Gypsum board containing highly absorbent paper and related methods

Abstract

A composite gypsum board and a method for manufacturing the composite gypsum board are disclosed. The board comprises at least one set gypsum layer sandwiched between two cover sheets. The set gypsum layer is formed from at least stucco and water. Stucco materials typically contain a high salt impurity content, for example, when the stucco is calcined from certain sources of low-quality synthetic gypsum. For example, in some embodiments, the salt is a chloride salt, such as sodium chloride (NaCl), potassium chloride (KCl), magnesium chloride (MgCl), and / or calcium chloride (CaCl). At least one of the cover sheets is composed of highly absorbent paper, which strengthens the bond between the set gypsum layer and the cover sheet.

Description

Technical Field

[0001] In building construction, one of the more common building elements for construction and renovation is often gypsum wallboard, known as drywall, gypsum board, gypsum panel, gypsum paneling, and ceiling tile. In chemical terms, gypsum is calcium sulfate dihydrate (CaSO4·2H2O).

[0002] Hardened gypsum (calcium sulfate dihydrate) is a well-known material used in such products. Panels containing hardened gypsum are often called gypsum boards, which include a board core (hardened gypsum core) sandwiched between two cover sheets, especially paper cover sheets. Such panels are commonly used in the construction of drywall for interior walls and ceilings of buildings. One or more higher-density regions, often called "skim coats", may be included as a layer at the interface between either surface of the board core, usually between the board core and the inner surface of the cover sheet or a coating thereon. The higher-density region may be adjacent to the lower-density region of the gypsum layer providing the gypsum core layer of the gypsum board.

[0003] During the manufacture of gypsum board, to form an aqueous gypsum slurry, stucco (containing calcium sulfate hemihydrate), water, and optionally other ingredients may be mixed, usually in a mixer. The term aqueous gypsum slurry or aqueous slurry or gypsum slurry is typically used for slurries both before and after the calcium sulfate hemihydrate is converted to calcium sulfate dihydrate. The gypsum slurry is formed and discharged from the mixer onto a moving conveyor that carries a first cover sheet, optionally having a skim coat. When present, the skim coat is applied upstream of the location where the gypsum slurry is discharged onto the first cover sheet. After applying the gypsum slurry to the first cover sheet, a second cover sheet, also optionally having a skim coat, is applied to the gypsum slurry to form a sandwich assembly having a desired thickness. Molding plates, rollers, etc. may assist in setting the desired thickness. Next, the gypsum slurry is hardened by forming set (i.e., rehydrated) gypsum through the reaction of stucco and water to form a matrix of crystalline hydrated gypsum (i.e., calcium sulfate dihydrate, also known as hardened gypsum). The desired hydration of the stucco promotes the formation of an interlocking matrix of hardened gypsum crystals, thereby imparting strength to the gypsum board. Heat may be applied (e.g., in a kiln) to drive off the remaining free (i.e., unreacted) water and obtain a dry product. Next, the hardened gypsum product is cut to form gypsum board having a desired length.

[0004] Gypsum (calcium sulfate dihydrate and impurities) suitable for use in wallboard may be obtained from both natural and synthetic resources and is then further processed.

[0005] Natural gypsum may be used by calcining its calcium sulfate dihydrate to produce the hemihydrate form. Gypsum from natural resources is a naturally occurring mineral and can be mined in rock form. Naturally occurring gypsum is a mineral commonly found in old salt lake beds, volcanic deposits, and clay layers. When mined, raw gypsum is generally found in the dihydrate form. Gypsum is also known as calcium sulfate dihydrate, terra alba, or land plaster. This material is also produced as a by-product of various industrial processes. For example, synthetic gypsum is a by-product of the flue gas desulfurization process from power plants. Gypsum contains approximately two molecules of water associated with each molecule of calcium sulfate.

[0006] Plaster of Paris is also known as calcined gypsum, stucco, calcium sulfate hemihydrate, calcium sulfate hemihydrate, or calcium sulfate hemihydrate.

[0007] When calcium sulfate dihydrate from any source is heated sufficiently in a process called calcination or roasting, the water of hydration is at least partially driven off, and depending on the temperature and exposure time, calcium sulfate hemihydrate (CaSO4·1 / 2H2O), which is provided in a material commonly called "stucco", or calcium sulfate anhydrite (CaSO4) can be formed. As used herein, the terms "stucco" and "calcined gypsum" refer to both the hemihydrate and anhydrite forms of calcium sulfate that may be included therein. The calcination of gypsum to produce the hemihydrate form is carried out by the following equation. CaSO4·2H2O→CaSO4·0.5H2O+1.5H2O

[0008] Calcined gypsum can react with water to form calcium sulfate dihydrate, which is a rigid product and is referred to herein as "hardened gypsum".

[0009] Gypsum can also be synthetically obtained, for example, as a by-product of industrial processes such as flue gas desulfurization from power plants (referred to as "synthetic gypsum" in the art). Natural or synthetic gypsum can typically be calcined at a temperature higher than 150 °C, thereby forming stucco (i.e., calcined gypsum in the form of calcium sulfate hemihydrate and / or calcium sulfate anhydrite), which may subsequently be rehydrated to form hardened gypsum in a desired shape such as a board.

[0010] Synthetic gypsum obtained from power plants is generally suitable for use in gypsum panels for construction projects. Synthetic gypsum is a by-product of the flue gas desulfurization process from power plants (also known as desulfurized gypsum or desulfogypsum or DSG). In particular, flue gas containing sulfur dioxide is wet scrubbed with lime or limestone, and the lime or limestone produces calcium sulfite in the following reaction. CaCO3 + SO2 → CaSO3 + CO2 Next, calcium sulfite is converted to calcium sulfate in the following reaction. CaSO3 + 2H2O + 1 / 2O2 → CaSO4·2H2O Next, the hemihydrate form may be produced by calcination in a similar manner as used for natural gypsum.

[0011] However, many conventional coal-fired power plants are being closed in favor of more environmentally friendly energy sources. The closure of coal-fired power plants is leading to an increasing shortage of synthetic gypsum suitable for the manufacture of gypsum panels. Low-quality synthetic gypsum is available from power plants and other alternative sources, but the gypsum from these alternative sources often contains relatively high concentrations of foreign salts, especially magnesium or sodium salts, particularly magnesium chloride and sodium chloride. Small amounts of potassium chloride and calcium chloride may also be present in the synthetic gypsum from alternative sources. Foreign salts can be a problem because they tend to reduce the adhesion between the board core and the cover sheet, especially the backsheet cover sheet.

[0012] This description of the background art has been made by the inventors to assist the reader, and it will be appreciated that neither the citation of prior art nor any of the problems shown indicate that those problems have themselves been recognized in the art. The principles described may, in some respects and embodiments, mitigate problems specific to other systems, but it will be understood that the scope of the protected technological innovation is defined by the appended claims, rather than by the ability of the claimed invention to solve any particular problem described herein.

Summary of the Invention

[0013] The present invention relates to a gypsum board and a method for manufacturing a gypsum board that exhibits good adhesion between a hardened gypsum layer and a cover sheet of the board. The present invention is particularly applicable to boards formed from stackco containing a high content of salt impurities. Generally, stackco is formed by firing gypsum from natural or synthetic sources. In nature, it is a common abundant mineral that can be mined from the ground. Synthetic forms of gypsum can be obtained as by-products from flue gas desulfurization (FGD) processes associated with coal-fired power plants that burn high-sulfur coal. In power plants, sulfur dioxide emissions are removed by a wet scrubbing process. When limestone slurry is injected, synthetic gypsum precipitates after fly ash is removed. For example, some forms of synthetic gypsum contain a high content of salt impurities, which then remain in the stackco formed as calcined gypsum. The salt impurities in synthetic gypsum can be caused, for example, by high-salt coal. These salt impurities have been found to have an adverse effect on the adhesion between the cover sheet (e.g., formed from paper) and the hardened gypsum layer (e.g., board core) within the board.

[0014] The present invention provides a product and a manufacturing method in which at least one hardened gypsum layer is sandwiched between two cover sheets, and at least one of the cover sheets is a high-absorbency paper. In this way, the present invention enables an improvement in adhesion even when the hardened gypsum layer is formed from a stackco derived from low-quality synthetic gypsum containing undesirable foreign salts such as chloride salts of NaCl, KCl, MgCl2, and / or CaCl2, which are known to interfere with the adhesion between paper and the core.

