HK1040233B - Gypsum-containing product having increased resistance to permanent deformation and method and composition for producing it - Google Patents

Description

Gypsum-containing articles having improved resistance to permanent deformation and methods and compositions for making the same

Technical Field

The present invention relates to methods and compositions for making set gypsum-containing articles, including, for example, gypsum board, reinforced gypsum composite board, stucco, machinable material, joint treatment material, and acoustical tile, and to methods and compositions for making these articles. More particularly, the present invention relates to set gypsum-containing articles having improved resistance to permanent deformation (e.g., sag resistance) through the use of one or more reinforcing materials. Some preferred embodiments of the present invention relate to methods of making such articles comprising hydrating calcined gypsum in the presence of a reinforcing material that imparts increased strength, resistance to permanent deformation (e.g., sag resistance) and dimensional stability (e.g., no shrinkage during drying of the set gypsum) to the set gypsum so hydrated. The reinforcing materials also impart other improved properties and advantages to the set gypsum-containing product when it is made. In another embodiment of the invention, the set gypsum is treated with one or more reinforcing materials to provide gypsum-containing products (hereinafter referred to as gypsum-containing products) with similar, if not identical, reinforcement, resistance to permanent deformation (e.g., sag resistance), dimensional stability, and other improved properties and advantages. In some embodiments of the invention, the set gypsum-containing product of the invention contains a relatively large amount of the hydrochloride salt, but generally avoids the adverse effects of such salt concentrations on the gypsum product.

Background

Many well-known practical articles contain an effective amount, often as the major component, of set gypsum (calcium sulfate dihydrate). Set gypsum, for example, is a major component of gypsum plasterboards used in typical drywall construction of interior walls and in building ceilings (see, for example, U.S. patents 4009062 and 2985,219). It is also a major component of gypsum/cellulose fiber composite boards and products, as disclosed in US 5320677. Products that fill joints between gypsum board edges often contain large amounts of gypsum (see, for example, U.S. patent No. US 3297601). For example, acoustical tiles used in suspended ceilings may contain a significant amount of set gypsum, as disclosed in U.S. patents 5395438 and 3246063. Conventional plasters, such as those typically used to create plaster surfaces for internal building walls, generally depend primarily on the formation of set gypsum. Many specialty materials, such as the refinable moulding and moulding materials disclosed in US patent US5534059, contain substantial amounts of gypsum.

Most such gypsum products are prepared by forming a mixture of calcined gypsum (calcium sulfate hemihydrate and/or calcium sulfate anhydrite) and water (and, where appropriate, other components), casting the mixture into a mold or onto a surface of a desired shape, forming a matrix of crystalline hydrated gypsum (calcium sulfate dihydrate) by reacting the calcined gypsum with water, and allowing the mixture to harden to form set (i.e., rehydrated) gypsum. Mild heating is then usually applied to remove the remaining free (unreacted) water and obtain a dry product. The set gypsum crystal cross-linked matrix is formed by the desired calcined gypsum hydration process, thereby imparting strength to the gypsum structure in the gypsum product.

All of the gypsum-containing products described above benefit if their constituent set gypsum crystal structures are strengthened in order to make the products more resistant to stresses that may be encountered during use.

Efforts have been made to replace the partially set gypsum matrix with lower density materials (e.g., expanded perlite or air voids) to produce many of these gypsum products that are lighter in weight. In this case, because the amount of set gypsum that provides the strength of the low density product is small, it is desirable to increase the strength of the set gypsum above the standard level, just to maintain the overall product strength at the level of the higher density products of the prior art.

Furthermore, in many of the components of such gypsum products, high resistance to permanent deformation (e.g., resistance to sagging), especially at high humidity and temperature, or even under load conditions, is desirable. The human eye is generally unable to detect gypsum board sag of less than about 0.1 inch per two feet of length of gypsum board. Therefore, gypsum products are required to resist permanent deformation over their lifetime. For example, gypsum boards and tiles are typically stored or used in a manner such that they are vertically disposed. If the set gypsum matrix in these articles does not sufficiently resist permanent deformation, especially at elevated temperatures, even under load, the article begins to sag in the area between the points where it is held or supported by the base structure. This can be unsightly and can result in an article that is difficult to use. In many applications, gypsum products must withstand loads, e.g., insulation or condensation loads, without appreciable sag. Accordingly, there is a continuing need to be able to form set gypsum having improved resistance to permanent deformation (e.g., sag resistance).

Set gypsum in gypsum products is also required to have good dimensional stability during the manufacture, processing and industrial use of the gypsum product. Set gypsum can shrink or expand, especially under conditions of changing temperature and humidity. For example, when moisture is absorbed by the crystal spaces of the gypsum matrix in a gypsum board or tile exposed to high humidity and temperature, the board expands due to moisture absorption, which can exacerbate sag. In addition, during the manufacture of set gypsum products, there is typically a significant amount of free (unreacted) water that remains in the matrix after the gypsum has set. This free water is typically subsequently removed by mild heating. As the evaporating water leaves the interstitial spaces of the gypsum matrix, the matrix tends to shrink due to the inherent forces of the set gypsum (i.e., the water holds together the separated portions of the matrix between the cross-linked set gypsum crystals, which then move closer together as the water evaporates).

There are many advantages if such dimensional instability can be avoided or reduced. For example, if the gypsum board does not shrink during drying, more products will be produced using existing gypsum board production methods, and gypsum products that rely on maintaining precise shapes and size ratios (such as used in molding and forming) will be better suited for their purposes. For example, some mortars intended for use on interior wall surfaces of buildings have advantages in that they do not shrink during drying, so that thicker layers of mortar can be used without fear of cracking, without the need to apply thin layers multiple times and so that it takes a long time to sufficiently dry between layer-to-layer applications.

Other particular problems exist with some specialty types of gypsum products. For example, the production of low density gypsum products often uses foaming agents to create water bubbles in the calcined gypsum slurry (flowable aqueous mixture) that, when set gypsum is formed, create corresponding permanent voids in the product. This is often problematic because the aqueous foam used is inherently unstable, so that many of the water bubbles collect and escape from the thinner slurry (as do the bubbles in a bubble bath) before the set gypsum is formed, and so a large amount of foaming agent must be used to create the desired amount of voids in the set gypsum in order to obtain a product of the desired density. This increases the cost and the risk of the chemical foaming agent having a detrimental effect on other components or characteristics of the gypsum product. It is therefore desirable to reduce the amount of foaming agent required to create the desired amount of voids in the set gypsum product.

