RU2816930C2 - Multilayer gypsum board, related methods and suspensions - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to production of gypsum plasterboards. Composite gypsum plasterboard comprises sheet core and concentrated layer. Core of the sheet contains hardened gypsum, is formed from the first suspension containing water and plaster, has the first and the second sides of the core, which are defined in opposite directions. Concentrated layer interconnected with the first face side of the core has a density in the dry state which is at least 1.1 times higher than that of the sheet core in the dry state, is formed from a second suspension containing water, gypsum plaster, starch thickener, at least one water-soluble cellulose ether and optionally a copolymer containing polyacrylamide and acrylic acid. Starch thickener used is an ether derivative of starch with a degree of substitution - the ratio of substituted groups to glucose links - of at least 0.5, untreated by heat treatment, obtained by grafting foreign groups to the hydroxyl group of the glucose link of the starch molecule, wherein foreign groups are selected from: ethyl, hydroxyl ethyl, hydroxyl propyl, acetate, phosphate, sulphate. At least one water-soluble cellulose ether is selected from: methylcellulose, ethylcellulose, hydroxyethylcellulose, propylcellulose, hydroxypropylcellulose and hydroxypropylmethylcellulose. Said starch thickener, water-soluble cellulose ether and copolymer are added to the second suspension to increase its viscosity by at least 100% for 30 s to prevent the second suspension from being washed out when the first suspension is distributed therein.

EFFECT: reduced weight of gypsum plasterboard while maintaining strength.

4 cl, 4 dwg, 2 tbl, 1 ex

Description

BACKGROUND OF THE ART

[0001] Set gypsum is a well-known material that is used in many products, including panels and other products for construction and renovation. One such panel (often called gypsum board) is made of a core of hardened gypsum sandwiched between two cover sheets (such as paperboard) and is typically used for plasterboarding the interior walls and ceilings of buildings. One or more dense layers, often referred to as "cover layers", may be contained on both sides of the core, typically at the interface between the paper and the core.

[0002] Gypsum (calcium sulfate dihydrate) occurs naturally and can be mined as a rock. It may also be synthetic (this type is referred to as "singpom" in the art), obtained as a by-product of industrial processes such as flue gas desulfurization. Gypsum of any origin (natural or synthetic) can be calcined at high temperature to form stucco gypsum (i.e. calcined gypsum in the form of calcium sulfate hemihydrate and/or calcium sulfate anhydrite) and then rehydrated to form a hardening gypsum of the desired form (e.g. sheet). During the sheet manufacturing process, stucco, water and other necessary ingredients are mixed, typically in a paddle mixer (as used herein as commonly understood in the art). A suspension is formed, which is unloaded from the mixer onto a moving conveyor carrying a cover sheet with one of the covering layers (if any) already applied (often in front of the mixer). The suspension is distributed over the paper (with an optional coating layer applied to the paper). To form a sandwich structure of the desired thickness, another cover sheet, with or without a capping layer, is applied to the slurry using, for example, a forming plate or similar device. The mixture is cast and allowed to harden to form hardened (ie, rehydrated) gypsum by reacting the calcined gypsum with water to form a matrix of crystalline hydrated gypsum (ie, calcium sulfate dihydrate). It is this desired hydration of the fired gypsum that makes it possible to form a matrix of interlocking hardened gypsum crystals, thereby imparting strength to the gypsum structure in the product. Heat (eg, in a drying oven) is required to remove the remaining free (i.e., unreacted) water and obtain a dry product.

[0003] Excess water that is diverted represents the uneconomical nature of the system. Removing water requires energy, and the production process is slowed down to allow the drying step. However, reducing the amount of water in the system without compromising other important aspects of a gypsum board such as a commercially available gypsum board product, including the weight and strength of the sheet, has proven to be very difficult.

[0004] Another objective is to reduce the weight of the gypsum board while maintaining strength. One measure of sheet strength is its “nail pull resistance,” sometimes simply referred to as “nail pull resistance.” To reduce the weight of the sheet, a foaming agent can be introduced into the suspension to create air voids in the final product. Replacing solid mass with air in a gypsum board frame reduces mass, but this loss of solid mass can also result in reduced strength. Compensating for strength loss is a major obstacle to weight reduction efforts in the art.

[0005] One method of making gypsum board with good strength is to use multiple layers of gypsum in the sheet. This method is not entirely satisfactory because if the sheet core slurry is spread over the secondary slurry before the secondary slurry has hardened or set, the secondary slurry may be subject to washout so that the secondary gypsum layer adjacent to the sheet core in the final plasterboard product will be heterogeneous.

[0006] It should be understood that this description of the prior art is provided by the inventors as an aid to the reader and should not be construed as a reference to prior art or as an indication that any of the stated problems are of great importance in the art. Although the principles described may, in some respects and in some embodiments, mitigate the problems inherent in other systems, it should be understood that the scope of protection of an innovation is determined by the appended claims and not by the ability of the claimed invention to solve any specific problem noted herein .

BRIEF DESCRIPTION OF THE INVENTION

[0007] Embodiments of this disclosure generally relate to a composite gypsum board comprising a core and a concentrated layer; suspensions for use in forming a concentrated layer; and a method for manufacturing the composite sheet. The suspension to create a concentrated layer is specially formulated from a starch thickener, cellulose and/or a copolymer containing polyacrylamide and acrylic acid. These ingredients are advantageously used in the formation of a multilayer sheet to reduce or eliminate washout when the core slurry (usually the primary slurry) is distributed over the concentrated layer slurry (usually the secondary slurry).

[0008] Thus, in one aspect of this disclosure there is provided a composite gypsum board comprising:

(a) a sheet core containing set gypsum and formed from a first slurry containing water and stucco, the core having first and second core sides that are defined in opposite directions; And

(b) a concentrated layer disposed in an interlocking relationship with the first face of the core, having a dry density of at least 1.1 times that of the dry core of the sheet, formed from a second slurry containing water, stucco,

(i) starch thickener - an ether derivative of starch with a degree of substitution - the ratio of substituted groups to glucose units - of at least 0.5, untreated by heat treatment, obtained by grafting foreign groups to the hydroxyl group of the glucose unit of the starch molecule, and the foreign groups are selected from: ethyl , hydroxylethyl, hydroxylpropyl, acetate, phosphate, sulfate,

(ii) at least one water-soluble cellulose ether selected from: methylcellulose, ethylcellulose, hydroxyethylcellulose, propylcellulose, hydroxypropylcellulose and hydroxypropylmethylcellulose,

and, optionally,

(iii) a copolymer comprising polyacrylamide and acrylic acid, wherein said starch thickener, water-soluble cellulose ester and copolymer are added to the second suspension to increase its viscosity by at least 100% within 30 seconds to prevent the second suspension from being washed out when the first suspension is distributed thereon .

According to one embodiment, there is provided a composite gypsum board, characterized in that the copolymer contains 20% by weight or less of acrylic acid and has a molecular weight of from 100,000 to 1,000,000. According to another embodiment, there is provided a composite gypsum board, characterized in that the concentrated layer is formed from a slurry containing a starch thickener, cellulose ether and a copolymer. According to yet another embodiment, a composite gypsum board is provided, characterized in that the first suspension optionally contains an improvement additive, the second suspension contains an improvement additive, wherein the improvement additive contains: (i) at least one pregelatinized starch having a viscosity of 20 centipoise to 700 centipoise when the viscosity is measured by exposing the starch to VMA conditions, and (ii) at least one crude starch having a peak viscosity of between 100 Brabender units and 900 Brabender units when the viscosity is measured by introducing the starch into suspension with water at a starch concentration of 15% solids basis and using a Viscograph-E set at 75 rpm and 700 cmg, in which the starch is heated from 25°C to 95°C at a rate of 3°C/minute , then the suspension is kept at 95°C for ten minutes, and then the starch is cooled to 50°C at a rate of -3°C/minute; when the enhancer is present in the first suspension, the enhancer is present in the second suspension at a higher concentration than in the first suspension.

[0009] In another aspect of this disclosure, a composite gypsum board is provided. The sheet contains a sheet core containing hardened gypsum formed from water, plaster and optionally an improving additive. The core has a dry density and a dry thickness and has first and second core surfaces. The sheet also contains a concentrated layer formed from water, stucco, an improver and at least one of the following: a starch thickener, cellulose and/or a copolymer containing polyacrylamide and acrylic acid. The concentrated layer is in relationship with the first side of the core and has a dry density and/or an average hardness of at least about 1.1 times that of the sheet core. When the improver is present during core forming, the improver is added at a higher concentration when forming the concentrated layer than when forming the core sheet.

[0010] In another aspect of this disclosure, a method for producing composite gypsum board is provided. The method includes preparing a first suspension containing stucco, water, an improving additive and at least one of the following: a starch thickener, cellulose and/or a copolymer containing polyacrylamide and acrylic acid. The method also includes mixing at least water, stucco, and optionally an improvement additive to form a second slurry. The first slurry is applied to bond with the first cover sheet to form a concentrated layer. The concentrated layer has a first side and a second side, with the first side of the concentrated layer facing the first cover sheet. The second slurry is applied to form an association with the concentrated layer to form a core sheet having a first side and a second side, with the first side of the core sheet facing the second side of the concentrated layer. A second cover sheet is applied to form an interconnection with a second side of the sheet core to form a sheet preform. The sheet blank is dried to form a sheet.

[0011] Another aspect of this disclosure provides a slurry containing water, stucco, an improver, and at least one of a starch thickener, cellulose, and/or a copolymer containing polyacrylamide and acrylic acid.

[0012] The concentrated layer is preferably formed from an improver, water and, for example, a binder material such as plaster of Paris to form a hydrated binder material such as set gypsum in a continuous crystalline matrix. The enhancer is preferably more concentrated (by weight percentage) in the concentrated layer than in the core of the leaf. As used herein, any reference to an enhancer that is "more concentrated" (or variations of the term) in the concentrated layer slurry than in the core sheet slurry includes situations where (a) both the concentrated layer and the core sheet molded from an enhancer, and (b) the concentrated layer is formed from an enhancer, but the core sheet contains zero or no enhancer.

[0013] In some embodiments, the concentrated layer has a density at least about 1.1 times greater than the density of the core sheet, and, in some embodiments, has a thickness of about 0.02 inches (about 0.05 cm ) to about 0.2 inches (about 0.5 cm). The core of the sheet has a thickness preferably greater than the thickness of the concentrated layer in some embodiments of the invention. An enhancement additive includes a strength additive described herein that helps provide the target strength properties described herein.

[0014] A sheet formed from a concentrated layer slurry containing a higher percentage by weight of an enhancement additive than the percentage in the core sheet slurry provides one or more of an efficiency or processing advantage. For example, the overall use of enhancer in a sheet can be reduced by focusing the use of enhancer on forming the lower weight, thinner section (i.e., concentrated layer) and using less or no enhancer when forming the higher weight, thinner section (i.e., the concentrated layer). e. leaf core). Surprisingly and unexpectedly, the concentrated layer formed with a higher weight percentage of the enhancement additive is able to distribute the target end properties throughout the core of the sheet, resulting in the sheet exhibiting strength properties. As a result, the sheet core can be manufactured with less enhancement additive and, in some embodiments, can be lighter and less dense than traditional sheet cores. In turn, the overall mass of the sheet can be reduced by reducing the density of the high mass section of the sheet (ie, the core).

[0015] For some enhancers, such as some pregelatinized starches, they may require water in suspension, that is, they increase the water requirement. By reducing the amount of improver in the core slurry, in some embodiments, the water requirement of the core slurry can be reduced. Thus, for example, the overall water use in sheet production can be reduced, which can further improve efficiency since less water is used in the system, resulting in less water having to be removed by heating in the oven. As a result, production line speed can be increased and drying costs can be reduced.

[0016] The composite gypsum board may have a density within a target range. In some embodiments, the sheet may be manufactured at ultra-low weight, for example, with a sheet density of about 33 pounds per cubic meter. foot or less. It should be understood that the weight of the sheet is a function of density and thickness. Thus, density can be used as a measure of sheet weight, as will be appreciated by those skilled in the art. Such ultra-low mass can be achieved without compromising the target strength properties. For example, in some embodiments, the composite drywall sheet may exhibit a nail pull resistance of at least about 65 lbf (e.g., at least about 72 lbf, at least about 77 lbf, etc.) according to with Method B of ASTM C473-10.

BRIEF DESCRIPTION OF SEVERAL TYPES OF GRAPHIC MATERIALS

[0017] In FIG. 1 is a schematic cross-sectional view of a composite gypsum board constructed in accordance with the principles of this disclosure.

[0018] In FIG. 2 depicts schematic flow diagrams of three alternative process flow diagrams (designated A, B, and C) that illustrate the steps for preparing core sheet and concentrated layer suspensions in accordance with the principles of this disclosure.

[0019] In FIG. 3 is a schematic cross-sectional view of a composite gypsum board constructed in accordance with the principles of this disclosure compared to the control sheet described in Example 1 herein.

[0020] In FIG. 4 is a schematic cross-sectional view of the composite gypsum board and control sheet of FIG. 3 after firing described in Example 1 of this document.

DETAILED DESCRIPTION OF THE INVENTION

[0021] Embodiments of the disclosure provide a multilayer composite sheet, a method for making the sheet, and a slurry. The composite sheet contains multiple layers that contain various cementitious compositions, for example, as a continuous crystalline matrix of set gypsum, in the final product. One layer forms the core of the slab, and the other layer forms the concentrated layer; in some embodiments, for example, a significant thickness (eg, at least about 0.02 inches or about 0.05 cm). In preferred embodiments, the core of the sheet is typically thicker than the concentrated layer and constitutes the bulk (eg, greater than about 60%, eg, greater than about 70%, greater than about 75%, etc.) of the core volume of the sheet. Typically, the sheet also contains an upper (front) and lower (back) cover sheet.

[0022] The concentrated layer is formed from a slurry of stucco containing water and one or more of the following agents: a starch thickener, cellulose, and/or a copolymer containing polyacrylamide and acrylic acid. The use of these ingredients in the concentrated layer surprisingly and surprisingly prevents the concentrated layer slurry from being washed out when the core slurry is applied to it during sheet formation. These agents successfully improve the cohesiveness of the concentrated layer suspension and are expected to have little or no effect on the setting time of the suspension. As a result, a uniformly distributed concentrated layer formed on the core of the sheet can be formed with a strong bond at their interface. These anti-leaching agents are preferably used in the dual mixer systems described herein, in which the core slurry is typically the primary slurry and is formed in the primary mixer and the concentrated layer slurry is the secondary slurry and is formed in the secondary mixer. In some embodiments, the starch thickener, cellulose, and/or copolymer increases the viscosity of the concentrated layer slurry by at least about 100% within 30 seconds of addition to the slurry, e.g., within 20 seconds, within 15 seconds, etc. For example, in some embodiments, the starch thickener, cellulose, and/or copolymer increases the viscosity of the first slurry by about 100% to about 500% within 30 seconds of addition to the slurry. It is believed that the thickening effect of the concentrated layer suspension slows the onset of washout, whereas a looser or less dense suspension is more prone to washout when the core leaf suspension is applied. Advantageously, the speed at which the concentrated slurry layer thickens (eg, less than about 30 seconds) provides effective thickening compatible with the configuration and production speed at the feed end (where the mixer is located and the slurries are applied) of the sheet plant. In particular, the concentrated layer suspension thickens and is applied in time for application of the core suspension without causing the concentrated layer suspension to wash out.

[0023] The primary core sheet slurry may contain a starch thickener, cellulose, and a copolymer containing polyacrylamide and acrylic acid, if desired. If included in the core leaf suspension, in preferred embodiments, the starch thickener, cellulose, and copolymer are present at a lower concentration than their amount in the concentrated layer suspension (for example, in an amount of from about 0.1% to about 5%) by weight plaster. However, in some embodiments, the primary core sheet slurry is substantially free of starch thickener, cellulose, and polyacrylamide-acrylic acid copolymer. In this context, “substantially free” means that the primary suspension contains: (i) 0% wt. or does not contain such a starch thickener, cellulose or a copolymer containing polyacrylamide and acrylic acid; (ii) ineffective quantity; or (iii) a minor amount of a starch thickener, cellulose or copolymer containing polyacrylamide and acrylic acid, for example, less than about 0.1% by weight of the stucco, less than about 0.05% by weight of the stucco, less than about 0.01% by weight of the stucco, weight of plaster, less than about 0.005% by weight of plaster, less than about 0.001% by weight of plaster, etc.

[0024] Both the core sheet and the concentrated layer are formed from a binder material and water. According to preferred embodiments of the disclosure, the concentrated layer has a higher density than the core of the sheet (eg, at least about 1.1 times higher). To create a lower density core sheet, blowing agents known in the art may be used in the core sheet, although other density reducing materials may be added to the core sheet slurry as an alternative or additional ingredient, such as lightweight filler, including, for example, lightweight aggregate or perlite, especially if the additional cost is acceptable. To achieve the target higher density in this layer, the concentrated layer may contain less or no blowing agent and/or less or no lightweight filler.

[0025] Without wishing to be limited by any particular theory, it is believed that the compositions and relationships between the respective layers in a composite sheet give the product surprising and unexpected properties. In particular, it is believed that the targeted use of an enhancement additive in a concentrated layer may be useful to impart targeted properties to the sheet and, if necessary, improve process efficiency. Additionally, in some embodiments, aspects such as (a) the thickness, density, and/or strength of the concentrated layer, and/or (b) the properties of the concentrated layer relative to the paper and core sheet, respectively, can be used to optimize sheet properties. Based at least in part on these aspects, it is believed that the target properties of the concentrated layer can be distributed and directed throughout the sheet, thereby facilitating the production of the composite sheet while maintaining, if necessary, the physical properties of the core of the sheet.

[0026] In accordance with some embodiments of the invention, the dry concentrated layer has a stiffness value that approximates that of the top cover sheet to which it is typically adjacent. In some embodiments, the concentrated layer has a higher stiffness value and/or hardness (a measure of strength) than the core sheet. Thus, in some embodiments, the concentrated layer may be located between a material with relatively good stiffness and strength (ie, the top cover sheet) and a material with lower stiffness and strength (ie, the core sheet). It will be understood that the amount of stiffness can be measured using Young's modulus, known in the art.

[0027] Without wishing to be limited by any particular theory, it is believed that adding a higher weight percentage of an enhancement additive that imparts the target strength properties to the concentrated layer provides effective target strength properties. The concentrated layer is located between the top cover sheet and preferably the lighter and weaker core sheet. Surprisingly and unexpectedly, the concentrated layer serves to absorb energy from the load and distribute the load more evenly across the core of the sheet and throughout the sheet, so that the load is expected to be more easily released and dissipated. Thus, the composite gypsum board of the invention will exhibit good strength properties and will produce a lighter weight sheet by achieving increased strength in a concentrated layer where the property can be distributed throughout the core of the sheet. For example, this advantage may be illustrated in some embodiments by good results in nail pull resistance, average gypsum layer hardness tests (e.g., cumulatively, i.e., across all gypsum layers), and/or flexural strength tests according to Method B ASTM 473-10, which is understood in the art.

Anti-leaching agents

[0028] In accordance with preferred embodiments of the disclosure, the concentrated layer is formed from at least one of the following: a copolymer containing polyacrylamide and acrylic acid, cellulose, and/or a starch thickener.

[0029] Any suitable copolymer of polyacrylamide and acrylic acid may be used if included. In some embodiments of the invention, the copolymer contains about 20% wt. or less acrylic acid. The copolymer may also have any suitable molecular weight, for example, from about 100,000 to about 1,000,000, or from about 200,000 to about 800,000, from about 300,000 to about 500,000, etc. The copolymer may also be used in any suitable amount. For example, in some embodiments, the copolymer, if incorporated, is present in the concentrated layer suspension in an amount of from about 0.01% to about 5.0% by weight of the stucco, or from about 0.1% to about 3.0 %, from about 0.5% to about 1.0%, etc.

