HK1117102A - Method of improving dispersant efficacy in making gypsum products - Google Patents

Abstract

The invention generally provides gypsum-containing slurries including stucco, trimetaphosphate salt, and naphthalenesulfonate dispersant, wherein the trimetaphosphate salt is present in an amount of at least about 0.12% by weight based on the weight of stucco. Other slurry additives can include accelerators, binders, starch, and paper fiber, glass fiber, and other known ingredients. The invention also comprises the gypsum-containing products made with such slurries, for example, gypsum wallboard, and a method of making gypsum wallboard.

Description

Method for improving the efficacy of dispersants in making gypsum products

Technical Field

The present invention relates to a method of reducing water demand in slurries used to make gypsum-containing products, and more particularly, to gypsum slurries containing trimetaphosphate and naphthalenesulfonate dispersants, and products made from the gypsum slurries. The invention also relates to a method of increasing the dry strength of gypsum-containing products, including wallboard, by using trimetaphosphate and naphthalenesulfonate dispersants.

Background

Certain characteristics of gypsum (calcium sulfate dihydrate) make it well suited for use in the manufacture of industrial and building products, such as gypsum wallboard. Gypsum is a plentiful and generally extremely inexpensive raw material that can be cast, molded or otherwise formed into useful shapes through the process of dehydration and rehydration. The basic material for making gypsum wallboard and other gypsum products is calcium sulfate in its semi-hydrated form (CaSO), commonly referred to as "stucco₄·1/2 H₂O), which is the conversion of the dihydrate form of calcium sulfate (CaSO) by heating₄·2H₂O), obtained by removing 1 to 1/2 water molecules thereof.

Conventional gypsum-containing products, such as gypsum wallboard, have a number of benefits, such as low cost and ease of processing. Trimetaphosphate salts have been used as an ingredient in slurries used to make such products to achieve various improvements to the process of making gypsum-containing products. For example, trimetaphosphate salts (such as sodium trimetaphosphate) will increase the compressive strength of gypsum-containing products, including gypsum wallboard. In the past, sodium trimetaphosphate and other trimetaphosphate salts have not been used in such applications in amounts greater than about 0.08% by weight based on the weight of stucco.

Large amounts of water need to be used in the gypsum slurry in order to ensure proper fluidity of the slurry. Unfortunately, most of the water must eventually be separated and removed by heating, which is costly due to the high cost of the fuel used in the heating process. The heating step is also rather time consuming. In the past, it has not been recognized that trimetaphosphate salts can affect the water demand of gypsum slurries. However, the inventors of the present invention have found that increasing the content of trimetaphosphate salt to an extent that has not been known so far in the presence of a specific dispersant makes it possible to achieve proper slurry fluidity, and unexpectedly reduce the amount of water. Of course, it is particularly desirable because increasing the trimetaphosphate salt content subsequently reduces fuel usage and processing time associated with subsequent processing steps to remove water. The present inventors have also found that the dry strength of gypsum board can be increased by using a trimetaphosphate plus naphthalenesulfonate dispersant.

Disclosure of Invention

The present invention generally comprises a slurry comprising stucco, trimetaphosphate salt, and naphthalenesulfonate dispersant. Sodium trimetaphosphate is present in an amount of at least about 0.12% by weight based on the weight of stucco. In a preferred embodiment, the trimetaphosphate salt is present in an amount from about 0.12% to about 0.4% by weight based on the weight of dry stucco. The naphthalenesulfonate dispersant is present in an amount from about 0.1% to 3.0% by weight based on the weight of dry stucco. Other slurry additives may include starch, accelerators, binders, paper or glass fibers, and other known ingredients. The invention also includes gypsum-containing products made with the slurry.

Preferably, the gypsum-containing product is gypsum wallboard. In this embodiment, the present invention constructs a gypsum wallboard comprising a set gypsum composition formed between two generally parallel cover sheets, the set gypsum composition being made using a gypsum-containing slurry comprised of water, stucco, sodium trimetaphosphate, and a naphthalenesulfonate dispersant, wherein the sodium trimetaphosphate is present in an amount of at least about 0.12% by weight based on the weight of stucco.

