RU2797758C2 - Gypsum board comprising a high level of salt chloride and a perforated sheet and method associated with them - Google Patents

Abstract

FIELD: construction materials.

SUBSTANCE: invention relates to a gypsum board formed from synthetic gypsum and other sources of gypsum having high concentrations of chloride salt, as well as to a method for making a gypsum board with at least a perforated back cover sheet, as well as a wall system where the gypsum board is used. A flat gypsum board comprises a board core layer comprising set gypsum; a front paper cover sheet, wherein the front paper cover sheet is free from a plurality of perforations; and a back paper cover sheet having a plurality of perforations extending therethrough; moreover, the stucco contains calcium sulphate hemihydrate, and the aqueous suspension comprises: at least 60% wt. of said calcium sulphate hemihydrate on a dry basis, from about 500 parts by weight to about 3000 parts by weight of chloride anions per 1,000,000 parts by weight of said calcium sulphate hemihydrate, and water at a weight ratio of water to calcium sulphate hemihydrate from 0.2:1 to 1.2:1, wherein the back cover sheet has a perforation coverage in the range of about 0.78 perforations/cm² (about 5 perforations/inch²) to about 7.75 perforations/cm² (about 50 perforations /inch²).

EFFECT: improved adhesion between the board core layer comprising a large amount of foreign salts and one or more cover sheets, in particular the back cover sheet.

10 cl, 9 dwg, 1 tbl

Description

FIELD OF TECHNOLOGY

[0001] This invention relates to gypsum board formed from synthetic gypsum and other sources of gypsum having high concentrations of chloride salt. The invention also provides a method for making gypsum board with at least a perforated back cover sheet to improve adhesion of the board core layer (gypsum core) to the back cover sheet compared to gypsum board without a perforated back cover sheet, as well as a wall system where gypsum board is used. plate.

BACKGROUND OF THE INVENTION

[0002] In the construction of buildings, one of the most common building elements for construction and renovation is gypsum wallboard, often referred to as dry plaster, gypsum board, gypsum panels, gypsum paneling, and ceiling tiles. From a chemical point of view, gypsum is calcium sulfate dihydrate (CaSO ₄ ⋅ 2H ₂ O).

[0003] Set gypsum (calcium sulfate dihydrate) is a well-known material that is used in such products. Set gypsum boards are often referred to as gypsum boards which comprise a board core layer (set gypsum core) sandwiched between two cover sheets, in particular between paper cover sheets. Such panels are usually used in the construction of drywall interior walls and ceilings of buildings. One or more denser areas, often referred to as "overlays", may be applied in layers to either face of the board core layer, typically at the interface (bond surface) between the board core layer and the inner surface of the cover sheet. The denser regions may be adjacent to the less dense region of the gypsum core after the gypsum has set.

[0004] During the production of gypsum board, stucco (containing calcium sulfate hemihydrate), water, and other ingredients may be mixed, typically in a mixer, to form an aqueous gypsum slurry as needed. Prior art terms: aqueous gypsum slurry, or aqueous slurry, or gypsum slurry are generally used for slurry both before and after the conversion of calcium sulfate hemihydrate to calcium sulfate dihydrate. The gypsum slurry is formed and discharged from the mixer onto a moving conveyor transporting a first cover sheet, optionally covered with a skim coat. If present, a top coat is applied up to the location where the gypsum slurry is discharged onto the first cover sheet. After applying the gypsum slurry to the first cover sheet, the gypsum slurry is overlaid with a second cover sheet, again optionally coated, to form a multi-layer assembly having the desired thickness. A forming plate, roller, and similar devices can assist in curing the desired thickness. The gypsum slurry is then left to set, forming a set (i.e., rehydrated) gypsum by reacting the calcined gypsum and water to form a matrix of crystalline hydrated gypsum (i.e., calcium sulfate dihydrate, also known as set gypsum). Hydration of calcined gypsum is a necessary condition for the formation of a cohesive matrix of hardened gypsum crystals, which as a result gives strength to the gypsum board. Heat (eg, using an oven) may be applied to remove remaining free (ie, unreacted) water and obtain a dry product. After that, the hardened gypsum product is cut to form gypsum boards of the desired length.

[0005] Gypsum (calcium sulfate dihydrate and any impurities) suitable for use in wallboard can be obtained from both natural and synthetic sources and then further processed.

[0006] Natural gypsum can be used by calcining its calcium sulfate dihydrate to form a hemihydrate. Gypsum from natural sources is a mineral of natural origin and can be mined as a hard rock. Gypsum of natural origin is a mineral commonly found in old salt lake deposits, in volcanic deposits, and in clayey formations. When mined, raw gypsum is generally in the dihydrate form. Gypsum is also known as calcium sulfate dihydrate, calcium sulfate (terra alba) or natural gypsum (landplaster). This material is also produced as a by-product of various industrial processes. For example, synthetic gypsum is a by-product of flue gas desulfurization processes in power plants. In gypsum, approximately two molecules of water are bound to each molecule of calcium sulfate.

[0007] Plaster of Paris is also known as calcined gypsum, stucco, or calcium sulfate hemihydrate.

(как правило, имеется в материале, обычно называемом «штукатурным гипсом») либо ангидрит сульфата кальция (CaSO₄), в зависимости от температуры и продолжительности воздействия. Используемые в данном документе термины «штукатурный гипс» и «кальцинированный гипс» относятся как к полугидратной, так и к ангидритной формам сульфата кальция, которые могут в них содержаться. Кальцинирование гипса с получением полугидратной формы происходит по следующему уравнению:[0008] In the event that calcium sulfate dihydrate from any source is heated sufficiently in a process called roasting or calcining, then the water of hydration is at least partially distilled off and calcium sulfate hemihydrate may be formed.

(generally found in a material commonly referred to as "stucco") or calcium sulfate anhydrite (CaSO ₄ ), depending on the temperature and duration of exposure. As used herein, the terms "stucco" and "calcined gypsum" refer to both the hemihydrate and anhydrite forms of calcium sulfate that they may contain. Calcination of gypsum to obtain a hemihydrate form occurs according to the following equation:

[0009] Calcined gypsum is capable of reacting with water to form calcium sulfate dihydrate, which is a solid product and is referred to herein as "set gypsum".

[0010] Gypsum can also be produced synthetically (referred to in the art as "singip") as a by-product of industrial processes such as flue gas desulfurization from power plants. Natural or synthetic gypsum can be calcined at high temperatures, typically above 150°C, to form stucco (i.e., calcined gypsum in the form of calcium sulfate hemihydrate and/or calcium sulfate anhydrite), which can be subsequently rehydrated to form hardened gypsum in the desired shape, such as slabs.

[0011] Synthetic gypsum obtained from power plants is generally suitable for use in gypsum panels intended for construction projects. Synthetic gypsum is a by-product of flue gas desulfurization processes from power plants (also known as desulfurization gypsum or desulfurized gypsum or DSG). Specifically, flue gas containing sulfur dioxide is scrubbed with lime or limestone to form calcium sulfite in the following reaction:

Calcium sulfite is then converted to calcium sulfate in the following reaction:

The hemihydrate form can then be obtained by calcination in a similar manner to that used for natural gypsum.

[0012] However, many traditional coal-fired power plants are being closed in favor of cleaner energy sources. The shutdown of coal-fired power plants has led to a growing shortage of synthetic gypsum suitable for the production of gypsum panels. Lower quality synthetic gypsum is available from power plants and other sources, but this gypsum from alternative sources often contains fairly high concentrations of foreign salts, in particular magnesium or sodium salts, more specifically magnesium chloride and sodium chloride. Small amounts of potassium chloride and calcium chloride may also be present in synthetic gypsum from alternative sources. Foreign salts can be problematic due to their tendency to reduce adhesion between the board core and the cover sheets, in particular the back paper cover sheet.

[0013] It should be understood that this description of the prior art is given by the inventors for the benefit of the reader, and should not be construed as a reference to the prior art or as an indication that any of these problems are of paramount importance in the art. Although the principles described may, in some respects and in some embodiments of the invention, overcome 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 particular problem noted in this document.

BRIEF DESCRIPTION OF THE INVENTION

[0014] The invention relates to gypsum boards having substantial adhesion between the core layer of the board and one or more cover sheets, in particular a back cover sheet, even when significant amounts of foreign salts, in particular chloride salts, and more specifically NaCl, are present. KCl, MgCl ₂ and/or CaCl ₂ . Methods are proposed for the production of gypsum boards from saline sources of gypsum, in particular from low quality synthetic gypsum. Improving the adhesion between the board core layer and the back cover sheet can be realized by including a plurality of perforations in the back cover sheet, in particular the back paper cover sheet.

[0015] Thus, in one aspect, the invention provides gypsum boards comprising a board core layer containing set gypsum and one or more chloride salts selected from the group consisting of NaCl, KCl, MgCl ₂ , CaCl ₂ , or any combination thereof .