[0030] Any suitable cellulose may be used if desired. Cellulose is generally water soluble. For example, in some embodiments, the cellulose is cellulose ether. In some embodiments, the cellulose is an alkylcellulose. In various embodiments, the cellulose may be in the form of one or more of methylcellulose, ethylcellulose, hydroxyethylcellulose, propylcellulose, hydroxypropylcellulose, and/or hydroxypropylmethylcellulose. The cellulose may have any suitable molecular weight, for example, a molecular weight of about 10,000 to about 1,000,000, or from about 50,000 to about 800,000, from about 100,000 to about 600,000, etc. Cellulose, if introduced, can be introduced in any suitable amount. For example, in some embodiments, cellulose is present in the concentrated layer suspension in an amount of from about 0.01% to about 0.6% by weight of the stucco, or from about 0.05% to about 0.5%, from about 0.1 % to about 0.4%, etc.

[0031] The starch thickener, if included, is typically a substituted starch. For example, a starch thickener can be modified by grafting foreign groups onto the hydroxyl group of the glucose unit of the molecule. Foreign groups may include, for example, ethyl, hydroxylethyl, hydroxylpropyl, acetate, phosphate and/or sulfate.

[0032] The degree of substitution (“DS”) is defined as the ratio of substituted groups to glucose units. Since each glucose has three hydroxyl units available for replacement, the maximum DS value is 3. Any suitable DS can be selected, for example, at least about 0.5, at least about 0.6, etc. (with a maximum of 3, 2.5, 2 or 1.5, etc.). In some embodiments, the starch is “highly substituted”, wherein the DS is at least about 0.7, for example, the DS is at least about 0.8, for example at least about 0.9, or at least about 1. B In some embodiments, the ratio is from about 0.8 to about 3, from about 0.8 to about 2.5, from about 0.8 to about 2, from about 0.8 to about 1.5, from about 0, 9 to about 3, from about 0.9 to about 2.5, from about 0.9 to about 2, from about 0.9 to about 1.5, from about 1 to about 3, from about 1 to about 2, 5, from about 1 to about 2, from about 1 to about 1.5, etc.

[0033] Starch thickener is generally soluble in cold water. Without wishing to be limited by any particular theory, substituted groups can disrupt or destroy the crystalline structure of raw starch and make the starch soluble in cold water. Thus, there is no need to pre-cook the starch. As a rule, substituted starches have a high viscosity, which allows you to change the rheology of the concentrated layer suspension and the thickening effect of the suspension. For example, the starch thickener may have a viscosity of at least about 1000 cP, measured in accordance with the Viscosity Measurement Assay (VMA) method. For example, in some embodiments of the invention, the starch thickener has a viscosity of from about 2000 to about 10,000, measured in accordance with the IIV method.

[0034] In some embodiments, the starch thickener is an ester derivative of starch. For example, the starch thickener may be carboxyethyl starch ester. In some embodiments, the starch thickener is a salt, such as the salt represented by the formula (C ₂ H ₄ O ₃ ) _x ⋅ (Na) _x , where X is the number of repeat units. For example, the number of repeat units may be, for example, at least about 600, at least about 1000, at least about 1500, at least about 1800, at least about 2000, at least about 2500, at least about 3000, at least about 4000, at least about 5000, etc. For example, in various embodiments of the invention, the number of repeat units may be from about 600 to about 1,000,000, for example, from about 600 to about 50,000, from about 600 to about 25,000, from about 600 to about 18,000, from about 1,000 to about 50,000, from from about 1000 to about 25000, from about 1000 to about 18000, from about 1500 to about 50000, from about 1500 to about 25000, from about 1500 to about 18000, from about 1800 to about 50000 from about 1800 to about 25000, from about 1800 to about 18,000, from about 2,000 to about 50,000, from about 2,000 to about 25,000, from about 2,000 to about 18,000, from about 2,500 to about 50,000, from about 2,500 to about 25,000, from about 2,500 to about 18,000, from about 3,000 to about 50,000, from about 3,000 to about 25,000, from about 3,000 to about 18,000, from about 4,000 to about 50,000, from about 4,000 to about 25,000, from about 4,000 to about 18,000, from about 5,000 to about 50,000, from about 5,000 to about 25,000 from about 5,000 to about 18,000, etc. In some embodiments, the substituted starch thickener may be in the form of GlucoSol® 1148, commercially available from Chemstar, Minneapolis, Minnesota, which is a sodium starch glycolate.

[0035] The starch thickener, if included, may be in any suitable amount. For example, in some embodiments, the starch thickener may be present in the concentrated layer suspension in an amount of from about 0.01% to about 5.0% by weight of the stucco, such as from about 0.05% to about 2.0% by weight of the stucco. gypsum or from about 0.1% to about 1.0% by weight of the stucco.

[0036] In some embodiments, the concentrated layer suspension contains a starch thickener and one or both of cellulose and a copolymer. In other embodiments, the concentrated layer suspension contains cellulose and one or both of a starch thickener and a copolymer. In other embodiments, the concentrated layer suspension contains a copolymer and one or both of a starch thickener and cellulose. In some embodiments, the concentrated layer suspension contains a starch thickener, cellulose, and a copolymer.

[0037] As discussed herein, a thickening starch is distinguished from a strength improver, which contains low or no substitution starch and lower viscosity, and which may be pregelatinized or uncooked if desired. In this regard, substitution generally reduces the strength improvement required from a strength improving starch additive. Without wishing to be limited by any particular theory, it is believed that substituted foreign groups tend to interfere with the relationship between starch and gypsum, thereby preventing optimal hydrogen bonding from forming. Thus, such substitution is undesirable from the point of view of creating a strength-improving component. Preferably, the starch selected as the strength-improving additive has an DS of zero; however, a small degree of substitution, although undesirable, may be acceptable, for example, an SZ of up to about 0.2 (or up to about 0.15, or up to about 0.1). The thickening starch of this invention is also different from migrating starches, which migrate to the gypsum layer-paper interface to improve bonding, since thickening starches are larger molecules with higher viscosity and do not tend to migrate.

[0038] For example, in some embodiments, as opposed to the thickening starch, the starch selected as the strength additive may be a pregelatinized starch having a lower viscosity than the starch thickening agent, for example, from about 20 centipoise to about 800 centipoise (e.g., about 20 centipoise to about 700 centipoise, about 20 centipoise to about 300 centipoise, about 30 centipoise to about 200 centipoise, etc.) when the viscosity is measured by exposing the starch to the conditions of the AIV method. In some embodiments, the strength-improving additive comprises at least one crude starch (e.g., unsubstituted) having a peak viscosity of from about 100 Brabender units to about 900 Brabender units, as measured by viscosity by adding the starch to a suspension with water at a starch concentration of 15 % in terms of solids, and using a Viscograph-E device set at 75 rpm and 700 cmg, the starch being heated from 25°C to 95°C at a rate of 3°C/minute, the suspension kept at 95°C for ten minutes, and the starch is cooled to 50°C at a rate of -3°C/minute.

Composition of leaf core and concentrated layer

[0039] In accordance with some embodiments of the disclosure, the composite gypsum board is designed to incorporate a enhancer at a higher concentration than the concentration of enhancer incorporated (if at all) into the core of the sheet. The resulting sheet can be molded to produce a composite gypsum board with targeted strength properties.

[0040] In accordance with some embodiments of the invention, it has been surprisingly and unexpectedly discovered that a higher concentration of enhancement additive in a concentrated layer relative to the core of the sheet provides effective performance of the sheet with respect to target strength properties, for example, one or more of nail pull resistance, strength compressive strength, bending strength, average hardness of the gypsum layer (for example, total), etc. Thus, the present inventors have discovered that the use of enhancers can be optimized in accordance with preferred embodiments of the invention by tailoring the formulations of the respective core sheet and concentrated layers to incorporate enhancers, which can provide greater impact on achieving target strength properties ( i.e., a higher mass percentage in the concentrated layer than in the core of the leaf) as well as a lower overall water requirement. This discovery provides significant benefits, including, but not limited to, reduction in overall additive consumption and therefore lower raw material costs, increased production efficiency, and increased product strength, for example, allowing for products with lower weight and sufficient strength properties.

[0041] In some embodiments, the concentrated layer slurry contains at least about 1.2 times the concentration of enhancement additive compared to the core sheet slurry, such as at least about 1.5 times at least about 1.7 times, at least about 2 times, at least about 2.5 times, at least about 3 times, at least about 3.5 times, at least about 4 times, at least about 4 times .5 times, at least about 5 times, at least about 6 times, etc., each of these ranges may have any suitable upper limit depending on the situation, such as, for example, about 60, about 50 , about 40, about 30, about 20, about 10, about 9, about 8, about 7, about 6.5, about 6, about 5.5, about 5, about 4.5, about 4, about 3.5 , about 3, about 2.5, about 2, about 1.5, etc. It should be understood that "higher concentration" as used herein refers to relative amounts of enhancer (by weight of stucco), as opposed to gross amounts of ingredients. Since the core sheet provides a greater volume of material and contribution to sheet thickness compared to that of the concentrated layer, it is possible that any particular additive may be present in a higher total gross amount in the core sheet suspension, such as pounds or kilograms, but more low mass concentration compared to the concentrated layer suspension, that is, in a lower relative amount, for example, in mass percent (% wt).

[0042] Surprisingly and unexpectedly, certain embodiments of the disclosure are effective in reducing overall water consumption in the manufacture of composite gypsum board. In this regard, by selecting appropriate compositions of the concentrated layer and core sheet, it is possible to reduce the total amount of water used to make the sheet, such that water use is optimized since water is present in higher concentration where it is most needed (e.g. concentrated layer) and in reduced quantities where it is less needed (for example, in the core of the leaf).

[0043] It should be understood that since the set gypsum is formed from a slurry of stucco (sometimes referred to as a gypsum slurry) containing water and stucco, the ratio of water to stucco (“WSHGS”) may be maintained. In some embodiments, the core of the sheet, which may constitute the bulk of the sheet, can be molded with a lower VSHG compared to the VSHG used to form the concentrated layer. Thus, the total consumption of water and VSHGS in the composite gypsum board as a whole can be successfully reduced in some embodiments of the invention, since the contribution to the total volume of the sheet of the concentrated layer is less than the contribution to the total volume of the slab of the core of the sheet.

[0044] The sheet core and concentrated layer can be formed with any suitable VSHGS. In some embodiments, the concentrated layer is formed from a slurry having a VSHG higher than the VSHG of the suspension used to form the core sheet. For example, in some embodiments of the invention, the concentrated layer is formed from a slurry having a VSHGS at least about 1.2 times higher than the VSHGS of the suspension used to form the core sheet (for example, at least about 1.5 times higher than at least about 1.7 times higher, at least about 2 times higher, at least about 2.2 times higher, at least about 2.5 times higher, at least about 2.7 times higher higher, at least about 3 times higher, at least about 3.2 times higher, at least about 3.5 times higher, at least about 3.7 times higher, at least about 4 times higher times higher, etc., each of these ranges may have any suitable upper limit, such as, for example, about 7, about 6.5, about 6, about 5.5, about 5, about 4 .5, about 4, about 3.5, about 3, about 2.5, about 2, about 1.5, etc.).

[0045] In some embodiments, the core of the sheet is formed from a slurry of stucco having a water-to-stucco ratio of about 0.3 to about 1.3, for example, about 0.3 to about 1.2, about 0. 3 to about 1.1, from about 0.3 to about 1, from about 0.3 to about 0.9, from about 0.4 to about 1.3, from about 0.4 to about 1.2, from about 0.4 to about 1.1, about 0.4 to about 1, about 0.4 to about 0.9, about 0.5 to about 1.3, about 0.5 to about 1, 2, from about 0.5 to about 1.1, from about 0.5 to about 1, from about 0.5 to about 0.9, from about 0.6 to about 1.3, from about 0.6 to about 1.2, about 0.6 to about 1.1, about 0.6 to about 1, about 0.6 to about 0.9, about 0.6 to about 0.8 or about 0 .6 to about 0.7.

[0046] In some embodiments, lower water-stucco ratios are preferred, e.g., about 0.3 to about 0.8, e.g., about 0.3 to about 0.7, about 0.3 to about 0.6, from about 0.3 to about 0.5, from about 0.3 to about 0.4, from about 0.4 to about 0.8, from about 0.4 to about 0.7, from about 0.4 to about 0.6, from about 0.4 to about 0.5, from about 0.5 to about 0.8, from about 0.5 to about 0.7, from about 0.5 to about 0 ,6, from about 0.6 to about 0.8, from about 0.6 to about 0.7, etc.

[0047] In some embodiments, the concentrated layer is formed from a slurry having a water-to-stucco ratio of from about 0.7 to about 2, such as, for example, from about 0.7 to about 1.7, from about 0.7 to about 1.4, from about 0.7 to about 1.2, from about 0.7 to about 1, from about 0.8 to about 2, from about 0.8 to about 1.7, from about 0, 8 to about 1.4, from about 0.8 to about 1.2, from about 0.8 to about 1, from about 1 to about 2, from about 1 to about 1.7, from about 1 to about 1, 4, from about 1 to about 1.2, from about 1.2 to about 2, from about 1.2 to about 1.7, from about 1.2 to about 1.4, from about 1.4 to about 2 , from about 1.4 to about 1.7, etc. The concentrated layer may have a higher water content to meet the water needs of the enhancers. Because in some embodiments the enhancer is more concentrated in the concentrated layer, the higher water requirement may be applied to an individual concentrated layer, thereby providing lower VSHG in the leaf core and, preferably, less water use overall, especially given the large contribution of the sheet core to the main volume of the composite sheet.

Composite Sheet Density

[0048] Composite gypsum board according to embodiments of this disclosure can be used with various required densities for gypsum board, that is, gypsum board or wallboard (which can cover such board used not only for walls, but also for ceilings and other places, as is understood in this field of technology). As noted herein, the weight of a sheet is a function of its thickness. Since sheets are typically manufactured in varying thicknesses (eg, 3/8 inch, 1/2 inch, 3/4 inch, one inch, etc.), sheet density is used herein as a measure of sheet weight. The benefits of composite gypsum board in opening embodiments can be observed over a range of dry densities, extending up to densities of heavier sheets, for example, about 43 lb/cu ft (about 690 kg/m ³ ) or less, namely from about 18 lb/cu. ft (about 290 kg/m ³ ) to about 43 lb/cu.ft., from about 20 lb./cu.ft. (about 320 kg/m ³ ) to about 43 lb./cu.ft., from about 20 lb./cu.ft. ft to about 40 lb/cu.ft (about 640 kg/m ³ ), from about 24 lb/cu.ft (about 380 kg/m ³ ) to about 43 lb/cu.ft, from about 27 lb/cu.ft. ft (about 430 kg/m ³ ) to about 43 lb/cu ft, from about 20 lb/cu ft to about 38 lb/cu ft (about 610 kg/m ³ ), from about 24 lb/cu. ft. to about 40 lb/cu.ft., from about 27 lb./cu.ft. ft. to about 40 lb/cu.m. ft., from about 20 lb/cu.m. ft. to about 37 lb/cu.m. ft (about 600 kg/m ³ ), from about 24 lbs/cu.m. ft. to about 37 lb/cu.m. ft., from about 27 lb/cu.m. ft. to about 37 lb/cu.m. ft., from about 20 lb/cu.m. ft. to about 35 lb/cu.ft. (560 kg/m ³ ), about 24 lb./cu.ft. to about 35 lb./cu.ft. ft., from about 27 lb/cu.m. ft. to about 35 lb/cu.m. ft etc. [0049] As noted herein, removing solids from gypsum board can result in significant difficulty in compensating for the associated loss of strength. Some embodiments of the disclosure surprisingly and unexpectedly allow the use of a lighter weight sheet with good strength, lower water requirements, and efficient use of the enhancement additive. For example, in some embodiments, the dry density of the sheet may be from about 16 lbs/cu. ft. to about 33 lb/cu.m. ft., for example, from about 16 lbs./cu.m. ft. to about 27 lb/cu.m. ft., from about 16 lb/cu.m. ft. to about 24 lb/cu.m. ft., from about 18 lb/cu.m. ft. to about 33 lb/cu.m. ft (about 530 kg/m ³ ), from about 18 lbs/cu. ft. to about 31 lb/cu.m. ft., from about 18 lb/cu.m. ft. to about 30 lb/cu.m. ft., about 18 lb/cu.ft. to about 27 lb./cu.ft., about 18 lb./cu.ft. to about 24 lb./cu.ft., about 20 lb./cu.ft. to about 33 lb./cu.ft. . ft., from about 20 lb/cu.m. ft. to about 32 lb/cu.m. ft (about 510 kg/m ³ ), from about 20 lb/cu.ft to about 31 lb/cu.ft (about 500 kg/m ³ ), from about 20 lb/cu.ft. ft. to about 30 lb/cu.m. ft (about 480 kg/m ³ ), from about 20 lbs/cu. ft. to about 29 lb/cu.m. ft (about 460 kg/m ³ ), from about 20 lbs/cu. ft. to about 28 lb/cu.m. ft (about 450 kg/m ³ ), from about 21 lb/cu. ft (about 340 kg/m ³ ) to about 33 lb/cu. ft., from about 21 lb/cu.m. ft. to about 32 lb/cu.m. ft., from about 21 lb/cu.m. ft. to about 33 lb/cu.m. ft., from about 21 lb/cu.m. ft. to about 32 lb/cu.m. ft., from about 21 lb/cu.m. ft. to about 31 lb/cu.m. ft., from about 21 lb/cu.m. ft. to about 30 lb/cu.m. ft., from about 21 lb/cu.m. ft. to about 29 lb/cu.m. ft., from about 21 lb/cu.m. ft. to about 28 lb/cu.m. ft., from about 24 lb/cu.m. ft. to about 33 lb/cu.m. ft., from about 24 lb/cu.m. ft. to about 32 lb/cu.m. ft., from about 24 lb/cu.m. ft. to 31 lb/cu.m. ft., from about 24 lb/cu.m. ft. to about 30 lb/cu.m. ft., from about 24 lb/cu.m. ft. to about 29 lb/cu.m. ft., from about 24 lb/cu.m. ft. to about 28 lb/cu.m. ft or from about 24 lb/cu.m. ft. to about 27 lb/cu.m. foot.

Structure and Assembly of Composite Sheet

[0050] To illustrate an embodiment of the disclosure, reference is made to FIG. 1, which is a schematic cross-sectional view of a composite gypsum board 10. The face paper 12 serves as a top cover sheet. Face paper 12 has a first side 14 and a second side 16. A core layer 18 is in relationship with a face paper 12. A core sheet 18 has a first side 20 and a second side 22. A sheet core 24 has a first side 26 and a second side 28. A back paper 30 serves as the lower cover sheet. The back paper 30 has a first side 32 and a second side 34. [0051] As seen in FIG. 1, the composite gypsum board 10 is folded such that side 16 of the face paper 12 faces the first side 20 of the concentrated layer 18, and the second side 22 of the concentrated layer 18 faces the first side 26 of the core 24. The second side 28 of the core 24 faces the first back side 32 paper 30.

[0052] It is understood that composite gypsum board in accordance with some embodiments of the invention can be constructed and used in the assembly, as is understood in the art. As will be appreciated, composite sheets generally can be attached in any suitable order to profiles formed from any suitable material, such as wood, metal or the like. The top or front cover sheet of the sheet faces outward and is typically decorated (e.g., paint, texture, wallpaper, etc.) during use, while the bottom or back cover sheet faces the profiles. During operation, there is usually a cavity behind the profile facing the back paper. If desired, insulating material known in the art can optionally be placed in the cavity. In one embodiment of the invention, the assembly includes two composite sheets connected by profiles, with a cavity between them facing the lower cover sheets of the respective sheets.