In another embodiment, the present invention provides a method of making gypsum wallboard by mixing a gypsum-containing slurry comprising water, stucco, sodium trimetaphosphate and a naphthalenesulfonate dispersant, wherein the sodium trimetaphosphate is present in an amount of at least about 0.12% by weight based on the weight of stucco. The resulting gypsum-containing slurry is deposited on a first paper cover sheet and a second paper cover sheet is placed over the deposited slurry to form a gypsum wallboard. After the gypsum-containing slurry has hardened sufficiently to allow cutting, the gypsum wallboard is cut and the resulting gypsum wallboard is dried. Other common ingredients may also be used in the slurry, including (as appropriate) accelerators, binders, starch, paper fiber, glass fiber, and other known ingredients. Soap foam is also typically added to reduce the density of the final gypsum wallboard product.

Drawings

Is free of

Detailed Description

According to one embodiment of the invention, a gypsum-containing product is provided that is made from a gypsum-containing slurry containing stucco, sodium trimetaphosphate, and a naphthalenesulfonate dispersant. Other ingredients that may be used in the slurry include starch, paper fiber, glass fiber, and accelerators. Soap foam is also typically added to the freshly formulated gypsum-containing slurry to reduce the density of the final gypsum-containing product (e.g., gypsum wallboard).

The combination of a minimum of at least about 0.12 to 0.4 weight percent trimetaphosphate salt and about 0.1 to about 3.0 weight percent naphthalenesulfonate dispersant (both based on the weight of dry stucco used in the gypsum slurry) unexpectedly significantly increases the flowability of the gypsum slurry. This will substantially reduce the amount of water required to prepare a gypsum slurry having sufficient fluidity to be used in the manufacture of gypsum-containing products, such as gypsum wallboard. It is believed that a level of trimetaphosphate salt (in the form of sodium trimetaphosphate) that is at least about 2 times the level in standard formulations will enhance the dispersant activity of the naphthalenesulfonate dispersant. It should be noted that in all embodiments of the present invention, a combination of a naphthalenesulfonate dispersant and a water-soluble metaphosphate or polyphosphate (and preferably a water-soluble trimetaphosphate) must be used.

The naphthalenesulfonate dispersants used in the present invention include polynaphthalenesulfonic acid and its salts (polynaphthalenesulfonates) and derivatives, which are condensation products of naphthalenesulfonic acids with formaldehyde. Particularly desirable polynaphthalenesulfonates include sodium and calcium naphthalenesulfonate. The average molecular weight of the naphthalene sulfonate may be in the range of about 3,000 to 20,000, but the molecular weight is preferably about 8,000 to 10,000. Higher molecular weight dispersants have higher viscosities and result in higher water requirements during the formulation process. Useful naphthalenesulfonates include DILOFLO available from GEO Specialty Chemicals, Cleveland, Ohio; DAXAD available from Hampshire Chemical Corp., Lexington, Massachusetts; and LOMAR D available from GEO specialty Chemicals, Lafayette, Indiana. The naphthalenesulfonates are preferably used in the form of aqueous solutions, for example, having a solids content in the range from 35 to 55% by weight. Most preferably, the naphthalene sulfonate is used in the form of an aqueous solution having, for example, a solids content in the range of about 40 to 45% by weight. Alternatively, the naphthalenesulfonates can be used in dry solid or powder form, as appropriate.

The polynaphthalenesulfonates useful in the present invention have the general structure (I):

wherein n is greater than 2, and wherein M is sodium, potassium, calcium, or the like.

The naphthalenesulfonate dispersant, preferably in the form of an about 45% by weight aqueous solution, based on the weight of dry stucco used in the gypsum composite formulation, must be used in an amount in the range of about 0.5% to about 2.5% by weight. A more preferred range of naphthalenesulfonate dispersant is from about 0.5% to about 1.5% by weight based on the weight of dry stucco, and a most preferred range is from about 0.7% to about 1.5% by weight based on the weight of dry stucco.

Stated another way, the naphthalenesulfonate dispersant must be used in an amount in the range of about 0.1% to about 3.0% by weight on a dry basis based on the weight of dry stucco used in the gypsum composite formulation. A more preferred range of naphthalenesulfonate dispersant (on a dry solids basis) is from about 0.25% to about 2.0% by weight based on the weight of dry stucco, and a most preferred range (on a dry solids basis) is from about 0.3% to about 0.7% by weight based on the weight of dry stucco.