There is also a need for a new and improved composition and method for producing set gypsum-containing products made from mixtures containing high concentrations (i.e., at least 0.015% by weight based on the weight of calcium sulfate material in the mixture) of chloride ions or salts thereof. The chloride ions or salts thereof may be impurities in the calcium sulfate material itself or in the water used in the mixture (e.g., seawater or brackish ground water) that could not have been used to prepare a stable set gypsum product prior to the present invention.

There is also a need for a new and improved composition and method for treating set gypsum to improve its strength, resistance to permanent deformation (e.g., sag resistance), and dimensional stability.

There is a continuing need for new and improved set gypsum products, and compositions and methods for producing the same, which solve, avoid or reduce the above-mentioned problems. The present invention meets these needs.

Summary of the invention

The present inventors have surprisingly discovered set gypsum-containing products and compositions and methods for making them that unexpectedly meet the above-described needs. Each of the embodiments of the present invention satisfies one or more of these needs.

The set gypsum-containing product of the invention having improved resistance to permanent deformation is prepared according to the invention by first forming a mixture of a calcium sulfate material, water, and an amount of one or more reinforcing materials selected from the group consisting of condensed phosphoric acids, each containing 2 or more phosphoric acid units; and condensed phosphates or condensed phosphate ions, each containing 2 or more phosphate units.

The mixture is then maintained under conditions sufficient for the calcium sulfate material to form an improved set gypsum material.

As used herein, the term "calcium sulfate material" refers to anhydrous calcium sulfate; calcium sulfate hemihydrate; calcium sulfate dihydrate; calcium and sulfate ions; or a mixture of any or all of them.

In some embodiments of the invention, the calcium sulfate material is primarily calcium sulfate hemihydrate. In this case, all of the above-mentioned reinforcing materials will give the set gypsum formed improved resistance to permanent deformation. However, some reinforcing materials (e.g., sodium trimetaphosphate (also referred to herein as STMP), sodium hexametaphosphate (also referred to herein as SHMP) having 6-27 repeating phosphate units, and ammonium polyphosphate (also referred to herein as APP) having 1000-3000 repeating phosphate units) will provide preferred advantages, such as greater sag resistance. Furthermore, APP provides the same sag resistance as that provided by STMP, even when added at only one-fourth of the STMP concentration.

In some preferred embodiments of the invention, this is achieved by adding trimetaphosphate ion to a mixture of calcined gypsum and water used to produce a set gypsum product (as used herein, the term "calcined gypsum" refers to alpha calcium sulfate hemihydrate, beta calcium sulfate hemihydrate, water-soluble calcium sulfate anhydrite, or mixtures of any or all of them, and the terms "set gypsum" and "hydrated gypsum" refer to calcium sulfate dihydrate). When the water in the mixture reacts spontaneously with the calcined gypsum to form set gypsum, we have surprisingly found that the set gypsum has improved strength, resistance to permanent deformation (e.g., sag resistance) and dimensional stability compared to set gypsum formed from a mixture that does not contain trimetaphosphate ions. The mechanism by which these properties are improved is not clear.

Furthermore, the present inventors have unexpectedly found that trimetaphosphate ions (like APP) do not retard the rate at which calcined gypsum forms set gypsum. In fact, in the range of use where the trimetaphosphate ion is added, the rate of hydration of calcined gypsum to form set gypsum is substantially accelerated when the amount of the trimetaphosphate ion added is relatively large. This is particularly surprising because of the increased strength of set gypsum, since it is generally believed in gypsum technology that phosphoric acid or phosphate materials retard the formation of set gypsum and reduce the strength of the formed gypsum. This is true for most of these species, but not for the trimetaphosphate ion.

Thus, in general, some preferred embodiments of the present invention provide a method of producing a set gypsum-containing product having improved strength, resistance to permanent deformation (e.g., sag resistance), and dimensional stability, comprising: a mixture of calcined gypsum, water, and trimetaphosphate ion is formed and maintained at conditions sufficient to convert calcined gypsum to set gypsum, e.g., preferably a temperature of less than about 120F.

In some preferred embodiments of the invention, the method is a method of producing a gypsum board having a core of set gypsum interlayer sandwiched between cover sheets of paper or other material. The board is prepared by forming a flowable mixture (slurry) of calcined gypsum, water and trimetaphosphate ions, depositing the mixture between cover plates, and allowing the resulting assembly to set and dry.

While the boards thus formed have all the desired improved properties of increased strength, resistance to permanent deformation (e.g., sag resistance) and dimensional stability, it has been observed for unknown reasons that the bond strength between the gypsum core and the cover board (which typically contains paper) can be lost or even lost when the board for some reason becomes wet or incompletely dried during manufacture, even when the board contains typical non-pregelatinized starches (e.g., acid-modified starches) which generally impart better integrity of the paper-to-core bond. The cover sheet can peel away from the gypsum board, which is unacceptable. The inventors fortunately have also discovered a solution to this potential problem. It has been found that this problem can be avoided by adding pregelatinized starch to the production slurry. The starch is then distributed throughout the formed gypsum core and it has been surprisingly found that doing so avoids weakening the bond between the core and the cover sheet.

Thus, in some embodiments of the present invention, compositions and methods are provided for producing further improved gypsum boards. The composition contains a mixture of water, calcined gypsum, trimetaphosphate ion, and pregelatinized starch. The method includes forming such mixtures, depositing them between cover plates, and allowing the resulting assembly to set and dry.

In the event that it is desired to produce lightweight gypsum board, the present invention provides compositions and methods for producing such lightweight gypsum board. The composition comprises a mixture of water, calcined gypsum, trimetaphosphate ion, and aqueous foam, and the method comprises forming such a mixture, depositing them between cover plates, and allowing the resulting assembly to set and dry. The composition and method provide lightweight boards because the bubbles of the water foam create corresponding air voids in the set gypsum core of the resulting board. The overall strength of the panel is higher than panels produced with water foam in the prior art mixture because the strength is increased by the trimetaphosphate ions in the mixture used to form the panels of the present invention. For example, a ceiling tile of 1/2 inches thick made according to the present invention has better resistance to permanent deformation (e.g., sag resistance) than a ceiling tile of 5/8 inches thick made using the prior art compositions and methods. Therefore, the present invention can significantly save the cost of producing the ceiling.

