1 to 10;

[0199] Optionally a retarder, preferably the retarder comprises sodium citrate.

[0200] Clause 17. A method for manufacturing a gypsum board using the setting stabilizer particles according to any one of clauses 1 to 10, the method comprising:

[0201] Preparing an aqueous gypsum slurry comprising a mixture of water, plaster and these setting stabilizer particles, wherein the plaster comprises hemihydrate calcium sulfate, and wherein the aqueous gypsum slurry comprises the following mixture:

[0202] At least 60% by weight, usually 60% to 98% by weight, preferably at least 70% by weight, more preferably at least 80% by weight, usually at least 90% by weight or usually at least 95% by weight of the said hemihydrate calcium sulfate on a dry (anhydrous) basis,

[0203] 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 these setting stabilizer particles,

[0204] 0% to 5% by weight of a hydrophobic material on a dry (anhydrous) basis, preferably no hydrophobic material is present, the hydrophobic material being selected from waxes and / or siloxanes, other than the hydrophobic material provided by these setting stabilizer particles, usually no siloxane is present, other than the siloxane provided by these setting stabilizer particles, and no wax is present, other than the wax provided by these setting stabilizer particles, and

[0205] Water in a weight ratio of water to the hemihydrate calcium sulfate of 0.2:1 to 1.2:1; and

[0206] Depositing a front cover sheet on a forming surface;

[0207] 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 is a foamed aqueous gypsum slurry;

[0208] Depositing a back cover sheet on the aqueous gypsum slurry;

[0209] Solidifying the hemihydrate calcium sulfate to form a panel comprising a gypsum core, the gypsum core comprising dihydrate calcium sulfate; and

[0210] Drying the panel and cutting the panel into gypsum boards having one or more predetermined sizes.

[0211] Clause 18. The method according to Clause 17, wherein the first portion of the gypsum slurry is set in an unfoamed state to contact the high-density region in the form of a layer of the front cover sheet, and the second portion of the gypsum slurry is set in a foamed state to contact the low-density region of the high-density region, the high-density region having a higher density than the low-density region; and

[0212] wherein the board core includes a solidified low-density region containing calcium sulfate dihydrate and a solidified high-density region containing calcium sulfate dihydrate, the solidified high-density region being interposed in the form of a layer between the solidified low-density region and the front cover sheet.

[0213] Clause 19. The method according to Clause 17, wherein at least one of the front cover sheet and the back cover sheet includes a glass mat facing sheet or a paper facing sheet.

[0214] Clause 20. The method according to Clause 17, wherein the low-density region has a total air volume of about 45% to about 80% by volume.

[0215] Clause 21. The method according to Clause 17, wherein the high-density region has a total void volume of about 30% or less by volume.

[0216] Clause 22. The method according to Clause 17, wherein the high-density region has a total void volume of about 10% or less by volume.

[0217] Clause 23. A gypsum board prepared by the method according to Clause 17.

[0218] Clause 24. A gypsum board made by solidifying a composition containing a slurry, the slurry comprising a mixture of:

[0219] water;

[0220] particles containing calcium sulfate hemihydrate;

[0221] solidification stabilizer particles according to any one of Clauses 1 to 10;

[0222] optionally a retarder, preferably the retarder comprises sodium citrate.

[0223] The following examples further illustrate the present invention, but should of course not be construed as limiting its scope in any way.

[0224] Example

[0225] In the following examples, a gypsum slurry was prepared by mixing 400 g of hemihydrate calcium sulfate, 400 g of water, and 20 g of a coagulant (solidification stabilizer particles). The slurry density was controlled by adding foam to a stirrer. The foam was prepared in a foam generator and added at a constant flow rate for exactly 7 seconds. After mixing the hemihydrate, coagulant, water, and foam in a stirrer with blades for a total of 20 seconds, the slurry was poured into a 1 / 2" thick pan with a 4" diameter. Four pans were cast under each condition. The pans were dried overnight at 110°F to achieve a constant weight. When the slurry solidified and dried, the amount of foam added within 7 seconds gave a dry density of 28 lb / ft 3 , provided that all the foam remained during mixing with the slurry. If some of the foam burst during mixing, the dry density would be higher. The pans were weighed to measure the average dry density.

[0226] Example 1 :

[0227] As a comparative example, three different types of hemihydrate calcium sulfate were prepared in the laboratory by calcining dihydrate calcium sulfate from different sources (Types A, B, and C) at 350°F for 40 minutes.