Any suitable water soluble metaphosphate or polyphosphate may be used in the present invention. Trimetaphosphate salts are preferably used, including double salts, i.e. trimetaphosphate salts having two cations. Particularly useful trimetaphosphate salts include sodium trimetaphosphate, potassium trimetaphosphate, calcium trimetaphosphate, sodium calcium trimetaphosphate, lithium trimetaphosphate, ammonium trimetaphosphate, the like, or combinations thereof. The preferred trimetaphosphate salt is sodium trimetaphosphate. Trimetaphosphate salts in aqueous solution having a solids content in the range of about 10-15% by weight, for example, are preferably used. Other cyclic or acyclic polyphosphates may also be used, as described in U.S. Pat. No. 6,409,825 to Yu et al, which is incorporated herein by reference.

Sodium trimetaphosphate is a known additive in gypsum-containing compositions, but is typically used in amounts ranging from about 0.05% to about 0.08% by weight based on the weight of dry stucco used in the gypsum slurry. In embodiments of the present invention, sodium trimetaphosphate (or other water-soluble metaphosphate or polyphosphate) must be present in an amount in the range of from about 0.12% to about 0.4% by weight based on the weight of dry stucco used in the gypsum composite formulation. The preferred range of sodium trimetaphosphate (or other water-soluble metaphosphate or polyphosphate) is from about 0.12% to about 0.3% by weight based on the weight of dry stucco used in the gypsum composite formulation.

There are two forms of stucco, α and β. These two types of stucco are made by different means of calcination. In the present invention, stucco in either the beta or alpha form can be used.

In gypsum-containing slurries prepared according to the present invention, starches (including especially pregelatinized starches) may be used. A preferred pregelatinized starch is a pregelatinized corn starch, e.g., available from Bunge Milling, St.LPre-gelatinized corn flour of ouis, Missouri, which has the following typical analysis: water 7.5%, protein 8.0%, oil 0.5%, crude fiber 0.5%, ash 0.3%; green strength 0.48 psi; and a bulk density of 35.0 lb/ft³. The pregelatinized corn starch can be used in an amount of up to about 10% by weight based on the weight of dry stucco used in the gypsum-containing slurry.

Other useful starches include acid-modified starches, such as acid-modified corn flours, e.g., HI-BOND available from BungeMilling, st. This starch has the following typical analysis: 10.0% of water, 1.4% of oil, 17.0% of soluble matter, 98.0% of alkaline fluidity and 30 lb/ff of bulk density³And a 20% slurry at a pH of 4.3. Another useful starch is non-pregelatinized wheat starch, such as ECOSOL-45 from ADM/Ogilvie, Montreal, Quebec, Canada, which has a maximum of 25% solubles.

Accelerators can be used in the gypsum-containing compositions of the present invention, as described in U.S. Pat. No. 6,409,825 to Yu et al, which is incorporated herein by reference. One desirable Heat Resistant Accelerator (HRA) can be made from dry-ground construction gypsum powder (landplaster) (calcium sulfate dihydrate). The HRA may be made using small amounts of additives (typically about 5% by weight) such as sugar, dextrose, boric acid, and starch. Sugar or dextrose are currently preferred. Another useful accelerator is a "climate stabilized accelerator" or "climate stabilized accelerator" (CSA), as described in U.S. patent No. 3,573,947, which is incorporated herein by reference.

The following examples further illustrate the invention. And should not be construed as limiting the scope of the invention in any way.

Example 1

Gypsum slurry formulation samples

The gypsum slurry formulations are shown in table 1 below. All values in table 1 are expressed as weight percent based on the weight of dry stucco. The values in parentheses are dry weight in pounds (lb/MSF).

TABLE 1

Components	Formulation A	Formulation B
Plaster (lb/MSF)	(732)	(704)
			Sodium trimetaphosphate	0.20(1.50)	0.30(2.14)
Dispersant (naphthalene sulfonate)	0.18(1.35)	0.581(4.05)
			Pregelatinized starch	2.7(20)	6.4(45)
Paperboard starch	0.41(3.0)	0
			Heat Resistant Accelerator (HRA)	(15)	(15)
Glass fiber	0.27(2.0)	0.28(2.0)
			Paper fiber	0	0.99(7.0)
Soap*	0.03(0.192)	0.03(0.192)
Total water volume (lb)	805	852
Water/stucco ratio	1.1	1.2

^*For pre-foaming.