[0015] Accordingly, in one aspect, the present invention provides a gypsum board comprising a hardened gypsum core disposed between a front cover sheet and a back cover sheet, said hardened gypsum core being formed from a slurry containing water, stackco, and a high salt impurity content (e.g., chloride salts). At least one of the cover sheets is a high-absorbency paper. As used herein, high-absorbency paper refers to paper that absorbs more water compared to conventional paper grades. Optionally, a front skim coat layer can be disposed between the first face of the hardened gypsum core and the face cover sheet, and a back skim coat layer can be disposed between the second face of the hardened gypsum core and the back cover sheet. In some embodiments, at least the back cover sheet is a high-absorbency paper.

[0016] In another aspect, the present invention provides a method of manufacturing a gypsum board. The method includes mixing at least water and a stucco having a high salt impurity content to form a first slurry. The first slurry is applied to form a cured gypsum board core in an adhesive relationship with a face cover sheet. The board core has a first face and a second face. The first face faces the face cover sheet. A back cover sheet is applied in an adhesive relationship to the second face of the board core to form a board precursor. At least one of the cover sheets is a high-absorption paper (e.g., in some embodiments, at least the back cover sheet). The board precursor is dried to form the board. Optionally, a face skim coat layer and a back skim coat layer can be provided on either side of the board core in any suitable manner. For example, in some embodiments, a second slurry containing at least stucco and water is applied to the face sheet before the first slurry is applied to the face sheet. The second slurry forms a face skim coat disposed between the face cover sheet and the board core. Similarly, optionally, a third slurry containing at least stucco and water can be applied to the back sheet before the back cover sheet is applied onto the board core. The third slurry forms a back skim coat disposed between the back cover sheet and the board core. The second and third slurries may be the same or different and, in preferred embodiments, are generally denser than the first slurry.

Brief Description of the Drawings

[0017]

Figure 1

[0018]

Figure 2

Modes for Carrying Out the Invention

[0019] The present invention is based at least in part on a board comprising at least one hardened gypsum layer sandwiched between two cover sheets, and at least one of the cover sheets is in the form of a high-absorbency paper in order to improve the adhesion between the hardened gypsum layer and the cover sheet. The present invention is particularly useful for gypsum boards in which the hardened gypsum layer is formed from a stack slurry containing a significant amount of foreign salts. For example, in some embodiments, the salts are chloride salts such as sodium chloride (NaCl), potassium chloride (KCl), magnesium chloride (MgCl2), and / or calcium chloride (CaCl2).

[0020] Such salts can be found, for example, in stack slurries where the stack is derived from low-quality synthetic gypsum. In this regard, usually, gypsum is procured for a board manufacturing facility and the gypsum is then fired to form the stack. Next, the stack is reacted with water to form a gypsum (i.e., calcium sulfate dihydrate) layer of a desired dimension. If the low-quality synthetic gypsum contains a significant amount of salt impurities, such salts remain in the stack after firing and thus are known to be present in the stack slurry. In some embodiments, the stack slurry contains a high-quality salt, for example, at least about 150 ppm of chloride anions per 1,000,000 parts by weight of the calcium sulfate hemihydrate, such as from about 150 ppm to about 2,000 ppm of chloride anions per 1,000,000 parts by weight of the calcium sulfate hemihydrate. The presence of a significant amount of salt impurities has been found to impede the adhesion between the board core and the paper cover sheet.

[0021] High-absorbency paper absorbs more moisture than conventional paper. When using a high-salt stackco, salts can migrate to the surface of the paper cover sheet, between the layers of the paper cover sheet, and at the interface between the paper cover sheet and the board core. As a result, adhesiveness can decrease and delamination may occur. Without wishing to be bound by a particular theory, the use of high-absorbency paper is thought to increase the amount of salt impurities that migrate to the outside of the cover paper, and correspondingly decrease the amount of salt that migrates to the interface between the cover sheet and the core. Further, during the drying process in a kiln, as moisture evaporates from the surface of the board, high-absorbency paper tends to absorb and evaporate moisture faster than conventional paper, and as a result, more salts are thought to migrate to the outside of the paper.

[0022] High-absorbency paper can have any suitable weight and thickness. Generally, the weight of the paper is determined by the basis weight, which refers to the weight per unit area. This can be expressed as pounds per 1000 square feet as the weight of the paper. In some embodiments, the high-absorbency paper has a basis weight of from about 30 lb / MSF to about 70 lb / MSF, such as from about 42 lb / MSF to about 60 lb / MSF, such as from about 45 lb / MSF to about 55 lb / MSF. In some embodiments, the high-absorbency paper has a caliper of from about 7 mils to about 20 mils, such as from about 10 mils to about 15 mils (e.g., about 12 mils). g / m 2 The water absorption of the surface over 60 seconds, represented by g / m, is measured in the Cobb test. In this test, on the surface of a 100 cm 2 sheet of paper, it is determined how many grams of water are absorbed based on the Cobb test. The procedure criteria for the Cobb test are described in TAPPI T 441.

[0023] High-absorbency paper can have any suitable water absorbency higher than that of conventional paper. The Cobb value on the adhesive side refers to the inside of the paper in contact with the gypsum slurry, and the Cobb value on the liner side refers to the outside of the paper not in contact with the slurry. These Cobb values are measured in accordance with the TAPPI standards described in the TAPPI T 441 test procedure. For example, in some embodiments, the high-absorbency paper has at least about 1.8 g / 100 cm 2 , such as about 1.8 g / 100 cm2 From about 3 g / 100 cm 2 , for example, about 1.8 g / 100 cm 2 to about 2.9 g / 100 cm 2 , about 1.8 g / 100 cm 2 to about 2.7 g / 100 cm 2 , about 1.8 g / 100 cm 2 to about 2.5 g / 100 cm 2 , about 2 g / 100 cm 2 to about 3 g / 100 cm 2 , about 2 g / 100 cm 2 to about 2.9 g / 100 cm 2 , about 2 g / 100 cm 2 to about 2.7 g / 100 cm 2 , about 2 g / 100 cm 2 to about 2.5 g / 100 cm 2 , about 2.1 g / 100 cm 2 to about 3 g / 100 cm 2 , about 2.1 g / 100 cm 2 to about 2.9 g / 100 cm 2 , about 2.1 g / 100 cm 2 to about 2.7 g / 100 cm 2 , about 2.1 g / 100 cm 2 to about 2.5 g / 100 cm 2 , about 2.2 g / 100 cm 2 to about 3 g / 100 cm 2 , about 2 g / 100 cm 2 to about 2.9 g / 100 cm 2 , about 2.2 g / 100 cm 2 to about 2.7 g / 100 cm 2 , or about 2.2 g / 100 cm 2 to about 2.5 g / 100 cm 2 , about 2.4 g / 100 cm 2 to about 3 g / 100 cm 2 , about 2.4 g / 100 cm 2 to about 2.9 g / 100 cm 2 , about 2.4 g / 100 cm 2 to about 2.7 g / 100 cm 2 etc. have cob values on the adhesive side.

[0024] In some embodiments, the high-absorbency paper has a liner-side cob value of at least about 0.5 g / 100 cm 2 , for example, from about 0.5 g / 100 cm 2 to about 1.5 g / 100 cm 2 , for example, from about 0.5 g / 100 cm 2 to about 1.2 g / 100 cm 2 , from about 0.7 g / 100 cm 2 to about 1.5 g / 100 cm 2 , from about 0.7 g / 100 cm 2 to about 1.2 g / 100 cm 2 , from about 0.9 g / 100 cm 2 to about 1.5 g / 100 cm 2 , from about 0.9 g / 100 cm 2 to about 1.2 g / 100 cm 2 and the like. Examples of high-absorbency papers include USG's Newsline Hi-Abs and News SHW HiAbs. Newsline Hi Abs has a basis weight of about 45 lb / MSF to about 48 lb / MSF. Newsline SHW Hi Abs is a super-high-absorbency paper and has a basis weight of about 53 to about 63.5 lb / MSF.