In particular, the invention provides a gypsum board comprising:

a board core layer containing set gypsum;

a front paper cover sheet having an outer surface and an inner surface, the inner surface being in contact with the first face of the board core layer; And

a back paper cover sheet having an outer surface and an inner surface, the inner surface being in contact with the second face of the board core layer;

wherein the board core layer is disposed between the front paper cover sheet and the back paper cover sheet, and the back paper cover sheet has a plurality of perforations passing through it; And

wherein the board core layer is obtained by solidifying an aqueous slurry containing water and stucco between the first cover sheet and the second cover sheet, the stucco containing calcium sulfate hemihydrate and one or more chloride salts, and the aqueous slurry containing:

at least 60% wt. the specified calcium sulfate hemihydrate on a dry (anhydrous) basis,

from about 500 ppm up to about 3000 ppm chloride anions per 1,000,000 parts by weight of said calcium sulfate hemihydrate, and

water at a mass ratio of water to calcium sulfate hemihydrate from 0.2:1 to 1.2:1.

[0016] The inner surface of the front paper cover sheet having an outer surface and an inner surface is in contact with the first face of the board core layer. The inner surface of the back paper cover sheet having an outer surface and an inner surface is also in contact with the second face of the board core layer. The back paper cover sheet has a plurality of perforations extending therethrough. More specifically, the outer surface of the rear paper cover sheet may be attached to the wall after the gypsum board has been installed, and the outer surface of the front paper cover sheet may face outward from the wall after the gypsum board has been installed. One or both of the cover sheets may include a paper cover sheet, which may be made from the same or different paper materials.

[0017] Calcium sulfate hemihydrate is present in the precipitated aqueous suspension of the invention in an amount of at least 60% wt. dry (anhydrous) materials in aqueous suspension. Preferably, calcium sulfate hemihydrate is at least 70% wt. dry (anhydrous) materials of an aqueous suspension, more preferably at least 80% wt. dry (anhydrous) materials in aqueous suspension. In typical compositions of wallboards according to the invention, dry (anhydrous) materials in aqueous suspension contain at least 90% wt. or at least 95% wt. calcium sulfate hemihydrate. The use of calcium sulfate anhydrite is also contemplated, although it is preferably used in small amounts of less than 20% wt. dry (anhydrous) materials in aqueous suspension.

[0018] Similarly, the calcium sulfate dihydrate present in the core layer of the gypsum board of the invention as a result of solidification of the aqueous suspension is at least 60% wt. core, preferably not less than 70% wt. and more preferably at least 80% wt. In typical wallboard compositions, dry (anhydrous) aqueous suspension materials contain at least 90% wt. or at least 95% wt. calcium sulfate dihydrate.

[0019] In one or more other aspects of the invention, the invention provides methods for making gypsum board having significant amounts of one or more foreign salts in the board's core layer. Gypsum boards can exhibit significant adhesion between the board core layer and the back cover sheet even when one or more foreign salts are present. These methods produce gypsum board with a back cover sheet having a plurality of perforations passing through it to improve adhesion of the board core layer to the back cover sheet compared to a gypsum board having no perforations in the cover sheet.

[0020] The methods of the invention include:

preparation of an aqueous slurry containing a mixture of water and stucco, wherein the stucco contains calcium sulfate hemihydrate, and any combination thereof, and the aqueous slurry contains a mixture of:

at least 60% wt. said calcium sulfate hemihydrate on a dry basis,

from about 500 ppm up to about 3000 ppm chloride anions per 1,000,000 parts by weight (wt. h.) of said calcium sulfate hemihydrate, and water at a mass ratio of water to calcium sulfate hemihydrate from 0.2:1 to 1.2:1; and distributing an aqueous suspension between the front paper cover sheet and the back paper cover sheet, each paper cover sheet having an inner surface and an outer surface, and the aqueous suspension is in contact with the inner surfaces of the front cover sheet and the rear cover sheet;

wherein the back paper cover sheet has a plurality of perforations extending therethrough;

solidifying calcium sulfate hemihydrate to form a panel containing a gypsum core layer containing calcium sulfate dihydrate; and

drying the panel; and cutting the panel into gypsum board having one or more predetermined dimensions.

From about 500 ppm up to about 3000 ppm chloride anions per 1,000,000 parts by weight of said calcium sulfate hemihydrate means that per 1,000,000 parts by weight of said calcium sulfate hemihydrate, the amount of chloride anions present is from about 500 ppm. up to about 3000 ppm

[0021] The concentration of chloride anions in the aqueous slurry used to make the gypsum board products of the invention and to carry out the methods of the invention may range from about 500 ppm. up to about 3000 ppm, typically from about 500 ppm up to about 2000 ppm per 1,000,000 parts by weight of calcium sulfate hemihydrate, more typically from about 500 ppm. up to about 1500 ppm per 1,000,000 parts by weight of calcium sulfate hemihydrate.

[0022] The chloride anions in the aqueous suspension used for the articles and methods of the invention may be from any source. In general, one or more chloride salts are present in the gypsum source used to form the core of the board of the invention. The source of the gypsum may be a source of synthetic gypsum, in particular a low quality synthetic gypsum obtained from a flue gas stream from a power plant. Thus, in general, the source of chloride anions is one or more chloride salts in the stucco used to prepare the aqueous slurry. Chloride anions are formed from the chloride atoms of one or more chloride salts in stucco when the stucco is used in aqueous slurries. Typically, one or more chloride salts are any of NaCl, KCl, MgCl ₂ , CaCl ₂ or any combination thereof. However, chloride anions can also arise from impurities, such as one or more chloride salts contained in the water used to prepare the gypsum slurry.

[0023] As a rule, an aqueous suspension of gypsum contains less than 10% wt. portland cement or other dry (anhydrous) based hydraulic cement, more typically none. As a rule, an aqueous suspension of gypsum contains less than 10% wt. fly ash on a dry (anhydrous) basis, more typically, none. As a rule, an aqueous suspension of gypsum contains less than 10% wt. calcium carbonate on a dry (anhydrous) basis, more typically, it is absent.

[0024] For the purposes of this description, a dry base means an anhydrous base.

[0025] All average molecular weights, percentages, and ratios used herein are by weight (ie, % wt.), unless otherwise indicated.

[0026] In one or more other aspects of the invention, a wall system is provided comprising a frame to which at least one gypsum board of the invention is attached, with the outer surface of the front cover sheet facing away from the frame. In a wall system, the drywall board can be on an interior wall or on the ceiling of a building. As a rule, the frame is made of wood or metal. Typically, at least one gypsum board is attached to the frame by one or more screws, nails, adhesives, or other mechanical fasteners.

[0027] The advantages of the present invention may become apparent to those skilled in the art from a review of the following detailed description taken in conjunction with the examples and the appended claims. However, it should be noted that while the invention is capable of various forms, this description is intended to be illustrative and not intended to limit the invention.

BRIEF DESCRIPTION OF GRAPHICS

[0028] In FIG. 1 illustrates a cross-sectional view of a gypsum board of the invention in which a board core layer (gypsum core) is positioned between a front cover sheet and a back cover sheet, the back cover sheet having a plurality of perforations passing through it.

[0029] In FIG. 2 illustrates a plan view (axially) of the gypsum board of FIG. 1, which better shows the arrangement of the plurality of perforations in the back cover sheet.

[0030] In FIG. 3 illustrates a perspective view of a gypsum board of the present invention attached to one side of a wall with a metal partition stud suitable for use in an exemplary wall system of the present invention.

[0031] In FIG. 4 is a photograph of a back cover sheet which has a plurality of perforations extending therethrough.

[0032] In FIG. 5-8 are photographs showing the effect of various salts on adhesion to the board core layer in 12" x 12" x 1/2" (30.48 cm x 30.48 cm x 1.27 cm) drywall boards with and without having perforations in the back cover sheet.

[0033] In FIG. 9 illustrates photographs comparing a board of the present invention having a perforated cover sheet with a board having an unperforated cover sheet to show the effect of perforation on a 12" x 12" x 1/2" drywall board (30.48 cm x 30, 48 cm x 1.27 cm) containing 30 ppm Cl ^- from NaCl per million parts of calcium sulfate hemihydrate.

DETAILED DESCRIPTION OF THE INVENTION

[0034] The present invention proposes the possibility of using gypsum containing relatively high amounts of foreign salts in the core layer of a gypsum board. Under normal circumstances, high salt concentrations in the board core layer can lead to insufficient adhesion between the board core layer and at least one of the front cover sheet and the back cover sheet, in particular the back cover sheet.

[0035] Surprisingly, perforating the back cover sheet of the gypsum board can improve its adhesion to the board core layer containing a large amount of foreign salts. The core layer of the board may be made from an aqueous slurry of stucco containing calcium sulfate hemihydrate and a large amount of foreign salts, in particular chloride salts. One or both of the cover sheets may be paper cover sheets, which may be made from the same or different paper materials. Optionally, the front cover sheet of the gypsum board can also be perforated, providing similar benefits. Additionally, optionally, various additives may be present in the core layer of the board or in the gypsum slurry used to form the core layer of the board. The board core layer may further comprise one or more high density areas (layers) in contact with and applied to the inner surface of the front cover sheet or back cover sheet. One or more areas of high density may be in contact with the interior of the low density core layer of the board.