¹1.28 wt% 45% aqueous solution

Example 2

Manufacture of wall panels

Gypsum wallboard samples were made according to Yu et al, U.S. patent No. 6,342,284 and Yu et al, U.S. patent No. 6,632,550, both incorporated herein by reference. As described in example 5 of these patents, the manufacturing process involves separately producing the foam, and introducing the foam into a slurry with other ingredients.

The test results for gypsum wallboard made using formulations a and B of example 1 and a control are shown in table 2 below. In this example and other examples below, nail pull resistance, core hardness, and bending strength tests were performed in accordance with ASTM C-473. Further, it should be noted that typical gypsum wallboard is about 1/2 inches thick and has a weight of between about 1600 to 1800 pounds (or lb/MSF) per 1000 square feet of material. ("MSF" is a standard abbreviation for one thousand square feet in the art, which is a measure of the area of the box, corrugated medium and wallboard.)

TABLE 2

Laboratory test results	Comparison paper board	Formulation A paperboard	Formulation B paperboard
				Paperboard weight (lb/MSF)	1587	1066	1042
Resistance to nail pulling (lb)	81.7	50.2	72.8
				Core hardness (lb)	16.3	5.2	11.6
Moist adhesive load (lb)	17.3	20.3	15.1
				Damp bond failure (%)	0.6	5	11.1
Flexural Strength, face Up (MD) (lb)	47	47.2	52.6
				Flexural Strength, face Down (MD) (lb)	51.5	66.7	78.8
Flexural strength, face up (XMD) (lb)	150	135.9	173.1
				Flexural strength, face down (XMD) (lb)	144.4	125.5	165.4

MD: longitudinal and horizontal

XMD: transverse direction

As described in Table 2, the gypsum wallboard made using the slurries of formulations A and B had significantly reduced weight compared to the control paperboard. Referring again to table 1, formulation a paperboard differed greatly from formulation B paperboard. The water/stucco (w/s) ratio was similar for formulation a and formulation B. A significantly higher level of naphthalenesulfonate dispersant was also used in formulation B. Furthermore, about 6 wt% of substantially more pregelatinized starch was used in formulation B, which increased over 100% over formulation a with a significant increase in strength. Even so, the water demand to produce the desired fluidity is still low for the formulation B slurry, differing by less than 10% compared to formulation a. The low water demand of both formulations is attributed to the synergistic effect of the combination of naphthalenesulfonate dispersant and sodium trimetaphosphate in the gypsum slurry, which allows for increased fluidity of the gypsum slurry even in the presence of substantially higher levels of pregelatinized starch.

As shown in table 2, wallboard made using the slurry of formulation B had substantially increased strength compared to wallboard made using the slurry of formulation a. By incorporating an increased amount of pregelatinized starch in combination with an increased amount of naphthalenesulfonate dispersant and sodium trimetaphosphate, the nail pull resistance of formulation B paperboard was improved by 45% over formulation a paperboard. A substantial increase in flexural strength was also observed in formulation B paperboard compared to formulation a paperboard.

Example 3

Weight reduction test of 1/2-inch gypsum wallboard

Other gypsum wallboard examples (cardboard C, D and E) including slurry formulations and test results are shown in Table 3 below. The slurry formulations in table 3 included the major components in the slurry. The values in parentheses are expressed in weight percent based on the weight of dry stucco.

TABLE 3

Experimental formulation Components/parameters	Comparison paper board	Formulation C paperboard	Formulation D paperboard	Formulation E paperboard
					Dry plaster (lb/MSF)	1300	1281	1196	1070
Accelerator (lb/MSF)	9.2	9.2	9.2	9.2
					DILOFLO1(lb/MSF)	4.1(0.32％)	8.1(0.63％)	8.1(0.68％)	8.1(0.76％)
Conventional starch (lb/MSF)	5.6(0.43％)	0	0	0
					Pregelatinized corn starch (lb/MSF)	0	10(0.78％)	10(0.84％)	10(0.93％)
Sodium trimetaphosphate (lb/MSF)	0.7(0.05％)	1.6(0.12％)	1.6(0.13％)	1.6(0.15％)
					Total water/stucco ratio (w/s)	0.82	0.82	0.82	0.84
Experimental formulation test results
					Dry paperboard weight (lb/MSF)	1611	1570	1451	1320
Resistance to nail pulling (lb)	77.3+	85.5	77.2	65.2