[0025] In embodiments where the board has only one highly absorbent cover sheet (e.g., the back cover sheet), the other cover sheet (e.g., the front cover sheet) can have any suitable basis weight and thickness. For example, in some embodiments, the other cover sheet can have a basis weight of from about 10 lb / msf to about 60 lb / msf, such as from about 10 lb / msf to about 55 lb / msf, from about 10 lb / msf to about 50 lb / msf, from about 10 lb / msf to about 40 lb / msf, from about 20 lb / msf to about 60 lb / msf, from about 20 lb / msf to about 55 lb / msf, from about 20 lb / msf to about 50 lb / msf, from about 20 lb / msf to about 40 lb / msf, from about 30 lb / msf to about 60 lb / msf, from about 30 lb / msf to about 55 lb / msf, from about 30 lb / msf to about 50 lb / msf, from about 30 lb / msf to about 40 lb / msf, etc. In some embodiments, the other cover sheet can have a weight of from about 15 lb / MSF to about 35 lb / msf, such as from about 20 lb / MSF to about 33 lb / msf, from about 20 lb / MSF to about 31 lb / msf, from about 20 lb / MSF to about 29 lb / msf, from about 20 lb / MSF to about 27 lb / msf, from about 15 lb / MSF to about 31 lb / msf, etc. Such weight paper can have a nominal thickness of from about 0.005 inches to about 0.015 inches, for example, from 0.007 to about 0.03 inches (e.g., about 0.01 inches). In some embodiments, the other cover sheet can be in the form of paper having a thickness of from about 0.008 inches to about 0.013 inches.

[0026] Optionally, the board can include a face skim coat and / or a back skim coat. In preferred embodiments, the skim coat layer is generally of higher density and very thin compared to the cured gypsum core. In some embodiments, the layer forming the cured gypsum core cumulatively contributes the most to the thickness of the gypsum layer and to the overall board. In some embodiments, the cured gypsum core constitutes a substantial thickness (e.g., at least about 90%, at least about 92%, at least about 95%, or at least about 97%) of the total thickness of all the gypsum layers. In some embodiments, the face and / or back skim coat layer has a dry thickness from about 0.125 inches (1 / 8 inch) to about 0.016 inches (1 / 64 inch). In preferred embodiments, at least one skim coat layer has a thickness from about 0.08 inches to about 0.02 inches, such as from about 0.08 inches to about 0.03 inches, from about 0.07 inches to about 0.02 inches, from about 0.07 inches to about 0.03 inches, from about 0.06 inches to about 0.02 inches, from about 0.06 inches to about 0.03 inches, from about 0.05 inches to about 0.02 inches, from about 0.05 inches to about 0.03 inches, from about 0.04 inches to about 0.02 inches, or from about 0.04 inches to about 0.03 inches.

[0027] In some embodiments, one or both of the skim coats can be prepared from a slurry containing skim coat starch, as described in U.S. Patent Application No. 62 / 930,965, filed November 5, 2019, which is incorporated herein by reference. Surprisingly and unexpectedly, it has been found that including skim coat starch in a very thin back skim coat further enhances the adhesion between the core and the back cover sheet. Without wishing to be bound by a particular theory, the presence of skim coat starch in the thin skim coat is thought to be effective in strengthening the adhesion between the cover sheet and the gypsum core because the starch acts as an adhesive that firmly bonds the paper fibers to the gypsum crystals in the core.

[0028] In a wall assembly, the board can be attached to a substrate, typically a stud of a framing structure. In the wall assembly, the back surface of the board (i.e., the outer surface of the back cover sheet) faces inward toward the stud, while the front surface of the board (i.e., the outer surface of the front cover sheet) is visible in a hanging state when the board is attached during use.

[0029] The stucco slurry used to make the hardened gypsum layer of the board contains stucco in the form of, for example, calcium sulfate alpha hemihydrate, calcium sulfate beta hemihydrate, and / or calcium sulfate anhydride. In addition to stucco and water, the board core is preferably formed from an agent that contributes to its low density, preferably a foaming agent, although in some embodiments, a low-density filler (e.g., perlite, low-density aggregate, etc.) can be used. Various foaming agent regimes are well known in the art. The foaming agent can be included to form a bubble distribution within the crystalline matrix of the hardened gypsum. In some embodiments, the foaming agent includes a major weight portion of an unstable component and a minor weight portion of a stabilizing component (e.g., when a blend of unstable and stable / unstable is combined). The weight ratio of the unstable component to the stabilizing component is effective to form a bubble distribution within the hardened gypsum core. See, for example, U.S. Pat. Nos. 5,643,510, 6,342,284, and 6,632,550. In some embodiments, the foaming agent includes an alkyl sulfate surfactant.

[0030] Many commercially known blowing agents are available, such as the HYONIC line of soap products from GEO Specialty Chemicals (Ambler, Pennsylvania) (e.g., 25AS), and can be used in accordance with embodiments of the present disclosure. 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 generated beforehand and then added to the stack slurry. The pre-generation can occur by inserting air into the aqueous blowing agent. Methods and apparatuses for generating foam are well known. See, for example, U.S. Patent Nos. 4,518,652, 2,080,009, and 2,017,022.

[0031] In some embodiments, the blowing agent comprises, consists of, or consists essentially of at least one alkyl sulfate, at least one alkyl ether sulfate, or any combination thereof, but essentially does not contain olefins (e.g., olefin sulfates) and / or alkynes. By essentially not containing olefins or alkynes, it means that the blowing agent (i) contains 0 wt% based on the weight of the stack, or there are no olefins and / or alkynes, or (ii) contains an ineffective amount, or (iii) contains a trace amount of olefins and / or alkynes. An example of an ineffective amount is an amount less than the threshold amount for achieving the intended purpose of using the blowing agent of olefins and / or alkynes, as understood by those skilled in the art. A trace amount can be, for example, less than about 0.001 wt% based on the weight of the stack, such as less than about 0.0005 wt%, less than about 0.001 wt%, less than about 0.00001 wt%, etc., as understood by those skilled in the art.

[0032] Some types of unstable soaps are alkyl sulfate surfactants having different chain lengths and different cations, in accordance with embodiments of the present disclosure. Suitable chain lengths are, for example, C8 - C 12 e.g., C8 - C10 or C 10 ~C 12 It may be. 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, blends thereof, and any combination thereof.

[0033] Some types of stable soaps are alkoxylated (e.g., ethoxylated) alkyl sulfate surfactants having different (generally longer) chain lengths and different cations according to embodiments of the present disclosure. Suitable chain lengths can be, for example, C 10 ~C 14 , for example, C 12 ~C 14 or C 10 ~C 12 It may be. Suitable cations include, for example, sodium, ammonium, magnesium, or potassium. Examples of stable soaps include, for example, sodium lauryl sulfate, potassium lauryl sulfate, magnesium lauryl sulfate, ammonium lauryl sulfate, blends thereof, and any combination thereof. In some embodiments, any combination of stable and unstable soaps from these listings can be used.

[0034] Examples of combinations of blowing agents and their addition in the preparation of foamed gypsum products are disclosed in U.S. Patent No. 5,643,510, which is incorporated herein by reference. For example, a first blowing agent that forms stable bubbles and a second blowing agent that forms unstable bubbles can be combined. In some embodiments, the first blowing agent is a soap, for example, an alkoxylated alkyl sulfate soap having an alkyl chain length of 8 to 12 carbon atoms and an alkoxy (e.g., ethoxy) group chain length of 1 to 4 units. The second blowing agent is optionally a non-alkoxylated (e.g., non-ethoxylated) alkyl sulfate soap having an alkyl chain length of 6 to 20 carbon atoms, for example, 6 to 18 or 6 to 16 carbon atoms. Adjusting the individual amounts of these two soaps is thought to enable control of the board foam structure in some embodiments until about 100% stable soap or about 100% unstable soap is achieved.

[0035] In some embodiments, as described in U.S. Patent Publications US 2017 / 0096369 A1, US 2017 / 0096366 A1, and US 2017 / 0152177 A1, the fatty alcohol can optionally be included in a premix for preparing a foam, for example, together with a blowing agent. This can better control the size and distribution of the foam (air) voids by improving the stability of the foam. The aliphatic alcohol can be any suitable aliphatic fatty alcohol. As defined throughout this specification, "aliphatic" refers to alkyl, alkenyl, or alkynyl, which may be substituted or unsubstituted, branched or unbranched, and saturated or unsaturated, and in some embodiments related to the carbon chains described herein, for example, C x ~C y (where x and y are integers). Thus, the term aliphatic also refers to chains having heteroatom substitutions that maintain the hydrophobicity of the group. The fatty alcohol can be a single compound or a combination of two or more compounds. In some embodiments, any fatty alcohol is C6~C 20Fatty alcohols (e.g., C6-C 18 , C6~C 116 , C6~C 14 , C6~C 12 , C6~C 10 , C6~C8, C8~C 16 , C8~C 14 , C8~C 12 , C8~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 Examples include octanol, nonanol, decanol, undecanol, dodecanol, or any combination thereof.

