Foamed gypsum with improved strength

Abstract

The present disclosure relates to gypsum slurries. In one aspect, a surfactant combination that contains (i) from 20 to 80 weight percent of an anionic di-aryl oxide surfactant; and (ii) from 20 to 80 weight percent of a nonionic sugar-based surfactant is useful as a foaming agent for gypsum slurry used to produce gypsum boards. Minimum ratios of the anionic to the nonionic surfactant may vary depending upon the lipophilic portion of the anionic surfactant. The resulting boards can have a desirable combination of weight and physical strength, as demonstrated by nail pull resistance.

Description

[0001] FOAMED GYPSUM WITH IMPROVED STRENGTH

[0002] FIELD

[0003] This invention relates to the field of gypsum boards.

[0004] INTRODUCTION

[0005] Gypsum comprises primarily calcium sulfate dihydrate (CaSOj • 2 FLO). Gypsum is the main component of gypsum boards, which contain a gypsum-containing core sandwiched between two cover sheets. The cover sheets typically comprise paper, although in some cases other materials can be used in addition to paper or in place of paper. The gypsum core can contain materials in addition to gypsum, such as fibers, starch, cellulose pulp, water-resistance additives such as wax- or asphalt emulsion, foaming agents such as surfactants and other additives. Gypsum boards are commonly known as drywall and are commonly used to make interior building walls and ceilings.

[0006] The core in a gypsum board normally has a foamed stmcture, to reduce the weight of the board for easier transport and use. Different levels of foaming can produce a standard board, which has a weight of about 8 kg / m2for a half-inch (1.26 cm) board, or a lightweight board, which has a weight of about 6 kg / m2for a half-inch board.

[0007] Gypsum boards are made in a multistep process. See, for example, US Patents 9,181,132 B2 and 9,889,579 B2. First, calcined gypsum is mixed with water, surfactant and optionally other core materials and foamed with air to make a foamed gypsum slurry. Calcined gypsum typically contains primarily calcium sulfate hemihydrate (CaSO4 • 0.5 FEO), but may also contain other forms of dehydrated gypsum such as anhydrite gypsum. It may also contain minor quantities of other materials such as halite, sulfur, silica, calcium carbonate and other salts and oxides of silicon and metals such as potassium, magnesium and iron. Calcined gypsum is often called stucco in technical documents relating to gypsum board, and is also called plaster of Paris.

[0008] Second, a core layer containing the foamed gypsum slurry is spread on a first cover sheet. Third, a second cover sheet is applied to the opposite side of the core layer to form the gypsum board. Fourth, the calcined gypsum interacts with water in the foamed gypsum slurry to make calcium sulfate dihydrate, which hardens the foamed gypsum slurry, and excess water is driven off with heat. Fifth, the dried gypsum board is cut and milled to the desired size.

[0009] Bubbles in the foamed gypsum slurry become voids in the core of the gypsum board. The size and arrangement of the voids affects physical properties of the gypsum board, such as density and nail pull strength. Surfactants are commonly used as foaming agents in the gypsum slurry. Stable surfactants typically generate small voids that are uniform sized. Unstable surfactants allow bubbles to coalesce, forming some larger voids that have more variation in size. In some cases, mixtures of stable and unstable surfactants have been used. See US Patent 5,643,510. It is desirable to identify new surfactant combinations that can improve the balance of density and strength in gypsum boards made by this process.

[0010] SUMMARY

[0011] In one embodiment, the present invention relates to a gypsum slurry that comprises:

[0012] (a) an aqueous solvent

[0013] (b) calcined gypsum in a quantity suitable to form a foamed gypsum slurry in the aqueous solvent;

[0014] (c) a surfactant combination in quantity suitable to create a foamed gypsum slurry, which surfactant combination contains:

[0015] (i) an anionic di-aryl oxide surfactant (“ADO surfactant”) that comprises (A) a di-aryl oxide moiety, (B) an aliphatic lipophilic moiety containing on average at least 8 carbon atoms bonded to the diaryl oxide moiety and (C) at least one pendant sulfonic acid or sulfonic acid salt moiety bonded to the di-aryl oxide moiety; and

[0016] (ii) a nonionic sugar-based surfactant (“NSB surfactant”), wherein the surfactant combination (1) contains from 20 to 80 weight percent of the ADO surfactant and from 80 to 20 weight percent of the NSB surfactant when the lipophilic moiety in the ADO surfactant is branched, and (2) contains more than 50 weight percent to 80 weight percent of the ADO surfactant and from 20 to less than 50 weight percent of the NSB surfactant when the lipophilic moiety in the ADO surfactant is linear, based only on the combined weight of the anionic surfactant and the NSB surfactant excluding solvents.