[0036] Without being bound by any theory or mechanism, it is believed that the perforations in the back cover sheet provide a conduit for outward migration of chloride salts released from the board core layer, which would otherwise aggregate detrimentally at the interface between the board core layer. and cover sheets. Instead, when perforations are present, chloride ions and their counterions (eg, Na ⁺ , K ⁺ , Mg ²⁺ and/or Ca ²⁺ ) can migrate at least partially through the perforations and potentially leave the surrounding drywall space. Alternatively, salts may be deposited inside or outside of the perforations on the outer surface of the back cover sheet. Due to salt deposition outside the perforations, the amount of "pure salt" between the paper and the core is reduced, hence less salt is present at the interface, resulting in a good bond between the paper and the core. In any case, this can lead to improved adhesion between the core layer of the board and the cover sheet.

[0037] In the event that the back cover sheet of the gypsum board is perforated in the manner described herein, the gypsum board may benefit from improved adhesion between the board core layer and the cover sheet(s) compared to gypsum board, which is such the same but without the perforation of the cover sheet(s). Accordingly, the present invention provides gypsum boards containing significant amounts of foreign salts in the core layer of the board, and methods for producing such gypsum boards using a source of gypsum containing significant amounts of foreign salts. Thus, to form a gypsum board, perforating at least one of the gypsum board cover sheets with a plurality of perforations, in particular the back cover sheet, may allow the use of lower quality gypsum sources containing excessive foreign salts, in particular chloride salts. Otherwise, such sources of gypsum may not be suitable for forming a gypsum board with sufficient adhesion between the board core layer and the cover sheets. The present invention effectively solves this problem.

[0038] Plasterboard

[0039] In FIG. 1 illustrates a cross-sectional view of a wall panel (gypsum board) 10 according to the invention in which a gypsum core (gypsum core layer) 12 (e.g., 0.5 inch (1.27 cm) thick) is sandwiched between a back paper cover sheet (back cover sheet). sheet) 14 and a facing paper cover sheet (front cover sheet) 18, each of which may be single or multi-layer paper. The back paper cover sheet (back cover sheet) 14 has perforations 20. The inside surface of the back paper cover sheet 14 forms the engagement side 24 of the back paper cover sheet 14 which faces the gypsum core 12. The inside surface of the facing paper cover sheet 18 forms the engagement side 28 which faces the gypsum core 12. The outer surface of the back paper cover sheet 14 faces the wall frame (see FIG. 3) of the room after the wall panel 10 is installed as an interior wall. The outer surface of the facing paper cover sheet 18 faces the interior of the room after the wall panel 10 is installed as an interior wall.

[0040] The back paper cover sheet (back cover sheet) 14 has a plurality of perforations 20 passing through it, in accordance with the present invention. On FIG. 2 illustrates a plan view (axial direction) of the wall panel 10 showing an exemplary configuration of the perforations 20 in the back paper cover sheet 14. As shown, the perforations 20 are structured in a regular arrangement of columns and rows. It should be appreciated that other patterned arrangements of perforations 20 are also within the scope of the invention, and the number, spacing, and coverage density of perforations 20 depicted should not be construed as limiting.

[0041] Unexpectedly, it has been found that the perforations 20 in the back paper cover sheet 14 increase the adhesion efficiency between the gypsum core 12 and the back paper cover sheet 14. The improved adhesion efficiency can be especially evident when the gypsum used to form the gypsum core 12 has a high salt concentration.

[0042] An optional thin, dense layer of gypsum (low density region) 22 lies between the gypsum core 12 and the facing paper cover sheet 18 to be in contact with the gypsum core 12 and the facing paper cover sheet 18. Thus, between the gypsum core 12 and the facing paper cover sheet 18. paper covering sheet 18 is a thin dense layer 22 of gypsum. Another optional thin dense layer of gypsum (not shown) may be interposed between and in contact with the gypsum core 12 and the back paper cover sheet 14. In general, the gypsum core 12 and the thin dense layer 22 of gypsum have the same composition and are adjacent to each other. Together, the gypsum core 12 and the thin dense layer 22 of gypsum can define the interior of the gypsum board 10, with the gypsum core 12 being a low density region or layer and the thin dense gypsum layer 22 being a relatively higher density region or layer. Typically, the aqueous slurry of gypsum used to form the gypsum core 12 is foamed. Thus, an area of low density can be formed from the gypsum slurry in the foamed state. Conversely, the aqueous slurry of gypsum used to form the thin dense layer 22 of gypsum is not foamed. Thus, a high density region can be formed from the non-foamed gypsum slurry. Thus, the thin dense layer 22 of gypsum is relatively denser than the rest of the gypsum core 12.

[0043] Thus, a region of high density may have lower porosity associated with it than an internal region of low density. Typically, a thin, dense layer of gypsum 22 is applied to the inside surface of the selected cover sheet. If a thin dense layer 22 of gypsum is present, then it is between the cover sheet and the low density area (gypsum core 12).

[0044] One or more chloride salts in the indicated amount may be present in the gypsum core 12 in accordance with this invention. If a high density region (thin dense layer 22 of gypsum) is included, then one or more chloride salts may also be present there. In general, one or more chloride salts may be selected from the group consisting of NaCl, KCl, MgCl ₂ , CaCl ₂ or any combination thereof.

[0045] The concentration of chloride anions in the aqueous slurry used to make the board core 12 and, if present, the high density region (thin dense layer 22 of gypsum) can range from about 500 ppm. up to about 3000 ppm, typically from about 500 ppm up to about 2000 ppm per 1,000,000 parts by weight of calcium sulfate hemihydrate, more typically from about 500 ppm. up to about 1500 ppm per 1,000,000 parts by weight of calcium sulfate hemihydrate.

[0046] Due to the passage of salt through the perforations, part of the salt from the original aqueous gypsum slurry may not remain in the core 12 and, if present, in the high density region (thin dense layer 22 of gypsum), but it may be in the pore of the perforation holes or on the outer surface of the paper sheet.

[0047] Manufacturing Methods

[0048] Various methods can be used to make the gypsum board of this invention from an aqueous slurry of gypsum containing calcium sulfate hemihydrate and a large amount of chloride salt. However, instead of a conventional gypsum source, a gypsum source containing one or more chloride salts may be used in the manufacturing process as described above.

обычно называемая «кальцинированный гипс» или «штукатурный гипс», которую получают посредством термического преобразования (кальцинирования) дигидратной формы сульфата кальция (CaSO₄).[0049] The main material from which gypsum wallboard and other gypsum products are made is the hemihydrate form of calcium sulfate.

commonly referred to as "calcined gypsum" or "plaster gypsum", which is obtained by thermal transformation (calcination) of the dihydrate form of calcium sulfate (CaSO ₄ ).

[0050] This invention encompasses methods for making gypsum board, including:

preparation of an aqueous slurry containing a mixture of water and stucco, wherein the stucco contains calcium sulfate hemihydrate and the aqueous slurry contains a mixture of:

at least 60% wt. said calcium sulfate hemihydrate on a dry basis,

from about 500 ppm up to about 3000 ppm chloride anions per 1,000,000 parts by weight (parts by weight) of said calcium sulfate hemihydrate, and

water at a mass ratio of water to calcium sulfate hemihydrate from 0.2:1 to 1.2:1; and

distributing the aqueous suspension between the front paper cover sheet and the back paper cover sheet, each paper cover sheet having an inner surface and an outer surface, and the aqueous suspension is in contact with the inner surfaces of the front paper cover sheet and the back paper cover sheet;

wherein the back paper cover sheet has a plurality of perforations extending therethrough;

solidifying calcium sulfate hemihydrate to form a panel containing a gypsum core layer containing calcium sulfate dihydrate; and

drying the panel; and cutting the panel into gypsum board having one or more predetermined dimensions.

[0051] Exemplary manufacturing techniques and equipment suitable for forming gypsum board in accordance with this invention can be found, for example, in US patent 7364676 and US patent application publication 2010/0247937, each of which is incorporated herein in its entirety by links. Briefly, such processes may include unloading the cover sheet onto a moving conveyor. Since gypsum board is usually formed "face down", this cover sheet corresponds to the facing paper cover sheet 18 at the completion of the manufacturing process. The gypsum slurry may be formulated in any suitable ratio of water to calcium sulfate hemihydrate for application to the cover sheet.

[0052] To produce gypsum board, stucco is mixed with water and additives to form an aqueous slurry that is continuously fed between continuous layers of paper on a board machine. One paper cover sheet is called the front paper sheet or facing sheet, and the other paper cover sheet is called the back paper sheet or back sheet. As the slab moves down the conveyor line to form the panel, the calcium sulfate recrystallizes or rehydrates back to its original stone state. As the gypsum hardens, the paper becomes chemically and mechanically bonded to the core layer of the board. The panel is then cut to length and transported through dryers to remove free moisture.