[0036] In some embodiments, the optional foam stabilizer comprises a fatty alcohol and is essentially free of a fatty acid alkyloamide or a carboxylic acid tauride. In some embodiments, the optional foam stabilizer is essentially free of glycol, although glycol may be included in some embodiments, for example, to allow for a higher surfactant content. Essentially free of any of the above components means that the foam stabilizer contains either (i) 0% by weight of any of these components, or (ii) an ineffective amount, or (iii) an insignificant amount of any of these components. An example of an ineffective amount would be an amount below the threshold amount for achieving the intended purpose of using any of these components, as would be understood by one skilled in the art. An insignificant amount, as would be understood by one skilled in the art, could be, for example, less than about 0.0001% by weight, e.g., less than about 0.00005%, less than about 0.00001%, less than about 0.000001%, etc., based on the weight of the stucco.

[0037] It has been found that suitable void distribution and wall thickness (independently) can be effective in enhancing strength, particularly in lower density boards (e.g., less than about 35 pcf). See, e.g., US2007 / 0048490 and US2008 / 0090068. Generally, evaporation water voids having voids of about 5 μm or less in diameter also contribute to the total void distribution along with the aforementioned air (bubble) voids. In some embodiments, the volume ratio of voids having a pore size greater than about 5 microns to voids having a pore size of about 5 microns or less is about 0.5:1 to about 9:1, e.g., about 0.7:1 to about 9:1, about 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, about 0.7:1 to about 6:1, about 1.4:1 to about 6:1, about 1.8:1 to about 6:1, 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, about 0.7:1 to about 2.3:1, about 0.8:1 to about 2.3:1, about 1.4:1 to about 2.3:1, about 1.8:1 to about 2.3:1, etc.

[0038] As used herein, the size of the voids is calculated from the maximum diameter of the individual voids within the core. The maximum diameter is the same as the ferret diameter. The maximum diameter of each defined void can be obtained from an image of the sample. The image can be taken using any suitable technique such as a scanning electron microscope (SEM) that provides a two-dimensional image. The pore sizes of a large number of voids can be measured in the SEM image such that the randomness of the cross-section (holes) of the voids can provide an average diameter. This calculation can be improved by measuring the voids in a plurality of randomly located images throughout the core of the sample. Additionally, constructing a three-dimensional solid model of the core based on several two-dimensional SEM images can also improve the calculation of the void size. Another technique is X-ray computed tomography (XMT) analysis that provides a three-dimensional image. Another technique is optical microscopy, where the light contrast can be used, for example, to assist in determining the depth of the voids. The voids can be measured either manually or using image analysis software, such as ImageJ developed by the NIH. Those skilled in the art will understand that the manual determination of the size and distribution of the voids from the image can be determined by visual observation of the dimensions of each void. The sample can be obtained by splitting a gypsum board.

[0039] The blowing agent can be included in the stack slurry in any suitable amount, for example, depending on the desired density. The solution of the blowing agent is prepared, for example, at about 0.5% (w / w). An appropriate amount of air is mixed with the appropriate amount of the solution of the blowing agent and added to the slurry. Depending on the amount of air required, the concentration of the solution of the blowing agent can vary from about 0.1% to about 1% (w / w). Since the skim coat layer has a higher density, the slurry for forming the skim coat layer can be made with fewer (or no) bubbles.

[0040] When included, the fatty alcohol can be present in the stucco slurry 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, e.g., from about 0.0001% to about 0.025% by weight of the stucco, from about 0.0001% to about 0.02% by weight of the stucco, or from about 0.0001% to about 0.01% by weight of the stucco. Because the slurry for the skim coat layer contains little or no foam, fatty alcohol may not be needed in the skim coat layer or may be included in a lesser amount, for example, from about 0.0001% to about 0.004% by weight of the stucco, e.g., from about 0.00001% to about 0.003% by weight of the stucco, from about 0.00001% to about 0.0015% by weight of the stucco, or from about 0.00001% to about 0.001% by weight of the stucco.

[0041] Other ingredients known in the art may also be included in the board core slurry, including, for example, accelerators, retarders, and the like. Accelerators may be in various forms (wet gypsum accelerators, heat-resistant accelerators, and weather-stabilizing accelerators). See, for example, U.S. Patent Nos. 3,573,947 and 6,409,825. In some embodiments in which accelerators and / or retarders are included, the accelerators and / or retarders may each be present in the stucco slurry in an amount on a solids basis of about 0% to about 10% by weight of the stucco (e.g., about 0.1% to about 10%), for example, about 0% to about 5% by weight of the stucco (e.g., about 0.1% to about 5%).

[0042] Additionally, in some embodiments, the gypsum layer can further comprise at least one dispersant to enhance fluidity. The dispersant may be included in the stucco slurry in dry form with other dry ingredients and / or in liquid form with other liquid ingredients. Examples of dispersants include naphthalene sulfonates, such as polynaphthalene sulfonic acid and its salts (polynaphthalene sulfonates) and derivatives, which are condensation products of naphthalene sulfonic acid and formaldehyde, and polycarboxylate dispersants, such as polycarboxylic acid ethers, e.g., PCE211, PCE111, 1641, 1641F, or PCE 2641 type dispersants, e.g., MELFLUX 2641F, MELFLUX 2651F, MELFLUX 1641F, MELFLUX 2500L dispersants (BASF), and COATEX Ethacryl M available from Coatex, Inc.; and / or lignosulfonates or sulfonated lignin. Lignosulfonates are water-soluble anionic polyelectrolyte polymers that are by-products of wood pulp production using sulfite pulping. One example of a lignin useful for practicing the principles of embodiments of the present disclosure is Malaspel C-21, available from Reed Lignin Company.

[0043] Low molecular weight dispersants are generally preferred. For naphthalene sulfonate dispersants, in some embodiments, they are selected to have a molecular weight of about 3,000 to about 10,000 (e.g., about 8,000 to about 10,000). In some embodiments, higher water demand naphthalene sulfonates, for example, with molecular weights greater than 10,000, can be used. As another example, for PCE211-type dispersants, in some embodiments, the molecular weight can be about 20,000 to about 60,000, which exhibits less retardation than dispersants with molecular weights greater than 60,000.

[0044] One example of a naphthalene sulfonate is DILOFLO, available from GEO Specialty Chemicals. DILOFLO is a 45% naphthalene sulfonate solution in water, although other aqueous solutions ranging, for example, from about 35% to about 55% by weight solids, are also readily available. The naphthalene sulfonate can be used in dry solid or powder form, such as, for example, LOMAR D, available from GEO Specialty Chemicals. Another example of a naphthalene sulfonate is DAXAD, available from GEO Specialty Chemicals (Ambler, PA).

[0045] When included, dispersants can be present in any suitable amount. In some embodiments, for example, the dispersant can be present in the stucco slurry in an amount of, for example, from about 0% to about 0.5%, such as from about 0.01% to about 0.7%, such as from about 0.01% to about 0.4%, such as from about 0.1% to about 0.2%, by weight of the stucco.

[0046] In some embodiments, the gypsum layer can optionally further comprise at least one phosphate-containing compound to enhance green strength, dimensional stability, and / or sag resistance. For example, in some embodiments, useful phosphate-containing components include water-soluble components, which may be in the form of ions, salts, or acids, i.e., condensed phosphoric acids, each of which contains two or more phosphoric acid units, condensed phosphate salts or ions, each of which contains two or more phosphate units, monobasic salts or monovalent ions of orthophosphate, and water-soluble acyclic polyphosphate salts. See, for example, U.S. Patent Nos. 6,342,284, 6,632,550, 6,815,049, and 6,822,033.

[0047] When added in some embodiments, the phosphate composition can enhance green strength, resistance to permanent deformation (e.g., sagging), dimensional stability, etc. Green strength refers to the strength of the board while it is still wet during manufacturing. Depending on the strictness of the manufacturing process, without sufficient green strength, the board precursor may be damaged on the production line.