The inventors have surprisingly found that there are other advantages to having a mixture containing trimetaphosphate ions in addition to aqueous foam. That is, it has been found that when the mixture contains trimetaphosphate ions, proportionately higher pores (more total pore volume) are produced per unit amount of aqueous foam used in the formed gypsum product. The reason for this is not clear, but it is advantageous to produce the desired amount of void volume in the set gypsum product, provided that a small amount of foaming agent is used. This in turn reduces the cost of production and the risk of detrimental effects of the chemical foaming agent on other components or characteristics of the gypsum product.

In some embodiments of the present invention, there are provided composite boards comprising set gypsum and a reinforcing material, prepared as follows: forming or depositing a mixture on a surface, wherein the mixture contains a reinforcing material, a calcium sulfate material, water, and an amount of one or more reinforcing materials selected from the group consisting of: condensed phosphoric acids, each containing 2 or more phosphoric acid units; and condensed phosphates or condensed phosphate ions, each containing 2 or more phosphate units. The mixture is then maintained under conditions sufficient for the calcium sulfate material to form a set gypsum material.

The present invention also provides a composite board comprising set gypsum and matrix particles, at least a portion of the set gypsum being located at and near the interstices of the matrix particles that are readily accessible. The plate is prepared by forming or depositing a mixture on the surface, wherein the mixture comprises: a matrix particle; calcium sulfate hemihydrate, at least a portion of which is in crystalline form, at and near the interstices of the matrix particles; water; and a suitable amount of one or more reinforcing materials selected from the group consisting of: condensed phosphoric acids, each containing 2 or more phosphoric acid units; and condensed phosphates or condensed phosphate ions, each containing 2 or more phosphate units. The mixture is then maintained under conditions sufficient for the calcium sulfate hemihydrate to form set gypsum, whereby the set gypsum portion at and near the readily accessible voids of the matrix particles is formed by in situ hydration of the calcium sulfate hemihydrate crystals in and near the voids of the matrix particles.

The present invention also provides set gypsum-containing machinable articles prepared by forming a mixture containing starch, water-redispersible polymer particles, a calcium sulfate material, water, and an amount of one or more reinforcing materials selected from the group consisting of: condensed phosphoric acids, each containing 2 or more phosphoric acid units; and condensed phosphates or condensed phosphate ions, each containing 2 or more phosphate units. The mixture is then maintained under conditions sufficient for the calcium sulfate material to form a set gypsum material.

The present invention also provides a set gypsum product for modifying a joint between edges of gypsum board, the product being prepared by filling a joint with a mixture comprising a binder, a thickener, a non-homogenizing agent, a calcium sulfate material, water and an amount of one or more reinforcing materials selected from the group consisting of: condensed phosphoric acids, each containing 2 or more phosphoric acid units; and condensed phosphates or condensed phosphate ions, each containing 2 or more phosphate units. The mixture is then maintained under conditions sufficient for the calcium sulfate material to form a set gypsum material.

The present invention also provides set gypsum-containing acoustical tiles prepared by forming or depositing in a tray trough a mixture comprising gelatinized starch, mineral wool, a calcium sulfate material, water, and an amount of one or more reinforcing materials selected from the group consisting of: condensed phosphoric acids, each containing 2 or more phosphoric acid units; and condensed phosphates or condensed phosphate ions, each containing 2 or more phosphate units. The mixture is then maintained under conditions sufficient for the calcium sulfate material to form a set gypsum material.

The present invention also provides another type of set gypsum-containing acoustical tile prepared by forming or depositing in a tray trough a mixture comprising gelatinized starch, expanded perlite particles, a fibrous reinforcing agent, a calcium sulfate material, water, and an amount of one or more reinforcing materials selected from the group consisting of: condensed phosphoric acids, each containing 2 or more phosphoric acid units; and condensed phosphates or condensed phosphate ions, each containing 2 or more phosphate units. The mixture is then maintained under conditions sufficient for the calcium sulfate material to form a set gypsum material.

The present invention also provides a set gypsum product prepared by forming a mixture of a reinforcing material, calcium sulfate dihydrate, and water. More specifically, these embodiments include treating the gypsum cast with a reinforcing material. It has been found that the resulting mixture of reinforcing material, water and calcium sulfate dihydrate provides a set gypsum product having improved strength, resistance to permanent deformation (e.g., sag resistance), and dimensional stability. This post-solidification treatment can be achieved by adding a reinforcing material, by spraying or soaking the calcium sulphate dihydrate cast body with the reinforcing material. In the case of such post-setting treatment, the reinforcing material may be selected from the following group: phosphoric acids, each containing 1 or more phosphoric acid units; condensed phosphates or condensed phosphate ions, each containing 2 or more phosphate units; and a monobasic salt or monovalent ion of orthophosphoric acid.

In some embodiments of the invention, compositions and methods are provided for producing set gypsum-containing products from mixtures containing high concentrations of chloride ions or salts thereof (i.e., at least 0.015% by weight based on the calcium sulfate material in the mixture). The chloride ions or salts thereof may be impurities in the calcium sulfate material itself or in the water used in the mixture (e.g., seawater or brackish ground water) that could not have been used to prepare a stable set gypsum product prior to the present invention.

In the pre-setting treatment of calcium sulfate materials according to the present invention, it has also been found that some reinforcing materials hinder the rate of hydration at which set gypsum is formed and adversely affect the strength of the set gypsum product. It has been found that this hindrance and the negative effect on strength can be improved or even overcome by including in the mixture, in a suitable manner, a suitable amount of coagulant.