[0017] In one embodiment, the present invention relates to a process to make a gypsum board comprising the steps of:

[0018] (a) applying a core layer containing foamed gypsum slurry directly or indirectly to a first cover sheet;

[0019] (b) applying a second cover sheet directly or indirectly to the core layer; and

[0020] (c) hardening and drying the core layer, wherein the foamed gypsum slurry contains a gypsum slurry from the first aspect of this invention.

[0021] In one embodiment, the present invention relates to a gypsum board comprising (1) a first cover sheet, (2) a core adhered directly or indirectly to the first cover sheet; and (3) a second cover sheet adhered directly or indirectly to the core opposite from the first cover sheet, wherein the core contains:

[0022] (a) gypsum; and

[0023] (b) from 0.004 to 0.5 weight percent, based on the weight of gypsum, of a surfactant combination that contains:

[0024] (i) an ADO surfactant that comprises (A) a di-aryl oxide moiety, (B) an aliphatic lipophilic moiety containing on average at least 8 carbon atoms bonded to the di-aryl oxide moiety and (C) at least one pendant sulfonic acid or sulfonic acid salt moiety bonded to the di-aryl oxide moiety; and

[0025] (ii) an NSB surfactant, wherein the surfactant combination (1) contains from 20 to 80 weight percent of the ADO surfactant and from 80 to 20 weight percent of the NSB surfactant when the lipophilic moiety in the ADO surfactant is branched, and (2) contains from more than 50 weight percent to 80 weight percent of the ADO surfactant and from 20 to less than 50 weight percent of the NSB surfactant when the lipophilic moiety in the ADO surfactant is linear, based only on the combined weight of the ADO surfactant and the NSB surfactant excluding solvents.

[0026] Gypsum boards made using the surfactant combinations of this invention can have lower weight or higher nail-pull strength or both as compared with gypsum boards that are foamed using conventional surfactants.

[0027] DETAILED DESCRIPTION

[0028] One aspect of this invention is a gypsum slurry that contains calcined gypsum, aqueous solvent and a surfactant combination as described further herein. The gypsum slurry is optionally foamed. The gypsum slurry optionally further contains other additives. A second aspect of this invention is a process which uses the foamed gypsum slurry to make a gypsum board as described further herein. A third aspect of the invention is a gypsum board, which can be made by the process of this invention as described further herein.

[0029] This invention uses gypsum, as is described in the Introduction.

[0030] At the beginning of this process, when the gypsum slurry is formed, the gypsum is calcined gypsum. The calcined gypsum is in the form of a powder that can be mixed with aqueous solvent. Calcined gypsum is commercially available from many sources as known to those of skill in the art. It can also be made by heating powdered gypsum according to known processes. Examples of suitable calcined gypsum and processes to make them are described in U.S. Patents 8,016,961 and 6,706,128.

[0031] The calcined gypsum is mixed with an aqueous solvent and a surfactant combination to form a slurry. The aqueous solvent contains primarily water. In some embodiments, the aqueous solvent may contain minor quantities of a cosolvent that is miscible with water such as alcohols and glycols. In some embodiments, the quantity of cosolvent is no more than 10 weight percent of the aqueous solvent, or no more than 5 weight percent or no more than 3 weight percent or no more than 1 weight percent. In some embodiments, the aqueous solvent contains essentially no (0 percent) cosolvent.

[0032] The weight ratio of aqueous solvent to calcined gypsum in the slurry is limited mainly by practical considerations. At high water-content, more energy and time is needed to dry the slurry. At low water-content, the slurry can be too viscous to spread easily on the first cover sheet and may harden prematurely. In some embodiments, the weight ratio of aqueous solvent to calcined gypsum is at least 0.5 or at least 0.6 or at least 0.7. In some embodiments the weight ratio of aqueous solvent to calcined gypsum is at most 2 or at most 1.5 or at most 1.4 or at most 1.3 or at most 1.2 or at most 1.1 or at most 1. For example, in some embodiments the weight ratio of aqueous solvent to calcined gypsum is from 0.70 to 1. The calcined gypsum reacts with water in the aqueous solvent after they are mixed, so that calcined gypsum in the gypsum slurry is in a state of transition from the hemihydrate form to the dihydrate form.