[0228] Type A: The dihydrate calcium sulfate was dry synthetic gypsum without any recycled waste, which contained a water repellent (siloxane) (control sample).

[0229] Type B: The dihydrate calcium sulfate was obtained by grinding drywall blocks without any water repellent.

[0230] Type C: The dihydrate calcium sulfate was obtained by grinding drywall blocks containing approximately 0.7 wt% of a siloxane-based water repellent.

[0231] The densities of Type A, Type B, and Type C blends containing hemihydrate calcium sulfate obtained by calcining Type A, Type B, and Type C sources of dihydrate calcium sulfate, respectively, are shown in Table 3.

[0232]

[0233] The results show the effect of using waste boards containing a water repellent (siloxane in this example) on the foam and the final density. Adding the siloxane-containing waste led to an increase in density by partially destroying the foam during mixing. The coagulant used in the experiments of the above comparative example was a control coagulant made by grinding gypsum (without siloxane-containing waste) and 5 wt% dextrin.

[0234] Example 2

[0235] In addition, the setting accelerator (setting stabilizer particles) of the present invention was prepared by grinding a plate containing 0.7 wt% of a siloxane-based water repellent and 5 wt% of dextrose in a ball mill for 10 minutes. When the setting accelerator (setting stabilizer particles) of the present invention was used to replace the setting accelerator in the above comparative example, it was found that the dry density was 27.9 lb / ft 3 , which was approximately the same as the control sample made without using siloxane-containing waste and was also similar to the target density of 28 lb / ft 3 . This demonstrates that when siloxane-containing waste is ground together with a suitable grinding aid (dextrose in this example) to prepare a setting accelerator for use in the preparation of gypsum boards, the siloxane-containing waste does not affect the foam.

[0236] The present invention provides and uses a setting-stabilized hemihydrate calcium sulfate cement or gypsum containing seeds of dihydrate calcium sulfate and an equal amount of a retarder, the seeds being protected from losing their hydrating water due to heating, thereby producing a gypsum whose setting time does not change when stored in the presence of heat or when accidentally mixed with accelerating or delaying effects, and for which the inventors claim protection.

[0237] Advantageously, the method described herein allows the recycling of gypsum materials that would otherwise not be suitable for reuse in new products. In particular, gypsum particles can still contain and be coated with one or more hydrophobic additives present in the solid layer forming the particles even when reduced in size, and this solid layer has previously been considered incompatible with incorporation into the aqueous gypsum slurry used in drywall manufacturing, especially in drywall containing a foam component. Previous attempts have revealed that hydrophobic gypsum particles break the bubble walls, resulting in a loss of slurry stability.

[0238] In particular, gypsum drywall containing a hydrophobic component (which would otherwise be discarded) can be recycled into new drywall having properties conforming to ASTM standard C1396 / C1396M-17. Various properties, such as flexural strength, hardness (core, ends, and edges), nail pull resistance, humidification deflection, end squareness, nominal thickness, rabbet or tapered edge depth, width, length, water resistance of the water-repellent gypsum panel product with core treatment, and surface water resistance of the gypsum panel product with a water-repellent surface, can be determined as described in ASTM C473-19.

[0239] All documents described herein are incorporated herein by reference for all purposes for which such practice is permitted, including any priority documents and / or test procedures, provided they are not inconsistent with the present disclosure. From the foregoing general description and specific embodiments, it will be apparent that while forms of the present disclosure have been illustrated and described, various modifications may be made without departing from the spirit and scope of the present disclosure. Accordingly, the present disclosure is not intended to be limited thereby. For example, the compositions described herein may be free of any component or ingredient not expressly recited or disclosed herein. Any method may lack any step not recited 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 should be understood that we also contemplate the same composition or group of elements preceded by the transitional phrases "consisting essentially of", "consisting of", "selected from the group consisting of", or "is", and vice versa.

[0240] Unless otherwise indicated, all numbers expressing quantities of ingredients, properties (such as molecular weight), reaction conditions, etc. used in the specification and associated claims are to be understood as being modified in all instances by the term "about". Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by the 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 least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

[0241] Whenever a numerical range having a lower and upper limit is disclosed, any number and any included range falling within that range are specifically disclosed. In particular, each value range disclosed herein (of the form "about a to about b", or equivalently "approximately a to b", or equivalently "about a - b") should be understood to set forth every number and range encompassed within the broader value range. Further, unless the patentee has otherwise expressly and clearly defined, the terms in the claims have their ordinary and customary meaning. Additionally, as used in the claims, the indefinite article "a" or "an" is defined herein to mean one or more of the elements it introduces.