It has also been found that gypsum boards having a desired shape can be made in accordance with the teachings of the present invention. Prior to the present invention, the change in shape of a regular gypsum panel was typically made by wetting the gypsum panel with water, weakening the gypsum panel and making it more flexible, then changing the shape of the gypsum panel as desired, and then waiting for the gypsum panel to dry. However, this prior art technique suffers from a number of manufacturing and installation disadvantages, since the wetting required to weaken the gypsum board and make it more flexible so that it can be changed to the desired shape requires a significant amount of time, i.e., at least 1 hour or more, and 12 hours is not uncommon. Further, this prior art cannot be easily changed to a desired plate shape. If the panel is not properly weakened, it is difficult to change the shape of the panel as desired. I.e. more force is required to change the shape of the plate as required, and if too much force is applied, the plate will break. Thus, methods and compositions that reduce wetting time and make it easier to manufacture and install gypsum boards of desired shapes are highly desirable.

According to a preferred embodiment of the invention, for example, a gypsum board can be weakened and made more flexible by spraying the gypsum board with an aqueous chloride solution containing any reinforcing material (as described in the summary of the invention above and in the examples below). The weakened, more flexible gypsum board is then easily shaped to the desired shape with less force than in the prior art, because the beneficial effect of the reinforcing material will maintain the desired shape of the deformed gypsum board after it has dried.

Description of the drawings

FIG. 1 is a graph depicting the product weight of gypsum board products, including gypsum boards of the present invention.

FIG. 2 is a graph comparing the sag resistance of gypsum boards made according to the present invention with commercially available gypsum boards, wherein all test boards were assembled using conventional staple fastening and screw-down ceiling connectors.

Fig. 3 is a graph comparing the sag resistance of gypsum boards made according to the present invention to commercially available gypsum boards, wherein all test boards were assembled using a conventional F2100 ceiling connector (i.e., adhesive).

FIG. 4 is a graph comparing the sag deflection effect of gypsum boards made according to the present invention with commercially available gypsum boards.

FIG. 5 is a graph depicting the effect of sag deviation on gypsum board treated in accordance with the present invention, which has been made using gypsum board including pre-set and dried gypsum (i.e., calcium sulfate dihydrate).

Description of the preferred embodiments

The present invention can be practiced with compositions and methods similar to those used in the art for making various set gypsum products. The compositions and methods of some preferred embodiments of the present invention differ from the prior art compositions and methods of making various set gypsum products primarily in that they contain trimetaphosphate salt such that in the methods of the present invention, the process of rehydrating calcined gypsum to form set gypsum is carried out in the presence of trimetaphosphate ions, thereby embodying the advantages of the present invention. In other aspects, the compositions and methods of the invention can be the same as the corresponding compositions and methods of the prior art.

The trimetaphosphate salt contained in the composition of the present invention may include any water-soluble trimetaphosphate salt that does not adversely interact with the other components of the composition. Examples of some practical salts include sodium trimetaphosphate, potassium trimetaphosphate, ammonium trimetaphosphate, lithium trimetaphosphate, aluminum trimetaphosphate, and mixtures of these salts. Sodium trimetaphosphate is preferred. It is readily commercially available, for example, from Solutia corporation of St.Louis, Missouri, a unit formerly Monsanto corporation of St.Louis, Missouri.

For use in a preferred method of practicing the invention, trimetaphosphate salt can be dissolved in an aqueous mixture of calcined gypsum to a concentration of from about 0.004 to about 2.0% by weight trimetaphosphate ion based on the weight of calcined gypsum. The preferred concentration of trimetaphosphate ion is from about 0.04 to about 0.16 weight percent. A more preferred concentration is about 0.08% by weight. If ease of storage and transport is required in the practice of some embodiments of the invention, the trimetaphosphate salt can be pre-dissolved in water and mixed into the mixture as an aqueous solution.

According to a preferred embodiment of the present invention, the trimetaphosphate ions need only be present in the aqueous mixture of calcined gypsum during hydration of calcined gypsum to form set gypsum. Thus, although it is generally more convenient, and thus preferred, to mix the trimetaphosphate ions into the mixture at an early stage, the trimetaphosphate ions can also be mixed into the mixture of calcined gypsum and water at a later stage. For example, in the preparation of a typical gypsum board, water and calcined gypsum are added together in a mixing apparatus, thoroughly mixed, and then typically deposited onto a cover sheet on a conveyor belt, and a second cover sheet is placed over the deposited mixture before a quantity of calcined gypsum is rehydrated to form set gypsum. Although it is more convenient to add the trimetaphosphate ion to the mixture in a mixing device during its preparation, the trimetaphosphate ion can also be added at a later stage, for example by spraying an aqueous solution of trimetaphosphate ions onto the aqueous mixture of calcined gypsum that has been deposited just prior to placing the second plate on the deposit so that the aqueous solution of trimetaphosphate ions wets out into the deposited mixture and they are present as bulk hydration occurs to form set gypsum.

Other alternative methods of adding trimetaphosphate ion to the mixture will be apparent to those of ordinary skill in the art and are, of course, within the scope of the present invention. For example, one or both cover sheets may be pre-coated with a trimetaphosphate salt so that when the deposited aqueous calcined gypsum mixture contacts the cover sheets, the trimetaphosphate salt dissolves and causes the trimetaphosphate ions to migrate into the mixture. Another alternative is to mix the trimetaphosphate salt with the gypsum even before heating to form calcined gypsum so that when the calcined gypsum is mixed with water and rehydration occurs, the salt is already present.

An alternative method of adding trimetaphosphate ions to the mixture is by adding the trimetaphosphate ions to the set gypsum by any suitable means, such as spraying or wetting the set gypsum with a solution containing trimetaphosphate. It has been found that the trimetaphosphate ions can migrate into the set gypsum by processing conventional paper sheets used in set gypsum.

The calcined gypsum used in the present invention may be present in the forms and concentrations typical for those used in the corresponding embodiments of the prior art. It may be natural or synthetic alpha calcium sulfate hemihydrate, beta calcium sulfate hemihydrate, water soluble calcium sulfate anhydrite or mixtures of any or all of them. In some preferred embodiments, calcium sulfate alpha hemihydrate is used because it produces set gypsum with higher strength. In other preferred embodiments, beta calcium sulfate hemihydrate or a mixture of beta calcium sulfate hemihydrate and water soluble calcium sulfate anhydrite is used.