[0033] The gypsum slurry further contains a surfactant combination that contains an ADO surfactant; and an NSB surfactant.

[0034] The ADO surfactant comprises (A) a di-aryl oxide moiety, (B) an aliphatic lipophilic moiety containing at least 8 carbon atoms bonded to the di-aryl oxide moiety and (C) at least one pendant sulfonic acid or sulfonic acid salt moiety bonded to the di-aryl oxide moiety. The di-aryl oxide moiety meets the following Formula 1 :

[0035] (1) Ar-O-Ar wherein each Ar is independently an aryl group, such as a phenyl, tolyl or cumenyl group. At least one of the aryl groups is bonded to the lipophilic moiety. At least one of the aryl groups has a pendant sulfonic acid or sulfonic acid salt moiety. In some embodiments, each aryl group has a pendant sulfonic acid or sulfonic acid salt moiety.

[0036] In some embodiments, the ADO surfactants meet the following Formula 2: wherein at least one A is a sulfonic acid or sulfonic acid salt moiety and at least one of R1and R2is a lipophilic moiety, as previously described. In some embodiments, A is independently at least one of sulfonic acid or a sulfonic acid salt moiety, and when only one A is sulfonic acid or a sulfonic acid salt moiety, the other A may be one hydrogen. In some embodiments, each A is independently a sulfonic acid or sulfonic acid salt moiety. In some embodiments, only one of R1and R2is a lipophilic moiety; in some embodiments, each of R1and R2is independently a lipophilic moiety. In some embodiments, the phenyl rings may contain one or more pendant lower alkyl groups, and in some embodiments the phenyl rings are unsubstituted.

[0037] The lipophilic moieties (R1and / or R2) contain on average at least 8 carbon atoms. In some embodiments, the lipophilic moieties contain on average at least 10 carbon atoms or at least 12 carbon atoms. In some embodiments, the lipophilic moieties contain on average at most 20 carbon atoms or at most 18 carbon atoms or at most 16 carbon atoms or at most 14 carbon atoms. Aliphatic groups in the lipophilic moiety may be linear or branched, but (as discussed below) we have discovered that branched lipophilic moieties permit a broader ratio of ADO surfactant to NSB surfactant in the surfactant combination than linear lipophilic moieties permit. Aliphatic groups in the lipophilic moiety may be saturated or unsaturated. In some embodiments, the lipophilic moiety is an alkyl group.

[0038] The ADO surfactant contains at least one pendant sulfonic acid group or sulfonic acid salt (A) bonded to the di-aryl oxide moiety. Examples of suitable sulfonic acid salts include alkaline or alkaline earth metal salts and ammonium salts.

[0039] Examples of ADO surfactants are sold commercially by The Dow Chemical Company under the DOWFAX™ trademarks. Others can be made by known processes such as those described in US Patent 6,743,764 Bl. Commercial ADO surfactants that contain di-aryl oxide moieties arc frequently sold as solutions containing 30 to 80 weight percent water.

[0040] NSB surfactants contain a hydrophilic sugar moiety linked to a lipophilic moiety. The lipophilic moiety has the description and examples described above and herein.

[0041] The hydrophilic moiety comprises one or more repeating monosaccharide units such as glucose, fructose, and galactose. In some embodiments, the monosaccharide units contain glucose, and in some embodiments the monosaccharide units consist essentially of glucose. In some embodiments, the hydrophilic moiety contains on average from 1 to 8 repeating monosaccharide units or from 1 to 6 repeating monosaccharide units or from 1 to 5 repeating monosaccharide units or from 1 to 4 repeating monosaccharide units or from 1 to 3 repeating monosaccharide units or from 1 to 2 repeating monosaccharide units.

[0042] Common examples of NSB surfactants include:

[0043] • Alkyl polyglucosides: Alkyl polyglucosides are produced by reacting a sugar or starch with a fatty alcohol in the presence of acid catalysts at elevated temperatures. They are used in personal care products and household cleaning products. Commonly available examples include decyl glucoside and lauryl glucoside.

[0044] • Sucrose esters: Sucrose esters are produced by the reaction of sucrose with fatty acid esters. They are used as emulsifiers and stabilizers in food and cosmetic products.