[0048] For example, a trimetaphosphate compound including sodium trimetaphosphate, potassium trimetaphosphate, lithium trimetaphosphate, and ammonium trimetaphosphate can be used. Sodium trimetaphosphate (STMP) is preferred, but other phosphates may be suitable. For example, sodium tetrametaphosphate, having about 6 to about 27 repeating phosphate units and the molecular formula Na n+2 P n O 3n+1 (where n = 6 - 27), sodium hexametaphosphate, potassium pyrophosphate having the molecular formula K4P2O7, trisodium dipotassium tripolyphosphate having the molecular formula Na3K2P3O 10 , sodium tripolyphosphate having the molecular formula Na5P3O 10 , sodium pyrophosphate having the molecular formula Na4P2O7, aluminum trimetaphosphate having the molecular formula Al(PO3)3, sodium acid pyrophosphate having the molecular formula Na2H2P2O7, ammonium polyphosphate having 1,000 - 3,000 repeating phosphate units and the molecular formula (NH4) n+2 P n O 3n+1 (where n = 1,000 - 3,000), or polyphosphoric acid having 2 or more repeating phosphate units and the molecular formula H n+2 P n O 3n+1 (where n is 2 or more).

[0049] When included, polyphosphate can be present in any suitable amount. To illustrate, in some embodiments, the polyphosphate can be present in the slurry in an amount of, for example, about 0.1% to about 1%, e.g., about 0.2% to about 0.4% by weight of the stucco, or about 0% to about 0.5%, e.g., about 0% to about 0.2% by weight of the stucco. Thus, the dispersant and polyphosphate, optionally, can be present in the stucco slurry in any suitable amount.

[0050] The board core is preferably formed to a desired total composite board density, e.g., about 16 pcf (about 260 kg / m 3 ) to about 40 pcf, e.g., about 18 pcf to about 40 pcf, 18 pcf to about 38 pcf, 18 pcf to about 36 pcf, 18 pcf to about 32 pcf, 20 pcf to about 40 pcf, 20 pcf to about 36 pcf, 20 pcf to about 32 pcf, 22 pcf to about 40 pcf, 22 pcf to about 36 pcf, 22 pcf to about 32 pcf, 26 pcf to about 40 pcf, 26 pcf to about 36 pcf, or 26 pcf to about 32 pcf. In some embodiments, the board core can have even lower densities, e.g., about 30 pcf or less, about 29 pcf (about 460 kg / m 3 ) or less, approximately 28 pcf or less, approximately 27 pcf (approximately 430 kg / m 3 ) or less, such as about 26 pcf or less. For example, in some embodiments, the core density is about 12 pcf (about 190 kg / m 3 ) ~ approx. 30 pcf, approx. 14 pcf (approx. 220 kg / m 3 ) ~ approx. 30 pcf, 16 pcf ~ approx. 30 pcf, 16 pcf ~ approx. 28 pcf, 16 pcf ~ approx. 26 pcf, 16 pcf ~ approx. 3 ), 18pcf to about 30pcf, 18pcf to about 28pcf, 18pcf to about 26pcf, 18pcf to about 24pcf, 20pcf to about 30pcf, 20pcf to about 28pcf, 20pcf to about 26pcf, 20pcf to about 24pcf, 22pcf to about 28pcf, etc.

[0051] In some embodiments, composite boards made according to the present disclosure meet the test protocol according to ASTM Standard C473-10. For example, in some embodiments, when the board is cast at a thickness of ½ inch, the dry board has a strength of at least about 67 lbs as determined according to ASTM C473-10 (Method B). f (pound force), e.g., at least about 68 lb f , at least about 70 lbs f , at least about 72 lbs f , at least about 74 lbs f , at least about 75 lbs f , at least about 76 lbs f , at least about 77 lbs f In various embodiments, the nail pull resistance is about 67 lb f ~approximately 100 lbs f , about 67lb f ~about 95lb f , about 67lb f ~approximately 90lb f , about 67lb f ~about 85lb f , about 67lb f ~about 80lb f , about 67lb f ~about 75lb f , approximately 68 lbs f ~approximately 100 lbs f , approximately 68 lbs f ~about 95lb f , approximately 68 lbs f ~approximately 90 lbs f , approximately 68 lbs f ~about 85lb f , approximately 68 lbs f ~about 80lb f , about 70lb f ~approximately 100 lbs f , about 70lb f ~about 95lb f , about 70lb f ~approximately 90lb f , about 70lb f ~about 85lb f , about 70lb f ~about 80lb f , about 72lb f~about 100 lb f 、about 72 lb f ~about 95 lb f 、about 72 lb f ~about 90 lb f 、about 72 lb f ~about 85 lb f 、about 72 lb f ~about 80 lb f 、about 72 lb f ~about 77 lb f 、about 72 lb f ~about 75 lb f 、about 75 lb f ~about 100 lb f 、about 75 lb f ~about 95 lb f 、about 75 lb f ~about 90 lb f 、about 75 lb f ~about 85 lb f 、about 75 lb f ~about 80 lb f 、about 75 lb f ~about 77 lb f 、about 77 lb f ~about 100 lb f 、about 77 lb f ~about 95 lb f 、about 77 lb f ~about 90 lb f 、about 77 lb f ~about 85 lb f 、or about 77 lb f ~about 80 lb f and may be

[0052] In some embodiments, the composite gypsum board is at least about 11 lb as determined according to ASTM C473-10, Method B f 、e.g., at least about 12 lb f 、at least about 13 lb f 、at least about 14 lb f 、at least about 15 lb f 、at least about 16 lb f 、at least about 17 lb f 、at least about 18 lb f 、at least about 19 lb f 、at least about 20 lbf 、at least about 21 lb f 、or at least about 22 lb f and can have an average core hardness of. In some embodiments, the board is about 11 lb f ~ about 25 lb f 、for example, about 11 lb f ~ about 22 lb f 、about 11 lb f ~ about 21 lb f 、about 11 lb f ~ about 20 lb f 、about 11 lb f ~ about 19 lb f 、about 11 lb f ~ about 18 lb f 、about 11 lb f ~ about 17 lb f 、about 11 lb f ~ about 16 lb f 、about 11 lb f ~ about 15 lb f 、about 11 lb f ~ about 14 lb f 、about 11 lb f ~ about 13 lb f 、about 11 lb f ~ about 12 lb f 、about 12 lb f ~ about 25 lb f 、about 12 lb f ~ about 22 lb f 、about 12 lb f ~ about 21 lb f 、about 12 lb f ~ about 20 lb f 、about 12 lb f ~ about 19 lb f 、about 12 lb f ~ about 18 lb f 、about 12 lb f ~ about 17 lb f 、about 12 lb f ~ about 16 lb f 、about 12 lb f ~ about 15 lb f 、about 12 lb f ~ about 14 lb f 、about 12 lb f ~ about 13 lb f 、about 13 lb f ~ about 25 lbf 、 about 13 lb f ~ about 22 lb f 、 about 13 lb f ~ about 21 lb f 、 about 13 lb f ~ about 20 lb f 、 about 13 lb f ~ about 19 lb f 、 about 13 lb f ~ about 18 lb f 、 about 13 lb f ~ about 17 lb f 、 about 13 lb f ~ about 16 lb f 、 about 13 lb f ~ about 15 lb f 、 about 13 lb f ~ about 14 lb f 、 about 14 lb f ~ about 25 lb f 、 about 14 lb f ~ about 22 lb f 、 about 14 lb f ~ about 21 lb f 、 about 14 lb f ~ about 20 lb f 、 about 14 lb f ~ about 19 lb f 、 about 14 lb f ~ about 18 lb f 、 about 14 lb f ~ about 17 lb f 、 about 14 lb f ~ about 16 lb f 、 about 14 lb f ~ about 15 lb f 、 about 15 lb f ~ about 25 lb f 、 about 15 lb f ~ about 22 lb f 、 about 15 lb f ~ about 21 lb f 、 about 15 lb f ~ about 20 lb f 、 about 15 lb f ~ about 19 lb f 、 about 15 lb f ~ about 18 lb f 、 about 15 lb f ~ about 17 lb f 、 about 15 lb f ~ about 16 lb f, about 16 lb f ~ about 25 lb f , about 16 lb f ~ about 22 lb f , about 16 lb f ~ about 21 lb f , about 16 lb f ~ about 20 lb f , about 16 lb f ~ about 19 lb f , about 16 lb f ~ about 18 lb f , about 16 lb f ~ about 17 lb f , about 17 lb f ~ about 25 lb f , about 17 lb f ~ about 22 lb f , about 17 lb f ~ about 21 lb f , about 17 lb f ~ about 20 lb f , about 17 lb f ~ about 19 lb f , about 17 lb f ~ about 18 lb f , about 18 lb f ~ about 25 lb f , about 18 lb f ~ about 22 lb f , about 18 lb f ~ about 21 lb f , about 18 lb f ~ about 20 lb f , about 18 lb f ~ about 19 lb f , about 19 lb f ~ about 25 lb f , about 19 lb f ~ about 22 lb f , about 19 lb f ~ about 21 lb f , about 19 lb f ~ about 20 lb f , about 21 lb f ~ about 25 lb f , about 21 lb f ~ about 22 lb f , or about 22 lb f ~ about 25 lb f can have a core hardness of