In the practice of the present invention, other conventional additives may be used in conventional amounts to impart desired characteristics and to facilitate manufacturing operations, such as water foams, set accelerators, set retarders, re-calcination inhibitors, binders, adhesives, dispersion aids, leveling or non-leveling agents, thickeners, bactericides, fungicides, pH adjusters, colorants, reinforcing materials, flame retardants, water repellents, fillers, and mixtures thereof.

In some preferred embodiments of the invention, the methods and compositions are used to make gypsum board comprising a core of set gypsum material sandwiched between cover sheets, with trimetaphosphate ions used in the amounts and manners described above. On the other hand, the compositions and methods can be used with the same components and in the same manner as corresponding compositions and methods of the prior art for making gypsum board, for example, as disclosed in U.S. Pat. Nos. 4009062 and 2985219, which are incorporated herein by reference. The boards made using this preferred inventive composition and method have improved strength, resistance to permanent deformation, and dimensional stability.

In a preferred method and composition for making gypsum board, the facing sheets of the board contain paper, and pregelatinized starch is also used, to avoid an otherwise somewhat increased risk of paper delamination under extremely humid conditions. The pre-gelatinization of the raw starch is achieved by cooking in water at a temperature of at least 185F or by other well-known methods.

Some examples of readily available pregelatinized starches that serve the purpose of the present invention are (marked by their commercial names): PCF1000 starch, sold by Lauhoff Grain company; AMERIKOR818 and HQM PREGEL starches, both sold by Archer Daniels Midland.

In order to use pregelatinized starches in the preferred embodiment of the invention, they are present in the aqueous mixture of calcined gypsum in an amount of from about 0.08 to about 0.5% by weight based on the weight of calcined gypsum. Preferably, the pregelatinized starch is present in an amount of about 0.16 to about 0.4% by weight. More preferably about 0.3% by weight. The pregelatinized starch of the embodiments of the present invention can also be used to replace all or part of the starch conventionally used in the prior art, if the corresponding embodiments of the prior art also contain starch that has not been pregelatinized, as is done in many cases.

In embodiments of the present invention where a foaming agent is used to create voids in the set gypsum product to provide a lightweight product, any of the conventional foaming agents known to be useful in preparing foamed set gypsum products can be used. Many such blowing agents are well known and readily available, for example from GEO Specialty Chemicals of Ambler, Pennsylvania. Further descriptions of useful blowing agents are found, for example, in: US patent US 4676835; 5158612, respectively; 5240639 and 5643510; and PCT International publication WO95/16515, published on 22.6.1995.

In many cases, it is preferable to create larger voids in the gypsum product to maintain its strength. This can be achieved by using a foaming agent that produces a foam, wherein the produced foam is less stable when in contact with the calcined gypsum slurry. Preferably, this is achieved by incorporating a large amount of a blowing agent known to produce less stable foams with a small amount of a blowing agent known to produce more stable foams.

Such foaming agent mixtures may be premixed "off-line", i.e., separately from the process of preparing the foamed gypsum product. However, it is preferred to mix such blowing agents both simultaneously and continuously, as an integral "in-line" part of the process. This can be done, for example, by pumping separate streams of different foaming agents and conveying the streams together or just before into a foam generator, the function of which is to produce a stream of aqueous foam that is subsequently injected and mixed with the calcined gypsum slurry. By mixing in this manner, the ratio of foaming agent in the mix can be simply and efficiently adjusted (e.g., by varying the flow rate of one or both of the individual streams) to produce the desired void characteristics in the foamed set gypsum product. Such adjustments will be made based on testing of the final article to determine if such adjustments are needed. This "in-line" mixing and conditioning is further described in U.S. patent No. 5643510 and co-pending U.S. patent application 08/577367, filed on 12/22 of 1995.

An example of a class of blowing agents useful for producing unstable foams has the formula

ROSO_3ΘM_{_} (Q)

Wherein R represents an alkyl group having 2 to 20 carbon atoms and M represents a cation. Preferably, R represents an alkyl group having 8 to 12 carbon atoms.

An example of a class of blowing agents useful for producing stable foams has the formula

CH₃(CH₂)_xCH₂(OCH₂CH₂)_YOSO_3ΘM_{_} (J)

Wherein X represents a number from 2 to 20, Y represents a number from 0 to 10 and the value is greater than 0 in at least 50% by weight of the blowing agent, and M represents a cation.

In some preferred embodiments of the present invention, blowing agents having the above formulas (Q) and (J) are mixed together such that the blowing agent portion of formula (Q) and the blowing agent portion of formula (J) (Y is O) together comprise from 86 to 99 weight percent of the formed blowing agent mixture.

In some preferred embodiments of the invention, the aqueous foam has been produced from a premixed blowing agent having the formula

CH₃(CH₂)_xCH₂(OCH₂CH₂)_YOSO_3ΘM_{_} (Z)

Wherein X represents a number from 2 to 20, Y represents a number from 0 to 10 and the value is 0 in at least 50% by weight of the blowing agent, and M represents a cation. Preferably, the blowing agent of formula (Z) has from 86 to 99% by weight of Y being O.

In some preferred embodiments of the present invention, the methods and compositions are used to prepare composite boards comprising set gypsum and particles of reinforcing material, using trimetaphosphate ion in the concentrations and manners described above. It is particularly preferred that the composite article comprises set gypsum and matrix particles, at least a portion of the set gypsum being located in and adjacent to the voids of the readily accessible matrix particles. The composition of the present invention comprises a mixture comprising: a matrix particle having an easily accessible void therein; calcined gypsum at least partially in crystalline form at and near the interstices of the matrix particles; and a water-soluble trimetaphosphate salt. The composition can be mixed with water to form a mixture of water of the present invention, matrix particles having readily accessible voids therein, calcined gypsum (at least a portion of which is in crystalline form at and near the voids of the matrix particles), and trimetaphosphate ions. The method includes forming such a mixture, depositing the mixture on a surface or injecting into a mold, allowing them to set and dry. In other aspects, the compositions and methods can be used in the same compositions and manner as corresponding compositions and methods of making composite panels in the prior art, for example, as disclosed in U.S. patent No. 5320677, which is incorporated herein by reference.