[0045] • Sorbitan esters: Sorbitan esters are produced by the reaction of sorbitan with fatty acids. They are used as emulsifiers and solubilizers.

[0046] In some embodiments, the NSB surfactant comprises an alkyl polyglucoside.

[0047] Suitable NSB surfactants are commercially available from The Dow Chemical Company under the TRITON™ trademark. Others can be made by the processes described above. Commercial NSB surfactants are frequently sold as solutions containing 30 to 80 weight percent water.

[0048] Suitable ratios of the ADO surfactant and the NSB surfactant in the surfactant combination depend on whether the lipophilic moiety on the ADO surfactant is linear or branched. When the lipophilic moiety on the ADO surfactant is branched:

[0049] • The surfactant combination contains from 20 to 80 weight percent ADO surfactant and from 80 to 20 weight percent NSB surfactant. • In some embodiments, the surfactant combination contains at least 25 weight percent ADO surfactant, or at least 35 weight percent or at least 45 weight percent or at least 50 weight percent or at least 60 weight percent or at least 70 weight percent; and contains at most 75 weight percent NSB surfactant, or at most 65 weight percent or at most 55 weight percent or at most 50 weight percent or at most 40 weight percent or at most 30 weight percent.

[0050] • In some embodiments, the surfactant combination contains at most 78 weight percent ADO surfactant, or at most 76 weight percent or at most 75 weight percent; and contains at least 22 weight percent NSB surfactant or at least 24 weight percent or at least 25 weight percent.

[0051] Each ratio stated above is based solely on the combined weight of the NSB surfactants and the ADO surfactants, excluding any solvents or other components.

[0052] When the lipophilic moiety on the ADO surfactant is linear:

[0053] • The surfactant combination contains more than 50 weight percent to 80 weight percent ADO surfactant and from less than 50 to 20 weight percent NSB surfactant.

[0054] • In some embodiments, the surfactant combination contains at least at least 55 weight percent ADO surfactant or at least 60 weight percent or at least 70 weight percent; and contains at most 45 weight percent NSB surfactant, or at most 40 weight percent or at most 30 weight percent.

[0055] • In some embodiments, the surfactant combination contains at most 78 weight percent ADO surfactant, or at most 76 weight percent or at most 75 weight percent; and contains at least 22 weight percent NSB surfactant or at least 24 weight percent or at least 25 weight percent.

[0056] Each ratio stated above is based solely on the combined weight of the NSB surfactants and the ADO surfactants, excluding any solvents or other components.

[0057] In some embodiments, when the lipophilic moiety on the ADO surfactant contains on average less than 12 carbon atoms, then the proportion of ADO surfactant in the surfactant combination is at the higher end of the stated range, such as at least 60 weight percent or at least 65 weight percent or at least 70 weight percent.

[0058] For clarity, the term “surfactant combination” does not imply that the NSB surfactants and the ADO surfactants must be blended together before they are added to the gypsum slurry. They may be prcblcndcd, or they may be added into the aqueous solvent or slurry at the same time, or they may be added into the aqueous solvent or slurry at separate times.

[0059] The ratio of surfactant combination to calcined gypsum in the gypsum slurry is suitable to produce a foamed gypsum slurry. In some embodiments, the weight ratio of surfactant combination to calcined gypsum is at least 0.005 weight percent or at least 0.008 weight percent or at least 0.01 weight percent or at least 0.012 weight percent or at least 0.013 weight percent. In some embodiments, the weight ratio of surfactant combination to calcined gypsum is at most 0.5 weight percent or at most 0.2 weight percent or at most 0.1 weight percent or at most 0.05 weight percent or at most 0.02 weight percent or at most 0.017 weight percent. Each ratio stated above is based solely on the surfactants in the surfactant combination, excluding any solvents, and on the weight of the calcined gypsum before it is added to the aqueous solvent.

[0060] The gypsum slurry may optionally contain other additives in addition to the surfactant combination. Examples of common additives include:

[0061] • fibers (such as cellulose or glass fibers),

[0062] • accelerators such as alum, finely ground calcium sulfate, potassium sulfate,

[0063] • retardants to delay setting such as EDTA and other chelants,

[0064] • starches,

[0065] • potash,

[0066] • clay,

[0067] • boric acid,

[0068] • dispersants such as calcium naphthalene sulfonate,

[0069] • fire resistance additives such as vermiculite,

[0070] • mildew retarders,

[0071] • thickeners,

[0072] • hydrophobic additives such as wax or polysiloxanes to improve water resistance, and

[0073] • adhesives such as ethylene vinyl alcohol.