Leaf core

[0053] The core of the sheet makes up the majority of the volume of the composite gypsum board sheet. In some embodiments, the core of the sheet constitutes at least about 60% of the sheet volume, such as at least about 70% of the sheet volume, at least about 80% of the sheet volume, at least about 90% of the sheet volume, at least about 92%, at least about 95%, at least about 97%, etc. Although the concentrated layer is considerably thick, the core of the leaf can be significantly thicker. For example, in some embodiments, the dry core of the sheet may have a dry thickness of from about 2.5 times to about 35 times that of the concentrated dry layer, such as from about 2.5 times to about 30 times, from about 2.5 times to about 25 times, from about 2.5 times to about 20 times, from about 2.5 times to about 15 times, from about 2.5 times to about 10 times, from about 2.5 times to about 5 times, from about 2.8 times to about 35 times, from about 2.8 times to about 30 times, from about 2.8 times to about 25 times, from about 2.8 times to about 20 times, from about 2.8 times to about 15 times, from about 2.8 times to about 10 times, from about 2.8 times to about 5 times, from about 5 times to about 35 times, from about 5 times to about 30 times, from about 5 times to about 25 times, about 5 times to about 20 times, about 5 times to about 15 times, or about 5 times to about 10 times that of the concentrated layer.

[0054] In some embodiments, the core sheet has a thickness of about 8 times to about 16 times that of the concentrated layer, e.g., about 8 times to about 12 times a thickness, about 9 times to about 16 times, from about 9 times to about 14 times, from about 9 times to about 12 times, from about 10 times to about 16 times, from about 10 times to about 14 times more than the concentrated layer, etc.

[0055] The core of the sheet consists of at least water and plaster. Stucco, as referred to throughout this document, may be in the form of alpha calcium sulfate hemihydrate, beta calcium sulfate hemihydrate, and/or calcium sulfate anhydrite. Stucco may be fibrous or non-fibrous. In addition to stucco and water, the core of the sheet is formed from an agent that promotes its lower density, such as low-density filler (eg, perlite, low-density aggregate, etc.) or blowing agents. Various modes of use of blowing agents are well known in the art. A blowing agent may be introduced to form air voids distributed within a continuous crystalline matrix of the setting gypsum. In some embodiments, the blowing agent comprises a major portion by weight of an unstable component and a minor portion by weight of a stable component (eg, when combining an unstable component with a mixture of stable and unstable components). The mass ratio of unstable component to stable component is sufficient to form distributed air voids within the set gypsum core. See, for example, US Pat. Nos. 5,643,510, 6,342,284, and 6,632,550. In some embodiments, the blowing agent comprises an alkyl sulfate surfactant.

[0056] Many commercially known blowing agents are available and can be used in accordance with embodiments of the disclosure, namely, the HYONIC line of (eg, 25AS) soap-based products from GEO Specialty Chemicals, Ambler, Pennsylvania. Other commercially available soaps include Polystep B25 from Stepan Company, Northfield, Illinois. The blowing agents described herein can be used alone or in combination with other blowing agents. The foam can be pre-formed and then added to the stucco slurry. Preformation may occur by introducing air into the aqueous blowing agent. Methods and apparatus for producing foam are well known. See, for example, US patents 4518652, 2080009 and 2017022.

[0057] In some embodiments, the blowing agent contains, consists of, or consists essentially of at least one alkyl sulfate, at least one alkyl ether sulfate, or any combination thereof, but is substantially free of an olefin (e.g., olefin sulfate) and/or alkyne. Substantially free of olefin or alkyne means that the blowing agent contains either (i) 0% wt. olefin and/or alkyne by weight of stucco, or does not contain olefin and/or alkyne, or (ii) an ineffective or (iii) insignificant amount of olefin and/or alkyne. An example of an ineffective amount is an amount below the threshold amount to achieve the intended purpose of using the olefin and/or alkyne blowing agent, as will be understood by one of ordinary skill in the art. The minor amount may be, for example, below about 0.001% by weight, such as below about 0.0005% by weight, below about 0.001% by weight, below about 0.00001% by weight, etc. from the mass of plaster, as will be clear to an ordinary person skilled in the art.

[0058] Certain types of unstable soaps, in accordance with embodiments of the disclosure, are alkyl sulfate surfactants with variable chain length and variable cations. A suitable chain length may be, for example, C ₈ -C ₁₂ , for example C ₈ -C ₁₀ or C ₁₀ -C ₁₂ . Suitable cations include, for example, sodium, ammonium, magnesium or potassium. Examples of unstable soaps include, for example, sodium dodecyl sulfate, magnesium dodecyl sulfate, sodium decyl sulfate, ammonium dodecyl sulfate, potassium dodecyl sulfate, potassium decyl sulfate, sodium octyl sulfate, magnesium decyl sulfate, ammonium decyl sulfate, mixtures thereof, and any combinations thereof.

[0059] Certain types of stable soaps, in accordance with embodiments of the disclosure, are alkoxylated (eg, ethoxylated) alkyl sulfate surfactants with variable (typically longer) chain length and variable cations. A suitable chain length may be, for example, C ₁₀ -C ₁₄ , for example C ₁₂ -C ₁₄ or C10-C12. Suitable cations include, for example, sodium, ammonium, magnesium or potassium. Examples of stable soaps include, for example, sodium laureth sulfate, potassium laureth sulfate, magnesium laureth sulfate, ammonium laureth sulfate, mixtures thereof, and any combination thereof. In some embodiments, any combination of stable and unstable soaps from these lists may be used.

[0060] Examples of combinations of blowing agents and their addition in the preparation of foamed gypsum products are disclosed in US Pat. No. 5,643,510, which is incorporated herein by reference. For example, a first blowing agent that produces a stable foam and a second blowing agent that produces an unstable foam may be combined. In some embodiments, the first blowing agent is a soap, for example, an alkoxylated alkyl sulfate soap with an alkyl chain length of 8-12 carbon atoms and an alkoxy group (eg, ethoxy) chain length of 1-4 units. The second blowing agent is optionally a non-alkoxylated (eg, non-ethoxylated) alkyl sulfate soap with an alkyl chain length of 6-20 carbon atoms, such as 6-18 or 6-16 carbon atoms. It is believed that adjusting appropriate amounts of these two soaps in accordance with some embodiments of the invention allows the structure of the foamed sheet to be controlled to achieve about 100% stable soap or about 100% unstable soap.

[0061] In some embodiments, the fatty alcohol may optionally be added along with a blowing agent, for example, to a foam premix. This can provide increased foam stability, allowing better control of the size and distribution of foam (air) bubbles. The fatty alcohol may be any suitable aliphatic fatty alcohol. It should be understood that, as defined throughout this document, "aliphatic" refers to alkyl, alkenyl, or alkynyl and may be substituted or unsubstituted, branched or unbranched, saturated or unsaturated, and, in relation to some embodiments of the invention, is designated by the indicated in this document, carbon chains, for example C _x -C _y , where x and y are integers. Thus, the term aliphatic also refers to chains with heteroatom substitution that retains the hydrophobicity of the group. The fatty alcohol may be a single compound or may be a combination of two or more compounds.

[0062] In some embodiments, the optional fatty alcohol is a _C6 - _C20 fatty alcohol (e.g., _C6 - _C18 , _C6 - _C16 , _C6 - _C14 , _C6 - _C12 , C ₆ -C ₁₀ , C ₆ -C ₈ , C ₈ -C ₁₆ , C ₈ -C ₁₄ , C ₈ -C ₁₂ , C ₈ -C ₁₀ , C ₁₀ -C ₁₆ , C ₁₀ -C ₁₄ , C ₁₀ -C ₁₂ , C ₁₂ -C ₁₆ , C ₁₂ -C ₁₄ or C ₁₄ -C ₁₆ -aliphatic fatty alcohol, etc.). Examples include octanol, nonanol, decanol, undecanol, dodecanol, or any combination thereof. A C ₁₀ -C ₂₀ fatty alcohol contains a linear or branched carbon C ₆ -C ₂₀ chain and at least one hydroxyl group. The hydroxyl group can be attached to any suitable position in the carbon chain, but preferably it is at or near any terminal carbon. In certain embodiments, the hydroxyl group may be attached at the α, β, or γ position of the carbon chain, for example, a _C6 - _C20 fatty alcohol may contain the following structural subunits: Thus, examples of target optional fatty alcohol in accordance with some embodiments of the invention include 1-dodecanol, 1-undecanol, 1-decanol, 1-nonanol, 1-octanol, or any combination thereof.

[0063] In some embodiments, the optional foam stabilizing agent contains a fatty alcohol and is substantially free of fatty acid alkylamides or carboxylic acid taurides. In some embodiments, the optional foam stabilizing agent is substantially free of glycol, although in some embodiments glycols may be introduced, for example, to provide a higher surfactant content. “Substantially free of any of the above ingredients” means that the foam stabilizing agent contains either (i) 0% wt. by weight of any of these ingredients, or (ii) an ineffective or (iii) insignificant amount of any of these ingredients. An example of an ineffective amount is an amount below the threshold for achieving the intended purpose of using any of these ingredients, as will be understood by one of ordinary skill in the art. The minor amount may be, for example, below about 0.0001% by weight, for example, below about 0.00005% by weight, below about 0.00001% by weight, below about 0.000001% by weight, etc. from the mass of plaster, which will be clear to the average person skilled in the art.

[0064] It has been found that suitable void distribution and wall thickness (independently) may be sufficient to improve strength, especially in lower density sheet (eg, lower than about 35 lb/ft2). See, for example, US 2007/0048490 and 2008/0090068. Evaporating water voids, typically having a diameter of about 5 µm or less, also contribute to the overall void distribution along with the aforementioned air (foam) voids. In some embodiments, the volume ratio of voids with a pore size greater than about 5 microns to voids with a pore size of about 5 microns or less is from about 0.5:1 to about 9:1, such as, for example, from about 0.7: 1 to about 9:1, about 0.8:1 to about 9:1, about 1.4:1 to about 9:1, about 1.8:1 to about 9:1, about 2, 3:1 to about 9:1, from about 0.7:1 to about 6:1, from about 1.4:1 to about 6:1, from about 1.8:1 to about 6:1, from about 0.7:1 to about 4:1, about 1.4:1 to about 4:1, about 1.8:1 to about 4:1, about 0.5:1 to about 2.3: 1, from about 0.7:1 to about 2.3:1, from about 0.8:1 to about 2.3:1, from about 1.4:1 to about 2.3:1, from about 1 .8:1 to about 2.3:1, etc.

[0065] In this context, void size is calculated based on the largest diameter of an individual void in the core. The largest diameter is the same as the Feret diameter. The largest diameter of each defined void can be obtained from an image of the sample. Images can be obtained using any suitable technique, such as scanning electron microscopy (SEM), which produces two-dimensional images. A large number of void sizes can be measured in an SEM image, so that the randomness of the cross sections (pores) of the voids can give an average diameter. Taking void measurements on multiple images randomly located throughout the sample core can improve this calculation. In addition, constructing a 3D stereological model of the core from multiple 2D SEM images can also improve void size calculations. Another technique is X-ray CT (X-ray CT) analysis, which produces a three-dimensional image. Another technique is optical microscopy, in which light contrast can help determine, for example, the depth of voids. Voids can be measured manually or using image analysis software such as ImageJ, developed by the NIH. One of ordinary skill in the art will appreciate that manually sizing voids and their distribution from images can be determined by visually observing the dimensions of each void. A sample can be obtained by cutting a plasterboard sheet.

[0066] The blowing agent may be added to the core suspension in any suitable amount, for example depending on the target density. In some embodiments, the blowing agent is present in the core sheet suspension, for example, in an amount of less than about 0.5% by weight of the stucco, namely, from about 0.01% to about 0.5%, from about 0. 01% to about 0.4%, from about 0.01% to about 0.3%, from about 0.01% to about 0.25%, from about 0.01% to about 0.2%, from about 0.01% to about 0.15%, from about 0.01% to about 0.1%, from about 0.02% to about 0.4%, from about 0.02% to about 0.3%, from about 0.02% to about 0.2%, etc., all based on the weight of the plaster. Because the concentrated layer has a higher density, the concentrated layer slurry can be prepared with less (or no) foam, for example, in an amount of from about 0.0001% to about 0.05% by weight of the stucco, e.g. about 0.0001% to about 0.025% by weight of stucco, from about 0.0001% to about 0.02% by weight of stucco, or from about 0.001% to about 0.015% by weight of stucco.

[0067] The fatty alcohol, if included, may be present in the core suspension in any suitable amount. In some embodiments, the fatty alcohol is present in the core slurry in an amount of from about 0.0001% to about 0.03% by weight of the stucco, for example, from about 0.0001% to about 0.025% by weight of the stucco, from about 0.0001% of about 0.02% by weight of stucco or from about 0.0001% to about 0.01% by weight of stucco. Since the concentrated layer suspension may contain less or no foam, no fatty alcohol is required in the concentrated layer or may be added in a smaller amount, namely from about 0.0001% to about 0.004% by weight of the stucco. for example, from about 0.00001% to about 0.003% by weight of stucco, from about 0.00001% to about 0.0015% by weight of stucco, or from about 0.00001% to about 0.001% by weight of stucco.

[0068] A strength enhancing agent as described herein may also optionally be included in the core sheet slurry. Other ingredients known in the art may also be included in the core leaf suspension, including, for example, accelerators, retarders, etc. Accelerators may be in various forms (eg, wet plaster accelerator, heat resistant accelerator, and weather stabilized accelerator). See, for example, US Pat. Nos. 3,573,947 and 6,409,825. In some embodiments in which an accelerator and/or retarder is added, each of the accelerator and/or retarder may be present in the core sheet stucco slurry in an amount on a dry basis a substance, for example, from about 0% to about 10% by weight of the stucco (for example, from about 0.1% to about 10%), such as, for example, from about 0% to about 5% by weight of the stucco (for example , from about 0.1% to about 5%).

[0069] Additionally, in some embodiments, the core sheet and/or concentrated layer may be further formed from at least one dispersant to enhance fluidity. Dispersants can be added to the stucco slurry in dry form along with other dry ingredients and/or in liquid form along with other liquid ingredients. Examples of dispersants include naphthalenesulfonates such as polynaphthalenesulfonic acid, its salts (polynaphthalenesulfonates) and derivatives, which are condensation products of naphthalenesulfonic acids and formaldehyde; as well as polycarboxylate dispersants, such as polycarboxylic ethers, for example dispersants of the type PCE211, PCE111, 1641, 1641F or PCE 2641, for example MELFLUX 2641F, MELFLUX 2651F, MELFLUX 1641F, MELFLUX 2500L (BASF) and COATEX Etha dispersants cryl M, available from Coatex, Inc.; and/or lignosulfonates or sulfonated lignin. Lignosulfonates are water-soluble anionic polyelectrolyte polymers, by-products of wood pulp production using sulfite pulping. One example of a lignin useful in the practice of the principles used in embodiments of the invention is Marasperse C-21, available from Reed Lignin Inc.

[0070] In general, lower molecular weight dispersants are preferred. With respect to naphthalene sulfonate dispersants, in some embodiments, they are selected to have a molecular weight of from about 3,000 to about 10,000 (eg, from about 8,000 to about 10,000). In some embodiments, naphthalene sulfonates with higher water requirements, such as those having a molecular weight greater than 10,000, may be used. As another illustration, for PCE211 type dispersants, in some embodiments, the molecular weight at which less retardation occurs than dispersants having molecular weight above 60,000 may range from about 20,000 to about 60,000.

[0071] One example of a naphthalene sulfonate is DILOFLO, available from GEO Specialty Chemicals. DILOFLO is a 45% solution of naphthalene sulfonate in water, although other aqueous solutions are also readily available, for example, ranging from about 35% to about 55% by weight solids. Naphthalene sulfonates can be used in dry solid or powder form, such as LOMAR D, available from GEO Specialty Chemicals. Another example of a naphthalene sulfonate is DAXAD, available from GEO Specialty Chemicals, Ambler, Pennsylvania.

[0072] The dispersant, if introduced, may be in any suitable amount. For example, in some embodiments, the dispersant may be present in the concentrated layer suspension in an amount, for example, from about 0.05% to about 0.5%, for example, from about 0.1% to about 0.2%, by weight of the stucco. , and may be present in the sheet core suspension in an amount, for example, from about 0% to about 0.7%, for example from 0% to about 0.4%, by weight of the stucco.

[0073] In some embodiments, the sheet core and/or concentrated layer may be further formed from at least one phosphate-containing compound if it is desired to improve wet strength, dimensional stability, and/or sag resistance. For example, phosphate-containing components useful in some embodiments of the invention include water-soluble components and may be in the form of an ion, salt or acid, namely, in the form of condensed phosphoric acids, each of which contains two or more phosphoric acid units; condensed phosphate salts or ions, each containing two or more phosphate units; and monobasic salts or monovalent orthophosphate ions, as well as in the form of a water-soluble acyclic polyphosphate salt. See, for example, US patents 6342284, 6632550, 6815049 and 6822033.

[0074] Phosphate compositions, when incorporated according to some embodiments of the invention, can improve wet strength, resistance to permanent deformation (eg, sagging), dimensional stability, etc. Wet strength refers to the strength of the sheet while it is still wet during production. Due to the stringent demands of the manufacturing process, without sufficient wet strength, the sheet blank may be damaged on the production line.

[0075] Trimetaphosphate compounds may be used, including, for example, sodium trimetaphosphate, potassium trimetaphosphate, lithium trimetaphosphate, and ammonium trimetaphosphate. Sodium trimetaphosphate (STP) is preferred, although other phosphates may be suitable, including, for example, sodium tetrametaphosphate, sodium hexametaphosphate containing from about 6 to about 27 repeating phosphate units and having the molecular formula _Nan + ₂ PnO _3n+1 where n=6-27; tetrapotassium pyrophosphate, having the molecular formula K ₄ R ₂ O ₇ ; trisodium dipotassium tripolyphosphate, having the molecular formula Na ₃ K ₂ P ₃ O ₁₀ ; sodium tripolyphosphate, having the molecular formula Na ₅ P ₃ O ₁₀ ; tetrasodium pyrophosphate, having the molecular formula Na ₄ P ₂ O ₇ ; aluminum trimetaphosphate having the molecular formula A1(PO ₃ ) ₃ ; sodium acid pyrophosphate having the molecular formula Na ₂ H ₂ P ₂ O ₇ ; ammonium polyphosphate containing 1000-3000 repeating phosphate units and having the molecular formula (NH ₄ ) _n+2 P _n O _3n+1 , where n=1000-3000; or a polyphosphoric acid containing two or more repeating phosphoric acid units and having the molecular formula H _n+2 P _n O _3n+1 where n is two or more.

[0076] The polyphosphate, if administered, may be in any suitable amount. By way of illustration, in some embodiments, the polyphosphate may be present in the concentrated layer suspension in an amount, for example, from about 0.1% to about 1%, for example, from about 0.2% to about 0.4%, by weight of the stucco, and present in the sheet core suspension in an amount, for example, from about 0% to about 0.5%, for example, from about 0% to about 0.2%, by weight of the stucco. Thus, the dispersant and polyphosphate may optionally be present in any suitable amount in the core slurry and/or concentrated layer slurry, such that in some embodiments, the core slurry contains a higher weight percentage of dispersant and/or polyphosphate than the concentrated layer slurry. In alternative embodiments, the dispersant and/or polyphosphate is added to the concentrated layer slurry at a higher weight percentage than the core slurry (including core slurries with zero dispersant and/or polyphosphate) (without or with a higher concentration of enhancer in the concentrated layer ).