[0053] The dry and/or wet components of the gypsum slurry are fed to a mixer (eg, a stick mixer) where they are mixed to form a gypsum slurry. The mixer has a main body and an outlet (for example, a receiving hopper with an outlet gate, known in the art, or an alternative device, for example, described in US patents 6494609 and 6874930, which are incorporated herein in their entirety by reference). In some process configurations, the outlet may include a slurry distributor with a single feed opening or with multiple feed openings, such as those described in US Patent Application Publications 2012/0168527 and 2012/0170403, which are incorporated herein in their entirety by reference. When using a slurry distributor with multiple feed openings, the outlet may include a suitable flow divider, such as described in US Patent Application Publication 2012/0170403. A blowing agent (generally soap) may be added to the outlet of the mixer (e.g., the closure, as described, for example, in US Pat. ). The slurry discharged from the outlet after adding all the ingredients, including the blowing agent, is the main gypsum slurry and is used to form the core layer of the board. This gypsum slurry is discharged onto a moveable front cover sheet.

[0054] After mixing, foam is optionally added to the aqueous slurry to reduce the density of the article. Foam is formed by combining soap and water. The foam is then injected into the aqueous slurry after it has exited the mixer via a hose or chute. The frothing ring is a device having a plurality of holes, which are arranged in a ring perpendicular to the axis of the hose, so that when passing through the frothing ring, foam is forced under pressure into an aqueous suspension. Foam is generally added to the slurry charge to reduce the density of the core layer, but not to the skim coat slurry charge.

[0055] When the foam and slurry are brought together, the resulting slurry is moved and poured onto a conveyor covered with the first piece of facing material, which is the front cover sheet (eg, face paper cover sheet 18). Another piece of facing material that is a perforated back cover sheet (eg, back paper cover sheet 14) is placed over the slurry, forming a slurry sandwich assembly between the two facing materials. The multilayer assembly is fed onto a forming board whose height determines the thickness of the drywall board. The solid sandwich assembly is then cut with a cutting knife into appropriate lengths, typically eight to twelve feet (2.44 m to 3.66 m). During this treatment, the slurry is allowed to set (set) to form a board core containing a cohesive crystalline matrix of set gypsum.

[0056] The plates are then transferred to a drying oven. The oven temperature is typically in the range of 450°F (232°C) to 500°F (260°C) maximum. Preferably, the oven has three or more temperature zones. In the first zone, with which the wet plate is in contact, the temperature rises to the maximum temperature, and in the last two zones the temperature slowly decreases. The blower for the first zone is located at the outlet of the zone, blowing air in a countercurrent direction in relation to the direction of movement of the plate. In the second and third zones, the blowers are located at the entrance to the zone, directing the flow of hot air parallel to the movement of the plate. Less heat in the last zone prevents dry areas of the board from calcining, resulting in poor paper adhesion. Typical oven dwell time is about forty minutes, but time will vary depending on line performance, platen humidity, and other factors.

[0057] As described above, one or both cover sheets in a gypsum board may optionally be in boundary contact with a high density region or layer of the board's core layer, also known as a surfacing layer. After hardening, the cover layer can adhere to the core layer of the board. By introducing foam into the outlet port, the secondary gypsum slurry stream can be removed from the mixer body prior to foaming to provide a slurry to form a skim coat. If present, a top coat may be applied to the movable front cover sheet prior to applying the bulk of the gypsum slurry to form the board core layer, with the top coat generally occurring before the mixer. After being discharged from the outlet channel, the gypsum slurry, if necessary, is spread over the front cover sheet (optionally covered with a top coat). At this point, the dispensed gypsum slurry is in contact with a second cover sheet, which may correspond to the back cover sheet. The resulting wet assembly is in the form of a sandwich assembly which is the precursor to the final gypsum board product. The back cover sheet may optionally be coated with a second top coat, which may be formed from the same or different secondary gypsum slurry as the top coat on the front cover sheet, if present.

[0058] A gypsum core (e.g., gypsum core 12 in FIG. 1) made from a set gypsum core slurry typically has a thickness of 0.25 inches (0.635 cm) to 1.5 inches (3.81 cm) and a density of 15 to 55 pounds/cubic feet (0.2403 to 0.881 g/cm ³ ). When foamed, the gypsum core obtained from the hardened foamed gypsum slurry has a total void volume of 10 to 92% vol., in particular 25 to 90% vol. and more specifically, from 30 to 85% vol. Conversely, the resulting coating layer, if present, has a total void volume of less than 30% vol.

[0059] The back cover sheet (back paper facing sheet) may be perforated before the back cover sheet comes into contact with the gypsum slurry. The back cover sheet can be obtained/purchased from the manufacturer with the perforations already in place, or the perforations can be made just prior to bringing the back cover sheet into contact with the gypsum slurry. As such, the perforations do not extend into the board core layer or gypsum slurry prior to setting. For example, a plurality of perforations can be made using a suitable wall panel perforator, such as those described in US Patent Application Publication 2018/0065336. However, it should be understood that any suitable wallboard perforating device may be used.

[0060] Gypsum and stucco (calcined gypsum)

[0061] The calcium sulfate hemihydrate component (generally contained in the starting material known as stucco or calcined gypsum) used to form the crystalline matrix of the gypsum panel core typically includes beta calcium sulfate hemihydrate, water soluble calcium sulfate anhydrite, alpha -calcium sulfate hemihydrate or mixtures of any or all of them derived from natural or synthetic sources. In some aspects, the stucco may include non-gypsum minerals, such as small amounts of clays or other components that are associated with the gypsum source or added during the calcining, processing, and/or delivery of the stucco to the mixer. Stucco plaster may be fibrous or non-fibrous. Typically, raw stucco contains at least 70% wt. calcium sulfate hemihydrate, preferably at least 80% wt. calcium sulfate hemihydrate, more preferably at least 85% wt. calcium sulfate hemihydrate and even more preferably at least 90% wt. calcium sulfate hemihydrate.

[0062] Chloride salts

[0063] The aqueous slurry of gypsum for forming the gypsum board of the invention comprises water and stucco, wherein the aqueous slurry of gypsum also contains chloride anions. The chloride anions may be derived from one or more chloride salts from any source. Typically, one or more chloride salts are present in the gypsum source used to form the core of the board of the invention. Thus, all or at least most of the one or more chloride salts can be introduced into the gypsum slurry from the gypsum source used. The source of the gypsum may be a source of synthetic gypsum, in particular a low quality synthetic gypsum obtained from a flue gas stream from a power plant. Such a low quality gypsum source may not otherwise be suitable for forming wallboard without the use of at least one layer of starch, in accordance with the present invention. One or more chloride salts can also be formed from impurities, for example one or more chloride salts in the water used to prepare the aqueous gypsum slurry.

[0064] Chloride salts are any salts that contain chloride. Thus they include monovalent salts of a chloride anion and a monovalent cation such as sodium or potassium. Thus, they include divalent salts of chloride anions and a divalent cation such as calcium or magnesium. Other chloride salts are also contemplated, for example trivalent salts of chloride anions and a trivalent cation.

[0065] The concentration of chloride anions of one or more chloride salts in the aqueous slurry used to make the core of the board and, if present, the high density region (thin dense layer of gypsum) of the invention may range from about 500 ppm. up to about 3000 ppm, typically from about 500 ppm up to about 2000 ppm per 1,000,000 parts by weight of calcium sulfate hemihydrate, more typically from about 500 ppm. up to about 1500 ppm per 1,000,000 parts by weight of calcium sulfate hemihydrate.

[0066] Additives

[0067] Other additives that may be present in the gypsum slurry used to form the core layer of the board include, but are not limited to, reinforcing agents, foam (derived from a suitable blowing agent), dispersants, polyphosphates (e.g., sodium trimetaphosphate), retarders. , accelerators, recalcination inhibitors, binders, adhesives, secondary dispersants, leveling or non-leveling agents, thickeners, bactericides, fungicides, pH regulators, buffers, colorants, reinforcing fillers, flame retardants, water repellents (e.g. siloxane), fillers, starches and mixtures of the above.

[0068] Additives and other components of the gypsum slurry can be added to the mixer in various ways. For example, various combinations of components may be premixed before being fed into the mixer as one or more dry components and/or as one or more wet components. The individual components can likewise be introduced into the mixer in wet or dry form. When administered wet, the components may be incorporated into a carrier liquid, eg water, at any suitable concentration.