[0074] Each of these additives is well known and commercially available. People of ordinary skill in the art can choose the correct levels of additives based on the intended use of the gypsum board.

[0075] In some embodiments, the gypsum slurry contains 0 weight percent additives, based on the weight of the calcined gypsum, or at least 1 weight percent or at least 2 weight percent. In some embodiments, the gypsum slurry contains at most 10 weight percent additives, based on the weight of the calcined gypsum, or at most 5 weight percent or at most 3 weight percent.

[0076] For use in this invention, the components of the gypsum slurry are mixed together and are foamed to make a foamed gypsum slurry. Foaming is accomplished by mixing at least aqueous solvent and the surfactant combination with air under conditions such that a foam forms. Processes to mix and foam the components of the slurry are commonly known in the gypsum board industry. See, for example, US Patents 2,079,565; 4,057,443 and 4,455,271 . Equipment to accomplish the mixing and foaming is commercially available with instructions for its use. Examples of suitable equipment include agitated vessels, static mixers and pin mixers.

[0077] Any practical order of adding, mixing and foaming the components may be used to form the foamed gypsum slurry. For example:

[0078] • In some embodiments, all components of the gypsum slurry are first mixed together, and then the slurry is foamed to make the foamed gypsum slurry. • In some embodiments, the surfactants and optionally other liquid components of the slurry are mixed with the aqueous solvent and foamed, and then dry calcined gypsum and any other solid components are added to the foam mixture to make the foamed gypsum slurry.

[0079] • In some embodiments, the surfactants and optionally other additives are mixed with aqueous solvent and foamed, separately the calcined gypsum and optionally other additives are mixed in aqueous solvent, and then the two mixtures are blended together to make the foamed gypsum slurry.

[0080] In some embodiments of the gypsum slurry, the NSB surfactant is a stable surfactant, which means that it forms stable bubbles which do not coalesce during the time that is needed for the gypsum slurry to harden. In some embodiments of the gypsum slurry, the ADO surfactant is an unstable surfactant, which means that it forms bubbles which coalesce and expand during the time that is needed for the gypsum slurry to harden. Combining the stable and unstable surfactant offers some control on the size and size distribution of voids in the resulting gypsum board.

[0081] In some embodiments, the density of the foamed gypsum slurry is at least 60 g / L or at least 65 g / L or at least 70 g / L or at least 75 g / L or at least 80 g / L. In some embodiments, the density of the foamed gypsum slurry is at most 240 g / L or at most 200 g / L or at most 160 g / L or at most 120 g / L or at most 100 g / L or at most 90 g / L or at most 85 g / L or at most 80 g / L. In some embodiments, the volume ratio of gas to slurry in the foamed gypsum slurry is at least 5.0: 1 or 5.5: 1 or at least 5.8:1 or at least 6.0:1. In some embodiments, the volume ratio of gas to slurry in the foam is at most 8.0: 1 or at most 7.5:1 or at most 7.0: 1 or at most 6.5: 1 or at most 6.2:1 or at most 6.0: 1.

[0082] In some embodiments, the 25% drainage time (the time needed for 25 percent of the water in the foam to settle out) of foamed gypsum slurry is at least 200 seconds or at least 225 seconds or at least 250 seconds, when measured according to the Test Methods. In some embodiments the 25% drainage time of the foamed gypsum slurry is at most 500 seconds or at most 400 seconds or at most 350 seconds or at most 325 seconds or at most 300 seconds, when measured according to the Test Methods.

[0083] In the process of this invention, a core layer containing the foamed gypsum slurry is applied directly or indirectly to a first cover sheet. Cover sheets can contain many different materials, such as paper, fiberglass, polymer, or metal foil. Most commonly, the cover sheet contains paper, but other materials can provide enhanced strength, toughness, moisture barrier, fire barrier or radiation barrier. In some embodiments, the cover sheet may contain additives or components that improve water, flame or mildew resistance. Indirect application means that in some embodiments an intervening layer may be between the cover sheet and the foamed gypsum slurry such as an adhesive layer or a water-resistance layer or a mesh of fibers. In some embodiments, the gypsum slurry is applied directly to the cover sheet.