[0077] The core sheet may have any suitable density useful for contributing to the target overall density of the composite sheet, such as, for example, a core density of about 16 lb/cu.m. ft (about 260 kg/m ³ ) to about 40 lb/cu. ft., for example, from about 18 lb/cu.m. ft. to about 40 lb/cu.m. ft., from 18 lb/cu.m. ft. to about 38 lb/cu.m. ft., from 18 lb/cu.m. ft. to about 36 lb/cu.m. ft., from 18 lb/cu.m. ft. to about 32 lb/cu.m. ft., from 20 lbs/cu.m. ft. to about 40 lb/cu.m. ft., from 20 lbs/cu.m. ft. to about 36 lb/cu.m. ft., from 20 lbs/cu.m. ft. to about 32 lb/cu.m. ft., from 22 lbs/cu.m. ft. to about 40 lb/cu.m. ft., from 22 lbs/cu.m. ft. to about 36 lb/cu.m. ft., from 22 lbs/cu.m. ft. to about 32 lb/cu.m. ft., from 26 lbs/cu.m. ft. to about 40 lb/cu.m. ft., from 26 lbs/cu.m. ft. to about 36 lb/cu.m. ft or from 26 lbs/cu.m. ft to 32 about lb/cu. foot. In some embodiments, the core sheet has an even lower density, for example, about 30 lbs/cu. ft. or less, about 29 lb/cu.m. ft (about 460 kg/m ³ ) or less, about 28 lb/cu. ft. or less, about 27 lb/cu. ft (about 430 kg/m ³ ) or less, about 26 lb/cu. foot or less, etc. For example, in some embodiments, the core density is from about 12 lb/cu. ft (about 190 kg/m ³ ) to about 30 lb/cu. ft., from about 14 lb/cu.m. ft (about 220 kg/m ³ ) to about 30 lb/cu. ft., from 16 lbs/cu.m. ft. to about 30 lb/cu.m. ft., from 16 lbs/cu.m. ft. to about 28 lb/cu.m. ft., from 16 lbs/cu.m. ft. to about 26 lb/cu.m. ft., from 16 lbs/cu.m. ft. to about 22 lb/cu.m. ft (about 350 kg/m ³ ), from 18 lbs/cu.m. ft. to about 30 lb/cu.m. ft., from 18 lb/cu.m. ft. to about 28 lb/cu.m. ft., from 18 lb/cu.m. ft. to about 26 lb/cu.m. ft., from 18 lb/cu.m. ft. to about 24 lb/cu.m. ft., from 20 lbs/cu.m. ft. to about 28 lb/cu.m. ft., from 20 lb/cu.m. ft. to about 26 lb/cu.m. ft., from 20 lb/cu.m. ft. to about 24 lb/cu.m. ft., from 22 lbs/cu.m. ft. to 28 lb/cu.m. ft etc.

Concentrated layer

[0078] A concentrated layer is "concentrated" in some embodiments due to the higher density and/or the presence of an enhancement additive in the concentrated layer suspension in an amount that is more concentrated than the amount by weight, if any, of the same enhancement additive in a suspension of the leaf core. In some embodiments, the concentrated layer has a density at least about 1.1 times the density of the core sheet, and/or has a significant thickness, such as at least about 0.02 inches (about 0.05 cm).

[0079] The concentrated layer is formed from a slurry containing water and a binder material, such as stucco, which hydrates to form a set hydrated material, such as a continuous crystalline matrix of set gypsum, in the final product. In preferred embodiments of the invention, the binder material is stucco and the slurry for forming the concentrated layer is a slurry of stucco. As noted, the concentrated layer forming slurry further contains an improvement additive at a higher relative mass concentration than the concentration of the improvement additive in the core sheet forming suspension. The concentrate layer slurry may optionally contain a blowing agent or other lightweight agent as described herein to achieve the target density of the concentrated layer.

In some embodiments, the blowing agent or other lightweight agent, if introduced, will be present in a smaller amount in suspension to form a concentrated layer; or the blowing agent may be "knocked out" at least to some extent to reduce the number of voids in the foam, as is known in the art, to achieve a target density higher than that of the core sheet. Thus, forming a concentrated layer at a target density using an effective (or zero) amount of a blowing agent or other lightweight agent can be achieved, as described herein, by one of ordinary skill in the art. Other ingredients, such as an accelerator and retarder, may be added to the concentrated layer if necessary, as described herein.

[0080] Fibers may be further incorporated into the concentrated layer as an optional additive to improve the gypsum board manufacturing process. In this regard, as explained herein, a concentrated layer of slurry can be applied to the paper, for example, at high speed and using a roller or other distribution means that forms a head of slurry that accumulates in front of the roller before it is evenly applied to the paper after the roll (and whereby the sheet edges are typically formed from a concentrated layer of slurry around the ends of the roll). The environment in which the concentrated layer is applied is non-stationary with three-dimensional fluctuations, which leads to the formation of undulating irregularities in the suspension, which can result in relatively large entrainment of air, which can lead to the formation of a rough, uneven suspension, which can lead to defects in the sheet, if this problem is not solved. Such defects may include the formation of large air pockets called voids or bubbles, as well as paper peeling, soft and/or hard edges, etc.

[0081] There are various mechanical and other treatment methods available to address the problem of ripples in the flow caused by unstable process environments, including the use of mechanical air pocket breaking parts known in the art, such as line vibrators, as well as slurry sprayer, various means for emptying the mixer, and adjustments to the formulation including water/plaster ratio, slurry viscosity, etc. However, as described in US Application No. 15/186,176, incorporated herein by reference, one method is to add fiber to a concentrated layer slurry, for example, in the die region where the concentrated layer is applied (preferably, for example, before the roll), as a means of producing a smoother suspension with less undulation and fewer air pockets. Without wishing to be bound by any particular theory, it is believed that the fibers successfully improve the rheology of the suspension to ensure smoother flow. The fibers are also believed to improve the hydrodynamic properties of the suspension so that the viscosity, rheology and force balance between the particles of the suspension are improved, the suspension is more evenly distributed on the application roll, and unwanted entrained air is more easily released from the suspension.

[0082] It should be understood that fiber such as fiberglass is not required in the concentrated layer. Defects, including bubbles, voids, peeling, poor edges, etc., can be controlled by other means, including a variety of mechanical or other means well known in the art. For example, mechanical vibrators can be used under the conveyor to remove large air pockets in the slurry. Additionally, other means of mechanically adjusting or changing other operating characteristics are understood, including the use of slurry spreaders, slurry distributors, pressure controls and adjustments to mixer emptying, line speed, formulation viscosity, etc. These examples of mechanical and other techniques can be used alone or in combination with glass to obtain acceptable results.

[0083] The fibers can be in the form of any suitable fibers. In some embodiments, the fibers may be in the form of one or more of glass fibers, mineral fibers, carbon fibers, paper fibers, and blends of such fibers, as well as other comparable fibers that provide comparable benefits to the process and/or end product. In some embodiments, glass fibers are included in the concentrated layer suspension and the resulting crystalline core structure. Fiberglass is preferred because it does not absorb water.

[0084] For certain fibers, such as glass fiber, it may be useful in some embodiments to optionally treat the fibers with a sizing agent to improve their properties and processing. For example, sizing agents can allow individual fibers to be sized, for example, to change the coating and surface properties, and these typically can be in the form of one or more of organosilanes, shaping agents, surfactants, defoamers, lubricants and/ or stabilizers. One of ordinary skill in the art will appreciate that the precise selection of each ingredient may vary depending on the properties of the fiber and the intended application. For example, the silanes can be, for example, amine-based, such as, for example, aminopropyltriethoxysilane or aminoethylaminopropyltrimethoxysilane, vinyl-based, such as, for example, vinyltrimethoxysilane or vinyltriacetoxysilane, alkyl-based, such as methyltrimethoxysilane or methyltriethanol, or a combination thereof.

[0085] Forming agents are often polymers and can be hydrophobic to provide targeted wetting characteristics and damage protection between fibers. Shaping agents may be in the form of, for example, polyurethanes, polyvinyl acetates, polyesters, polyalkenes and epoxy resins. Optionally, cationic lubricants may be added, which may be in the form of aliphatic ethanolamides, such as stearic ethanolamide or polyethyleneimine polyamides, alkyl amidoalkyl sultaines or polyethylene oxide, or any combination thereof. Surfactants may optionally be added to emulsify the forming agent, for example when the forming agent is hydrophobic. In some embodiments, the surfactant, if introduced, is nonionic or weakly cationic and may be in the amide form or other suitable form, for example, polyoxyethylene glycol alkyl ethers, polyethylene glycol-polypropylene glycol copolymers, cocamide monoethanolamine, or any combination thereof. Defoamers can be beneficial because they control foaming with the fiberglass, and any suitable defoamer can be used. For example, suitable defoamers may be siloxane, oil or polymer based, such as, but not limited to, mineral oil, waxes, ethylene bis-stearamide, silicone oil, polyethylene glycol-polypropylene glycol copolymer defoamers, or any combination thereof. Stabilizers provide the benefit of stabilizing the sizing agent formulation, and any suitable stabilizer can be used. In some embodiments, an additive such as a lubricant provides a positive surface charge, which is believed to further improve the flow of the suspension.

[0086] A sizing agent, if included, may be added to the suspension to form a concentrated layer in any suitable amount. For example, the sizing agent may be present in an amount of about 0.02% wt. up to about 2% wt. fibers, for example, from about 0.05% wt. up to about 1% wt. or from about 0.1% wt. up to about 1.5% wt. fibers With respect to the weight percentages of the ingredients provided herein, relative to either the core sheet suspension or the concentrated layer suspension, in some embodiments, the concentrated layer and/or core sheet in the final sheet may contain the specified ingredient in an amount within the specified ranges . [0087] The fibers (eg, glass fibers) can be of any suitable length. For example, in some embodiments, the fibers may have an average length of from about 0.125 inch to about 1 inch, such as from about 0.125 inch to about 0.75 inch. .9 cm), about 0.125 inch to about 0.5 inch (about 1.3 cm), about 0.125 inch to about 0.375 inch (about 1 cm), about 0.125 inch to about 0.25 inch (about 0 .6 cm), about 0.25 inch to about 1 inch, about 0.25 inch to about 0.75 inch, about 0.25 inch to about 0.5 inch, about 0.25 inch to about 0.375 inch, from about 0.375 inch to about 1 inch, from about 0.375 inch to about 0.75 inch, from about 0.375 inch to about 0.5 inch, from about 0.5 inch to about 1 inch, from about 0.5 inch to about 0.75 inch or from about 0.75 inch to about 1 inch.

[0088] The fibers (eg, glass fibers) may have any suitable average diameter. For example, in some embodiments, the fibers may have an average diameter of from about 5 microns to about 20 microns, from about 10 microns to about 15 microns, from about 10 microns to about 20 microns, from about 8 microns to about 18 microns, from about 5 microns to about 25 microns, from about 9 microns to about 20 microns, from about 10 microns to about 18 microns, from about 7 microns to about 18 microns, from about 10 microns to about 25 microns, diameter from about 11 to about 17 micron or diameter from about 15 microns to about 17 microns.

[0089] In some embodiments, such glass fibers may have an average length of from about 0.5 to about 0.675 inches (about 1.7 cm) and a diameter of from about 13 to about 16 microns, an average length of from about 0.5 to about 0 .75 inches and a diameter of about 11 to about 17 microns, or an average fiber length of 0.5 inches and an average diameter of about 15.24 microns to about 16.51 microns.

[0090] Fiber shape factor refers to the length divided by the diameter, and in practice is believed to influence the flow characteristics of the slurry. To harmonize units, lengths in inches can be converted to microns so that the values are dimensionless. In some embodiments, the preferred aspect ratio is from about 200 to about 2000, such as from about 400 to about 1300, such as from about 800 to about 1500, from about 250 to about 1000, from about 500 to about 1500, or from about 700 to about 1600, from about 800 to about 1400.

[0091] Fibers, such as glass fibers, if included, are in suspension to form the concentrated layer in any suitable amount, for example, from about 0.1% to about 3%, for example, from about 0.13% to about 2. 5% or from about 0.5% to about 1% by weight of the stucco, and are present in the core of the sheet in any suitable amount, for example, from about 0% to about 1%, for example, from 0% to about 0.5% from the mass of plaster. If desired, fiber (and the aforementioned related additives such as sizing agent, etc.) may also be incorporated into the core in any suitable amount, such as these listed weight percentages.

[0092] It is desirable that the concentrated layer has a significant thickness. In some embodiments, the concentrated layer has a dry thickness of at least about 0.02 inches (about 0.05 cm), such as about 0.02 inches to about 0.2 inches (about 0.5 cm). cm). For example, in various embodiments of the invention, the concentrated layer has a significant thickness with a minimum thickness of at least about 0.025 inches (about 0.06 cm), at least about 0.03 inches (about 0.075 cm), at least about 0.035 inches ( about 0.09 cm), at least about 0.04 inch (about 0.1 cm), at least about 0.045 inch (about 0.11 cm), at least about 0.05 inch (about 0.13 cm) cm), at least about 0.055 inch (about 0.14 cm), at least about 0.06 inch (about 0.15 cm), at least about 0.065 inch (about 0.17 cm), at least about 0.07 inch (about 0.18 cm), at least about 0.075 inch (about 0.19 cm), at least about 0.08 inch (about 0.2 cm), at least about 0.085 inch ( about 0.22 cm), at least about 0.09 inch (about 0.23 cm), at least about 0.095 inch (about 0.24 cm), at least about 0.1 inch (about 0.254 cm) at least about 0.11 inches (about 0.28 cm), at least about 0.12 inches (about 0.3 cm), at least about 0.13 inches (about 0.33 cm), according to at least about 0.14 inches (about 0.36 cm), at least about 0.15 inches (about 0.38 cm), or at least about 0.16 inches (about 0.41 cm); wherein each of these ranges has a suitable, mathematically acceptable upper limit, such as, for example, about 0.2 inches, about 0.185 inches (about 0.47 cm), about 0.175 inches (about 0.45 cm), about 0. 16 inches, about 0.15 inches (about 0.38 cm), about 0.145 inches (about 0.37 cm), about 0.13 inches, about 0.12 inches (about 0.3 cm), 0.1 inches , about 0.09 inch (0.23 cm), about 0.08 inch, about 0.07 inch, about 0.06 inch, about 0.055 inch, about 0.05 inch, about 0.045 inch, about 0.04 inch , about 0.035 inches, etc.

[0093] By way of illustration, and not limitation, the concentrated layer in a dry state may have a thickness of from about 0.02 inch to about 0.175 inch, such as from about 0.02 inch to about 0.15 inch, from about 0. 02 inches to about 0.12 inches, from about 0.02 inches to about 0.1 inches, from about 0.02 inches to about 0.08 inches, from about 0.02 inches to about 0.055 inches, from about 0. 02 inches to about 0.05 inches, from about 0.02 inches to about 0.04 inches, from about 0.02 inches to about 0.03 inches, from about 0.03 inches to about 0.2 inches, from about 0.03 inch to about 0.175 inch, about 0.03 inch to about 0.15 inch, about 0.03 inch to about 0.12 inch, about 0.03 inch to about 0.1 inch, about 0.03 inch to about 0.08 inch, about 0.03 inch to about 0.055 inch, about 0.03 inch to about 0.05 inch, about 0.04 inch to about 0.2 inch, about 0.04 inch to about 0.175 inch, about 0.04 inch to about 0.15 inch, about 0.04 inch to about 0.12 inch, about 0.04 inch to about 0.1 inch, about 0.04 inch to about 0.08 inch, about 0.04 inch to about 0.055 inch, about 0.04 inch to about 0.05 inch, about 0.05 inch to about 0.2 inch, about 0.05 inch to about 0.175 inch, about 0.05 inch to about 0.15 inch, about 0.05 inch to about 0.12 inch, about 0.05 inch to about 0.1 inch, about 0.05 inch to about 0.8 inch, about 0.06 inch to about 0.2 inch, about 0.06 inch to about 0.175 inch, about 0.06 inch to about 0.15 inch, about 0.06 inch to about 0.12 inch, about 0.06 inch to about 0.1 inch, about 0.06 inch to about 0.8 inch, etc.

[0094] The concentrated layer preferably has a higher dry density than the sheet core density and/or dry strength. For example, in some embodiments, the concentrated layer has a density that is at least about 1.1 times the density of the core sheet, such as at least about 1.2 times, at least about 1.3 times, at least about 1.4 times greater, at least about 1.5 times greater, at least about 1.6 times greater, at least about 1.7 times greater, at least about 1.8 times greater times larger, at least about 1.9 times larger, at least about 2 times larger, etc., each of these ranges having a suitable, mathematically acceptable upper limit, such as, for example, about 3 times larger , about 2.9 times more, about 2.8 times more, about 2.7 times more, about 2.6 times more, about 2.5 times more, about 2.4 times more, about 2 ,3 times more, about 2.2 times more, about 2.1 times, about 2 times, about 1.9 times more, about 1.8 times more, about 1.7 times, about 1 .6 times more, about 1.5 times more, about 1.4 times more, about 1.3 times more and about 1.2 times more.

[0095] Thus, for example, the concentrated layer may have a dry density that is from about 1.1 to about 3 times the density of the core sheet, for example, from about 1.1 to about 3 times, from about 1.1 to about 2.7 times, from about 1.1 to about 2.5 times, from about 1.1 to about 2.2 times, from about 1.1 to about 2 times, from about 1.1 to about 1, 7 times, about 1.1 to about 1.5 times, about 1.1 to about 1.4 times, about 1.1 to about 1.3 times, about 1.2 to about 3 times, from about 1.2 to about 2.5 times, about 1.2 to about 2.2 times, about 1.2 to about 2 times, about 1.2 to about 1.7 times, about 1.2 to about 1.5 times from about 1.2 to about 1.4 times, from about 1.2 to about 1.3 times, from about 1.3 to about 3 times, from about 1.3 to about 2.5 times, from about 1.3 to about 2 times, from about 1.3 to about 1.7 times, from about 1.3 to about 1.5 times, from about 1.3 to about 1.4 times, from about 1.4 to about 3 times, about 1.4 to about 2.5 times, about 1.4 to about 2.5 times, about 1.4 to about 2 times, about 1.4 to about 1.7 times, from about 1.4 to about 1.6 times, from about 1.4 to about 1.5 times, from about 1.5 to about 3 times, from about 1.5 to about 2.5 times, from about 1, 5 to about 2 times, about 1.5 to about 1.8 times, about 1.5 to about 1.7 times, about 1.5 to about 1.6 times, about 1.6 to about 3 times, from about 1.6 to about 2.5 times, from about 1.6 to about 2 times, from about 1.1 to about 1.8 times, from about 1.7 to about 3 times, from about 1, 7 to about 2.5 times, from about 1.7 to about 2.2 times, from about 1.7 to about 2 times, from about 1.7 to about 1.9 times, from about 1.8 to about 3 times, from about 1.8 to about 2.7 times, from about 1.8 to about 2.5 times, from about 1.8 to about 2.2 times, from about 1.8 to about 2 times, from about 1, 9 to about 3 times, about 1.9 to about 2.7 times, about 1.9 to about 2.5 times, about 1.9 to about 2.2 times, about 2 to about 3 times and etc.

[0096] The composite gypsum board may be formulated to exhibit any suitable dry density difference between the concentrated layer and the core of the sheet. In some embodiments, the difference in density between the concentrated layer and the core sheet may be at least about 8 lb/cu. ft (about 130 kg/m ³ ). For example, in some embodiments, the difference in dry density between the concentrated layer and the tie layer may be at least about 10 lbs/cu. ft., at least about 12 lb/cu.m. ft., at least about 14 lb/cu.m. ft., at least about 16 lb/cu.m. ft., at least about 18 lb/cu.m. ft., at least about 20 lb/cu.m. ft etc. In some embodiments, the difference in density between the concentrated layer and the board core ranges from about 8 lb/cu. ft. to about 50 lb/cu.m. ft., for example from about 8 lbs./cu.m. ft. to about 45 lb/cu.m. ft (about 720 kg/m ³ ), from about 8 lbs/cu. ft. to about 40 lb/cu.m. ft., from about 8 lbs./cu.m. ft. to about 35 lb/cu.m. ft., from 8 lbs./cu.m. ft. to about 30 lb/cu.m. ft., from about 8 lbs./cu.m. ft. to about 25 lb/cu.m. ft (about 400 kg/m ³ ), from about 8 lbs/cu.m. ft. to about 20 lb/cu.m. ft., about 8 lbs/cu. ft. to about 15 lb/cu.m. ft (about 240 kg/m ³ ), from about 8 lbs/cu.m. ft to about 12 lb/cu. ft., from about 10 lbs./cu.m. ft (about 160 kg/m ³ ) to about 50 lb/cu. ft., from about 10 lbs./cu.m. ft. to about 45 lb/cu.m. ft., from about 10 lbs./cu.m. ft. to about 40 lb/cu.m. ft., from about 10 lbs./cu.m. ft. to about 35 lb/cu.m. ft., from about 10 lbs./cu.m. ft. to about 30 lb/cu.m. ft., from about 10 lbs./cu.m. ft. to about 25 lb/cu.m. ft., from about 10 lbs./cu.m. ft. to about 20 lb/cu.m. ft., from about 10 lbs./cu.m. ft. to about 15 lb/cu.m. ft., from about 15 lb/cu.m. ft. to about 50 lb/cu.m. ft (about 800 kg/m ³ ), from about 15 lbs/cu.m. ft. to about 45 lb/cu.m. ft., from about 15 lb/cu.m. ft. to about 40 lb/cu.m. ft., from about 15 lb/cu.m. ft. to about 35 lb/cu.m. ft., from about 15 lb/cu.m. ft. to about 30 lb/cu.m. ft., from about 15 lb/cu.m. ft. to about 25 lb/cu.m. ft., from about 15 lb/cu.m. ft. to about 20 lb/cu.m. ft., from about 20 lb/cu.m. ft. to about 50 lb/cu.m. ft., from about 20 lb/cu.m. ft. to about 45 lb/cu.m. ft., from about 20 lb/cu.m. ft. to about 40 lb/cu.m. ft., from about 20 lb/cu.m. ft. to about 35 lb/cu.m. ft., from about 20 lb/cu.m. ft. to about 30 lb/cu.m. ft., from about 20 lb/cu.m. ft. to about 25 lb/cu.m. ft., from about 25 lbs./cu.m. ft. to about 35 lb/cu.m. ft., from about 25 lbs./cu.m. ft. to about 30 lb/cu.m. ft etc.