Claims

1. A plurality of setting stabilizer particles, the plurality of setting stabilizer particles comprising: A particle core, the particle core comprising 50 wt% to 98 wt%, preferably 70 wt% to 98 wt% or 70 wt% to 95 wt% of calcium sulfate dihydrate and 0.05 wt% to 10 wt%, preferably 0.5 wt% to 5 wt% of a hydrophobic material selected from wax and / or silicone, and A coating on the particle core, the coating comprising an anti-dehydration substance selected from the group consisting of sugars, dextrins, and polyhydric alcohols such as glycerol or polyethylene glycol, in a ratio of about 5 parts to 25 parts of anti-dehydration substance per 100 parts by weight of calcium sulfate dihydrate.

2. The setting stabilizer particles according to claim 1, wherein the anti-dehydration substance comprises at least one of hexose or corn sugar.

3. The setting stabilizer particles according to claim 1, wherein the anti-dehydration substance comprises a substance selected from the group consisting of dextrin and polyhydric alcohols.

4. The setting stabilizer particles according to claim 1, the setting stabilizer particles comprising sugar-coated calcium sulfate dihydrate particles.

5. A method for preparing the setting stabilizer particles according to any one of claims 1 to 4, the method comprising: Applying an anti-dehydration substance selected from the group consisting of sugars, dextrins, and polyhydric alcohols such as glycerol or polyglycol in a ratio of about 5 parts to 25 parts of anti-dehydration substance per 100 parts by weight of calcium sulfate dihydrate to feed particles of waste gypsum board material to produce setting stabilizer particles, the feed particles of waste gypsum board material comprising 50 wt% to 98 wt% calcium sulfate dihydrate and 0.05 wt% to 10 wt% of a hydrophobic material selected from wax and / or silicone, wherein the applying is generally carried out by coating with any suitable mechanical or chemical means, such as by grinding or spraying the feed particles of waste gypsum board material with the anti-dehydration substance.

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

7. A gypsum, the gypsum comprising: Particles comprising calcium sulfate hemihydrate; The setting stabilizer particles according to any one of claims 1 to 4; Optionally a retarder, preferably the retarder comprises sodium citrate.

8. A method for manufacturing a gypsum board using the setting stabilizer particles according to any one of claims 1 to 4, the method comprising: Preparing an aqueous gypsum slurry comprising a mixture of water, plaster, and the setting stabilizer particles, wherein the plaster comprises calcium sulfate hemihydrate, and wherein the aqueous gypsum slurry comprises a mixture of the following: At least 60% by weight, usually 60% to 98% by weight, preferably at least 70% by weight, more preferably at least 80% by weight, usually at least 90% by weight or usually at least 95% by weight of said calcium sulfate hemihydrate, calculated on an 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 said setting stabilizer particles, 0% to 5% by weight of a hydrophobic material calculated on an anhydrous basis, preferably no hydrophobic material is present, said hydrophobic material being selected from waxes and / or siloxanes, other than the hydrophobic material provided by said setting stabilizer particles, usually no siloxane is present other than the siloxane provided by said setting stabilizer particles, and no wax is present other than the wax provided by said setting stabilizer particles, and Water in a weight ratio of water to said calcium sulfate hemihydrate of 0.2:1 to 1.2:1; and Depositing a front cover sheet on a forming surface; Depositing said aqueous gypsum slurry on said front cover sheet to form a layer of said aqueous gypsum slurry, preferably, the aqueous gypsum slurry deposited for said core layer is a foamed aqueous gypsum slurry; Depositing a back cover sheet on said aqueous gypsum slurry; Solidifying said calcium sulfate hemihydrate to form a panel comprising a gypsum core, said gypsum core comprising calcium sulfate dihydrate; And Drying said panel and cutting said panel into gypsum boards having one or more predetermined dimensions.

9. A gypsum board prepared by the method according to claim 8.

10. A gypsum board made by solidifying a composition comprising a slurry, said slurry comprising a mixture of: Water; Particles comprising calcium sulfate hemihydrate; Setting stabilizer particles according to any one of claims 1 to 4; Optionally a retarder, preferably said retarder comprises sodium citrate.

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