[0084] The core layer containing foamed gypsum slurry can be applied by pouring and optionally spreading the foamed gypsum slurry using known methods and equipment. See, for example, “Making Gypsum Board”, published by the Gypsum Association at https: / / gypsum.org / making-gypsum-board / and “Plasterboard Production” published by Knauf factories / plasterboard-production. In some embodiments, the layer of foamed gypsum slurry covers most or all of the cover sheet in a substantially uniform thickness. In some embodiments, the thickness of the foamed gypsum slurry layer is at least 14 inch (0.6 cm) or at least 1 / 3 inch (0.8 cm) or at least inch (1 cm). In some embodiments, the thickness of the foamed gypsum slurry layer is at most 2 inches (5 cm) or at most 1 inch (3 cm) or at most % inch (2 cm). Optionally, the core may contain two or more layers of the foamed gypsum slurry that have similar or different compositions. Optionally, the core may further contain one or more layers of another material in addition to the layer of foamed gypsum slurry. Optionally, a roller or knife edge presses or planes the core layer to uniform thickness.

[0085] A second cover sheet is applied directly or indirectly to the core layer. The second cover sheet may be the same or different from the first cover sheet. In some embodiments, one cover sheet is a face sheet, which may optionally be selected for appearance or easy adhesion of coatings or moisture resistance. In some embodiments, the one cover sheet is a back sheet, which may optionally be selected to supply improved physical properties or barrier properties. Optionally, a roller presses the board to desired uniform thickness after the second cover sheet is applied.

[0086] The product of this step is a board comprising two cover sheets with a core that contains the foamed gypsum slurry sandwiched between them. Within the foamed gypsum slurry, calcined gypsum interacts with water to form dihydrate gypsum, which hardens the core. The core is allowed to harden, and the gypsum board is heated to drive off excess water and dry the board. The hardening and the drying may take place separately or at the same time.

[0087] In some embodiments, the first and second cover sheet are part of a continuous roll. The second step of the process makes a continuous strip of gypsum board containing two cover sheets and foamed gypsum slurry. In the third step of the process, the continuous strip of gypsum board moves along a belt until it hardens enough to maintain its shape when cut. Then the continuous strip of gypsum board is cut into separate sheets. The separate sheets a placed in an oven to complete the hardening and drying step.

[0088] After drying the gypsum board may optionally be finished, such as by trimming edges.

[0089] The product of the process is a gypsum board comprising (1) a first cover sheet, (2) a core adhered directly or indirectly to the first cover sheet; and (3) a second cover sheet adhered directly or indirectly to the core opposite from the first cover sheet, wherein the core contains:

[0090] (a) gypsum; and

[0091] (b) from 0.004 to 0.5 weight percent, based on the weight of gypsum, of a surfactant combination that contains:

[0092] (i) an ADO surfactant as previously described; and

[0093] (ii) an NSB surfactant as previously described.

[0094] As previously described, the surfactant combination (1) contains from 20 to 80 weight percent of the ADO surfactant and from 80 to 20 weight percent of the NSB surfactant when the lipophilic moiety in the ADO surfactant is branched, and (2) contains more than 50 weight percent to 80 weight percent of the ADO surfactant and from 80 to less than 50 weight percent of the NSB surfactant when the lipophilic moiety in the ADO surfactant is linear

[0095] The gypsum in the core reflects the calcined gypsum that was added to the gypsum slurry, except the gypsum in the core is primarily calcium sulfate dihydrate, whereas the calcined gypsum is usually calcium sulfate hemihydrate. As a result of this change, the gypsum in the core is typically heavier than the calcined gypsum that was added to the gypsum slurry, such as about 15-20 percent heavier.

[0096] The surfactant combination has the same description and exemplary embodiments as already discussed. The quantity of surfactant combination in the core reflects the quantity of surfactant combination in the gypsum slurry. However, the weight ratio of surfactant to gypsum in the core may be slightly lower than in the slurry because the gypsum in the core is heavier than the calcined gypsum added to the gypsum slurry. In some embodiments, the weight ratio of surfactant combination to gypsum in the core is at least 0.006 weight percent or at least 0.008 weight percent or at least 0.01 weight percent. In some embodiments, the weight ratio of surfactant combination to gypsum in the core is at most 0.43 weight percent or at most 0.17 weight percent or at most 0.1 weight percent or at most 0.09 weight percent or at most 0.04 weight percent or at most 0.02 weight percent or at most 0.015 weight percent.