In some preferred embodiments of the present invention, the methods and compositions are used to prepare machinable materials using trimetaphosphate ion in the concentrations and manners described above. In some preferred forms of these embodiments, the composition contains a mixture of calcined gypsum, water-soluble trimetaphosphate salt, starch, and water-redispersible polymer particles. The composition is mixed with water to form a mixture of water, calcined gypsum, trimetaphosphate ion, starch, and water-redispersible polymer particles of the present invention. The method includes forming such a mixture, depositing the mixture on a surface or injecting into a mold, allowing them to set and dry. In other respects, the compositions and methods can be used in the same manner and in the same compositions and methods as are used in the prior art for making corresponding machinable stucco materials, except for the incorporation of trimetaphosphate and trimetaphosphate ions, as disclosed, for example, in U.S. patent No. 5534059, which is incorporated herein by reference.

In some preferred embodiments of the invention, the methods and compositions are used to prepare materials for use in modifying the joint between the edges of gypsum boards using trimetaphosphate or trimetaphosphate ion at the concentrations described above. In other respects, the compositions and methods can be used in the same manner and in the same compositions and methods as the corresponding compositions and methods used in the prior art for preparing joint-modifying materials, for example, as disclosed in U.S. Pat. No. 5,3297601, which is incorporated herein by reference, except that the trimetaphosphate salt and trimetaphosphate ion are incorporated. In some preferred forms of this embodiment, the composition contains a mixture of calcined gypsum, a water-soluble trimetaphosphate salt, a binder, a thickener, and a non-homogenizing agent. The composition may be mixed with water to form a mixture of calcined gypsum, trimetaphosphate ion, binder, thickener, and non-homogenizing agent of the present invention. The method includes forming such a mixture, injecting the mixture into the joint between the edges of the gypsum board, allowing them to set and dry.

In this preferred joint modification embodiment, the binder, thickener and non-leveling agent are selected from components well known to those skilled in the joint compound art. For example, the binder may be a conventional latex binder, with poly (vinyl acetate) and ethylene-vinyl acetate copolymers being preferred, and their content in the composition is about 1-15% by weight. Examples of useful thickeners are cellulosic thickeners such as ethylhydroxyethyl cellulose, hydroxypropyl methylcellulose, methylhydroxypropyl cellulose or hydroxyethyl cellulose, which are present in the composition in an amount of about 0.1 to 2% by weight. Examples of suitable non-homogenizing agents are attapulgite, sepiolite, bentonite and montmorillonite clays, which are present in the composition in an amount of about 1-10% by weight.

In some preferred embodiments of the present invention, the methods and compositions are used to make acoustical tiles using the above-described concentrations of trimetaphosphate ion. In some preferred forms of this embodiment, the composition contains water, calcined gypsum, trimetaphosphate ion, a mixture of gelatinized starch and mineral wool, or a mixture of water, calcined gypsum, trimetaphosphate ion, gelatinized starch, expanded perlite particles, and a fiber reinforcement. The method includes forming such a mixture, casting the mixture into a tray trough, allowing them to set and dry. In other respects, the compositions and methods can be practiced with the same components and in the same manner as the corresponding compositions and methods of the prior art for making acoustical tiles, except for the introduction of trimetaphosphate ions, as disclosed, for example, in U.S. patent nos. 5395438 and 3246063, which are incorporated herein by reference.

The following examples further illustrate some preferred embodiments of the present invention and compare them to methods and compositions outside the scope of the present invention. Unless otherwise indicated, the concentrations of the materials in the compositions and mixtures are in percent by weight based on the weight of calcined gypsum. The abbreviation "STMP" means sodium trimetaphosphate and the abbreviation "TMP" means trimetaphosphate.

Example 1

Cubic compressive strength of laboratory

Gypsum product samples were prepared according to the present invention and compared for compressive strength to samples prepared using different methods and compositions. The test was performed according to ASTM C472-93.

Preparation of test specimens with dry mixing: 500g beta calcium sulfate hemihydrate; 0.6g of a coagulant containing finely ground particles of calcium sulphate dihydrate coated with sugar to maintain effectiveness and heated as described in us patent 3573947 (the contents of which are incorporated herein by reference); and 0g of additive (control sample), 0.5-2g of STMP (preferred invention sample) or 0.5-2g of other phosphate additives (comparative sample). The samples were then mixed with 700ml tap water at a temperature of 70F in a 2 litre WARING mixer, allowed to wet for 5 seconds and mixed at low speed for 10 seconds. The slurry thus formed was cast into a mold to make cubes (2 inches per side). After the calcium sulfate hemihydrate sets to form gypsum (calcium sulfate dihydrate), the cubes are removed from the mold and dried in a 112F air oven for at least 72 hours, or until their weight ceases to change. The dried cubes had a density of about 44 pounds per foot³(pcf)。

The compressive strength of each cube was determined on a SATEC tester. The average of the three samples is shown as the result in table 1 below. The strength values of the control samples varied because various sources of beta calcium sulfate hemihydrate and/or different batches of beta calcium sulfate hemihydrate were used. The results in the table show the pounds per inch²(psi) measured compressive strength and% change in strength (% Δ) from the relevant control. The measurements were estimated to have experimental errors of about +/-5% (thus showing a 10% increase in intensity compared to the control group, actually in the range of 5-15%).

TABLE 1

Compressive strength

Additive agent	0% additive (psi)	0.1% of additive (psi;% Delta)	0.2% of additive (psi;% Delta)	0.4% of additive (psi;% Delta)	0.8% of additive (psi;% Delta)
						STMP	987	1054；6.8	1075；8.9	1072；8.6	------------
STMP	724	843；16.4	957；32.2	865；19.5	783；8.1
						STMP	742	819；10.4	850；14.6	------------	------------
STMP	714	800；12.0	834；16.8	------------	------------
						STMP	842	985；17.0	1005；19.4	1053；25.1	611；-27.4
STMP	682	803；17.7	826；21.1	887；30.1	------------
						Sodium phosphate	950	951；0.1	929；-2.2	------------	------------
Sodium tripolyphosphate	950	993；4.5	873；-8.1	------------	------------
						Sodium hexametaphosphate	950	845；-11.1	552；-41.9	------------	------------
Dicalcium phosphate	763	769；0.8	775；1.6	761；-0.3	------------
						Disodium phosphate	763	757；-0.8	728；-4.6	700；-8.3	------------
Monocalcium phosphate monohydrate	763	786；3.0	766；0.4	824；8.0	------------

The data in Table 1 illustrate that the strength of the inventive Sample (STMP) is generally significantly increased as compared to the control, while the strength of the comparative sample is generally increased little, or not increased, or even significantly decreased.