⁺ASTM standards: 77 lb

¹Aqueous naphthalene sulfonate solution with DILOFLO of 45%

As set forth in Table 3, both paperboard C, D and E were made from slurries having substantially increased amounts of starch, DILOFLO dispersant and sodium trimetaphosphate (about a two-fold increase in starch and dispersant as a percentage; and 2 to 3-fold increase in trimetaphosphate) as compared to control paperboard while maintaining a constant w/s ratio. However, the strength as measured by nail pull resistance was not significantly affected and the paperboard weight was significantly reduced. Thus, in this example of an embodiment of the present invention, the novel formulation (such as paperboard D) can formulate increased starch in a flowable slurry that maintains suitable strength while also being convenient to use.

Example 4

Wet gypsum cube Strength test

The wet cube strength test was conducted in the laboratory to determine its wet compressive strength by using Southard CKS cardboard stucco and tap water available from United States Gypsum corp. The following laboratory test procedure was used.

Stucco (1000g), CSA (2g) and tap water (1200cc) were used for each cast wet gypsum cube at approximately 70F. First, pregelatinized corn starch (20g, 2.0% by weight of stucco) and CSA (2g, 0.2% by weight of stucco) were thoroughly dry-blended with stucco in a plastic bag, which was then mixed with a tap water solution containing naphthalenesulfonate dispersant and sodium trimetaphosphate. The dispersant used was DILOFLO dispersant (1.0-2.0%, as described in table 4). Varying amounts of sodium trimetaphosphate as shown in table 4 were also used.

Initially, the dry ingredients and aqueous solution were combined in a laboratory Warnig blender, the resulting mixture was soaked for 10 seconds, and then the mixture was mixed at low speed for 10 seconds to make a slurry. The slurry thus formed was poured into three 2 "x 2" cube molds. The cast cubes were then removed from the mold, weighed and sealed in a plastic bag to prevent moisture loss, followed by a compressive strength test. The compressive strength of the wet cubes was measured using an ATS machine and recorded as an average of pounds per square inch (psi). The results obtained were as follows:

TABLE 4

Test sample numbering	Sodium trimetaphosphate, g (% by weight based on dry stucco)	DILOFLO1(weight% based on dry mortar)	Wet cube weight (2 ". times.2"), g	Wet cube compressive strength, psi
					1	0	1.5	183.57	321
2	0.5(0.05)	1.5	183.11	357
					3	1(0.1)	1.5	183.19	360
4	2(0.2)	1.5	183.51	361
					5	4(0.4)	1.5	183.65	381
6	10(1.0)	1.5	183.47	369
					7	0	1.0	184.02	345
8	0.5(0.05)	1.0	183.66	349
					9	1(0.1)	1.0	183.93	356
10	2(0.2)	1.0	182.67	366
					11	4(0.4)	1.0	183.53	365
12	10(1.0)	1.0	183.48	341
					13	0	2.0	183.33	345
14	0.5 (0.05)	2.0	184.06	356
					15	1(0.1)	2.0	184.3	363
16	2(0.2)	2.0	184.02	363
					17	4(0.4)	2.0	183.5	368
18	10(1.0)	2.0	182.68	339

¹Aqueous naphthalene sulfonate solution with DILOFLO of 45%

As set forth in Table 4, inventive samples 4-5, 10-11, and 17 having a sodium trimetaphosphate content within the range of about 0.12-0.4% generally had superior wet cube compression strength compared to samples having a sodium trimetaphosphate content outside this range.

Example 5

Factory production experiment of 1/2-inch lightweight gypsum wallboard

Other experiments (test boards 1 and 2) were performed, including slurry formulations and test results are shown in table 5 below. The slurry formulations in table 5 included the major components in the slurry. The values in parentheses are expressed in weight percent based on the weight of dry stucco.