[0097] The gypsum core optionally contains other additives as previously discussed for the gypsum slurry.

[0098] After the gypsum core has been dried, it typically contains about 2 water molecules for each calcium sulfate molecule, which are incorporated into the crystal structure to the gypsum. In some embodiments, it contains only low levels of other free water.

[0099] In some embodiments, a standard gypsum board has a weight of no more than 8.5 kg / m2per each Vi inch (1.27 cm) of average thickness or no more than 8 kg / m2or no more than 7.8 kg / m2. In some embodiments, a standard gypsum board has a weight of at least 6.5 kg / m2per each Vi inch (1.27 cm) of average thickness or at least 7.0 kg / m2or at least 7.5 kg / m2.

[0100] In some embodiments, a lightweight gypsum board has a weight of no more than 6.5 kg / m2per eachx / 2 inch (1.27 cm) of average thickness or no more than 6.2 kg / m2or no more than 6.1 kg / m2. In some embodiments, a lightweight gypsum board has a weight of at least 5 kg / m2per eachx / 2 inch (1.27 cm) of average thickness or at least 5.5 kg / m2or at least 5.7 kg / m2or at least 6.0 kg / m2.

[0101] In some embodiments, the core of the gypsum board comprises at least 35 volume percent void volume or at least 40 volume percent or at least 45 volume percent or at least 48 volume percent. In some embodiments, the core of the gypsum board comprises at most 70 volume percent void volume or at most 65 volume percent or at most 62 volume percent or at most 60 volume percent. In some embodiments, the ratio of standard deviation / mean for pore volume is at least 0.5 or at least 0.6 or at least 0.7 or at least 0.8. In some embodiments, the ratio of standard deviation / mean for pore volume is at most 2 or at most 1.8 or at most 1.6 or at most 1.4 or at most 1.3.

[0102] In some embodiments, the gypsum board has a nail pull strength of at least 100 N or at least

[0103] 110 N or at least 120 N or at least 130 N or at least 140 N or at least 150 N or at least 160 N, when tested according to the test methods. There is no maximum desired nail pull strength as long as the board retains low enough weight, but in some cases nail pull strength over 200 N or 180 N may be unnecessary.

[0104] The gypsum boards of this invention can be used for ordinary uses of gypsum board, such as walls, ceilings and other internal surfaces of buildings. Test Methods

[0105] Unless stated otherwise, measurements listed in this application are made using the following test methods:

[0106] Examples The following examples illustrate specific embodiments of the invention, but do not limit the broadest scope of the invention.

[0107] The surfactants in Table 1 are used for the Examples:

[0108] Table 1

[0109] Preparation of gypsum boards

[0110] The surfactants shown in Table 2 are mixed with 60 g of water and foamed in a Hobart mixer using a paddle at speed 3 to a total volume of 750 mL. Calcined gypsum (200 g) and water (as per Table 2) are added to a 500 mL Waring blender and hand stirred for 10 s. The quantity of water is selected based on what is necessary to fully wet the calcined gypsum and form a slurry. A 1 g quantity of calcium naphthalene sulfonate dispersant is added to the blender and the contents are pulsed on high for 25-30 s. The gypsum-water slurry is weighed into a clean Hobart mixing bowl and the appropriate amount of foam is weighed into the slurry. The foam and gypsum slurry are mixed with a paddle at speed 2 for 25- 30 s until fully incorporated. The foamed mixture is poured into rectangular molds of 4”x6”x0.5” and placed in an oven at 80 °C for 10 min for setting. Once set, the boards are dried at 60 °C for 2-4 h. The density of each board and the nail pull strength of each board is measured. Results are listed in table 2 with the “IE#” samples representing inventive examples and the “CE#” samples representing comparative examples.

[0111] a - Total water, including water added to the surfactant. b - weight percent based on weight of calcined gypsum.

