US 20140178624A1 (19) United States (12) Patent Application Publication (10) Pub. No.: US 2014/0178624 A1 Tilford (43) Pub. Date: J 1111. 26, 2014 (54) BASE-MEDIATED HYDROPHOBING Publication Classi?cation COMPOSITIONS AND PROCESSES (5 1) Int. Cl. (71) Applicant: Georgia-Paci?c Gypsum LLC, Atlanta, C04B 11/00 (2006.01) GA (US) E04C 2/26 (2006.01) _ _ _ (52) US. Cl. (72) Inventorl Robert Wllllam Tllford, Stone CPC .. C04B 11/00 (2013.01); E04C 2/26 (2013.01) Mountaln, GA (US) USPC ............................ .. 428/67; 106/781; 106/678 (73) Assignee: Georgia-Paci?c Gypsum LLC, Atlanta, GA (US) (57) ABSTRACT (21) APP1~ NO-3 14/ 108,713 Water-resistant gypsum boards and compositions and meth _ _ ods for their manufacture are provided. The methods include (22) Flled' Dec“ 17’ 2013 forming a mixture of water, hydroxide, and siliconate, adding Related US. Application Data slloxane'to the mixture, adding calcmm sulfate hemi-hydrate to the mixture to form an aqueous slurry, cunng the aqueous (60) Provisional application No. 61/739,862, ?led on Dec. slurry under heat, drying the aqueous slurry, and forming a 20, 2012. water-resistant gypsum board. US 2014/0178624 A1 Jun. 26, 2014 BASE-MEDIATED HYDROPHOBING includes a gypsum core that is made of a mixture of calcium COMPOSITIONS AND PROCESSES sulfate hemi-hydrate, siloxane, hydroxide, and a ?brous mat at least partially penetrating a surface of the gypsum core. In CROSS-REFERENCE TO RELATED certain embodiments, the gypsum core also includes silicon APPLICATIONS ate. [0001] This application claims priority to US. Provisional [0009] In yet another aspect, a composition for the manu Application No. 61/739,862, ?led Dec. 20, 2012, which is facture of gypsum board is provided, including calcium sul incorporated herein by reference in its entirety. fate hemi-hydrate, hydroxide, and siloxane. In certain BACKGROUND embodiments, the composition also includes siliconate. [0002] The present invention relates generally to the ?eld of DETAILED DESCRIPTION gypsum boards, and more particularly to water-resistant gyp sum boards and methods for their manufacture. [0010] Disclosed herein are water-resistant gypsum boards [0003] Gypsum boards are commonly used as the exterior sheathing panels in building construction. Because sheathing and methods for their manufacture. As used herein, the term panels may be exposed to water or high humidity, gypsum “water-resistant” refers to the ability of a prefabricated gyp boards for these applications should be water-resistant to sum product, such as a gypsum board, to limit the uptake of reduce or eliminate: loss of board strength, microbiological water by the gypsum substrate and retain the dimensional growth, and delamination of facings. Accordingly, many stability and mechanical integrity of the product. For attempts have been made to improve the water-resistance of example, water resistance may be measured by the amount of the set gypsum that forms the gypsum boards, which has a water uptake by a gypsum product when immersed in water tendency to absorb water. for a set period. [0004] These attempts have included the incorporation of [0011] Gypsum boards are commonly made by mixing cal water-resistant additives such as metallic soaps, asphalts, cined calcium sulfate dihydrate, such as calcium sulfate siloxanes, and resins into the gypsum slurry, as well as coat hemi-hydrate, with water and any additives to form a slurry. ing ?nished gypsum boards with water-resistant ?lms or coat In the slurry, the calcined gypsum reacts with water to form ings. For example, one siloxane additive that has been used to calcium sulfate dihydrate, which may be formed and dried to improve the water-resistance of gypsum products is polym produce a fairly hard and rigid product referred to as set ethylhydrogensiloxane (PMHS). Generally, a small amount sum. of siloxane is added to the gypsum slurry before the board is formed and dried. It has been observed, however, that the [0012] The boards described herein utilize a siloxane addi siloxane frequently does not completely cure in a reasonable tive to impart water-resistance properties to the set gypsum. period of time or never completely cures. In these cases, the Upon curing the siloxane, it is believed that the polymers water resistance does not develop to a satisfactory level and crosslink to form a hydrophobic barrier. Curing of the silox the siloxane can be released as aVOC from the ?nished board. ane may be done thermally and/or with curing agents. In [0005] It has been determined that for such siloxane addi certain embodiments, the siloxane has the structure: tives to cure properly during the gypsum board manufacture process, they may be thermally cured or cured with a curing agent. For example, curing agents may