[0097] The concentrated layer may have any suitable dry density to meet the objectives of the embodiments described herein. In some embodiments, the concentrated layer has a dry density of about 28 lb/cu ft to about 70 lb/cu ft (about 1120 kg/m ³ ), namely, from about 28 lb/cu ft to about 65 lb/cu.ft. (about 1040 kg/m ³ ), from about 28 lb./cu.ft. to about 60 lb./cu.ft. ft (about 960 kg/m ³ ), from about 28 lbs/cu. ft. to about 55 lb/cu.m. ft (about 880 kg/m ³ ), from about 28 lbs/cu. ft. to about 50 lb/cu.m. ft., from about 28 lb/cu.m. ft. to about 45 lb/cu.m. ft., from about 28 lb/cu.m. ft. to about 40 lb/cu.m. ft., from about 28 lb/cu.m. ft. to about 35 lb/cu.m. ft., from about 34 lb/cu.m. ft. to about 70 lb/cu.m. ft., from about 34 lb/cu.m. ft. to about 65 lb/cu.m. ft., from about 34 lb/cu.m. ft. to about 60 lb/cu.m. ft., from about 34 lb/cu.m. ft. to about 55 lb/cu.m. ft., from about 34 lb/cu.m. ft. to about 50 lb/cu.m. ft., from about 34 lb/cu.m. ft. to about 45 lb/cu.m. ft., from about 34 lb/cu.m. ft. to about 40 lb/cu.m. ft., from about 38 lb/cu.m. ft. to about 70 lb/cu.m. ft., from about 38 lb/cu.m. ft. to about 65 lb/cu.m. ft., from about 38 lb/cu.m. ft. to about 60 lb/cu.m. ft., from about 38 lb/cu.m. ft. to about 55 lb/cu.m. ft., from about 38 lb/cu.m. ft. to about 50 lb/cu.m. ft., from about 38 lb/cu.m. ft. to about 45 lb/cu.m. ft., from about 40 lb/cu.m. ft. to about 70 lb/cu.m. ft., from about 40 lb/cu.m. ft. to about 65 lb/cu.m. ft., from about 40 lb/cu.m. ft. to about 60 lb/cu.m. ft., from about 40 lb/cu.m. ft. to about 55 lb/cu.m. ft., from about 40 lb/cu.m. ft. to about 50 lb/cu.m. ft., from about 40 lb/cu.m. ft. to about 45 lb/cu.m. ft or from about 36 lb/cu.m. ft. to about 38 lb/cu.m. foot.

[0098] The concentrated layer typically has a dry stiffness value greater than the dry stiffness value of the core sheet. As noted earlier in this paper, Young's modulus of elasticity can be used as a measure of dry stiffness. In some embodiments, the concentrated layer in the dry state has a Young's modulus of at least about 1.5 times the Young's modulus of the leaf core, such as 2 times the Young's modulus of the leaf core, such as, for example, about 2 times to about 10 times, from about 2 times to about 8 times, from about 2 times to about 6 times, from about 2 times to about 4 times, from about 3 times to about 10 times, from about 3 times to about 8 times, from about 3 times to about 6 times, from about 3 times to about 5 times, from about 4 times to about 10 times, from about 4 times to about 8 times, from about 4 times to about 6 times, from about 5 times to about 10 times, from about 5 times to about 8 times, from about 6 times to about 10 times, from about 6 times to about 8 times, etc. In some embodiments, the concentrated layer has a stiffness value that is closer to the stiffness value of the top and/or bottom cover sheet than to the stiffness of the core sheet when each stiffness value is measured by Young's modulus. In some embodiments, the concentrated layer has a Young's modulus of stiffness that is from about 0.1 to about 0.5 Young's modulus for at least one of the cover sheets.

Cover sheets

[0099] The cover sheets can be of any suitable shape. It should be understood that, with respect to cover sheets, the terms "front" and "top" sheet are used interchangeably herein, while the terms "back" and "bottom" are likewise used interchangeably herein. For example, the cover sheets may contain cellulose fibers, glass fibers, ceramic fibers, mineral wool, or a combination of the above materials. One or both sheets may consist of single sheets or multiple sheets. In preferred embodiments of the invention, the cover sheets contain cellulose fiber. For example, a sheet of paper such as manila paper or kraft paper can be used as the back sheet. Suitable papers for the cover sheet include 7-ply Manila and 3-ply News-Line, or 7-ply paper available from United States Gypsum Corporation, Chicago, IL; 3-ply Gray-Back and 3-ply Manila Ivory, available from International Paper, Newport, Indiana; and heavyweight Manila paper and MH Manila HT (high strength) paper available from United States Gypsum Corporation, Chicago, IL. A typical cover sheet paper is 5-ply NewsLine. In some embodiments, the backsheet may optionally include perforations, such as pin holes. Such perforations facilitate oven drying by allowing the steam generated during the heating process to escape.

[0100] In addition, paper (eg, cellulose) may contain any other material or combination of materials. For example, one or both sheets, particularly the front (top) sheet, may contain polyvinyl alcohol, boric acid, or a polyphosphate as described herein (eg, sodium trimetaphosphate) to improve the strength of the paper. In some embodiments, the paper may be contacted with a solution of one or more of polyvinyl alcohol, boric acid, and/or polyphosphate such that the paper is at least partially wetted. In some embodiments, the paper may be at least partially saturated. In some embodiments, polyvinyl alcohol, boric acid, and/or polyphosphate can penetrate the fibers of the paper. The solution of polyvinyl alcohol, boric acid and/or polyphosphate may be in any suitable amount and may be applied in any suitable manner as will be understood in the art. For example, the solution may be about 1% to about 5% by weight solids of each ingredient in water selected from polyvinyl alcohol, boric acid and/or polyphosphate, which may be added in one solution or, if necessary, in multiple solutions .

[0101] In some embodiments, one or both sheets may contain fiberglass, ceramic fiber, mineral wool, or a combination of the above materials. One or both of the sheets of this disclosure may be generally hydrophilic, which means that the sheet is at least partially capable of adsorbing water molecules to the surface of the sheet and/or absorbing water molecules into the middle of the sheet.

[0102] In other embodiments, the cover sheets may be "substantially free" of glass fibers, ceramic fibers, mineral wool, or mixtures thereof, meaning that the cover sheets contain either (i) 0% by weight. by weight of the sheet, or not contain such glass fibers, ceramic fibers, mineral wool or a mixture thereof, or (ii) an ineffective, or (iii) insignificant amount of glass fibers, ceramic fibers, mineral wool or a mixture thereof. An example of an ineffective amount is an amount below the threshold for achieving the intended purpose of using fiberglass, ceramic fibers, mineral wool, or a mixture thereof, as would be understood by one of ordinary skill in the art. The minor amount may be, for example, below about 5% by weight, for example, below about 2% by weight, below about 1% by weight, below about 0.5% by weight, below about 0.2% by weight, below about 0.1% by weight or less than about 0.01% by weight of the stucco, as would be apparent to one of ordinary skill in the art. However, if desired in alternative embodiments of the invention, such ingredients may be included in the coating sheets.

[0103] In some embodiments, the thermal conductivity of the top and/or bottom sheet is less than about 0.1 V/(mK). For example, the thermal conductivity of the top and/or bottom sheet is less than about 0.05 W/(mK).

[0104] Optionally, in some embodiments of the invention, one or both of the cover sheets may optionally contain any suitable amount of an inorganic compound or mixture of inorganic compounds that suitably imparts greater fire resistance if such properties are desired. Examples of suitable inorganic compounds include aluminum trihydrate and magnesium hydroxide. For example, the cover sheets may contain any inorganic compound or mixture of inorganic compounds with a high content of water of crystallization, or any compound that releases water when heated. In some embodiments, the amount of the inorganic compound or the entire mixture of inorganic compounds in the sheet is in the range from about 0.1% to about 30% by weight of the sheet. The inorganic compound or inorganic compounds used in the sheet may have any suitable particle size or suitable particle size distribution.

[0105] Aluminum trihydrate (TGA), also known as alumina trihydrate and hydrated alumina, can improve fire resistance due to its water of crystallization or constitutional water content. In some embodiments, TGA can be added in an amount of from about 5% to about 30% of the total weight of the sheet. TGA is generally very stable at room temperature. At temperatures above about 180°C to 205°C, TGA typically undergoes endothermic decomposition, releasing water vapor. The heat of decomposition of such TGA additives exceeds about 1000 J/gram, and in one embodiment of the invention - about 1170 J/gram. Without being limited by theory, it is believed that the TGA additive decomposes when heated above 205°C, releasing about 35% of the water of crystallization in the form of water vapor in accordance with the following equation: A1(OH) ₃ →Al ₂ O ₃ +3H ₂ O.

[0106] A cover sheet containing inorganic particles with a high water content, such as TGA, can improve the fire resistance of the composite sheet. In some embodiments, an inorganic compound or mixture of compounds is incorporated into the sheet. A covering sheet, such as TGA containing paper, can be prepared by first diluting cellulose fiber in water to a consistency of about 1%, and then mixing with TGA particles in a specified ratio. The mixture can be poured into a mold, which may have a wire mesh at the bottom to drain the water. After draining, the TGA fibers and particles remain on the wire. The wet sheet can be transferred to blotting paper and dried at a temperature of about 200 to 360°F. [0107] In some embodiments involving incorporation into a cover sheet or stucco slurry, for example, TGA particles smaller than about 20 microns are preferred, but any suitable source or grade of TGA can be used. For example, TGA can be obtained from commercial suppliers such as Huber under the brand names SB 432 (10 µm) or Hydral® 710 (1 µm).

[0108] In some embodiments, the cover sheet may contain magnesium hydroxide. In these embodiments, the magnesium hydroxide additive preferably has a heat of decomposition greater than about 1000 J/gram, namely about 1350 J/gram, at a temperature of 180°C to 205°C or higher. In such embodiments, any suitable magnesium hydroxide may be used, for example, commercially available from suppliers including Akrochem Corp., Akron, Ohio.

[0109] In other embodiments, the cover sheets may be "substantially free" of inorganic compounds such as TGA, magnesium hydroxide, or mixtures thereof, meaning that the cover sheets contain either (i) 0% by weight of the sheet or not contain inorganic compounds such as TGA, magnesium hydroxide or mixtures thereof, or (ii) an ineffective or (iii) insignificant amount of inorganic compounds such as TGA, magnesium hydroxide or a mixture thereof. An example of an ineffective amount is an amount below the threshold amount to achieve the intended purpose of using inorganic compounds such as TGA, magnesium hydroxide, or mixtures thereof, as will be understood by one of ordinary skill in the art. The minor amount may be, for example, below about 5% by weight, for example, below about 2% by weight, below about 1% by weight, below about 0.5% by weight, below about 0.1% by weight, below about 0.05% wt., below about 0.01% wt. etc.

[0110] The cover sheets may also have any suitable overall thickness. In some embodiments, at least one of the cover sheets has a relatively thick thickness, such as at least about 0.014 inches thick. In some embodiments, it is preferred that the thickness be even greater, for example, at least about 0.015 inch, at least about 0.016 inch, at least about 0.017 inch, at least about 0.018 inch, at least about 0.019 inch, at least about 0.020 inch, at least about 0.021 inch, at least about 0.022 inch, or at least about 0.023 inch. Any suitable upper limit for these ranges may be adopted, for example, an upper range limit of about 0.030 inch, about 0.027 inch, about 0.025 inch, about 0.024 inch, about 0.023 inch, about 0.022 inch, about 0.021 inch, about 0.020 inch, about 0.019 inch, about 0.018 inch, etc. The total sheet thickness refers to the sum of the thicknesses of each sheet attached to the gypsum sheet.

[0111] The cover sheets can be of any suitable density. In some embodiments, at least one of the cover sheets, such as the top (face) cover sheet, has a density that is equal to or greater than the density of the concentrated layer. For example, in some embodiments of the invention, at least one or both cover sheets have a density of at least about 36 lbs/cu. ft., for example, from about 36 lb/cu.m. ft. to about 46 lb/cu.m. ft., from about 36 lb/cu.m. ft. to about 44 lb/cu.m. ft., from about 36 lb/cu.m. ft. to about 42 lb/cu.ft., from about 36 lb./cu.ft. ft. to about 40 lb/cu.m. ft., about 38 lb/cu.ft. to about 46 lb./cu.ft., about 38 lb./cu.ft. to about 44 lb./cu.ft., about 38 lb./cu.ft. to about 42 lb./cu.ft. .ft etc.

[0112] The cover sheet may be of any suitable weight. For example, in some embodiments, cover sheets with a lower basis weight (eg, formed from paper), such as, for example, at least about 33 lbs/1000 sq. m., may be used. ft (about 160 g/ ^m2 ), for example, from about 33 lb/1000 sq. ft. to about 65 lbs/1000 sq. ft (about 320 g/ ^m2 ), from about 33 lb/1000 sq. ft. to about 60 lbs/1000 sq. ft. (approx. 290 g/ ^m2 ), from 33 lb/1000 sq. ft. to about 58 lbs/1000 sq. ft (about 280 g/ ^m2 ), from about 33 lb/1000 sq. ft. to about 55 lbs/1000 sq. ft (about 270 g/ ^m2 ), from about 33 lb/1000 sq. ft. to about 50 lbs/1000 sq. ft (about 240 g/ ^m2 ), from about 33 lb/1000 sq. ft. to about 45 lbs/1000 sq. ft. (about 220 g/ ^m2 ), etc., or less than about 45 lbs/1000 sq. ft. In other embodiments, one or both of the cover sheets have a basis weight of about 38 lbs/1000 sq. ft (about 190 g/ ^m2 ) to about 65 lb/1000 sq. ft., from about 38 lbs/1000 sq. ft. to about 60 lbs/1000 sq. ft., from about 38 lbs/1000 sq. ft. to about 58 lbs/1000 sq. ft., from about 38 lbs/1000 sq. ft. to about 55 lbs/1000 sq. ft., from about 38 lbs/1000 sq. ft. to about 50 lbs/1000 sq. ft., or from about 38 lbs/1000 sq. ft. to about 45 lbs/1000 sq. ft.

[0113] However, if necessary, in some embodiments of the invention, a higher basis weight may be used, for example, to further improve nail pull-out resistance or to simplify processing, for example, to achieve desired tactile characteristics for end users. Accordingly, one or both of the cover sheets may have a basis weight of, for example, at least about 45 lbs/1000 sq. ft. (e.g., about 45 lbs/1000 sq. ft. to about 65 lbs./1000 sq. ft., about 45 lbs./1000 sq. ft. to about 60 lbs./1000 sq. ft., from about 45 lbs./1000 sq. ft. ft. to about 55 lbs/1000 sq. ft., from about 50 lbs./1000 sq. ft. to about 65 lbs./1000 sq. ft., from about 50 lbs./1000 sq. ft. to about 60 lbs./1000 sq. ft., etc. .d.). Optionally, in some embodiments of the invention, one cover sheet (e.g., the "face" paper side after installation) may have the above-mentioned higher basis weight, for example, to improve resistance to nail pull-out and for improved processing, while the other cover sheet (e.g. "back" sheet after sheet installation) may have a slightly lower basis weight if desired (e.g., a basis weight of less than 45 lbs/1000 sq. ft., e.g., about 33 lbs./1000 sq. ft. to 45 lbs./1000 sq. ft.). ft. or about 33 lbs/1000 sq. ft. to about 40 lbs./1000 sq. ft.).

Improvement additive

[0114] The improver provides targeted strength properties. In preferred embodiments of the invention, the enhancer is more concentrated in the concentrated layer suspension than in the core (and/or final layers in the gypsum board product) suspension as discussed herein. Examples of suitable strength enhancing additives include starch, polyvinyl alcohol, boric acid, gypsum cement, nanocellulose, microcellulose, or any combination thereof. The use of the term "improving additive" herein in the singular is for convenience, but is understood to include the plural, i.e. more than one enhancement additive in combination, as will be readily understood by one of ordinary skill in the art. Thus, the enhancement additive may contain one or more of starch, polyvinyl alcohol, boric acid, gypsum cement, nanocellulose and/or microcellulose.

[0115] In some embodiments, the enhancement additive contains an ingredient, such as starch, that is effective in increasing the dry strength of the composite gypsum board compared to the strength of the composite sheet without the ingredient such as starch (e.g., by increasing compressive strength, resistance to nail pull-out, bending strength, average hardness of gypsum layers separately or in combination, or other strength parameter). With regard to starch, any suitable strength-enhancing starch can be used, including hydroxyalkylated starches such as hydroxyethylated or hydroxypropylated starch or a combination thereof, raw starches or pregelatinized starches, which are generally preferred over acid-modified migratory starches which typically provide strengthening the bond between the paper and the core, but not improving the strength of the core. However, if necessary, in some embodiments of the invention, acid-modified migratory starch may be introduced along with a improving additive.

[0116] Starch can be cooked or raw. Crude starches are characterized as being insoluble in cold water and having a semicrystalline structure. Typically, raw starches are produced by wet milling and are not modified by heating the wet starch as is the case with cooked starches. Cooked starches are characterized as being cold water soluble and having a non-crystalline structure. Cooked starches are produced by heating wet starch and can also be produced, for example, by extrusion methods. See, for example, co-pending US patent applications 14/494547, 14/044582 and 13/835002, extrusion methods from which are incorporated by reference.

[0117] Cooked starches are sometimes referred to as pregelatinized starches because the crystalline structure of the starch granules melts and results in gelatinization of the starch, which is characterized by the disappearance of birefringence under a polarized light microscope. Preferred starches, whether raw or cooked, are distinguished from acid-modified migratory starches, which do not impart the same strength properties, and are used in the art to improve paper-core adhesion as they migrate to the paper-core interface due to their shorter chain length. Acid-modified migratory starches have a minimum molecular weight, typically lower than about 6000 Daltons. In some embodiments, preferred starches according to embodiments of the disclosure have higher molecular weights, such as at least about 30,000 daltons.