Claims

CLAIMS:

1. A gypsum slurry comprising:(a) an aqueous solvent;(b) calcined gypsum in a quantity suitable to form a foamed gypsum slurry in the aqueous solvent; and(c) a surfactant combination in a quantity suitable to create a foamed gypsum slurry, which surfactant combination contains:(i) an anionic di-aryl oxide surfactant (“ADO surfactant”), that comprises (A) a diaryl oxide moiety; (B) an aliphatic lipophilic moiety containing on average at least 8 carbon atoms bonded to the di-aryl oxide moiety and (C) at least one pendant sulfonic acid or sulfonic acid salt moiety bonded to the di-aryl oxide moiety; and(ii) a nonionic sugar-based surfactant (“NSB surfactant”), wherein the surfactant combination (1) contains from 20 to 80 weight percent of the ADO surfactant and from 80 to 20 weight percent of the NSB surfactant when the lipophilic moiety in the ADO surfactant is branched, and (2) contains more than 50 weight percent to 80 weight percent of the ADO surfactant and from 20 to less than 50 weight percent of the NSB surfactant when the lipophilic moiety in the ADO surfactant is linear, based only on the combined weight of the anionic surfactant and the NSB surfactant excluding solvents.

2. A process to make a gypsum board comprising the steps of:(a) applying a core layer containing foamed gypsum slurry directly or indirectly to a first cover sheet;(b) applying a second cover sheet directly or indirectly to the core layer; and(c) hardening and drying the core layer, wherein the foamed gypsum slurry contains the gypsum slurry of Claim 1.

3. A gypsum board comprising (1) a first cover sheet, (2) a core adhered directly or indirectly to the first cover sheet; and (3) a second cover sheet adhered directly or indirectly to the core opposite from the first cover sheet, wherein the core contains:(a) gypsum; and(b) from 0.004 to 0.5 weight percent, based on the weight of gypsum, of a surfactant combination that contains:(i) an anionic di-aryl oxide surfactant (“ADO surfactant”), that comprises (A) a diaryl oxide moiety, (B) an aliphatic lipophilic moiety containing on average at least 8 carbon atoms bonded to the di-aryl oxide moiety and (C) at least one pendant sulfonic acid or sulfonic acid salt moiety bonded to the di-aryl oxide moiety; and(ii) a nonionic sugar-based surfactant (“NSB surfactant”), wherein the surfactant combination ( 1 ) contains from 20 to 80 weight percent of the ADO surfactant and from 80 to 20 weight percent of the NSB surfactant when the lipophilic moiety in the ADO surfactant is branched, and (2) contains more than 50 weight percent to 80 weight percent of the ADO surfactant and from 20 to less than 50 weight percent of the NSB surfactant when the lipophilic moiety in the ADO surfactant is linear, based only on the combined weight of the anionic surfactant and the NSB surfactant excluding solvents.

4. The gypsum board of Claim 3 wherein the ADO surfactant meets Formula 2:wherein at least one A contains a pendant sulfonic acid or sulfonic acid salt moiety and at least one of R1and R2is an aliphatic lipophilic moiety containing on average at least 8 carbon atoms.

5. The gypsum board of Claim 4 wherein the lipophilic moieties in the ADO surfactant contain on average from 10 to 18 carbon atoms .

6. The gypsum board of Claim 5 wherein the lipophilic moieties in the ADO surfactant are linear and the surfactant combination contains at least 60 weight percent ADO surfactant, based only on the combined weight of the anionic surfactant and the NSB surfactant excluding solvents.

7. The gypsum board of Claim 6 where in the nonionic sugar-based surfactant is an alkyl glucoside surfactant.

8. The gypsum board of Claim 7 wherein the alkyl glucoside surfactant contains a hydrophilic moiety that contains from 1 to 5 glucose repeating units and contains a lipophilic moiety that contains on average from 8 to 16 carbon atoms.

9. The gypsum board of Claim 7 wherein the ratio of surfactant combination to gypsum is from 0.01 to 0.02 weight percent.

10. The gypsum board of Claim 5 wherein the lipophilic moieties in the ADO surfactant are branched.

11. The gypsum board of Claim 10 where in the nonionic sugar-based surfactant is an alkyl glucoside surfactant.

12. The gypsum board of Claim 11 wherein the alkyl glucoside surfactant contains a hydrophilic moiety that contains from 1 to 5 glucose repeating units and contains a lipophilic moiety that contains on average from 8 to 16 carbon atoms.

13. The gypsum board of Claim 11 wherein the ratio of surfactant combination to gypsum is from 0.01 to 0.02 weight percent.

14. The gypsum board of any one of Claims 3 to 13 wherein the gypsum board has a weight from 5 kg / m2to 6.2 kg / m2per each 1 / 2 inch of average thickness.

15. The gypsum board of Claim 14 wherein the gypsum board has a nail pull strength of at least 100 N.

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