Example 2

Permanent deformation resistance (sag resistance of plasterboard laboratory)

In the laboratory, gypsum board samples were prepared according to the present invention and compared to sample boards prepared using methods and compositions outside the scope of the present invention for resistance to permanent deformation.

The samples were prepared by mixing the mix in a 5 liter WARING mixer at low speed for 10 seconds: 1.5kg beta calcium sulfate hemihydrate; 2g of the above coagulant; 2 liters of tap water; and 0g of additive (control), 3g of STMP (inventive) or 3g of further additive (comparative). The slurry thus formed was cast into a tray tank to prepare gypsum flat plate samples, each having a size of about 6X 24X 1/2 inches. After the calcium sulfate hemihydrate sets to form gypsum (calcium sulfate dihydrate), the boards are dried in a 112F oven until their weight stops changing. The final weight of each panel was recorded. To avoid the effect of the cover paper on the sag performance of the gypsum board under wet conditions, no paper overlay was applied to the boards.

Each drying panel was then laid flat on two horizontal locations of 1/2 inch wide supports, the length of which extended the full width of the support panel, one at each end of the panel. The panel was held in this position for a specified period of time (4 days in this example) under continuous ambient conditions of 90F temperature and 90% relative humidity. The degree of sag of the panel was then determined by measuring the distance (in inches) between the center of the top surface of the panel and an imaginary horizontal plane between the edges of the top surface at the ends of the panel. It is believed that the resistance of the set gypsum matrix of the board to permanent deformation is inversely proportional to the degree of sag of the board. Thus, the greater the degree of sag, the lower the relative permanent set resistance of the set gypsum matrix-containing board.

The test for resistance to permanent deformation, including the composition and concentration of the additives (% by weight based on calcium sulfate hemihydrate), the final weight of the board and the measured degree of sag, is shown in table 2. The additives used in the comparative samples (outside the scope of the invention) represent other materials that have been tried to improve the resistance of gypsum board to sagging under high humidity conditions.

TABLE 2

Degree of gypsum board sag

Additive agent	Additive (weight%)	Plate weight (g)	Plate droop (inch)
				None (control group)	0	830	0.519
STMP	0.2	838	0.015
				Boric acid	0.2	829	0.160
Sodium aluminium phosphate	0.2	835	0.550
				Wax emulsion	7.5	718	0.411
Glass fiber	0.2	838	0.549
				Glass fiber and boric acid	0.2+0.2	825	0.161

The data in table 2 show that the panels prepared according to the invention (STMP) are more resistant to sagging (and therefore also to permanent deformation) than the control and the non-inventive comparative panels. In addition, the sag rate of the panels made according to the present invention is much less than 0.1 inch per 2 feet of panel sag, and thus is not readily observable to the human eye.

Example 3

Permanent deformation resistance (sag resistance of gypsum board production line)

Fig. 1 shows a comparison of the weight of the articles, and fig. 2 and 3 show the sag resistance of such articles. The product weight of the 1/2 inch indoor ceiling tile of the invention (i.e., mixing trimetaphosphate salt with calcined Gypsum and water) was the same as the weight of 1/2 inch SHEETROCK conventional Gypsum board in a room made by United States Gypsum Company. The average 1/2 inch indoor ceiling shown in fig. 1 is a Gold Bond — high strength ceiling made by National Gypsum Company (National Gypsum Company). The average 5/8 inch gypsum board shown in FIG. 1 is SHEETROCK _5/8 inch Firecode type X gypsum board manufactured by American Gypsum.

FIG. 2 is a graph comparing the sag resistance of gypsum boards made according to the present invention with the sag resistance of the above-described commercially available gypsum boards, all of which were installed using conventional staple and screw-down ceiling connectors.

FIG. 3 is a graph comparing the sag resistance of gypsum boards made according to the present invention to the sag resistance of the above-described commercially available gypsum boards, all of which were installed using a conventional F2100 two-part polyurethane adhesive ceiling joint.

The following is a detailed description of gypsum board and other constructions for making ceiling tiles for use in sag comparison depicted in fig. 2 and 3:

A. gypsum board

1.1/2 inch by 48 inch by 96 inch, prepared according to the invention.

2.1/2 inch by 48 inch by 96 inch, national gypsum company Gold Bond high strength ceiling.

3.1/2 inch by 48 inch by 96 inch, conventional SHEETROCK _ Gypsum board manufactured by American Gypsum.

4.5/8 inch by 48 inch by 96 inch, SHEETROCK _ FIRECode type X gypsum board, manufactured by American Gypsum company.

B. Framework-18 inches high by 102 inches long, made of nominally 2 inches by 3 inches wood joined by r.j.cole joint compound-USG tuff setting HES joint compound. Seam tape-USG fiberglass mesh self-adhesive attachment seam tape.

C. Vapor Barrier coating- #4512 Silver Vapor Barrier (Silver Vapor Barrier), entry: 246900.

D. Insulation-Delta blown Insulation (Blowing Insulation) blown cotton, rock wool mineral fibers.

E. Spray Texture (Texture) -USG SHEETROCK _ ceiling spray Texture Q T Medium poly.

F. Fasteners-1 inch crown (c.) x 1.25 inch long (1g.) x ga.u-type nails, and #6 x 1.25 long drywall screw nails. Foamseal company's F2100 two-part polyurethane adhesive. Ceiling structure

A. 2 x 4 blocks are attached to both ends of the frame to make a frame.

B. A 12(12) block of gypsum board was attached to the framing frame with F2100 adhesive. The average edge curl (bead) width measured on the gypsum board was 1 inch.

C. The ceilings were carefully raised and placed on top of the pre-constructed four walls to make an 8 feet by 48 feet house.

D. The ceiling assembly was attached to the ceiling of the wall and secured around the wall with #8 x 3.5 inch screws. The gypsum panels are attached to the frame using screws and staples to form a second ceiling panel. It is also lifted and attached to the four (4) walls.