[0069] Fibers may optionally be used in the methods and compositions of this invention. The fibers may include mineral fibers (also known as mineral wool), glass fibers, carbon fibers and blends of such fibers, as well as other comparable fibers providing comparable benefits to wallboard. For example, glass fibers may be incorporated into the gypsum core slurry and/or the overcoat slurry, resulting in a core crystalline structure. Glass fibers in such aspects may have an average length of about 0.5 (1.27 cm) to about 0.75 inches (1.91 cm) and a diameter of about 11 to about 17 microns. In other aspects, such glass fiber may have an average length of from about 0.5 (1.27 cm) to about 0.675 inches (1.71 cm) and a diameter of from about 13 to about 16 microns. In other aspects, E-glass fibers having a softening point greater than about 800°C or greater than at least about 900°C are used. Instead of or in combination with glass fiber, mineral wool or carbon fibers known to those skilled in the art may be used.

[0070] The fibers, if included, may be present in the gypsum core slurry and/or the cover layer slurry in amounts based on dry matter per 100 wt. hours (wt. hours = parts by weight) calcium sulfate hemihydrate, from about 0.5 to about 10 wt. hours; preferably, from about 1 to about 8 wt. hours; more preferably, from about 2 to about 7 wt. hours; and most preferably, from about 3 to about 6 wt. h. Also, fibers may be absent.

[0071] Optionally, one or more phosphate-containing compounds may also be included in the suspension, if desired. For example, these phosphate-containing components may 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 units of phosphoric acid; salts or ions of condensed phosphates, each containing two or more phosphate units; and monobasic salts or monovalent ions of orthophosphates, as well as in the form of water-soluble acyclic polyphosphate salts. Illustrative examples are described in US Pat. Nos. 6,342,284; 6632550; 6815049; and 6822033, which are incorporated herein in their entirety by reference.

где n=6-27, тетракалий пирофосфат, имеющий молекулярную формулу K₄P₂O₇, тринатрий-дикалий триполифосфат, имеющий молекулярную формулу Na₃K₂P₃O₁₀, триполифосфат натрия, имеющий молекулярную формулу Na₅P₃O₁₀, тетранатрий пирофосфат, имеющий молекулярную формулу Na₄P₂O₇, триметафосфат алюминия, имеющий молекулярную формулу Al(РО₃)₃, пирофосфат натрия кислый, имеющий молекулярную формулу Na₂H₂P₂O₇, полифосфат аммония, имеющий 1000-3000 повторяющихся фосфатных звеньев и имеющий молекулярную формулу

где n=1000-3000, или полифосфорная кислота, имеющая два или более повторяющихся звеньев фосфорной кислоты и имеющая молекулярную формулу

где n равен двум или более.[0072] Phosphate-containing components can enhance green strength, resistance to permanent deformation (eg, sag), dimensional stability, and the like. Trimetaphosphate compounds may be used, including, for example, sodium trimetaphosphate, potassium trimetaphosphate, lithium trimetaphosphate, and ammonium trimetaphosphate. Sodium trimetaphosphate (STMP) is widely used, although other phosphates may be suitable, including, for example, sodium tetrametaphosphate, sodium hexametaphosphate having from about 6 to about 27 repeating phosphate units and having the molecular formula

where n=6-27, tetrapotassium pyrophosphate having the molecular formula K ₄ P 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 Al(PO ₃ ) ₃ , acidic sodium pyrophosphate having the molecular formula Na ₂ H ₂ P ₂ O ₇ , ammonium polyphosphate having 1000-3000 repeats phosphate units and having the molecular formula

where n=1000-3000, or a polyphosphoric acid having two or more repeating units of phosphoric acid and having the molecular formula

where n is two or more.

[0073] Phosphates are typically added in dry form and/or liquid form in an aqueous solution along with dry ingredients added to the slurry mixer, along with liquid ingredients added to the mixer, or in other steps or procedures.

[0074] If phosphate is present, it can be incorporated into the gypsum slurry in dry form or as an aqueous solution (eg, a phosphate solution at a concentration of from about 5% to about 20%, for example, about 10%). If phosphate is included, it may be present in any suitable amounts (on a solids weight basis), for example, from about 0.01% to about 0.5% by weight of the stucco, for example, from about 0.03% up to about 0.4%, from about 0.1% to about 0.3%, or from about 0.12% to about 0.4% by weight of the stucco. Phosphate may also be absent.

[0075] The gypsum slurry may optionally include at least one dispersant to improve fluidity. The dispersant(s) may be added to the gypsum slurry in dry form, optionally with other additives, and/or in liquid form, optionally with other liquid components. Examples of suitable dispersants include naphthalenesulfonates, eg polynaphthalenesulfonic acid and its salts (polynaphthalenesulfonates) and derivatives, which are condensation products of naphthalenesulfonic acids and formaldehyde, and polycarboxylate dispersants, eg polycarboxylic esters. Other examples of suitable dispersants include lignosulfonates or sulfonated lignin. Lignosulfonates are water-soluble anionic polyelectrolyte polymers that are by-products of wood pulp production using sulphite pulping.

[0076] Lower molecular weight dispersants may be desirable. Lower molecular weight naphthalenesulfonate dispersants may be preferred because they tend to require less water than higher viscosity, higher molecular weight dispersants. Thus, molecular weights from about 3,000 to about 10,000 (eg, from about 8,000 to about 10,000) may be desirable molecular weights for a dispersant. If desired, the molecular weight of polycarboxylate dispersants may be from about 20,000 to about 60,000 and may exhibit less set retardation than dispersants having a molecular weight greater than about 60,000.

[0077] Typical naphthalenesulfonates are a solution of naphthalenesulfonate in water with a solids content of naphthalenesulfonate ranging from about 35 wt. up to about 55% wt. However, if desired, the naphthalenesulfonates may be used in solid or powder form.

[0078] If a dispersant is present, then it can be included in the gypsum slurry in any suitable amounts (in terms of solids weight ratio), for example, from about 0.1% to about 5% by weight of the stucco, for example, from about 0.1% to about 4%, about 0.1% to about 3%, about 0.2% to about 3%, about 0.5% to about 3%, about 0.5% to about 2.5%, about 0.5% to about 2%, about 0.5% to about 1.5%, and similar amounts. Also, any one or more of the polynaphthalenesulfonates, polycarboxylic acid ethers, or lignosulfonates may be absent.

[0079] Accelerators and/or retarders can be added to the gypsum core slurry and/or the cover layer slurry to change the rate at which the calcium sulfate hemihydrate hydration reactions proceed. Suitable accelerators may include, for example, a wet gypsum set accelerator, a heat resistant set accelerator (HRA), or a climate set accelerator (CSA). "CSA" is an accelerator containing 95% calcium sulfate dihydrate ground with 5% sugar and heated to 250°F (121°C) to caramelize the sugar. The CSA is available from USG Corporation and is manufactured under US Pat. Nos. 3,573,947 and 6,409,825, incorporated herein by reference. Another preferred set accelerator is potassium sulfate. Heat Resistant Set Accelerator (HRA), which is the preferred set accelerator, is calcium sulfate dihydrate freshly ground with sugar in a ratio of about 5 pounds (2.268 kg) to 25 pounds (11.340 kg) of sugar per 100 pounds (45.359 kg) of calcium sulfate dihydrate . This is further described in US Pat. No. 2,078,199, incorporated herein by reference. They are both preferred set accelerators. If an accelerator and/or retarder is present, each may be included in the gypsum slurry in a dry matter amount of, for example, from about 0% to about 10% by weight of the stucco (for example, from about 0. 1% to about 10%), for example, from about 0% to about 5% by weight of the stucco (eg, from about 0.1% to about 5%). Suitable accelerators may include, for example, calcium sulfate dihydrate, carbohydrate-coated calcium sulfate, calcium sulfate dihydrate/organic phosphonate, and calcium sulfate dihydrate/organic phosphate. Accelerators and/or retarders may also be absent.

[0080] Foam (also known as foamed water), optionally, may be incorporated into the gypsum core slurry and/or the top layer slurry (preferably the gypsum core slurry) in amounts that provide the aforementioned reduced core density and panel weight. The blowing agent for producing foam is typically a soap or other suitable surfactant. Incorporation of foam into the gypsum core slurry in the proper amounts, formulations and process will produce the desired network and void distribution within the core of the finally dried wallboards. This void structure reduces the amount of gypsum and other core constituents, as well as core density and weight, while maintaining the desired structural and strength properties of the panel. Blowing agents, if present, may contain a major part by weight of the unstable component and a small part by weight of the stable component (eg when combining the unstable component with a mixture of stable and unstable components). The weight ratio of unstable component to stable component is effective to form distributed air voids within the set gypsum core, as described in US Pat. Nos. 5,643,510; 6342284; and 6632550, which are incorporated herein in their entirety by reference. Approaches for adding foam to a gypsum core slurry are known in the art, and one example of such an approach is discussed in US Pat. No. 5,683,635, the disclosure of which is incorporated herein by reference. Voids from evaporating water, typically having a diameter of about 5 microns or less, also contribute to the overall distribution of voids along with the aforementioned air (foam) voids. The volume ratio of voids with a pore size greater than about 5 microns to voids with a pore size of about 5 microns or less is from about 0.5:1 to about 9:1, for example, from about 0.7:1 to about 9:1 , from about 1.8:1 to about 2.3:1 or similar ratios. The blowing agent is present in the gypsum slurry in an amount, such as less than about 0.5% by weight of the stucco, such as about 0.01% to about 0.5%, about 0.01% to about 0.2%. , about 0.02% to about 0.4%, about 0.02% to about 0.2%, about 0.01% to about 0.1%, or similar amounts. Also, foaming agents may be absent.