[0118] For example, in some embodiments, the starch added to the concentrated layer suspension may have a molecular weight of from about 30,000 Dalton to about 150,000,000 Dalton, for example, from about 30,000 Dalton to about 150,000,000 Dalton, from about 30,000 Dalton to about 100,000,000 Dalton , from about 30,000 Dalton to about 50,000,000 Dalton, from about 30,000 Dalton to about 10,000,000 Dalton, from about 30,000 Dalton to about 5,000,000 Dalton, from about 30,000 Dalton to about 1,000,000 Dalton, from about 30,000 Dalton to about 500,000 Dalton, from about 30,000 Dalton to about 100,000 Dalton, from about 50,000 Dalton to about 150,000,000 Dalton, from about 50,000 Dalton to about 100,000,000 Dalton, from about 50,000 Dalton to about 50,000,000 Dalton, from about 50,000 Dalton to about 10,000,000 Dalton, from about 50 000 Dalton to about 5,000,000 Dalton, from about 50,000 Dalton to about 1,000,000 Dalton, from about 50,000 Dalton to about 500,000 Dalton, from about 50,000 Dalton to about 100,000 Dalton, from about 100,000 Dalton to about 150,000,000 Dalton, from about 100,000 Dalton to about 10,000,000 0 Dalton, from about 100,000 Dalton to about 50000000 Dalton, from about 100000 Dalton to about 10000000 Dalton, from about 100000 Dalton to about 5000000 Dalton, from about 100000 Dalton to about 100000 Dalton, from about 100000 Dalton to about 500000 Dalton or from about 1000 00 Dalton to about 100,000 Dalton, etc. .d. [0119] The properties of raw starches include low viscosity in cold water (ie, at a temperature of 77°F (25°C)), in contrast to the properties of pregelatinized starches, which include their instantaneous high viscosity in cold water. Crude starches typically have a cold water viscosity, as measured by a modified rapid viscosity test method, of about 10 centipoise or less (eg, about 1 centipoise to about 10 centipoise, e.g., about 3 centipoise to about 7 centipoise). The rapid viscosity test method is explained in the text by Deffenbaugh, L.B. and Walker, S.E., "Comparison of Starch Pasting Properties in the Brabender Viscoamylograph and the Rapid Visco-Analyzer," Cereal Chemistry, Vol.66, No. 6, pp.493-499 (1989), and modified as defined herein with respect to sample preparation and test profile as follows. Add starch (20 g, dry) to water (180 g) in a Waring blender (Model 31BL92) over 15 seconds while blending at low speed. Starch solution (28 g) is weighed into a measuring cup. The speed of rotation of the blades of the express viscosity analyzer is set to 160 rpm. The test profile is set to an initial temperature of 25°C for 10 min. The temperature is increased to 93°C at a heating rate of 15°C/min. The temperature is maintained at 93°C for 5 minutes. The temperature is reduced to 50°C at a cooling rate of -15°C/min; and maintain at 50°C for 1 min. The viscosity value measured after 30 seconds is used as the starch viscosity.

[0120] Pregelatinized starches have a "flash" high viscosity in cold water because the starch tends to dissolve instantly in water. Cooked or pregelatinized starches typically have a cold water viscosity, measured according to a modified rapid viscosity test method, of at least about 100 centipoise (e.g., about 50 centipoise to about 1000 centipoise, namely, about 350 centipoise up to about 1000 centipoise).

[0121] In some embodiments, raw starches are selected because they are easily mixed with water. This is due to their low viscosity in water. Pregelatinized starches can sometimes cause fisheye formation, which is a condition characterized by one or more large lumps that form in an aqueous solution during the mixing process. Without wishing to be bound by any particular theory, it is believed that during the mixing process the formation of large lumps is caused by the rapid absorption of water by the starch to form a viscous film on the surface of the lump which prevents water from penetrating into the lump. The fish eye condition is thought to be excluded for raw starches due to their insolubility in cold water, which causes the starch granules to separate. However, it should be understood that pregelatinized starches can be used in accordance with embodiments of the disclosure because they are desirable to provide functional groups that allow hydrogen bonding between the starch and the gypsum crystals.

[0122] Examples of suitable raw starches include, but are not limited to, one or more of natural grain starches, natural root starches, natural tuber starches, and/or chemically modified starches, with specific representative examples including, for example, corn starch (conventional, waxy and/or high amylose), wheat starch type A, wheat starch type B, pea starch, acid-modified starches with a molecular weight of at least about 30,000 Daltons, substituted starches having substituted groups (for example, acetate, phosphate, hydroxyethyl, hydroxypropyl) on the hydroxyl groups of starch or any combination thereof. In some embodiments, the raw starch does not include pea starch.

[0123] Any suitable pregelatinized starch can be incorporated into the improver as described in US 2014/0113124 A1 and US 2015/0010767-A1, which include described methods for its preparation and target viscosity ranges. The pregelatinized starch, if incorporated, can be of any suitable viscosity. In some embodiments, the pregelatinized starch is a medium viscosity starch measured according to the Viscosity Measurement Test Method (VMA) known in the art and set forth, for example, in US 2014/0113124 A1, the VMA method of which is included in this document by reference.

[0124] The target pregelatinized starches in accordance with some embodiments of the invention may have an average viscosity, for example, measured in a solution with 15% wt. starch in water, from about 20 centipoise to about 700 centipoise, for example, from about 20 centipoise to about 600 centipoise, from about 20 centipoise to about 500 centipoise, from about 20 centipoise to about 400 centipoise, from about 20 centipoise to about 300 centipoise , from about 20 centipoise to about 200 centipoise, from about 20 centipoise to about 100 centipoise, from about 30 centipoise to about 700 centipoise, from about 30 centipoise to about 600 centipoise, from about 30 centipoise to about 500 centipoise, from about 30 centipoise to about 400 centipoise, from about 30 centipoise to about 300 centipoise, from about 30 centipoise to about 200 centipoise, from about 30 to about 100 centipoise, from about 50 centipoise to about 700 centipoise, from about 50 centipoise to about 600 centipoise, from about 50 centipoise to about 500 centipoise, from about 50 centipoise to about 400 centipoise, from about 50 centipoise to about 300 centipoise, from about 50 centipoise to about 200 centipoise, from about 50 centipoise to about 100 centipoise, from about 70 centipoise to about 700 centipoise, from about 70 centipoise to about 600 centipoise, from about 70 centipoise to about 500 centipoise, from about 70 centipoise to about 400 centipoise, from about 70 centipoise to about 300 centipoise, from about 70 centipoise to about 200 centipoise, from about 70 centipoise to about 100 centipoise, from about 100 centipoise to about 700 centipoise, from about 100 centipoise to about 600 centipoise, from about 100 centipoise to about 500 centipoise, from about 100 centipoise to about 400 centipoise, from about 100 centipoise to about 300 centipoise, from about 100 to about 200 centipoise, etc.

[0125] In some embodiments, the pregelatinized starch can be produced as an extruded starch, for example, where the starch is produced by pregelatinization and acid modification in a single extruder step, as described in US 2015/0010767-A1, extrusion process from which is incorporated herein by reference. Briefly, any suitable extruder may be used, such as a single screw extruder (for example, the Advantage 50, available from American Extrusion International, located in South Beloit, Illinois) or a twin screw extruder (for example, the Wenger TX52, available from Wenger, located in Sabetha, Kansas). Typically, in some embodiments, the following are mixed: (a) a pregelatinized starch precursor, i.e. ungelatinized starch, (b) an acid in the form of a weak acid that does not substantially chelate calcium ions, and/or a small amount of a strong acid, and (c) water, and is charged into the extruder. In some embodiments, additional water may be added to the extruder. In some embodiments, for example, aluminum sulfate (alum) is a suitable weak acid for use in preparing wet starch because it does not substantially chelate calcium ions.

[0126] For example, in some embodiments of the invention, the weak acid is introduced in an amount of about 0.5% wt. up to about 5% wt. from the mass of starch. The amount of strong acid is relatively small, for example about 0.05% by weight. by weight of starch or less, for example, from about 0.0001% wt. up to about 0.05% wt. The amounts of strong acid used in accordance with some embodiments of the disclosure are significantly less than those added to conventional systems that used, for example, at least about 2 g of sulfuric acid per 35 g of starch. In some embodiments, a strong acid in small amounts as described above may be used in combination with a weak acid that does not chelate calcium ions, such as alum, as described herein.

[0127] While in the extruder, the combination of heating elements and mechanical separation melts and pregelatinizes the starch, and a weak acid partially hydrolyzes the starch to the target molecular weight, reflected, if necessary, by the viscosity described herein. For example, wet starch can be pregelatinized and acid modified in a die extruder at a temperature of about 150°C (about 300°F) to about 210°C (about 410°F). The pressure inside the extruder is determined by the feedstock being extruded, moisture content, die temperature, and screw speed, as will be apparent to one of ordinary skill in the art. For example, the extruder pressure may be at least about 2000 psi. inch (about 13800 kPa), for example, from about 2000 psi. inch to about 5000 psi. inch (34500 kPa). Conditions in the extruder due to mechanical energy will also cause the starch molecules to decompose, which has partly the same effect as acid modification. It is believed that because extruder conditions (eg, high reaction temperature and high pressure) in accordance with some embodiments facilitate this chemical reaction, a weak acid and/or small amounts of a strong acid can be used.

[0128] Cold water solubility refers to pregelatinized starch having any solubility in water at room temperature (about 25°C). In some embodiments, the pregelatinized starch is partially hydrolyzed and may have a target cold water solubility of about 70% to about 100%, about 75% to about 100%, about 80% to about 100%, about 85% to about 100%, from about 90% to about 100%, from about 95% to about 100%, from about 70% to about 99%, etc., from about 75% to about 99%, from about 80% to about 99%, from about 85% to about 99%, from about 90% to about 99%, from about 95% to about 99%. In some embodiments, the pregelatinized starch has a cold water viscosity (10% solids, 25°C) of about 10 BU to about 120 BU; Viscosity is measured according to the Brabender method, in which viscosity is measured using a CW Brabender viscograph, such as Viscograph-E, which uses reactive torque for dynamic measurements. For example, the cold water viscosity may be, for example, from about 20 BU to about 110 BU, from about 30 BU to about 100 BU, from about 40 BU to about 90 BU, from about 50 BU to about 80 BU, or from about 60 BU to about 70 BU. It should be noted that, as defined herein, Brabender units are measured using a 16 fl oz (about 500 ^cc ) sample cup with a 700 cc cartridge at 75 rpm. One of ordinary skill in the art will also readily understand that Brabender units can be converted to other viscosity units, namely centipoise (eg, cP=BE X 2.1 when the measuring cartridge is 700 cmg) or Krebs units.

[0129] In some embodiments, the starch has a cold water viscosity in a 10% starch-water suspension of from about 60 cP to about 160 cP, measured at 25° C. using a Brookfield viscometer with a No. 2 spindle and a rotation speed of 30 rpm For example, the cold water viscosity of a 10% starch in water suspension measured at 25° C. may be from about 60 cP to about 150 cP, from about 60 cP to about 120 cP, from about 60 cP to about 100 cP , from about 70 cP to about 150 cP, from about 70 cP to about 120 cP, from about 70 cP to about 100 cP, from about 80 cP to about 150 cP, from about 80 cP to about 120 cP, from about 80 cP to about 100 cP, from about 90 cP to about 150 cP, from about 90 cP to about 120 cP, from about 100 cP to about 150 cP, or from about 100 cP to about 120 cP.

[0130] Any type of starch described herein as a improver, if administered, may be present in any suitable amount. In some embodiments, the starch is present in a concentrated layer in an amount of from about 5% to about 40% by weight of the stucco, for example, from about 5% to about 35% by weight of the stucco, from about 5% to about 30% by weight plaster, from about 5% to about 25%, from about 5% to about 20%, from about 5% to about 15%, from about 5% to about 10%, from about 10% to about 30%, from about 10% to about 25%, from about 10% to about 20%, from about 10% to about 15%, etc. The starch may be present in the core of the sheet in an amount of from about 0% to about 4% by weight of the stucco, for example, from about 0.1% to about 4% by weight of the stucco, from about 0.1% to about 3% by weight stucco, from about 0.1% to about 2% by weight of stucco, from about 0.1% to about 1% by weight of stucco, from about 1% to about 4% by weight of stucco, from about 1% up to about 3% by weight of stucco, from about 1% to about 2% by weight of stucco, etc.

[0131] In some embodiments, the improver, with or without starch, may contain polyvinyl alcohol and/or boric acid to improve strength. In some embodiments, both polyvinyl alcohol and boric acid and starch are present. Without wishing to be bound by theory, it is believed that boric acid acts as a crosslinking agent for polyvinyl alcohol and starch to further improve the starch. In some embodiments, the concentration of polyvinyl alcohol and/or boric acid in the concentrated layer is believed to have a positive effect on the strength of the face paper; this can be done by soaking the face paper in polyvinyl alcohol and/or boric acid as described herein.

[0132] Polyvinyl alcohol and boric acid, if introduced, can be in any suitable quantities. For example, in some embodiments, the polyvinyl alcohol may be present in the concentrated layer in an amount of from about 1% to about 5% by weight of the stucco. In addition, the polyvinyl alcohol may be present in the core of the sheet in an amount of from about 0% to about 1% by weight of the stucco. Boric acid may be present in the concentrated layer in an amount of from about 0.1% to about 1% by weight of the stucco, and may be present in the core of the sheet in an amount of from about 0% to about 0.1% by weight of the stucco.

[0133] In some embodiments, the enhancement additive optionally contains nanocellulose, microcellulose, or any combination thereof to improve strength, such as nail pull resistance or other strength parameter. Nanocellulose, microcellulose, or a combination thereof, if included, may be present in any suitable amount, such as, for example, present in a concentrated layer suspension in an amount of, for example, from about 0.01% to about 2%, for example, from about 0. 05% to about 1% by weight of the stucco, and in the core sheet suspension in an amount of, for example, from about 0% to about 0.5%, for example, from 0% to about 0.01% by weight of the stucco.

[0134] In some embodiments, the enhancement additive may contain gypsum cement to improve strength, such as nail pull resistance or other strength parameter. Gypsum cement is optional and may be in any suitable amount. For example, in some embodiments, it may be included in the concentrated layer in an amount from about 5% to about 30% by weight of the stucco, and may be present in the core of the sheet in an amount from about 0% to about 10% by weight of the stucco.

Sheet strength

[0135] In some embodiments of the invention, the composite sheet manufactured according to the disclosure complies with test reports according to ASTM C473-10. For example, in some embodiments in which the sheet is cast at a thickness of 1/2 inch, the sheet has a dry nail pull resistance, determined in accordance with ASTM C473-10 (Method B), of at least about 65 _lbs . force) e.g., at least about 68 _lbs , at least about 70 _lbs , at least about 72 _lbs , at least about 74 _lbs , at least about 75 _lbs , at least about 76 lbs _with , at least about 77 pounds _with , etc. In various embodiments, the nail pull resistance may be from about 65 lbs _to about 100 _lbs , from about 65 lbs _to about 95 _lbs , from about 65 lbs _to about 90 _lbs , from about 65 lbs _to about 85 _lbs , from about 65 lbs _to about 80 _lbs , from about 65 lbs _to about 75 _lbs , from about 68 lbs _to about 100 _lbs , from about 68 _lbs to about 95 _lbs , from about 68 _lbsF to about 90 _lbsF , from about 68 lbsF _to about 85 _lbsF , from about 68 lbsF _to about 80 _lbsF , from about 70 lbsF _to about 100 _lbsF , from about 70 lbsF _to about 95 _lbs , from about 70 lbs _to about 90 _lbs , from about 70 lbs _to about 85 _lbs , from about 70 lbs _to about 80 _lbs , from about 72 lbs _to about 100 _lbs , from about 72 lbs _to about 95 _lbs , from about 72 lbs _to about 90 _lbs , from about 72 lbs _to about 85 _lbs , from about 72 lbs _to about 80 _lbs , from about 72 lbs _to about 77 lbs _s , from about 72 lbs _to about 75 _lbs , from about 75 lbs _to about 100 _lbs , from about 75 lbs _to about 95 _lbs , from about 75 lbs _to about 90 _lbs , from about 75 lbs _from to about 85 _lbs , from about 75 lbs _to about 80 _lbs , from about 75 lbs _to about 77 _lbs , from about 77 lbs _to about 100 _lbs , from about 77 lbs _to about 95 _lbs , from about 77 lbs _to about 90 _lbs , from about 77 lbs _to about 85 lbs _or from about 77 lbs _to about 80 _lbs .

[0136] In some embodiments, the sheet may have an average hardness over all one or more gypsum layers (e.g., over the entire core and/or concentrated layer, preferably over all gypsum layers combined) determined in accordance with ASTM C473-10 Method B , at least about 11 _lbs , for example, at least about 12 _lbs , at least about 13 _lbs , at least about 14 _lbs , at least about 15 _lbs , at least about 16 _lbs , at least about 17 _lbs , at least about 18 _lbs , at least about 19 _lbs , at least about 20 _lbs , at least about 21 _lbs, or at least about 22 lbs _. In some embodiments, the sheet may have an average gypsum layer hardness of from about 11 lbs _to about 25 _lbs , for example, from about 11 lbs _to about 22 _lbs , from about 11 lbs _to about 21 _lbs , from about 11 lbs _to about 20 _lbs , from about 11 _lbs , to about 19 _lbs , from about 11 lbs _to about 18 _lbs , from about 11 lbs _to about 17 _lbs , from about 11 lbs _to about 16 _lbs , from about 11 lbs _to about 15 _lbs , from about 11 lbs _to about 14 _lbs , from about 11 lbs _to about 13 _lbs , from about 11 lbs _to about 12 _lbs , from about 12 lbs _to about 25 _lbs , from about 12 lbs _to about 22 _lbs , from about 12 lbs _to about 21 _lbs , from about 12 lbs _to about 20 _lbs , from about 12 lbs _to about 19 _lbs , from about 12 lbs _to about 18 _lbs , from about 12 lbs _to about 17 _lbs , from about 12 lbs _to about 16 _lbs , from about 12 lbs _to about 15 _lbs , from about 12 lbs _to about 14 _lbs , from about 12 lbs _to about 13 _lbs , from about 13 lbs _to about 25 _lbs , from about 13 lbs _to about 22 _lbs , from about 13 lbs _to about 21 _lbs , from about 13 lbs _to about 20 _lbs , about 13 lbs _to about 19 _lbs , from about 13 lbs _to about 18 _lbs , from about 13 lbs _to about 17 _lbs , from about 13 lbs _to about 16 _lbs , from about 13 lbs _to about 15 _lbs , from about 13 lbs _to about 14 _lbs , from about 14 lbs _to about 25 _lbs , from about 14 lbs _to about 22 _lbs , from about 14 lbs _to about 21 _lbs , from about 14 lbs _to about 20 _lbs , from about 14 lbs _to about 19 _lbs , from about 14 lbs _to about 18 _lbs , from about 14 lbs _to about 17 _lbs , about 14 lbs _from to about 16 _lbs , from about 14 lbs _to about 15 _lbs , from about 15 lbs _to about 25 _lbs , from about 15 lbs _to about 22 _lbs , from about 15 lbs _to about 21 _lbs , from about 15 lbs _to about 20 _lbs , from about 15 lbs _to about 19 _lbs , from about 15 lbs _to about 18 _lbs , from about 15 lbs _to about 17 _lbs , from about 15 _lbs to about 16 _lbs , from about 16 lbs _to about 25 _lbs , from about 16 lbs _to about 22 _lbs , from about 16 lbs _to about 21 _lbs , from about 16 lbs _to about 20 _lbs , from about 16 lbs _to about 19 _lbs , from about 16 lbs _to about 18 _lbs , from about 16 lbs _to about 17 _lbs , from about 17 lbs _to about 25 _lbs , from about 17 lbs _to about 22 _lbs , about 17 lbs _to about 21 _lbs , about 17 lbs _to about 20 _lbs , from about 17 lbs _to about 19 _lbs , from about 17 lbs _to about 18 _lbs , from about 18 lbs _to about 25 _lbs , from about 18 lbs _to about 22 _lbs , from about 18 lbs _to about 21 _lbs , from about 18 lbs _to about 20 _lbs , from about 18 lbs _to about 19 _lbs , from about 19 lbs _to about 25 _lbs , from about 19 lbs _to about 22 _lbs , from about 19 lbs _to about 21 _lbs , from about 19 lbs _to about 20 _lbs , from about 21 lbs _to about 25 _lbs , from about 21 lbs _to about 22 lbs _, or from about 22 _lbs to about 25 _lbs .

[0137] In some embodiments, the concentrated layer has an average dry hardness of at least about 1.5 times the average dry hardness of the sheet core, the average hardness being measured in accordance with ASTM C-473-10; for example, at least about 2 times more, 2.5 times more, 3 times more, 3.5 times more, 4 times more, 4.5 times more, etc., each of These ranges may have any mathematically suitable upper limit, such as 8, 7, 6, 5, 4, 3 or 2.