TABLE 5

Experimental formulation Components/parameters	Control paperboard 1	Factory formulation test cardboard 1	Control paperboard 2	Plant formulation laboratory cardboard 2
					Dry plaster (lb/MSF)	1308	1160	1212	1120
DILOFLO1(lb/MSF)	5.98(0.457％)	7.98(0.688％)	7.18(0.592％)	8.99(0.803％)
					Conventional starch (lb/MSF)	5.0(0.38％)	0	4.6(0.38％)	0
Pregelatinized corn starch (lb/MSF)	2.0(0.15％)	10(0.86％)	2.5(0.21％)	9.0(0.80％)
					Sodium trimetaphosphate (lb/MSF)	0.7(0.05％)	2.0(0.17％)	0.6(0.05％)	1.6(0.14％)
Total water/stucco ratio (w/s)	0.79	0.77	0.86	0.84
					Experimental formulation test results
Dry paperboard weight (lb/MSF)	1619	1456	1553	1443
					Resistance to nail pulling (lb)	81.5+	82.4	80.7	80.4
Average flexural Strength (MD) (lb)	41.7	43.7	44.8	46.9
					Average flexural strength (XMD) (lb)	134.1	135.5	146	137.2
Average moisture bonding2Load (lb)	19.2	17.7	20.9	19.1
					Moisture bonding2，3Destruction (%)	1.6	0.1	0.5	0

⁺ASTM standards: 77 lb

MD: longitudinal direction

XMD: transverse direction

¹Aqueous naphthalene sulfonate solution with DILOFLO of 45%

²90 deg.F/90% relative humidity

³It will be appreciated that under these test conditions, a percent failure of < 50% is acceptable.

As described in table 5, both the experimental boards 1 and 2 were made from slurries with substantially increased amounts of starch, DILOFLO dispersant and sodium trimetaphosphate compared to the control boards while the w/s ratio remained constant. However, the strength as measured by the nail pull resistance and bending resistance tests is still maintained or improved and the board weight is significantly reduced. Thus, in this example of an embodiment of the present invention, the novel formulation (such as the experimental paperboards 1 and 2) can formulate increased trimetaphosphate and starch in a flowable slurry for ease of use while also maintaining adequate strength.

Example 6

Factory production experiment of 1/2-inch ultra-light gypsum wallboard

Other experiments (experimental boards 3 and 4) were performed as in example 2 using formulation B (example 1), but pregelatinized corn starch was prepared with water at a concentration of 10% (wet starch formulation) and a blend of HYONIC PFM soap (available from GEO Specialty Chemicals, Lafayette, Indiana) was used. For example, the experimental paperboard 3 was made with a HYONIC PFM 10/HYONIC PFM 33 blend in the range of 65-70 wt%/35-30 wt%. For example, the experimental paperboard 4 was manufactured with 70/30wt./wt. HYONIC PFM 10/HYONIC PFM 33 blend. The experimental results are shown in table 6 below.

TABLE 6

Laboratory test results	Experimental cardboard 3 (formulation B plus HYONIC soap blend 65/35) (n ═ 12)	Experimental cardboard 4 (formulation B plus HYONIC soap blend 70/30) (n ═ 34)*
			Paperboard weight (lb/MSF)	1106	1013
Resistance to nail pulla(lb)	85.5	80.3
			Core hardnessb(lb)	12.4	＞15
Average bending strengthc(MD)(lb)	55.6	60.31
			Average bending strengthd(XMD)(lb)	140.1	142.31

^*Except as noted.

¹n＝4

MD: longitudinal direction

XMD: transverse direction

^aASTM standards: 77 lb

^bASTM standards: 11 lb

^cASTM standards: 36 lb

^dASTM standards: 107 lb

As set forth in table 6, the strength characteristics as measured by nail pull and core hardness were all higher than the ASTM standard. Flexural strength was also measured to be higher than ASTM standards. Furthermore, in this example of an embodiment of the present invention, the novel formulation (such as the experimental paperboards 3 and 4) can formulate increased trimetaphosphate and starch in a flowable slurry for ease of use while also maintaining adequate strength.

The use of the terms "a" and "an" and "the" and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary terms (e.g., "such as") provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. It should be understood that the examples are given for illustrative purposes only and should not be taken as limiting the scope of the invention.

Claims (18)

1. A gypsum-containing slurry comprising: water, stucco, sodium trimetaphosphate, and a naphthalenesulfonate dispersant, wherein the sodium trimetaphosphate is present in an amount of at least about 0.12% by weight based on the weight of stucco.

2. The gypsum-containing slurry of claim 1, wherein the naphthalenesulfonate dispersant is present in an amount from about 0.1% to about 3.0% by weight based on the weight of stucco.