[0081] Components may also be included in the gypsum slurry to provide fire resistance and/or water resistance. Examples include, for example, siloxanes (water resistance); fibers; heat-absorbing additives, for example, aluminum trihydrite (ΑΤΗ, aluminum trihydrite), magnesium hydroxide or similar additives; and/or high thermal expansion particles (eg, expanding to about 300% or more of their original volume when heated for about one hour at 1560°F (849°C)). Further description of such additives can be found in US Pat. No. 8,323,785, which is incorporated herein by reference in its entirety. Vermiculite with a high coefficient of thermal expansion may be included, although other fire resistant materials may be included. Flame retardant or waterproof additives, if present, may be included in the composition, if desired, in any suitable amount depending on, for example, the degree of fire resistance and similar performance parameters. For example, if fire retardant or waterproof additives are included, they may individually be present in an amount of from about 0.5% to about 10% by weight of the stucco, for example, from about 1% to about 10%, from about 1% to about 8 %, from about 2% to about 10%, from about 2% to about 8% and in a similar amount. If the composition includes a siloxane, it is desirable that it be introduced in the form of an emulsion. The slurry can then be formed and dried under conditions that promote polymerization of the siloxane to form a highly crosslinked silicone resin. A catalyst may be added to the gypsum slurry to help polymerize the siloxane to form a highly crosslinked silicone resin. As the siloxane, a solvent-free methylhydrosiloxane liquid can be used. This product is a liquid siloxane containing no water or solvents. It is contemplated that, if desired, from about 0.3% to about 1.0% siloxane, based on the weight of the dry ingredients, may be used. For example, if desired, from about 0.4% to about 0.8% siloxane, based on the weight of dry stucco, may be present in the gypsum slurry. Also, any one or more of these flame retardant and/or watertight components may be omitted. For example, siloxane may be absent.

[0082] The starch, if present, may be pregelatinized (cooked) starch and/or raw starch. In this regard, starches are classified as carbohydrates and contain two types of polysaccharides: straight-chain amylose and branched amylopectin. The starch granules are semi-crystalline, as seen, for example, in polarized light, and they are insoluble at or near room temperature. Raw starches are characterized as being insoluble in cold water and having a semi-crystalline structure. Generally, raw starches are obtained by wet milling and are not modified by heating the wet starch as is the case with cooked starches. Pregelatinized or cooked starches are characterized as being cold water soluble and having a non-crystalline structure. Also starch may be absent.

[0083] Water

[0084] Water is added to the suspension in any amount that makes the suspension flowable. The amount of water used varies greatly depending on the application in which it is used, the strictly appropriate dispersant used, the properties of the calcium sulfate hemihydrate, and the additives used.

[0085] To better control the properties of both the slurry and the set gypsum, the water used to prepare the slurry should be as pure as practicable. It is well known that salts and organic compounds modify slurry set time and range widely from set accelerators to set inhibitors. Some impurities lead to disturbances in the structure, since a cohesive matrix of dihydrate crystals is formed, which reduces the strength of the set product. Thus, the strength and consistency of the product is improved by using water that is as free from contaminants as is practical.

[0086] Water may be present in the gypsum core slurry and/or the top coat slurry of this invention at a weight ratio of water to calcium sulfate hemihydrate of about 0.2:1 to about 1.2:1; preferably from about 0.3:1 to about 1.1:1; more preferably from about 0.6:1 to about 1:1; most preferably from 0.7:1 to 0.95:1; and typically about 0.85:1.

[0087] Back cover sheet, front cover sheet and perforations

[0088] The back paper cover sheet and the front cover sheet may be made from any suitable paper material having any suitable basis weight.

[0089] In accordance with the present invention, only the back cover sheet of the gypsum board has a plurality of perforations extending therethrough. The back cover sheet is made of perforated paper.

[0090] The back and front cover sheets are made of paper. However, the paper materials for each cover sheet may be the same or different.

[0091] Various grades of paper can be used in gypsum panels, including Manila brand paper with a smooth film finish is often used as the facing paper cover sheet, and Newsline paper with a rougher finish is often used as the back paper cover sheet. As a rule, paper of both grades is multi-layered, with at least one decorative top layer and several layers of filler. However, if desired, at least one paper cover sheet, or both paper cover sheets, can be made from single ply paper.

[0092] If desired, to improve strength (e.g., nail pull strength), especially for lower density gypsum boards, one or both cover sheets may be formed from paper having a basis weight of, e.g., at least about 45 pounds. /MSF (219.5 g/m ² ) (e.g., about 45 to about 65 lb/MSF (317.0 g/m ² ), about 45 to about 60 lb/MSF (292.6 g/m ² ), from about 45 to about 55 lb/MSF (268.3 g/m ² ), from about 50 lb/MSF (243.9 g/m ² ) to about 65 lb/MSF from about 50 to about 60 lb/ MSF or equivalent basis weight). If desired, the front cover sheet may have a higher basis weight than the back cover sheet, which may provide improved nail pull resistance and handling. If desired, the back cover sheet may have a lower basis weight (eg, a basis weight of less than 45 lb/MSF, eg, from about 33 lb/MSF (161.0 g/m ² ) to 45 lb/MSF (eg, from about 33 up to about 40 lb/MSF (195.1 g/m ² )).

[0093] As mentioned above, the back cover sheet contains a plurality of perforations. The plurality of perforations may be provided on the back cover sheet in any suitable manner. Typically, the perforations are arranged in a pattern, such as a regular grid or an array of perforations (see, for example, FIG. 2). Other structured perforation arrangements are also within the scope of this invention, and the specific arrangement of perforations shown in FIG. 2 should not be considered limiting. Exemplary equipment for perforating one or more cover sheets in gypsum board in a manner compatible with the present invention is described in US Patent Application Publication 2018/0065336, which is incorporated herein by reference in its entirety.

[0094] The perforations in the cover sheet have a shape, size, and perforation density suitable for maintaining drying and/or promoting adhesion in drywall board.

[0095] Generally, perforations are substantially circular in shape. However, it should be appreciated that the perforations may have alternative geometries, such as oval, triangular, square, rectangular, or the like. Depending on the requirements for a particular application, any combination of round and non-circular perforations may be present. Any combination of non-circular perforations may be present.

[0096] Each of the perforations in the cover sheet(s), particularly in the back cover sheet, may define a hole having a size that ranges from about 0.005 inches (0.013 cm) to about 0.1 inches (0.254 cm) in its largest transverse dimension, preferably from about 0.01 inch (0.025 cm) to about 0.1 inch, and more preferably from about 0.01 inch to about 0.02 inch (0.051 cm ). The term "largest transverse dimension" means the largest dimension measured for each perforation in the plane of the cover sheet(s). For round perforations, the largest transverse dimension is the diameter of the round hole.

[0097] The perforations in the back cover sheet are generally uniform in size and shape. However, the perforations may be of mixed sizes and/or shapes. The dimensions of the perforations, whether the same or different, may be within any of the ranges indicated above. Moreover, if at least some of the perforations have different shapes, then a first plurality of perforations having a first shape and a first size and a second plurality of perforations having a different shape and/or a different size may be present. For example, the first plurality of perforations and the second plurality of perforations may be of different shapes but substantially the same size. [0098] Perforation coverage density refers to the number of perforations per unit area in the back cover sheet. The perforations present in the back cover sheet have a suitable perforation coverage density to ensure effective adhesion to the core layer of the board. The perforation density in the cover sheet(s) may be from about 5 to about 50 perforations/inch ² (from about 0.78 to about 7.75 perforations/cm ² ), preferably from about 12 to about 25 perforations holes/inch ² (from about 1.86 to about 3.88 perforations/cm ² ), for example, from about 10 to about 15 perforations/inch ² (from about 1.55 to about 2.33 perforations/cm 2 ² ) or, for example, about 15 to about 20 perforations/inch ² (about 2.33 to about 3.1 perforations/cm ² ).

[0099] Typically, perforations occupy 0.1 to 10%, more typically 0.5 to 5%, of the surface of the back cover sheet.

[00100] Systems

[00101] In FIG. 3 illustrates a perspective view of an exemplary cladding system 30 that may be used in an exterior wall system of the present invention. On FIG. 3 illustrates a metal stud wall "frame" 32 that includes a plurality of metal studs 34, a top rail 36, and a bottom rail 38. Gypsum boards 10 (FIG. 1) may be attached in any known manner to one or both sides of the metal studs 34, to close the wall and form the inner surface or surfaces of the wall or ceiling. A typical metal stud wall "frame" can be made in accordance with US Pat. invention. This metal frame system is provided merely as an example, as other metal frames may also be used. In addition, alternatively, the stud wall may comprise wood studs.