[0138] With respect to flexural strength, in some embodiments, when cast into 1/2-inch thick sheet, the sheet has a flexural strength, as determined by ASTM C473, that is at least about 36 lbs _in the longitudinal direction (e.g. at least about 38 _lbs , at least about 40 lbs _{, etc.} ) and/or at least about 107 _lbs (e.g., at least about 110 _lbs , at least about 112 lbs, _and etc.) in the transverse direction. In various embodiments, the sheet may have a longitudinal flexural strength of from about 36 lbs _to about 60 _lbs , for example, from about 36 lbs _to about 55 _lbs , from about 36 lbs _to about 50 _lbs , from about 36 lbs _to about 45 _lbs , from about 36 lbs _to about 40 _lbs , from about 36 lbs _to about 38 _lbs , from about 38 lbs _to about 60 _lbs , from about 38 lbs _to about 55 _lbs , from about 38 lbs _to about 50 _lbs , from about 38 lbs _to about 45 _lbs , from about 38 lbs _to about 40 _lbs , from about 40 lbs _to about 60 _lbs , from about 40 lbs _to about 55 _lbs , from about 40 lbs _to about 50 lbs _, or from about 40 lbs _to about 45 lbs _. In various embodiments, the sheet may have a transverse flexural strength of from about 107 lbs _to about 130 _lbs , for example, from about 107 lbs _to about 125 _lbs , from about 107 lbs _to about 120 _lbs , from about 107 lbs _to about 115 _lbs , from about 107 _lbs to about 112 _lbs , from about 107 lbs _to about 110 _lbs , from about 110 lbs _to about 130 _lbs , from about 110 lbs _to about 125 _lbs , from about 110 lbs _to about 120 _lbs , from about 110 lbs _to about 115 _lbs , from about 110 lbs _to about 112 _lbs , from about 112 lbs _to about 130 _lbs , from about 112 lbs _to about 125 _lbs , from about 112 lbs _to about 120 lbs _or from about 112 lbs _to about 115 _lbs .

[0139] Advantageously, in various embodiments of the invention, at various sheet densities described herein, the dry gypsum board may have a compressive strength of at least about 170 psig (1170 kPa), for example, from about 170 psig. sq. in. to about 1,000 psig (6,900 kPa), about 170 psig to about 900 psig (6,200 kPa), about 170 psig to about 800 psig (5,500 kPa ), about 170 psi to about 700 psi (4800 kPa), about 170 psi to about 600 psi (4100 kPa), about 170 psi to about 500 psi (3,450 kPa), from about 170 psi to about 450 psi (3,100 kPa), from about 170 psi to about 400 psi (2,760 kPa), from about 170 psi to about 350 psi (2410 kPa), about 170 psi to about 300 psi (2070 kPa), or about 170 psi to about 250 psi ( 1720 kPa). In some embodiments, the sheet has a compressive strength of at least about 450 psi (3100 kPa), at least about 500 psi (3450 kPa), at least about 550 psi (3800 kPa ), at least about 600 psi (4100 kPa), at least about 650 psi (4500 kPa), at least about 700 psi (4800 kPa), at least about 750 psi per square inch (5200 kPa), at least about 800 psi (5500 kPa), at least about 850 psi (5850 kPa), at least about 900 psi (6200 kPa), at least about 950 psi (6550 kPa) or at least about 1000 psi (6900 kPa). Additionally, in some embodiments, the compressive strength may be limited to any two of the above values. For example, the compressive strength may be from about 450 psi to about 1000 psi (e.g., from about 500 psi to about 900 psi, from about 600 psi to about 800 psi per square inch, etc.). Compressive strength can be measured using a materials testing system commercially available as machine model ATS 1610 from Applied Test Systems, Butler, Pennsylvania. The load is applied continuously and without discontinuity at a rate of 1 in/min.

[0140] Due at least in part to the concentrated layer and its advantages, surprisingly and unexpectedly, these standards (eg, nail pull resistance, flexural strength, and hardness of the gypsum layer) can be met even with ultra-low density sheet (eg, about 33 lb/ cu.ft. or less, namely, about 32 lb/cu.ft. or less, 31 lb./cu.ft. or less, 30 lb./cu.ft. or less, 29 lb./cu.ft. or less, 28 lb./cu.ft. .ft or less, 27 lb/cu ft or less, 26 lb/cu ft or less, etc.) as described herein. Moreover, these standards can surprisingly be met in some embodiments of the invention by using less total amount of enhancer and with a lighter, weaker and/or softer core and/or with lower overall water use, such that embodiments of the invention provide production efficiency.

Method for manufacturing composite plasterboard sheet

[0141] Composite gypsum board in accordance with embodiments of the disclosure can be manufactured on typical gypsum board production lines. For example, sheet manufacturing techniques are described, for example, in US Pat. No. 7,364,676 and US Patent Application Publication 2010/0247937. Briefly, the method typically involves feeding a cover sheet onto a moving conveyor. Since the gypsum board is typically formed "face down", in such embodiments the cover sheet is a "face" cover sheet.

[0142] In accordance with aspects of the invention, two separate suspensions are formed. One slurry is a slurry of plaster used to form the core of the sheet, and the other slurry is used to form the concentrated layer. The concentrated layer may be formed from any suitable material, including a binder material such as plaster of Paris, which is hydrated to form a set material, such as set gypsum. Thus, in various embodiments of the invention, suspensions containing the desired binder material can be prepared. As described herein, in some embodiments in which both the sheet core and the concentrated layer are formed from stucco slurries, the stucco slurry used to form the sheet core may have a lower VSHG than the VSHG of the stucco slurry used to make the concentrated sheet. layer.

[0143] As noted herein, the blowing agent (or other lightweight material) is typically more predominant in the core sheet suspension to provide a lower density, although some foam or lightweight material may be incorporated into the concentrated suspension. layer provided that the density parameters are achieved. In some embodiments, the concentration of the improving agent may be higher in the concentrated layer, and in some embodiments, some of the improving agent may not even be present in the core leaf suspension. Accordingly, the supply lines to the respective mixers can be adjusted accordingly, which is within the average skill level of the average person.

[0144] The two suspensions can be prepared by any suitable method. For example, two separate mixers can be used in which the raw materials are mixed to form respective suspensions. Mixers can be connected in series or not connected. Alternatively, a single mixer can be used to form both slurry streams. In FIG. 2 depicts three alternative block diagrams showing examples of how suspensions can be formed in accordance with this disclosure. As can be seen in image A in FIG. 2, a single mixer can be used, whereas in B and C the two slurries are formed in separate mixers, for example as "finger mixers" or "fingerless mixers" if necessary. As seen in flow charts B and C, when efficiency is desired, the mixer used for the concentrated layer may have a smaller mixing volume in some embodiments of the invention because the amount of slurry required to apply the concentrated layer is less than the amount of slurry that is applied for forming the core of the sheet. The "main" mixer (i.e., for forming the core sheet slurry) has a main body and an outlet port (e.g., a receiving hopper with an outlet gate known in the art, or a modified outlet device (MED) described in US patents 6494609 and 6874930). As can be seen in all three images A-C, a blowing agent may be added to the mixer outlet (eg, the valve described in, for example, US Pat. Nos. 5,683,635 and 6,494,609).

[0145] Diagram A illustrates an embodiment in which the steps are performed using a single mixer, that is, the main mixer 100. Stucco 102 and water 104 are introduced into the main mixer 100, while foam 106 is introduced downstream into the outlet channel 108, which may include a modified outlet device or container, which means that no foam is introduced into the body of the main mixer 100. The portion of the slurry 110 that is substantially free of foam is discharged from the mixer 100 through an outlet, such as typically an outlet 108. to form a suspension 112 concentrated layer. The main mixer 100 acts as a pump to displace the unfoamed slurry 110 from the smaller concentrated layer slurry outlet that passes through the slurry injection line. Additives 114, in particular the improver, are injected in wet form into the slurry injection line through the injection ports. The inventors have found that it is desirable for the line to be long enough, as determined by one of ordinary skill in the art, to ensure uniform mixing of the slurry, including the improver. There is no need for separate injection of plaster or water. As can be seen in Image A, the edge slurry streams 116 and 118 can also be discharged from the main mixer 100 without foam so that they have the target hardness for use in edges, as is known in the art.

[0146] In Diagram B, it can be seen that two mixers 200 and 202 are connected in series. Stucco 204 and water 206 are introduced into the main mixer 200. Foam 208 is introduced downstream of the main mixer body 200 into an outlet channel 210 (which may include a modified outlet structure or container). Thus, the non-foamed slurry 212 can exit the mixer 200 through the outlet and be introduced into a smaller secondary concentrate layer mixer 202, into which dry and wet additives 214 can be separately added (e.g., in separate lines), including improver, to provide the target concentration effect. The edge slurry streams 214 and 216 are also shown exiting from a channel separate from the main outlet 210 to minimize foaming therein and provide target hardness.

[0147] In Diagram C you can see that there are two mixers 300 and 302, but the slurries are prepared separately, with each mixer having its own inlets for stucco and water, if necessary. Specifically, plaster 304 and water 306 are introduced into the main mixer 300. Foam 308 is introduced downstream of the body of the main mixer 300 into an outlet channel 310 (which may include a container or a modified outlet device described in US Pat. Nos. 6,494,609 and 6,874,930). The edge slurry streams 312 and 314 may exit from a channel separate from the main outlet 310 to minimize foaming therein and provide target hardness. The secondary mixer 302 for forming the concentrated layer slurry 316 may introduce and mix the stucco 318 and water 320. Dry and wet additives (e.g., in separate lines), including the enhancer described herein, can be added to the concentrated layer mixer 302 . As such, the concentrated layer slurry 316 is prepared separately from the core slurry formed in the main mixer 300.

[0148] In some embodiments, if desired, the edge slurries may be drawn from the concentrated bed mixer rather than the main mixer. The edges may be denser than the core of the sheet in some embodiments, and, for example, may have the same density as the concentrated layer. For example, when laying down a concentrated layer, a portion of the concentrated layer slurry may flow around the ends of the roller to form the edges of the final product, as shown in FIG. 5 and 6 relative to one end. The length of the roller may be configured (eg, to be shorter than the width of the paper) to provide edges in this manner.

[0149] In some embodiments, the outlet port may include a slurry distributor with a single feed port or multiple feed ports, as described, for example, in US Patent Application Publication 2012/0168527 A1 (application No. 13/341016) and Patent Application Publication USA 2012/0170403 A1 (application No. 13/341209). In these embodiments, when using a slurry distributor with multiple feed openings, the outlet channel may include a suitable flow separator, for example, as described in US Patent Application Publication 2012/0170403 A1.

[0150] The sheet is formed into a multilayer structure, typically simultaneously and continuously, as will be understood in the art. The front cover sheet moves along the conveyor in the form of a continuous belt. After being discharged from the mixer, the concentrated layer suspension is applied to a moving front cover sheet. In addition, hard edges, as is known in the art, for convenience and if necessary, can be formed, for example, from the same slurry stream that forms the concentrated layer.

[0151] The core sheet slurry is then applied to a moving face paper carrying the concentrated layer slurry and covered with a second cover sheet (typically a "back" cover sheet) to form a wet assembly system in a multi-layer structure that constitutes the sheet preform for the final product. The back (bottom) cover sheet may optionally comprise a topcoat, which may be formed from the same gypsum slurry as the concentrated layer, or a different gypsum slurry. The cover sheets may be formed from paper, fibrous fabric, or other type of material (eg, foil, plastic, glass mat, nonwoven material, eg, a mixture of cellulosic and inorganic filler, etc.). In some embodiments of the invention, the concentrated layer is applied to both main sides of the sheet, that is, in an interlocking state with the top and bottom sheets.

[0152] The wet assembly system thus obtained is fed to a forming section, in which the product is machined to size to the desired thickness (eg, by means of a forming plate), and to one or more cutting sections, in which it is cut to the desired length. The prefabricated system is allowed to cure while wet to form an interlocking crystalline matrix of set gypsum, and excess water is removed through a drying process (eg, by transporting the prefabricated system through a drying oven). Surprisingly and unexpectedly, it has been found that the sheet produced by this invention requires significantly less time for the drying process due to the low water requirement inherent in the structure and composition of the sheet. This is beneficial because it reduces energy costs.

[0153] In the manufacture of gypsum board, vibration is also often used to remove large voids or air pockets from the applied slurry. Each of the above steps, as well as methods and equipment for performing such steps, are known in the art.

Typical embodiments of the invention

[0154] The invention is further illustrated by the following exemplary embodiments. However, the invention is not limited to the embodiments given below.

[0155] (1) A composite gypsum board sheet, slurry, or sheet manufacturing method described herein.

[0156] (2) A composite gypsum board comprising: (a) a sheet core containing set gypsum and formed from a first slurry containing water and stucco, the core having a first and a second core side; and (b) a concentrated layer applied in an interlocking state with the first face of the core and formed from a second suspension containing water, stucco and at least one of the following: (i) a starch thickener,

(ii) cellulose and/or (iii) a copolymer containing polyacrylamide and acrylic acid.

[0157] (3) The composite gypsum board of Embodiment 2, wherein the first slurry is substantially free of (i) starch thickener, (ii) cellulose, and

(iii) a copolymer containing polyacrylamide and acrylic acid.

[0158] (4) The composite gypsum board of embodiments 2 or 3, wherein the starch thickener, cellulose, and/or copolymer increase the viscosity of the first slurry by at least about 100% within 30 seconds.

[0159] (5) The composite gypsum board of Embodiment 4, wherein the starch thickener, cellulose, and/or copolymer increase the viscosity of the first slurry by about 100% to about 500% within 30 seconds.

[0160] (6) A composite gypsum board comprising: (a) a sheet core containing set gypsum and formed from water, stucco and optionally an improving additive, the core having a dry density and a dry thickness, wherein the core determines the first and second sides of the core in the opposite direction; and (b) a concentrated layer formed from water, stucco, improver and at least one of the following: (i) a starch thickener, (ii) cellulose and/or (iii) a copolymer containing polyacrylamide and acrylic acid; (c) a concentrated layer applied in an interlocking relationship with the first face of the core, wherein the concentrated layer has a dry density and/or nail pull resistance at least about 1.1 times greater than that of the core sheet; and (d) when the improver is present during core formation, the improver is added at a higher concentration when forming the concentrated layer than when forming the core sheet.

[0161] (7) The composite gypsum board of Embodiments 2 to 6, wherein the core of the sheet has a first thickness and the concentrated layer has a second thickness, and wherein the first dry thickness is greater than the second dry thickness.

[0162] (8) The composite gypsum board of any one of embodiments 2 to 7, wherein the concentrated layer has a first surface and a second surface; the first surface of the concentrated layer faces the first side of the core of the sheet; the sheet further comprises a top cover sheet facing the second side of the concentrated layer.

[0163] (9) The composite gypsum board of any one of embodiments 2-8, further comprising a bottom cover sheet facing a second side of the sheet core.

[0164] (10) The composite gypsum board of any one of embodiments 6-9, wherein water, stucco, and a concentrated layer builder are in suspension, and a starch thickener, cellulose, and/or copolymer increases the viscosity of the suspension by at least to about 100% for 30 seconds.

[0165] (11) The composite gypsum board of Embodiment 10, wherein water, stucco, and a concentrated layer builder are in suspension and a starch thickener, cellulose, and/or copolymer increase the viscosity of the suspension by about 100% to about 500% for 30 seconds. [0166] (12) The composite gypsum board according to any one of embodiments 2-11, in which the copolymer contains about 20% wt. or less acrylic acid.

[0167] (13) The composite gypsum board of any one of embodiments 2-12, wherein the copolymer has a molecular weight of from about 100,000 to about 1,000,000.

[0168] (14) The composite gypsum board of any one of embodiments 2-13, wherein water, stucco, and a concentrated layer builder are in suspension, and wherein the copolymer is in suspension in an amount of about 0.1% up to about 5.0% by weight of plaster.

[0169] (15) The composite gypsum board of any one of embodiments 2-14, wherein the cellulose is water soluble.

[0170] (16) The composite gypsum board of any one of embodiments 2-15, wherein the cellulose is cellulose ether.

[0171] (17) The composite gypsum board of any one of embodiments 2-16, wherein the cellulose is alkyl cellulose.

[0172] (18) The composite gypsum board of any one of embodiments 2-17, wherein the cellulose is in the form of one or more of methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, propyl cellulose, hydroxypropyl cellulose, and/or hydroxypropyl methyl cellulose.

[0173] (19) The composite gypsum board of any one of embodiments 2-18, wherein the cellulose has a molecular weight of from about 10,000 to about 1,000,000.

[0174] (20) The composite gypsum board of any one of Embodiments 2-19, wherein water, stucco, and a concentrated layer builder are in suspension, and wherein cellulose is present in the suspension in an amount of about 0.1% up to about 5.0% by weight of plaster.

[0175] (21) The composite gypsum board of any one of embodiments 2-20, wherein the starch thickener is a substituted starch.

[0176] (22) The composite gypsum board of any one of embodiments 2-21, wherein the starch thickener is cold water soluble.

[0177] (23) The composite gypsum board of any one of embodiments 2-22, wherein the starch thickener has a viscosity, measured in accordance with the IIV method, of at least about 1000 cP.

[0178] (24) The composite gypsum board of Embodiment 23, wherein the starch thickener has a viscosity, measured in accordance with the IIV method, from about 2000 cP to about 10,000 cP.

[0179] (25) The composite gypsum board of any one of embodiments 2-24, wherein the starch thickener is modified by grafting foreign groups to the hydroxyl group of the glucose unit of the molecule.

[0180] (26) The composite gypsum board of Embodiment 25, wherein the foreign groups include ethyl, hydroxylethyl, hydroxylpropyl, acetate, phosphate, and/or sulfate.

[0181] (27) The composite gypsum board of any one of embodiments 2-26, wherein the starch thickener is not pregelatinized.

[0182] (28) The composite gypsum board of any one of embodiments 2-27, wherein the starch thickener is an ester derivative of starch.

[0183] (29) The composite gypsum board of any one of embodiments 2-28, wherein the starch thickener is a carboxyethyl starch ether.

[0184] (30) The composite gypsum board of embodiments 28 or 29, wherein the starch thickener is a salt.

[0185] (31) The composite gypsum board of Embodiment 30, wherein the starch thickener is sodium starch glycolate. [0186] (32) The composite gypsum board of Embodiment 30, wherein the starch thickener has the molecular formula (C ₂ H ₄ O ₃ ) _x ⋅(Na) _x , where X is the number of repeat units and ranges from about 1800 to about 18000.

[0187] (33) The composite gypsum board of any one of embodiments 2-32, wherein water, stucco, and a concentrated layer builder are in suspension, and a starch thickener is present in the suspension in an amount of from about 0.1% to about 5.0% by weight of plaster.

[0188] (34) The composite gypsum board of any one of embodiments 2-33, wherein the concentrated layer is formed from a slurry containing a starch thickener and one or both of cellulose and a copolymer.

[0189] (35) The composite gypsum board of any one of embodiments 2-33, wherein the concentrated layer is formed from a slurry containing cellulose and one or both of a starch thickener and a copolymer.

[0190] (36) The composite gypsum board of any one of embodiments 2-33, wherein the concentrated layer is formed from a slurry containing a copolymer and one or both of a starch thickener and cellulose.

[0191] (37) The composite gypsum board of any one of embodiments 2-33, wherein the concentrated layer is formed from a slurry containing a starch thickener, cellulose, and a copolymer.

[0192] (38) The composite gypsum board of any one of embodiments 6-37, wherein the improver contains unsubstituted starch.

[0193] (39) The composite gypsum board of any one of embodiments 6-38, wherein the improver comprises pregelatinized starch.

[0194] (40) The composite gypsum board of Embodiment 39, wherein the pregelatinized starch has a viscosity of about 20 centipoise to about 700 centipoise when the viscosity is measured by exposing the starch to the conditions of the AIV method.