include siliconates, such as potassium methyl siliconate or sodium methyl sili conate. When a thermal siloxane curing process only is used, it is critical that the temperature of the slurry reach curing temperature. Otherwise, the siloxane curing reaction may not be completed for sometime after manufacture. Curing agents must be provided in amounts that do not cure the siloxane too wherein R1 is H, halogen, alkyl, aryl, heteroaryl, cycloalkyl, rapidly and do not interfere with the rehydration and setting of haloalkyl, haloaryl, perhaloalkyl, or perhaloaryl, R2 is H, the gypsum during the board manufacturing process. halogen, alkyl, aryl, heteroaryl, cycloalkyl, haloalkyl, [0006] Accordingly, it would be desirable to provide haloaryl, perhaloalkyl, or perhaloaryl, and n is 1-100. For improved water-resistant gypsum boards utiliZing siloxanes, example, the siloxane may be poly(methylhydrogensiloxane) and methods and compositions for their manufacture. (PMHS), which has a single hydrogen atom directly bonded to the silicon atom in the backbone. The other substituent may SUMMARY be any alkyl group or halogen substituted alkyl chain. For example, PMHS may include XIAMETER 1107, which is [0007] In one aspect, a method is provided for making a water-resistant gypsum board. The method includes forming commercially available from Dow Corning Corporation a mixture of water, hydroxide, adding siloxane to the mixture, (Midland, Mich.), or BLUESIL WR 68, which is commer adding calcium sulfate hemi-hydrate to the mixture to form an cially available from Bluestar Silicones USA (East Brun aqueous slurry, curing the aqueous slurry under heat, drying swick, N.J.). the aqueous slurry, and forming a water-resistant gypsum [0013] Siliconate may be used as a curing agent for silox board. In certain embodiments, the mixture also includes ane-containing gypsum boards. It is believed that the basic siliconate. siliconate accelerates the curing process of the siloxane by [0008] In another aspect, water-resistant gypsum boards increasing the pH of the slurry containing the siloxane, are provided that are made from the methods described thereby catalyZing polymer crosslinking. In certain embodi herein. In one embodiment, a water-resistant gypsum board ments, a siliconate curing agent has the structure: US 2014/0178624 A1 Jun. 26, 2014 [0019] In certain embodiments, the hydroxide includes sodium hydroxide, potassium hydroxide, lithium hydroxide, or a combination thereof. The hydroxide may be a metal hydroxide. For example, the hydroxide may be sodium OM hydroxide, potassium hydroxide, lithium hydroxide, rubidium hydroxide, caesium hydroxide, francium hydrox ide, calcium dihydroxide, magnesium dihydroxide, beryl wherein R is H, halogen, alkyl, aryl, heteroaryl, cycloalkyl, lium dihydroxide, strontium dihydroxide, barium dihydrox haloalkyl, haloaryl, perhaloalkyl or perhaloaryl, and M, in ide, and radium dihydroxide or a combination thereof. For each occurrence independently, is sodium, potassium, or example, the hydroxide may be in solid form or in solution lithium. For example, the siliconate may be sodium methyl form. In one embodiment, a hydroxide solution may include siliconate, potassium methyl siliconate, or a combination hydroxide in an amount from about 10 to about 50 weight thereof. percent in water. For example, the hydroxide solution may [0014] It is generally believed that strong bases should not include hydroxide in an amount of about 20 weight percent in be used as curing agents because the higherpH interferes with water. the rehydration of the gypsum in the slurry and may be cor [0020] In certain embodiments, the siliconate has the struc rosive to the gypsum. However, because water chemistry may ture: vary based on manufacturing conditions, weak bases may not raise the pH of the slurry to the level necessary to completely cure the siloxane. Without being bound by a particular theory, Applicants believe certain siloxanes require a pH of 9 or above to cure. Water may have a pH of aron 6-8. Thus, the addition of a relatively small amount of a weak base to the OM gypsum slurry containing a siloxane may not be effective to cause the pH adjustment necessary to cure the siloxane. [0015] Applicant has surprisingly found that hydroxides, wherein R is H, halogen, alkyl, aryl, heteroaryl, cycloalkyl, such as sodium hydroxide, potassium hydroxide, lithium haloalkyl, haloaryl, perhaloalkyl, or perhaloaryl; and M, in hydroxide, or combinations thereof, may replace or be used in each occurrence independently, is sodium, potassium, or combination with current curing agents, without causing cor lithium. For example, the siliconate may be sodium methyl rosion of the gypsum or interfering with its rehydration. siliconate, potassium methyl siliconate,