[00102] The following examples provide additional explanation for the present invention, but, of course, should not be construed as limiting its scope.

EXAMPLES

[00103] Gypsum core (suspension) compositions were prepared with a high concentration of various salts as indicated in Table 1. The source of chloride anions (samples #1 - #4) was sodium chloride (NaCl), magnesium chloride (MgCl ₂ ) or calcium chloride (CaCl ₂ ). Each of samples #1-#4 also contained sodium trimetaphosphate (TMP). To test the effect of TMP on the insolation of other salts, samples #5 and #6 contained only TMP.

дюйма (0,635 см). Диаметр перфорационных отверстий составлял около 0,01-0,02 дюйма (около 0,0254 до 0,0508 см).[00104] For the perforated paper sheet tested in these examples, the distance between adjacent perforations was

inches (0.635 cm). The diameter of the perforations was about 0.01-0.02 inches (about 0.0254 to 0.0508 cm).

дюйма (0,635 см). Диаметр перфорационных отверстий составлял около 0,01-0,02 дюйма (около 0,0254 до 0,0508 см).[00105] 12" x 12" x 1/2" (30.48 cm x 30.48 cm x 1.27 cm) envelopes were made using Manila paper (48#/MSF) as the front cover sheet and Newsline paper ( 42#/MSF) as the back cover sheet. Before pouring the slurry formulations (Table 1) into the envelope, half of the Newsline paper (6 inches x 12 inches (15.24 x 30.48 cm)) was perforated using a wallboard punch as shown in FIG. 4. The distance between adjacent perforations was

inches (0.635 cm). The diameter of the perforations was about 0.01-0.02 inches (about 0.0254 to 0.0508 cm).

[00106] Slurry formulations (Table 1) were prepared by soaking dry powders in solution for 10 seconds and mixing for 10 seconds in a Hobart mixer, followed by injection of the resulting foam for 8 seconds and mixing for another 2 seconds. The suspension thus obtained was poured into each of the envelopes. After the slurry had set and solidified, the envelope was sealed using paper tape. The sealed plate was dried at 450°F (232.2°C) for 20 minutes and then transferred to a 350°F (176.7°C) oven. After drying at 350°F for 15 minutes, the board was further dried at 110°F (43.3°C) overnight.

[00107] The results of the perforation of the back cover sheet were evaluated by the X-notch method to check the adherence of the paper to the core. Several X-shaped cuts were made on the back paper of the finished wallboard samples. At least two X-shaped cuts were made in the perforated portion of the back paper and at least two X-shaped cuts were made in the non-perforated portion (FIG. 4). The size of the X-shaped incision was approximately 2 inches x 2 inches (5.08 cm x 5.08 cm). Paper was peeled off from the center of the notch. The samples were evaluated qualitatively in comparison to each other by evaluating the amount of paper remaining on the gypsum core on one side of the back paper compared to the other (ie, perforated areas versus non-perforated areas). With good adhesion to the gypsum core, a thin layer of paper remains on the core. Conversely, if there is poor adhesion to the core, then the paper peels off the core and leaves most of the core exposed.

[00108] In Fig. 5-9 are photographs showing the effect of various salts on adhesion within gypsum boards of the invention, with or without perforations in the back cover sheet.

[00109] In FIG. 5-8 illustrate photographs of samples of plates No. 1 - No. 4, respectively.

[00110] In Fig. 5 illustrates the effect of perforation on a 12" x 12" x 1/2" (30.48 cm x 30.48 cm x 1.27 cm) slab sample #1 containing 600 ppm. Cl ^- from NaCl.

[00111] In Fig. 6 illustrates the effect of perforation on a 12" x 12" x 1/2" (30.48 cm x 30.48 cm x 1.27 cm) slab sample #2 containing 800 ppm. Cl ^- from NaCl.

[00112] In Fig. 7 illustrates the effect of perforation on a 12" x 12" x 1/2" (30.48 cm x 30.48 cm x 1.27 cm) board sample #3 containing 800 ppm. Cl ^- from CaCl ₂ .

[00113] In Fig. 8 illustrates the effect of perforation on a 12" x 12" x 1/2" (30.48 cm x 30.48 cm x 1.27 cm) slab #4 sample containing 800 ppm. Cl ^- from MgCl ₂ .

[00114] In Fig. 5-8 for Board Samples #1 #4 show less paper separation in the perforated area of the back cover sheet compared to the non-perforated area. Less exposed plaster was present in the perforated area due to less paper separation. Thus, at each concentration of all salts tested, improved adhesion to the board core layer was realized in the perforated portion of the back cover sheet.

[00115] In FIG. 9 illustrates the effects of perforation and non-perforation on a 12" x 12" x 1/2" (30.48 cm x 30.48 cm x 1.27 cm) slab having a gypsum core made from stucco gypsum containing 30 m. d. Cl ^- from NaCl per million parts of calcium sulfate hemihydrate. This stucco is a normal stucco with a low content of chloride salt. On FIG. 9, a cover sheet having perforations was used in the experimental sample of board No. 5. On FIG. 9, a cover sheet having no perforations was used in the control board #6.

[00116] Comparison of the experimental sample plate No. 5 of Fig. 9 and plate sample No. 6 of FIG. 9 shows that when using a low chloride content, the perforations did not improve adhesion to the same extent as in the samples with a high chloride content.

[00117] The foregoing are merely examples of the invention. One of ordinary skill in the art will appreciate that each of these examples may be used in various combinations with other aspects of the invention set forth herein.

ITEMS OF THE INVENTION

[00118] The following paragraphs describe various aspects of the present invention:

[00119] Item 1. Gypsum board, comprising:

a board core layer containing set gypsum;

a front paper cover sheet having an outer surface and an inner surface, the inner surface being in contact with the first face of the board core layer; And

a back paper cover sheet having an outer surface and an inner surface, the inner surface being in contact with the second face of the board core layer;

wherein the board core layer is disposed between the front paper cover sheet and the back paper cover sheet, and the rear perforated paper cover sheet has a plurality of perforations passing through it; And

wherein the board core layer is obtained by solidifying an aqueous slurry containing water and stucco between the first cover sheet and the second cover sheet, the stucco containing calcium sulfate hemihydrate and the aqueous slurry containing:

at least 60% wt. said calcium sulfate hemihydrate on a dry basis,

from about 500 ppm up to about 3000 ppm chloride anions per 1,000,000 parts by weight of said calcium sulfate hemihydrate, and

water at a mass ratio of water to calcium sulfate hemihydrate from 0.2:1 to 1.2:1.

[00120] Claim 2. The drywall board of claim 1, wherein the front

the cover sheet is a front paper cover sheet and the back cover sheet is a back paper cover sheet.

[00121] Claim 3. The gypsum board of claim 1 or 2, wherein the plurality of perforations are arranged in a pattern.

[00122] Claim 4. The gypsum board of any one of the preceding claims, wherein the plurality of perforations are substantially circular in shape.

[00123] Claim 5. The drywall board of any one of the preceding claims, wherein each perforation defines a hole size in the range of about 0.005 inches to about 0.1 inches (about 0.0127 cm to 0.254 cm).

[00124] Claim 6. The gypsum board of any one of the preceding claims, wherein each perforation defines a hole size in the range of about 0.01 inch to about 0.02 inch (about 0.0254 cm to 0.0508 cm).

[00125] Claim 7. The gypsum board of any one of the preceding claims, wherein the back cover sheet has a perforation density in the range of about 5 perforations/inch ² to about 50 perforations/inch ² (from about 0.78 to about 7 .75 perforations/cm ² ).

[00126] Claim 8. The gypsum board of any one of the preceding claims, wherein the back cover sheet has a perforation density in the range of about 12 perforations/inch ² to about 25 perforations/inch ² (from about 1.86 to about 3 .88 perforations/cm ² ).

[00127] Claim 9. The gypsum board of any one of the preceding claims, wherein the core layer of the board has a low density region and at least one high density region, with at least one high density region layered between the low density region and the front cover sheet or back cover sheet.

[00128] Claim 10. The gypsum board of claim 9, wherein the low density region is located between the first high density region located as a first layer in contact with the front cover sheet and the second high density region located as a second layer in contact with back cover sheet.

[00129] Claim 11. The gypsum board of claim 9 or 10, wherein the low density region is formed from a foamed gypsum slurry and contains a plurality of voids.

[00130] Claim 12. The gypsum board of any one of the preceding claims, wherein the set gypsum is formed from synthetic gypsum containing one or more chloride salts, said chloride salts providing at least a portion of said chloride anions.

[00131] Claim 13. The gypsum board of claim 12, wherein the aqueous slurry contains from about 1000 ppm. up to about 3000 ppm chloride anions per 1,000,000 parts by weight of said calcium sulfate hemihydrate.