3. The gypsum-containing slurry of claim 1, wherein the naphthalenesulfonate dispersant is present in an amount from about 0.25% to about 2.0% by weight based on the weight of stucco.

4. The gypsum-containing slurry of claim 1, wherein the naphthalenesulfonate dispersant is present in an amount from about 0.3% to about 0.7% by weight based on the weight of stucco.

5. The gypsum-containing slurry of claim 1, wherein the naphthalenesulfonate dispersant is in the form of an aqueous solution containing about 40% to about 45% by weight naphthalenesulfonate and the aqueous solution is present in an amount from about 0.5% to about 2.5% by weight based on the weight of stucco.

6. The gypsum-containing slurry of claim 1, wherein the naphthalenesulfonate dispersant is in the form of an aqueous solution containing about 40% to about 45% by weight naphthalenesulfonate and the aqueous solution is present in an amount from about 0.5% to about 1.5% by weight based on the weight of stucco.

7. The gypsum-containing slurry of claim 1, wherein the naphthalenesulfonate dispersant is in the form of an aqueous solution containing about 40% to about 45% by weight naphthalenesulfonate and the aqueous solution is present in an amount from about 0.7% to about 1.5% by weight based on the weight of stucco.

8. A gypsum wallboard comprising:

a set gypsum composition formed between two substantially parallel cover sheets, the set gypsum composition made using a gypsum-containing slurry comprising:

water, stucco, sodium trimetaphosphate, and a naphthalenesulfonate dispersant, wherein the sodium trimetaphosphate is present in an amount of at least about 0.12% by weight based on the weight of stucco.

9. The gypsum wallboard of claim 8, wherein the naphthalenesulfonate dispersant is present in an amount from about 0.1% to about 3.0% by weight based on the weight of stucco.

10. The gypsum wallboard of claim 8, wherein the naphthalenesulfonate dispersant is present in an amount from about 0.25% to about 2.0% by weight based on the weight of stucco.

11. The gypsum wallboard of claim 8, wherein the naphthalenesulfonate dispersant is present in an amount from about 0.3% to about 0.7% by weight based on the weight of stucco.

12. The gypsum wallboard of claim 8, wherein the naphthalenesulfonate dispersant is in the form of an aqueous solution containing about 40% to about 45% by weight naphthalenesulfonate and the aqueous solution is present in an amount from about 0.5% to about 2.5% by weight based on the weight of stucco.

13. The gypsum wallboard of claim 8, wherein the naphthalenesulfonate dispersant is in the form of an aqueous solution containing about 40% to about 45% by weight naphthalenesulfonate and the aqueous solution is present in an amount from about 0.5% to about 1.5% by weight based on the weight of stucco.

14. The gypsum wallboard of claim 8, wherein the naphthalenesulfonate dispersant is in the form of an aqueous solution containing about 40% to about 45% by weight naphthalenesulfonate and the aqueous solution is present in an amount from about 0.7% to about 1.5% by weight based on the weight of stucco.

15. A method of manufacturing gypsum wallboard comprising the steps of:

(a) mixing a gypsum-containing slurry comprising:

water, stucco, sodium trimetaphosphate, and a naphthalenesulfonate dispersant,

wherein the sodium trimetaphosphate is present in an amount of at least about 0.12% by weight based on the weight of stucco;

(b) depositing the gypsum-containing slurry on a first cover sheet;

(c) placing a second cover sheet over the deposited slurry to form a gypsum wallboard;

(d) cutting the gypsum wallboard after the gypsum-containing slurry has hardened sufficiently to allow cutting; and

(e) drying the gypsum wallboard.

16. The method of claim 15, wherein the first cover sheet and the second cover sheet are both made of paper.

17. The method of claim 15, wherein the sodium trimetaphosphate is present in an amount from about 0.12% to about 0.4% by weight based on the weight of stucco, and the naphthalenesulfonate dispersant is present in an amount from about 0.1% to about 3.0% by weight based on the weight of stucco.

18. The method of claim 15 wherein the sodium trimetaphosphate is present in an amount from about 0.12% to about 0.4% by weight based on the weight of stucco, and the naphthalenesulfonate dispersant is in the form of an aqueous solution containing about 40% to about 45% by weight naphthalenesulfonate and the aqueous solution is present in an amount from about 0.5% to about 2.5% by weight based on the weight of stucco.