[0053] With respect to bending strength, in some embodiments, when casting into a 1 / 2-inch thick board, the dry board has at least about 36 lb in the machine direction as determined in accordance with ASTM standard C473-10 f (e.g., at least about 38 lb f , at least about 40 lb f etc.), and / or at least about 107 lb in the width direction f (e.g., at least about 110 lb f , at least about 112 lb f etc.). In various embodiments, the board has a bending strength of about 36 lb f to about 60 lb f , for example, about 36 lb f to about 55 lb f , about 36 lb f to about 50 lb f , about 36 lb f to about 45 lb f , about 36 lb f to about 40 lb f , about 36 lb f to about 38 lb f , about 38 lb f to about 60 lb f , about 38 lb f to about 55 lb f , about 38 lb f to about 50 lb f , about 38 lb f to about 45 lb f , about 38 lb f to about 40 lb f , about 40 lb f to about 60 lb f , about 40 lb f to about 55 lb f , about 40 lb f to about 50 lb f , or about 40 lb f to about 45 lb f in the machine direction. In various embodiments, the board has a bending strength of about 107 lb f to about 130 lb f , for example, about 107 lb f to about 125 lb f , about 107 lb f~approximately 120 lbs f , about 107lb f ~about 115lb f , about 107lb f ~about 112lb f , about 107lb f ~about 110lb f , about 110lb f ~approximately 130 lbs f , about 110lb f ~about 125lb f , about 110lb f ~approximately 120 lbs f , about 110lb f ~about 115lb f , about 110lb f ~about 112lb f , about 112lb f ~approximately 130 lbs f , about 112lb f ~about 125lb f , about 112lb f ~approximately 120 lbs f , or about 112 lbs f ~about 115lb f The bending strength in the width direction can be

[0054] Advantageously, in various embodiments at various board densities described herein, the dry composite gypsum board can have a compressive strength of at least about 170 psi (1,170 kPa), for example, from about 170 psi to about 1,000 psi (6,900 kPa), 170 psi to about 900 psi (6,200 kPa), about 170 psi to about 800 psi (5,500 kPa), about 170 psi to about 700 psi (4,800 kPa), about 170 psi to about 600 psi (4,100 kPa), about 170 psi to about 500 psi (3,450 kPa), about 170 psi to about 450 psi (3,100 kPa), about 170 psi to about 400 psi (2,760 kPa), about 170 psi to about 350 psi (2,410 kPa), about 170 psi to about 300 psi (2,070 kPa), or about 170 psi to about 250 psi (1,720 kPa). In some embodiments, the board has a compressive strength of at least about 450 psi (3,100 kPa), at least about 500 psi (3,450 kPa), at least about 550 psi (3,800 kPa), at least about 600 psi (4,100 kPa), at least about 650 psi (4,500 kPa), at least about 700 psi (4,800 kPa), at least about 750 psi (5,200 kPa), at least about 800 psi (5,500 kPa), at least about 850 psi (5,850 kPa), at least about 900 psi (6,200 kPa), at least about 950 psi (6,550 kPa), or at least about 1,000 psi (6,900 kPa). Further, in some embodiments, the compressive strength can be limited by any two of the foregoing points. For example, the compressive strength can be between about 450 psi and about 1,000 psi (e.g., between about 500 psi and about 900 psi, between about 600 psi and about 800 psi, etc.). As used herein, the compressive strength is measured using a materials testing system commercially available as the ATS machine model 1610 from Applied Test Systems (Butler, Pennsylvania). The load is applied continuously without impact at a rate of 1 inch per minute.

[0055] The gypsum board according to an embodiment of the present invention can be produced on a typical gypsum wallboard manufacturing line. For example, board manufacturing techniques are described, for example, in U.S. Patent No. 7,364,676, U.S. Patent Application Publication No. 2010 / 0247937, and U.S. Patent Application No. 16 / 581,070. Briefly, the process typically involves discharging a cover sheet onto a moving conveyor. Since the gypsum board is usually formed "backward", this cover sheet is the "front" cover sheet in such embodiments. Front and / or back skim coats, as known in the art, can be included as needed.

[0056] In some embodiments, one or both of the skim coat layers have an average dry core hardness that is at least about 1.5 times greater than the average dry core hardness of the board core, and the average core hardness is measured in accordance with ASTM C-473-07 and is, for example, at least about 2 times greater, 2.5 times greater, 3 times greater, 3.5 times greater, 4 times greater, 4.5 times greater, etc., and each of these ranges can have any mathematically appropriate upper limit, such as 8, 7, 6, 5, 4, 3, or 2.

[0057] The slurries for forming the board core and for forming the skim coat layer can be formed in any suitable manner. For example, it is also possible to develop both slurry streams using one mixer. The mixer can be in the form of, for example, a "pin mixer" or a "pinless mixer" as required, in which the raw materials are agitated. Alternatively, two or more separate mixers can be used. The plurality of mixers can be in series or not connected. Examples of mixers are described in European Patent 1 637 302 B1, European Patent 2 929 996 B1, European Patent Application 3 342 571 A1, and US Patent Application 2017 / 0008192 A1. For efficiency, as required, since the amount of slurry that needs to be applied to the skim coat layer is less than the amount of slurry applied to form the board core, the mixer used for the skim coat layer can, in some embodiments, have a smaller mixing volume capacity. The "main" mixer (i.e., for forming the board core slurry) comprises a body and a discharge conduit (e.g., an arrangement of a gate - canister - boot known in the art, or a modified outlet design (MOD) arrangement described in US Patents Nos. 6,494,609 and 6,874,930). The blowing agent can be added into the discharge conduit of the mixer (e.g., within the gate as described in US Patents Nos. 5,683,635 and 6,494,609).

[0058] In some embodiments, it will be understood that the discharge conduit can include a slurry dispenser having either a single supply port or a plurality of supply ports, such as those described in US Patent Application Publication No. 2012 / 0168527A1 (Application No. 13 / 341,016) and US Patent Application Publication No. 2012 / 0170403A1 (Application No. 13 / 341,209). In those embodiments, by using a slurry dispenser having a plurality of supply inlets, the discharge conduit can include a suitable diverter, as described in US Patent Application Publication No. 2012 / 0170403 A1.

[0059] As is understood in the art, the boards are typically formed in a sandwich structure simultaneously and continuously. The top cover sheet moves as a continuous ribbon on a moving conveyor. After being discharged from the mixer, the slurry of the top skim coat layer is applied to the moving top cover sheet (for example). Also, a hard edge known in the art can be formed, if desired, for example, for convenience, from the same slurry stream that forms the skim coat layer (for example, the top and / or bottom skim coat layers).

[0060] Next, the board core slurry is applied over the skim coat layer and covered with a second cover sheet (typically a "bottom" cover sheet) to form a wet assembly in the form of a sandwich structure that is the board precursor of the final product. The bottom (back) cover sheet can support a bottom skim coat layer that optionally contains skim coat starch as described herein to enhance the adhesion between the back paper and the board core. The bottom skim coat layer can be formed from the same or a different gypsum slurry as the top skim coat layer. In some embodiments, the skim coat layer is applied to the back side of the board, i.e., in an adhesive relationship to the bottom (back) cover sheet, but no skim coat layer is applied between the core and the top cover sheet.