[00132] Item 14. A method of making a drywall board, comprising:

preparation of an aqueous slurry containing a mixture of water and stucco, wherein the stucco contains calcium sulfate hemihydrate and the aqueous slurry contains a mixture of:

at least 60% wt. said calcium sulfate hemihydrate on a dry basis,

from about 500 ppm up to about 3000 ppm chloride anions per 1,000,000 parts by weight of said calcium sulfate hemihydrate, and

water at a mass ratio of water to calcium sulfate hemihydrate from 0.2:1 to 1.2:1;

distributing the aqueous suspension between the front cover sheet and the back cover sheet, each cover sheet having an inner surface and an outer surface;

wherein the back cover sheet has a plurality of perforations passing through it, and the aqueous slurry is in contact with the inner surfaces of the front cover sheet and the back cover sheet;

solidifying calcium sulfate hemihydrate to form a panel containing a gypsum core layer containing calcium sulfate dihydrate;

drying the panel; and cutting the panel into gypsum board having one or more predetermined dimensions.

[00133] Item 15. The method of claim 14, further comprising: making a plurality of punch holes in the back cover sheet using a wall panel puncher.

[00134] Item 16. The method of claim 14 or 15, wherein the plurality of perforations are present in the back cover sheet before the back cover sheet is brought into contact with the aqueous slurry.

[00135] Claim 17. The method of claim 14 or 15, wherein the paper for the back paper cover sheet is fed from a multi-perforated roll provided in the back cover sheet before the back cover sheet is brought into contact with the aqueous slurry.

[00136] Item 18. The method according to any one of paragraphs. 14-17 wherein at least a portion of the aqueous slurry is in a foamed state when distributed between the front cover sheet and the back cover sheet.

[00137] Claim 19. The method of claim 18 wherein the first portion of the aqueous slurry is dispensed in a non-foamed state as a first high density area in the form of a layer that is in contact with the front cover sheet and the second portion of the aqueous slurry is dispensed in a foamed state as the low density region which is in contact with the first high density region.

[00138] Claim 20. The method of claim 19, wherein the low density region is located between the first high density region and the second high density region in the form of a layer that is in contact with the back cover sheet.

[00139] Item 21. The method according to any one of paragraphs. 14-20, wherein calcium sulfate hemihydrate comprises a synthetic gypsum containing one or more chloride salts.

[00140] Item 22. A wall system comprising a frame to which at least one gypsum board according to any one of paragraphs is attached. 1-13 with the outer surface of the front cover sheet facing away from the frame.

[00141] Item 23. The wall system of claim 22, wherein the drywall board is on an interior wall or ceiling of a building.

[00142] Item 24. Wall system according to item 22 or 23, in which the frame is made of wood.

[00143] Item 25. Wall system according to item 22 or 23, in which the frame is made of metal.

[00144] Item 26. Wall system according to any one of paragraphs. 22-25, in which at least one drywall board is attached to the frame by means of one or more screws, nails, or adhesive.

[00145] To those of ordinary skill in the art, variations of the specifically disclosed invention may become apparent upon reading the foregoing description. The inventors expect those skilled in the art to make use of such variations where appropriate, and the inventors expect the invention to be practiced in a manner other than specifically described herein. Accordingly, this invention contains all changes and equivalents to the subject matter of the invention, listed in the claims attached to this document, in accordance with the norms of the current legislation. Moreover, the invention covers any combination of the above described elements in all their possible variations, unless otherwise indicated in this document, or this clearly does not contradict the context.

[00146] All references mentioned herein are hereby incorporated by reference to the same extent as in the case of individual and separate indication for each link to include its content by reference and set forth herein in its entirety.

[00147] The terms given in the singular and in the form of the term "at least one", as well as similar references in the context of the description of this invention (especially in the context of the following claims) are intended to cover both the singular and the plural, if this document does not indicate otherwise, or unless it is clearly contrary to the context. The use of the term "at least one" followed by a listing of one or more elements (e.g., "at least one of A and B") should be understood as one element selected from the listed elements (A or B) or any a combination of two or more of the listed elements (A and B), unless otherwise specified in this document, or unless it clearly contradicts the context. "Coupling" does not mean that the two layers are in direct contact. The terms "comprising," "having," "including," and "comprising" are intended to be non-limiting terms (i.e., meaning "including, but not limited to") unless otherwise noted. The enumeration of ranges of values in this document is intended to be used as a symbolic way of individually referring to each individual value belonging to a given range, unless otherwise noted in this document, with each individual value included in the description in the same way as individually specified in this document. All of the methods described herein may be performed in any acceptable order, unless otherwise specified in this document or clearly inconsistent with the context. The use of any and all examples or exemplary language (eg, "for example") given in this document is intended solely to better illustrate the invention and does not limit the scope of the invention unless otherwise stated. No wording in the description is intended to indicate any non-declared element as being essential to the practice of the invention.

Claims (29)

1. Flat gypsum board containing: a board core layer containing set gypsum; a front paper cover sheet having an outer surface and an inner surface, the inner surface being in contact with the first face of the board core layer, the front paper cover sheet being free from a plurality of perforations; And a back paper cover sheet having an outer surface and an inner surface, the inner surface being in contact with the second face of the board core layer; wherein the board core layer is disposed between the front paper cover sheet and the back paper cover sheet, and the back paper cover sheet has a plurality of perforations passing through it; And wherein the board core layer is obtained by solidifying an aqueous slurry containing water and stucco between a front paper cover sheet and a back paper cover sheet, the stucco containing calcium sulfate hemihydrate and the aqueous slurry containing: at least 60% wt. said calcium sulfate hemihydrate on a dry basis, from about 500 parts by weight to about 3000 parts by weight of chloride anions per 1,000,000 parts by weight of said calcium sulfate hemihydrate, and water at a mass ratio of water to calcium sulfate hemihydrate from 0.2:1 to 1.2:1, wherein the back coversheet has a perforation coverage in the range of about 0.78 perforations/cm ² - about 5 perforations/in ² to about 7.75 perforations/cm ² - about 50 perforations/in ² . 2. The plate according to claim 1, in which the aqueous suspension contains: at least 90% wt. calcium sulfate hemihydrate on a dry basis, wherein the aqueous suspension contains from about 500 parts by weight to about 2000 parts by weight of chloride anions per 1,000,000 parts by weight of said calcium sulfate hemihydrate, and wherein each perforation has a hole size in the range of about 0.0254 cm - about 0.01 inch to about 0.0508 cm - about 0.02 inch. 3. The board of claim 1, wherein each perforation has a hole size in the range of about 0.0127 cm - about 0.005 inch to about 0.254 cm - about 0.1 inch. 4. The board according to claim 1, wherein the back paper cover sheet has a perforation coverage density in the range of 1.86 perforations/ ^cm2 - 12 perforations/in2 to ^3.88 perforations/ ^cm2 - 25 perforations/ inch ² . 5. The board of claim 1, wherein the set gypsum is formed from synthetic gypsum containing one or more chloride salts, said chloride salts providing at least a portion of said chloride anions. 6. The board of claim 5 wherein the aqueous slurry contains from about 1000 parts by weight to about 3000 parts by weight of chloride anions per 1,000,000 parts by weight of said calcium sulfate hemihydrate. 7. A method for manufacturing a flat gypsum board according to claim 1, including: preparing an aqueous suspension containing a mixture of water and stucco, moreover, the stucco contains calcium sulfate hemihydrate, and the aqueous suspension contains a mixture of: at least 60% wt. said calcium sulfate hemihydrate on a dry basis, from about 500 parts by weight to about 3000 parts by weight of chloride anions per 1,000,000 parts by weight of said calcium sulfate hemihydrate, and water at a mass ratio of water to calcium sulfate hemihydrate from 0.2:1 to 1.2:1; distributing the aqueous slurry between the front paper cover sheet and the back paper cover sheet, each paper cover sheet having an inner surface and an outer surface; wherein the back paper cover sheet has a plurality of perforations passing through it, and the aqueous slurry is in contact with the inside surfaces of the front paper cover sheet and the back paper cover sheet, the back cover sheet having a perforation coverage density in the range of about 0.78 perf. holes/cm ² - about 5 perforations/inch ² to about 7.75 perforations/cm ² - about 50 perforations/inch ² ; solidifying calcium sulfate hemihydrate to form a panel containing a gypsum core layer containing calcium sulfate dihydrate; drying the panel; and cutting the panel into gypsum board having one or more predetermined dimensions. 8. The method of claim 7, further comprising: making a plurality of punch holes in the back paper coversheet using a wall panel puncher. 9. The method of claim 7, wherein the paper for the back paper cover sheet is fed from a roller having a plurality of perforations present in the back paper cover sheet before the back paper cover sheet is brought into contact with the aqueous slurry. 10. A wall system comprising a wall frame to which at least one gypsum board of claim 1 is attached, with the back paper cover sheet in contact with the wall frame and the outer surface of the front cover sheet facing away from the frame.

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