[0195] (41) The composite gypsum board of Embodiment 40, wherein the pregelatinized starch has a viscosity, measured according to the IIV method, of about 30 centipoise to about 200 centipoise.

[0196] (42) The composite gypsum board of any one of embodiments 6-38, wherein the improver comprises at least one raw starch having a peak viscosity of from about 100 Brabender units to about 900 Brabender units, as measured by injecting the starch into suspension with water at a starch concentration of 15% in terms of solids, and using a Viscograph-E device set at 75 rpm and 700 cmg, in which the starch is heated from 25 ° C to 95 ° C at a speed of 3 ° C/minute, then the suspension is kept at 95°C for ten minutes, and then the starch is cooled to 50°C at a rate of -3°C/minute.

[0197] (43) A method of making composite gypsum board, comprising: (a) preparing a first slurry containing stucco, water, an improver and at least one of the following: (i) a starch thickener, (ii) cellulose and/or (iii) a copolymer containing polyacrylamide and acrylic acid; (b) mixing at least water, stucco and optionally an improvement additive to form a second slurry; (c) applying the first slurry in an interlocking manner to the first coating sheet to form a concentrated layer, the concentrated layer having a first side and a second side, with the front side of the first concentrated layer facing the first coating sheet; (d) applying a second slurry in an interlocking manner to the concentrated layer to form a sheet core having a first side and a second side, the first side of the sheet core facing the second side of the concentrated layer; (f) applying a second cover sheet in interlocking relationship with a second face of the core sheet to form a sheet blank; and (f) drying the sheet blank to form a sheet.

[0198] (44) The method of embodiment 43, wherein the second suspension is substantially free of (i) starch thickener, (ii) cellulose, and (iii) polyacrylamide-acrylic acid copolymer.

[0199] (45) The method of embodiments 43 or 44, wherein the starch thickener, cellulose, and/or copolymer increases the viscosity of the first slurry by at least about 100% within 30 seconds.

[0200] (46) The method of Embodiment 45, wherein the starch thickener, cellulose, and/or copolymer increase the viscosity of the first slurry by about 100% to about 500% within 30 seconds.

[0201] (47) The method of embodiments 43-46, wherein the core sheet has a first dry thickness and the concentrated layer has a second dry thickness, and wherein the first dry thickness is greater than the second dry thickness condition.

[0202] (48) The method of any one of embodiments 43-47, wherein the copolymer contains about 20% by weight or less of acrylic acid.

[0203] (49) The method of any one of embodiments 43-48, wherein the copolymer has a molecular weight of from about 100,000 to about 1,000,000.

[0204] (50) The method of any one of embodiments 43-49, wherein the copolymer is present in the first slurry in an amount of from about 0.1% to about 5.0% by weight of the stucco.

[0205] (51) The method of any one of embodiments 43-50, wherein the cellulose is water soluble.

[0206] (52) The method of any one of embodiments 43-51, wherein the cellulose is cellulose ether.

[0207] (53) The method of any one of embodiments 43-52, wherein the cellulose is an alkylcellulose.

[0208] (54) The method of any one of embodiments 43-53, wherein the cellulose is in the form of one or more of methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, propyl cellulose, hydroxypropyl cellulose, and/or hydroxypropyl methyl cellulose.

[0209] (55) The method of any one of embodiments 43-54, wherein the cellulose has a molecular weight of from about 10,000 to about 1,000,000.

[0210] (56) The method of any one of embodiments 43-55, wherein cellulose is present in the first slurry in an amount of from about 0.1% to about 5.0% by weight of the stucco.

[0211] (57) The method of any one of embodiments 43-56, wherein the starch thickener is a substituted starch.

[0212] (58) The method of any one of embodiments 43-57, wherein the starch thickener is soluble in cold water.

[0213] (59) The method of any one of embodiments 43-58, wherein the starch thickener has a viscosity, measured in accordance with the IIV method, of at least about 1000 cP.

[0214] (60) The method of Embodiment 59, wherein the starch thickener has a viscosity, measured according to the IIV method, from about 2000 cP to about 8000 cP.

[0215] (61) The method of any one of embodiments 43-60, wherein the starch thickener is modified by grafting foreign groups to the hydroxyl group of the glucose unit of the molecule.

[0216] (62) The method of embodiment 61, wherein the foreign groups include ethyl, hydroxylethyl, hydroxylpropyl, acetate, phosphate and/or sulfate.

[0217] (63) The method of any one of embodiments 43-62, wherein the starch thickener is not pregelatinized.

[0218] (64) The method of any one of embodiments 43-63, wherein the starch thickener is an ester derivative of starch.

[0219] (65) The method of any one of embodiments 43-64, wherein the starch thickener is a starch carboxyethyl ester.

[0220] (66) The method of embodiments 64 or 65, wherein the starch thickener is a salt.

[0221] (67) The method of Embodiment 66, wherein the starch thickener is sodium starch glycolate.

[0222] (68) The method of Embodiment 66, wherein the starch thickener has the molecular formula (C ₂ H ₄ O ₃ ) _x ⋅(Na) _x , where X is the number of repeat units and is from about 1800 to about 18000.

[0223] (69) The method of any one of embodiments 43-68, wherein the starch thickener is present in the first slurry in an amount of from about 0.1% to about 5.0% by weight of the stucco.

[0224] (70) The method of any one of embodiments 43-69, wherein the first suspension contains a starch thickener and one or both of cellulose and a copolymer. [0225] (71) The method of any one of embodiments 43-69, wherein the first suspension comprises cellulose and one or both of a starch thickener and a copolymer.

[0226] (72) The method of any one of embodiments 43-69, wherein the first suspension comprises a copolymer and one or both of a starch thickener and cellulose.

[0227] (73) The method of any one of embodiments 43-69, wherein the first suspension comprises a starch thickener, cellulose, and a copolymer.

[0228] (74) The method of any one of embodiments 43-73, wherein the improver comprises unsubstituted starch.

[0229] (75) The method of any one of embodiments 43-74, wherein the improver comprises pregelatinized starch.

[0230] (76) The method of Embodiment 75, wherein the pregelatinized starch has a viscosity of from about 20 centipoise to about 700 centipoise when the viscosity is measured by exposing the starch to the conditions of the AIV method.

[0231] (77) The method of embodiment 76, wherein the pregelatinized starch has a viscosity, measured according to the IIV method, of about 30 centipoise to about 200 centipoise.

[0232] (78) The method of any one of embodiments 43-77, wherein the improver comprises at least one crude starch having a peak viscosity of from about 100 Brabender units to about 900 Brabender units, as measured by viscosity by adding the starch to a suspension with water at a starch concentration of 15% in terms of solids, and using a Viscograph-E device set at 75 rpm and 700 cmg, in which the starch is heated from 25 ° C to 95 ° C at a speed of 3 ° C / minute, then the suspension is kept at 95°C for ten minutes, and then the starch is cooled to 50°C at a rate of -3°C/minute.

[0233] (79) A slurry containing water, stucco, an improver, and at least one of (a) a starch thickener, (b) cellulose, or (c) a copolymer containing polyacrylamide and acrylic acid.

[0234] (80) The slurry of embodiment 79, wherein the starch thickener, cellulose, and/or copolymer increases the viscosity of the slurry by at least about 100% within 30 seconds.

[0235] (81) The slurry of embodiment 80, wherein the starch thickener, cellulose, and/or copolymer increases the viscosity of the slurry by about 100% to about 500% within 30 seconds.

[0236] (82) The suspension of any one of embodiments 79-81, wherein the copolymer contains about 20 weight percent or less acrylic acid.

[0237] (83) The suspension of any one of embodiments 79-82, wherein the copolymer has a molecular weight of from about 100,000 to about 1,000,000.

[0238] (84) The slurry of any one of embodiments 79-83, wherein the copolymer is present in an amount of from about 0.1% to about 5.0% by weight of the stucco.

[0239] (85) The suspension of any one of embodiments 79-84, wherein the cellulose is water soluble.

[0240] (86) The suspension of any one of embodiments 79-85, wherein the cellulose is cellulose ether.

[0241] (87) The suspension of any one of embodiments 79-86, wherein the cellulose is an alkylcellulose.

[0242] (88) The suspension of any one of embodiments 79-87, wherein the cellulose is in the form of one or more of methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, propyl cellulose, hydroxypropyl cellulose, and/or hydroxypropyl methyl cellulose.

[0243] (89) The suspension of any one of embodiments 79-88, wherein the cellulose has a molecular weight of from about 10,000 to about 1,000,000.

[0244] (90) The slurry of any one of embodiments 79-89, wherein cellulose is present in an amount of from about 0.1% to about 5.0% by weight of the stucco.

[0245] (91) The suspension of any one of embodiments 79-90, wherein the starch thickener is a substituted starch.

[0246] (92) The suspension of any one of embodiments 79-91, wherein the starch thickener is soluble in cold water.

[0247] (93) The suspension of any one of embodiments 79-92, wherein the starch thickener has a viscosity, measured in accordance with the IIV method, of at least about 1000 cP.

[0248] (94) The slurry of Embodiment 93, wherein the starch thickener has a viscosity, measured in accordance with the IIV method, of from about 2000 to about 8000.

[0249] (95) The suspension of any one of embodiments 79-94, wherein the starch thickener is modified by grafting foreign groups to the hydroxyl group of the glucose unit of the molecule.

[0250] (96) The suspension of embodiment 95, wherein the foreign groups include ethyl, hydroxylethyl, hydroxylpropyl, acetate, phosphate, and/or sulfate.

[0251] (97) The suspension of any one of embodiments 79-96, wherein the starch thickener is not pregelatinized.

[0252] (98) The suspension of any one of embodiments 79-97, wherein the starch thickener is an ester derivative of starch.

[0253] (99) The suspension of any one of embodiments 79-98, wherein the starch thickener is a starch carboxyethyl ether.

[0254] (100) The slurry of embodiments 98 or 99, wherein the starch thickener is a salt.

[0255] (101) The suspension of embodiment 100, wherein the starch thickener is sodium starch glycolate.

[0256] (102) The slurry of Embodiment 100, wherein the starch thickener has the molecular formula (C ₂ H ₄ O ₃ ) _x ⋅ (Na) _x , where X is the number of repeat units and ranges from about 1800 to about 18,000.

[0257] (103) The slurry of any one of embodiments 79-102, wherein water, stucco, and a concentrated layer builder are in slurry, and a starch thickener is present in the slurry in an amount of from about 0.1% to about 5% .0% by weight of plaster.

[0258] (104) The slurry as in any one of embodiments 79-103, wherein the slurry contains a starch thickener and one or both of cellulose and copolymers thereof.

[0259] (105) The suspension of any one of embodiments 79-103, wherein the suspension contains cellulose and one or both of a starch thickener and a copolymer.

[0260] (106) The suspension of any one of embodiments 79-103, wherein the suspension contains a copolymer and one or both of a starch thickener and cellulose.

[0261] (107) The suspension of any one of embodiments 79-103, wherein the suspension contains a starch thickener, cellulose, and a copolymer.

[0262] (108) The suspension of any one of embodiments 79-107, wherein the improver contains unsubstituted starch.

[0263] (109) The suspension of any one of embodiments 79-108, wherein the improver comprises pregelatinized starch.

[0264] (110) The suspension of Embodiment 109, wherein the pregelatinized starch has a viscosity of about 20 centipoise to about 700 centipoise when the viscosity is measured by exposing the starch to conditions consistent with the IIV method.

[0265] (111) The suspension of Embodiment 110, wherein the pregelatinized starch has a viscosity, measured according to the IIV method, of about 30 centipoise to about 200 centipoise.

[0266] (112) The suspension of any one of embodiments 79-111, wherein the improver comprises at least one crude starch having a peak viscosity of from about 100 Brabender units to about 900 Brabender units, as measured by adding the starch to a suspension with water at a starch concentration of 15% in terms of solids, and using a Viscograph-E device set at 75 rpm and 700 cmg, in which the starch is heated from 25 ° C to 95 ° C at a speed of 3 ° C / minute, then the suspension is kept at 95°C for ten minutes, and then the starch is cooled to 50°C at a rate of -3°C/minute.

[0267] It should be noted that the above are merely examples of embodiments of the invention. Other exemplary embodiments of the invention will be apparent from the full description given herein. One of ordinary skill in the art will also appreciate that each of these embodiments may be used in various combinations with other embodiments provided herein.

Examples

[0268] The following Example(s) further illustrate the present invention, but certainly should not be construed as limiting the scope of the invention.

EXAMPLE 1

[0269] This example demonstrates a composite gypsum board with a concentrated layer uniformly distributed throughout the core of the sheet with strong interfacial bonding.

[0270] Two 6.0 x 6.0 inch multilayer sheets (paper-concentrated layer-core-paper) were prepared in the laboratory. The core and concentrated layer formulations are shown in Tables 1 and 2 below. It is clear that vermiculite is not necessary, however vermiculite improves fire resistance, but fire resistance is not required for sheets by disclosure. It will also be understood that these compositions are merely representative, but other compositions are possible as described in the disclosure. The blowing agent was in the form of a 0.5% solution of Hyonic™ PFM-33 soap (available from GEO Specialty Chemicals, Ambler, PA).

[0271] The concentrated layer shown in Tables 1 and 2 is abbreviated "KS". Sheet 1A is a multi-layer sheet consisting of a core and a concentrated layer without thickener. Sheet 1 B is a multi-layer sheet consisting of a core and a concentrated thickener layer.

[0272] The core slurry was prepared by soaking the dry powders in the solution for 5 seconds and mixing for 10 seconds in a Hobart mixer, followed by foam injection for 8 seconds and mixing for an additional 2 seconds. [0273] The concentrated layer slurry was prepared by soaking the dry powders in the solution for 5 seconds and mixing for 7 seconds in a Waring mixer. Both the core suspension and the concentrated layer suspension were prepared simultaneously. A thin plastic frame (external dimension 6.5 inches × 6.5 inches × 1/16 inches and internal dimensions 6.0 inches × 6.0 inches × 1/16 inches) was used as a mold for the concentrated layer. A thick plastic frame (external dimension 6.5 inches × 6.5 inches × 1/2 inches and internal dimension 6.0 inches × 6.0 inches × 1/2 inches) was used as a mold for the core. The concentrated layer mold was placed on 6.5" x 6.5" face paper. The concentrated layer suspension was poured into the concentrated layer mold and spread evenly with a spatula. The core mold was then placed on top of the concentrated layer mold. The core slurry was then poured onto the concentrated layer and the core was covered with 6.5" x 6.5" backing paper. After both slurries had set and solidified, the 6" x 6" sheet was cut and removed from the molds. The sheet was dried at 110°F for 24 hours.

[0274] This example shows that the use of anti-leaching agents, as described herein, is useful for forming a uniform concentrated layer. In FIG. 3 shows cross sections of sheet 1A and sheet 1B after drying at 110°F for 24 hours. Sheet 1A does not contain a uniform concentrated layer, and part of the concentrated layer has been washed away, while sheet 1B contains a dense and uniform concentrated layer on top of the core.

[0275] In FIG. 4 shows cross sections of sheet 1A and sheet 1B after firing at 600° C. for 1 hour. The concentrated layers on both samples show good adhesion to the core, indicating that the addition of a thickener improves the adhesion ability of the concentrated layer suspension, but does not affect the hydration process of the gypsum.

[0276] The contents of all references, including publications, patent applications and patents cited herein, are incorporated herein by reference to the same extent that each reference is individually and separately stated to incorporate its contents by reference and its presentation in this document in its entirety.

[0277] Terms used in the singular and in the form of the term “at least one” and similar references (especially in the context of the following claims) are intended to include both the singular and the plural unless otherwise specified herein otherwise, or unless it clearly contradicts the context. The use of the term “at least one” followed by a listing of one or more elements (for example, “at least one of A and B”) is to be understood as one element selected from the listed elements (A or B) or any combination of two or more of the listed elements (A and B), unless otherwise specified herein or unless clearly inconsistent with the context. As used herein, it should be understood that the term “in an interlocking relationship” does not necessarily mean that the two layers are in direct contact. The terms “comprising,” “having,” “including,” and “consisting of” are intended to be non-limiting terms (i.e., meaning “including but not limited to”) unless otherwise noted. In addition, wherever “comprising” (or its equivalent) is said, “comprising” is considered to include “consisting essentially of” and “consisting of.” Thus, an implementation "comprising" (one) elements) supports implementations "consisting essentially of" and "consisting of" the listed elements. Wherever “consisting essentially of” is said, “consisting of” is considered to be included. Thus, an implementation "consisting essentially of" (one) element(s) supports implementations "consisting of" the listed elements. The listing of ranges of values in this document is intended solely for use as a symbolic means of individually referencing each individual value within that range, unless otherwise specified herein, with each individual value included in the description as individually listed herein. The term "typical" refers to an example and is not intended to suggest a better example. All methods described herein may be performed in any suitable order unless otherwise indicated herein or unless clearly inconsistent with the context. The use of any and all examples or representative language (eg, “such as”) provided herein is intended solely to better illustrate the invention and is not intended to limit the scope of the invention unless otherwise stated. Not a single wording in the description implies an indication of any non-claimed element as essential for the practical implementation of the invention.

[0278] This document describes preferred embodiments of this invention, including the best, in the opinion of the applicants, way of implementing the invention. For those of ordinary skill in the art, variations in such preferred embodiments of the invention may become apparent upon reading the foregoing description. The inventors expect that those skilled in the art will use such embodiments when appropriate, and the inventors expect that the invention will be practiced in a manner other than that specifically described herein. Accordingly, this invention contains all changes and equivalents to the subject matter of the invention listed in the claims appended to this document, in accordance with the provisions of current legislation. Moreover, any combination of the above-described elements in all their possible variations is covered by the invention, unless otherwise indicated herein or clearly contrary to the context.

Claims (16)

1. Composite gypsum board containing: (a) a sheet core containing set gypsum and formed from a first slurry containing water and stucco, the core having first and second core sides that are defined in opposite directions; And (b) a concentrated layer disposed in an interlocking relationship with the first face of the core, having a dry density of at least 1.1 times that of the dry core of the sheet, formed from a second slurry containing water, stucco, (i) starch thickener - an ether derivative of starch with a degree of substitution - the ratio of substituted groups to glucose units - of at least 0.5, untreated by heat treatment, obtained by grafting foreign groups to the hydroxyl group of the glucose unit of the starch molecule, and the foreign groups are selected from: ethyl , hydroxylethyl, hydroxylpropyl, acetate, phosphate, sulfate, (ii) at least one water-soluble cellulose ether selected from: methylcellulose, ethylcellulose, hydroxyethylcellulose, propylcellulose, hydroxypropylcellulose and hydroxypropylmethylcellulose, and, optionally, (iii) a copolymer containing polyacrylamide and acrylic acid, wherein said starch thickener, water-soluble cellulose ether and copolymer are introduced into the second suspension to increase its viscosity by at least 100% within 30 seconds to prevent the second suspension from being washed out when the first suspension is distributed thereon. 2. Composite gypsum board according to claim 1, characterized in that the copolymer contains 20 wt.% or less acrylic acid and has a molecular weight of 100,000 to 1,000,000. 3. Composite plasterboard sheet according to claim 1 or 2, characterized in that the concentrated layer is formed from a suspension containing a starch thickener, cellulose ether and a copolymer. 4. Composite plasterboard sheet according to any one of paragraphs. 1-3, characterized in that the first suspension optionally contains an improving additive, the second suspension contains an improving additive, wherein the improving additive contains: (i) at least one pregelatinized starch having a viscosity of from 20 centipoise to 700 centipoise when the viscosity is measured by subjecting the starch to VMA conditions, and (ii) at least one crude starch having a peak viscosity of between 100 Brabender units and 900 Brabender units, the viscosity being measured by suspending the starch with water at a starch concentration of 15% on a solids basis and using a Viscograph apparatus -E set at 75 rpm and 700 cmg, in which the starch is heated from 25°C to 95°C at a rate of 3°C/min, then the suspension is kept at 95°C for ten minutes and then the starch is cooled to 50°С at a speed of -3°С/min; when the enhancer is present in the first suspension, the enhancer is present in the second suspension at a higher concentration than in the first suspension.