[0061] In some embodiments, the top sheet (which is face down at the wet end of the board machine) can be manufactured to be slightly wider than the width of the final board product so that the ends of the paper can be folded and overlapped at the ends of the board to align the ends of the paper with the bottom sheet (which is face up at the wet end of the board machine) to form a board envelope. For example, for a board with a nominal width of 48 inches, the top sheet can have a width of about 50 inches or more (for example, about 50 to about 52 inches, for example, about 50.375 inches). Correspondingly, in some embodiments, the bottom sheet can be manufactured to be narrower than the width of the board. Thus, for a board with a nominal width of 48 inches, the bottom sheet can have a width of less than about 48 inches (for example, about 46.5 to about 47.5 inches, for example, about 47.125 inches).

[0062] The wet assembly thus provided is conveyed to a forming station where the product is sized to a desired thickness (e.g., via a forming plate), and to one or more knife sections where it is cut to a desired length. The wet assembly is enabled to harden to form an interlocking crystal matrix of hardened gypsum, and excess water is removed using a drying process (e.g., by transporting the assembly through a kiln).

[0063] Also, it is common to use vibration in the manufacture of gypsum boards to remove large gaps or air pockets from the deposited slurry. Each of the above steps, as well as the processes and apparatus for carrying out such steps, are known in the art.

[0064] The present invention is further illustrated by the following exemplary sections. However, the present invention is not limited to the following sections.

[0065] (1) The gypsum board or method of making a gypsum board described herein.

[0066] (2) A gypsum board comprising a hardened gypsum core disposed between a front cover sheet and a back cover sheet, wherein the hardened gypsum core is formed from a slurry containing water, stackco, and a high salt impurity content, and at least one of the cover sheets is a high-absorbency paper.

[0067] (3) The gypsum board of (2), further comprising a front skim coat disposed between the front cover sheet and the hardened gypsum core.

[0068] (4) The gypsum board of (2) or (3), further comprising a back skim coat disposed between the back cover sheet and the hardened gypsum core.

[0069] (5) The gypsum board according to any one of (2) to (4), wherein the back cover sheet is a high-absorbency paper.

[0070] (6) The front and / or back skim coat of the gypsum board according to any one of (3) to (5) has a dry thickness of from about 0.125 inches (1 / 8 inch) to about 0.016 inches (1 / 64 inch), for example from about 0.08 inches (1 / 12 inch) to about 0.03 inches (1 / 32 inch).

[0071] (7) The high-salt impurity of the gypsum board according to any one of (2) to (6) contains at least about 150 ppm of chloride anions per 1,000,000 parts by weight of the stacker.

[0072] (8) The salt impurity of the gypsum board according to any one of (2) to (7) contains a chloride salt such as sodium chloride, potassium chloride, magnesium chloride, or calcium chloride.

[0073] (9) The high-absorption paper of the gypsum board according to any one of (2) to (8) has an adhesion-side cob value of at least about 2.1 g / 100 cm 2 according to the cob test.

[0074] (10) The high-absorption paper of the gypsum board according to any one of (2) to (9) has an adhesion-side cob value of from about 2.1 g / 100 cm 2 to about 3.1 g / 100 cm 2 according to the cob test.

[0075] (11) The high-absorption paper of the gypsum board according to any one of (2) to (10) has a basis weight of from about 35 lb / MSF to about 65 lb / MSF, for example from about 38 lb / MSF to about 60 lb / MSF, for example from about 42 lb / MSF to about 55 lb / MSF.

[0076] (12) The high-absorption paper of the gypsum board according to any one of (2) to (11) has a caliper of from about 10 mils to about 15 mils.

[0077] (13) A method of manufacturing a gypsum board, comprising: (a) mixing at least water and a stucco containing a high salt impurity content to form a first slurry; (b) applying the first slurry to form a board core in an adhesive relationship with a surface cover sheet, the board core having a first surface and a second surface, the first surface facing the surface cover sheet; (c) applying a back cover sheet in an adhesive relationship to the second surface of the board core to form a board precursor, at least one of the cover sheets being a high-absorbency paper; and (d) drying the board precursor to form a board.

[0078] (14) The method according to (13), further comprising applying a second slurry containing at least stucco and water to a front cover to form a front skim coat disposed between the surface cover sheet and the board core.

[0079] (15) The method according to (13) or (14), further comprising applying a third slurry containing at least stucco and water to a back cover to form a back skim coat disposed between the back cover sheet and the board core, the second and third slurries being the same or different.

[0080] (16) The method according to any one of (13) to (15), wherein the back cover sheet is a high-absorbency paper.

[0081] (17) The method according to any one of (13) to (16), wherein the front and / or back skim coat has a dry thickness of from about 0.125 inches (1 / 8 inch) to about 0.016 inches (1 / 64 inch), for example from about 0.08 inches (1 / 12 inch) to about 0.03 inches (1 / 32 inch).

[0082] (18) The method according to any one of (13) to (17), wherein the high salt impurity contains at least about 150 ppm of chloride anions per 1,000,000 parts by weight of the stucco.

[0083] (19) The method according to any one of (13) to (18), wherein the salt impurities include chloride salts such as sodium chloride, potassium chloride, magnesium chloride, or calcium chloride.

[0084] (20) The highly absorbent paper has a Cobb test result of at least about 2.1 g / 100 cm 2 The method according to any one of (13) to (19), wherein the adhesive side Cobb value is

[0085] (21) The highly absorbent paper has a Cobb test result of about 2.1 g / 100 cm 2 Approximately 3.1g / 100cm 2 The method according to any one of (13) to (20), wherein the adhesive side Cobb value is

[0086] (22) The method according to any one of (13) to (21), wherein the highly absorbent paper has a basis weight of about 40 lb / MSF to about 65 lb / MSF, for example, about 42 lb / MSF to about 60 lb / MSF, for example, about 45 lb / MSF to about 55 lb / MSF.

[0087] (23) The method according to any one of (13) to (22), wherein the highly absorbent paper has a caliper of about 10 mils to about 15 mils.

[0088] It should be noted that the foregoing paragraphs are illustrative and non-limiting. Other exemplary embodiments will be apparent from the entire description of this specification. Those skilled in the art will also understand that each of these embodiments may be used in various combinations with the other embodiments provided herein.

[0089] The following examples further illustrate the invention but, of course, should not be construed as in any way limiting its scope. Example 1

[0090] This example demonstrates the effectiveness of using highly absorbent paper as a cover sheet for wallboard containing a set gypsum layer prepared from stucco containing a high content of salt impurities. The highly absorbent paper strengthens the bond between the paper and the set gypsum core when the set gypsum layer is formed from a slurry containing a high concentration of salt.

[0091] Specifically, three 1 / 2-inch thick boards (1A-1C) were prepared on a wallboard manufacturing production line. These boards contained a set gypsum layer prepared according to the formulation in Table 1 sandwiched between front and back cover sheets. Board 1A was a control board in which the set gypsum core was prepared without high-salt impurities. The set gypsum core of each of boards 1B and 1C was prepared by adding a mixture of sodium chloride and magnesium chloride to the formulation set forth in Table 1 to introduce 600 ppm of chloride ions. The amounts of the ingredients in Table 1 are listed in lb / MSF. [Table 1]

[0092] In Table 1, HRA refers to heat accelerator. Pregelatinized starch is pregelatinized cornstarch with a cold water viscosity of 90 centipoise. Uncooked starch is uncooked acid-modified cornstarch with a hot water viscosity of 180 BU. The dispersant is naphthalene sulfonic acid. The retarder is pentasodium diethylenetriamine pentaacetate. STMP refers to sodium trimetaphosphate. Foams were prepared using the HYONIC line of soap products (e.g., 25AS) from GEO Specialty Chemicals (Ambler, Pennsylvania) and Polystep B25 from Stepan Company (Northfield, Illinois).

[0093] The face cover sheets (manila) of each of Boards 1A to 1C are papers having a basis weight of 50 lb and are of a conventional (ordinary) composition without high absorption characteristics. The back cover sheets (Newsline) of Comparative Boards 1A and 1B are papers having a basis weight of 47 lb of a conventional composition, and the back cover sheet of Board 1C is a high-absorption paper having a basis weight of 47 lb. Comparative Board 1A has a weight of 1307 lb / MSF, and Boards 1B and 1C have a weight of 1305 lb / MSF.

[0094] To determine the effect on the adhesion between each cover sheet of each board and the hardened gypsum layer, tests were conducted. After the boards were taken out of the kiln on the production line, they were cut into 5.5”×5.875” samples. On the surface of each board, a straight score with a depth of 1 / 8 inch was created 1.0 inch from and parallel to one of the 5.875-inch edges, and each board was conditioned overnight in a room at 75°F / 50% relative humidity (“RH”). Next, the conditioned samples were placed in a room at 90°F / 90% RH. A wet adhesion test was conducted on both the front and back surfaces of the boards that had been placed in the 90°F / 90% RH room for 3 hours, 16 hours, and 1 week, respectively. The humidified boards were tested according to the following humidified board test.

[0095] The humidified board was snapped along the score without breaking or stressing the paper on the back side of the board, causing the larger (4.5”×5.875”) portion of the board sample to rotate and be pushed downward with the surface facing up, thereby attempting to forcibly peel the back paper on the back side of the board from the larger portion. The force was increased until the two portions of the board were completely separated. The higher the wet adhesion load, the better the adhesion between the paper and the core. Next, the back surface of the larger portion was examined to determine the percentage of the surface of the back paper that was completely separated from the core (referred to as the “breakage rate”).

[0096] As shown in Table 2, the front sides of the boards under all three conditions showed similar humid adhesion loads and a 0% failure rate of the adhesion between the paper and the core. Figure 1 shows photographs of all three conditions after the adhesion test. As shown in Figure 1, good adhesion between the paper and the core was observed for each condition.

Table 2

[0097] However, as shown in Table 3, the results of humid adhesion from the back side of the board were different. Figure 2 shows photographs of all three conditions after the adhesion test. As shown in Figure 2, the adjusted board 1B showed insufficient adhesion between the paper and the core, while the adjusted boards 1A and 1C showed good adhesion between the paper and the core. The control board 1A without added salt had a high humid adhesion load and a 0% failure rate between the normal back paper and the gypsum core. On the other hand, when 600 ppm of chloride was added to the gypsum slurry, board 1B showed a much lower humid adhesion load and a failure rate exceeding 60% between the normal Newsline back paper and the gypsum core.

Table 3

[0098] Unlike board 1B, when high-absorbency paper was used as the back paper, board 1C formed from the same stack slurry formulation as board 1B showed a much higher humid adhesion load and a 0% failure rate for the adhesion between the paper and the core. This indicates that high-absorbency paper strengthens the adhesion between the paper and the core, especially when the wall board contains a high concentration of salt.

[0099] All references, including publications, patent applications, and patents listed in this specification, are hereby incorporated by reference in their entirety to the same extent as if each reference had been individually and specifically indicated to be incorporated by reference and were set forth in full herein.

[0100] In the context of describing the present invention (in particular, in the context of the following claims), the use of the terms "a", "an", "the", and "at least one", as well as similar directives, is to be construed as encompassing both the singular and the plural, unless otherwise specified herein or the context clearly dictates otherwise. The use of the term "at least one" following a list of one or more items (e.g., "at least one of A and B") is to be construed, unless otherwise specified herein or the context clearly dictates otherwise, as meaning either one item selected from the listed items (A or B) or any combination of two or more of the listed items (A and B). The terms "comprising", "having", "including", and "containing" are to be construed as non-limiting terms (i.e., meaning "including but not limited to") unless otherwise stated. The recitation of a range of values herein is merely intended to provide a convenient way of referring individually to each separate value within the range, and each separate value is incorporated herein as if it were individually recited herein. All methods described herein can be performed in any suitable order, unless otherwise specified herein or the context clearly dictates otherwise. The use of any examples or exemplary terms provided herein (e.g., "such as") is merely intended to make the understanding of the present invention easier and does not impose a limitation on the scope of the present invention unless otherwise recited in the claims. Terms herein are not to be construed as indicating an essential element for the practice of the invention that is not claimed.

[0101] Preferred embodiments of the invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those skilled in the art upon reading the above description. The inventors expect those skilled in the art to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, the invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Further, any combination of the above-described elements in all possible variations, unless otherwise specifically described herein or clearly inconsistent in context, is included by the invention.

Claims

1. A gypsum board comprising a set gypsum core disposed between a face cover sheet and a back cover sheet, the set gypsum core being formed from a slurry comprising water, stucco, and high-salt impurities, the high-salt impurities comprising at least 150 ppm of chloride ions (Cl-) per stucco, the back cover sheet comprising paper, the paper having a glue-side Cobb value of at least 2.1 g / 100 cm2 according to a Cobb test, the paper having a basis weight of 35 lb / MSF to 65 lb / MSF, and a thickness of 0.005 inch to 0.015 inch, the paper enabling superior adhesion between the set gypsum core and the back cover sheet of the gypsum board compared to a reference board made with a back cover sheet comprising paper having a glue-side Cobb value of less than 2.1 g / 100 cm2.

2. 2. The gypsum board of claim 1, further comprising a face skim coat disposed between the face cover sheet and the set gypsum core, and / or a back skim coat disposed between the back cover sheet and the set gypsum core.

3. 3. The gypsum board of claim 2, wherein the face and / or back skim coat has a dry thickness of 0.125 inch (1 / 8 inch) to 0.016 inch (1 / 64 inch).

4. 10. The gypsum board of claim 1, wherein the high salt impurities include sodium chloride, potassium chloride, magnesium chloride, calcium chloride, or any combination thereof.

5. According to the bump test, the paper has a bump value on the adhesive side of 2.1 g / 100 cm ２ to 3.1 g / 100 cm ２ The gypsum board according to claim 1, having the above value.

6. 10. The gypsum board of claim 1, wherein the paper has a basis weight of 40 lb / MSF to 65 lb / MSF.

7. 10. The gypsum board of claim 1, wherein the paper has a caliper of 10 mils to 15 mils.

8. A method for manufacturing gypsum board, comprising: (a) mixing at least water and stucco containing high salt impurities to form a first slurry, the high salt impurities comprising at least 150 ppm chloride ions (Cl − ) per stucco; (b) applying the first slurry to form a board core in adhesive relationship to a face cover sheet, the board core having a first side and a second side, the first side facing the face cover sheet; (c) applying a back cover sheet in an adhesive relationship to the second face of the board core to form a board precursor, wherein the back cover sheet includes paper, the paper having an adhesive side cob value of at least 2.1 g / 100 cm2 according to a cob test, the paper having a basis weight of from 35 lb / MSF to 65 lb / MSF, the thickness of the paper being from 0.005 inches to 0.015 inches, the paper enabling excellent adhesion between the board core of the gypsum board and the back cover sheet as compared to a reference board made of a back cover sheet including paper having an adhesive side cob value of less than 2.1 g / 100 cm2; (d) drying the board precursor to form a board; A method comprising.

9. The method of claim 8, further comprising applying a second slurry comprising at least stackco and water to a face sheet to form a face skim coat disposed between the face cover sheet and the board core.

10. The method of claim 9, further comprising applying a third slurry comprising at least stackco and water to a back paper to form a back skim coat disposed between the back cover sheet and the board core, the second and third slurries being the same or different.

11. The gypsum board further comprises a face skim coat disposed between the face cover sheet and the board core, and / or a back skim coat disposed between the back cover sheet and the board core, the face and / or back skim coat having a dry thickness of from 0.125 inches (1 / 8 inch) to 0.016 inches (1 / 64 inch). The method of claim 8.

12. The method of claim 8, wherein the high salt impurities include sodium chloride, potassium chloride, magnesium chloride, or calcium chloride.

13. According to the cob test, the paper has a cob value on the adhesive side of 2.1 g / 100 cm ２ to 3.1 g / 100 cm ２ The method according to claim 8, having a cob value on the adhesive side of

14. The method of claim 8, wherein the paper has a basis weight of from 40 lb / MSF to 65 lb / MSF.

15. The method of claim 8, wherein the paper has a caliper of from 10 mils to 15 mils.

16. The gypsum board of claim 1, wherein the paper has a liner side cob value of at least 0.5 g / 100 cm2 according to a cob test.

17. The method of claim 8, wherein the paper has a liner side Cobb value of at least 0.5 g / 100 cm 2 according to the Cobb test.

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