In each ceiling, 3(3) gypsum boards of various types are used to form 2(2) ceilings. One ceiling was mechanically fixed (see fig. 2) while the other ceiling was fixed with only F2100 urethane adhesive (see fig. 3). Gypsum boards of different gypsum board types are laid alternately flat along the ceiling. The frames used were 8 feet 5 inches long by 18 inches high, and spaced 24 inches apart ("o.c.") on center.

The ceiling was mechanically secured at 12 inches along the center of the field frame using 1 inch crown x 1.25 inch long x 16Ga. staples at 7 inch centers along the joint and #6 x 1.25 inch long drywall screws.

Adhesively attached ceilings use a bead (bead) of about 1.25 inches along the frame. The hems are used on one side of the site frame and along the hems on both sides of the gypsum joint frame.

The plasterboard is attached so that its paper-wrapped edge is aligned parallel to the frame chord.

After taping the plaster joint, the starting position was determined. Next, the ceiling tile is coated with a vapor barrier coating and then painted with a texture (textured). Immediately after texturing, a second reading was taken. Rock wool insulation is then blown to the top of the frame. A third reading is then taken. The temperature and humidity are increased while blowing the insulating material to the top of the frame. The target temperature and humidity were 90 — and 90% relative humidity. These conditions were maintained for 7 days while measuring deviations every morning and afternoon. After 7 days, the houses were opened and they were allowed to cool to room temperature. The measurement of sag was read for another 3(3) days and the test was terminated.

As shown in fig. 2 and 3, the gypsum board made according to the present invention has significantly better sag resistance than other gypsum boards and below the visual limit of about 0.1 inch per 2 foot length of board sag.

Example 4

Nail pull resistance of laboratory gypsum board

Typical paper-faced gypsum board samples produced according to the present invention and prepared in the laboratory were compared to control boards for nail pull resistance. Nail pull resistance is a composite measure of the strength of the gypsum board core, its paper facing strength, and the bond between the paper and the gypsum. This test measures the maximum force required to pull a headed nail through the board until significant cracking of the board occurs and is performed according to ASTM C473-95.

Slurry was prepared in a HOBART mixer with medium speed mixing for 40 seconds: 3.0kg beta calcium sulfate hemihydrate; 5g of the above coagulant; 10g of LC-211 starch (dry milled acid modified non-pregelatinized wheat starch for gypsum board formation, commonly included in prior art formulations, sold by Archer Daniels Midland Milling, Inc.); 20g of hammer-broken fine paper fibers; 3 liters of tap water; 0-6g STMP; and 0-30g of PCF1000 pregelatinized corn starch, sold by the company Lauhoff Grain.

The slurry thus formed was cast on top of paper in a tray tank and then coated on top of it to prepare flat gypsum board samples each having dimensions of 14 x 24 x 1/2 inches. The paper on one side is a multi-ply having manila outer plies (ply) and the paper on the other side is a multi-ply newsprint strip (newstone), both of which are typical papers used in the gypsum board industry to make paper-faced gypsum board. Each panel was then held in a 350F oven until they lost 25% by weight, and then transferred and held in a 112F oven until they reached a constant weight.

The final panel weight and nail pull resistance were determined. The results are shown in Table 3.

TABLE 3

Nail pull resistance

STMP concentration (% by weight)	PCF1000 starch (% by weight)	Plate weight (lbs/1000 ft)2)	Nail pull resistance (lbs)
				0	0	2465	150
0.1	0	2454	155
				0.2	0	2326	158
0.1	0.5	2458	168
				0.2	1.0	2495	176

The results in table 3 show that the panels prepared according to the invention have a very high overall strength (nail pull resistance) compared to the control panels.

Example 5

Production line gypsum board dimensional stability and permanent deformation resistance

In a typical large-scale production line, paper-faced foamed gypsum board is produced in an industrial gypsum board production facility. Gypsum boards were prepared with various concentrations of trimetaphosphate ion and compared to control boards (prepared without the addition of trimetaphosphate ion) for dimensional stability and resistance to permanent deformation. In making some gypsum boards, the gypsum boards are made using methods and components typical of those used in the art for making gypsum boards, except for the use of trimetaphosphate ions. The components and their approximate weight percentages (expressed in narrower ranges by weight of calcined gypsum used) are shown in Table 4.

TABLE 4

Components for producing gypsum boards

Components	By weight%
		Beta calcium sulfate hemihydrate	100
Water (W)	94-98
		Setting accelerator	1.1-1.6
Starch	0.5-0.7
		Dispersing agent	0.20-0.22
Paper fiber	0.5-0.7
		Retarder	0.07-0.09
Foaming agent	0.02-0.03
		Sodium trimetaphosphate ("STMP")	0-0.16
Re-calcination inhibitor	0.13-0.14

In table 4: coagulants include sugar-coated finely ground particles of calcium sulfate dihydrate as described in U.S. patent 3573947, wherein the coagulant is not heated during its preparation; the starch was a dry milled acid modified HI-BOND starch available from Lauhoff Grain; the dispersant was DILOFLO, a naphthalenesulfonate salt available from GEO Specialty Chemicals, Ambler, Peng; the paper fiber is hammer-type broken fine paper fiber; the retarder was VERSENEX80, a chelating agent available from Rogers, Van Walters & of Kirkland, Washington; the blowing agent was WITCOLATE1276 available from Witco corporation of Greenwich, Connecticut; sodium trimetaphosphate was purchased from Monsanto corporation of st.louis, Missouri; the recalcination inhibitor was CERELOSE2001, used to reduce plate end (board end) recalcification of dextrose during drying.

Gypsum board was produced on a 4 foot wide continuous line: continuously adding the components to a mixer and mixing to form an aqueous slurry (in a separate foam generating system, a foaming agent is used to generate a water foam; the foam is fed into the slurry through the mixer); continuously depositing the slurry on a paper face sheet (overlay paper) on a moving conveyor; another paper face sheet (bottom paper) was laid over the deposited slurry to form an 1/2 inch thick gypsum board; cutting the moving gypsum board so that the size of the panels is about 12 x 4 feet and 1/2 inches thick when the calcium sulfate hemihydrate hydrates to form calcium sulfate dihydrate to a degree sufficient to harden the slurry enough to be cut accurately; the gypsum board is dried in a heated multi-tier oven.

The resistance of the panels to permanent deformation was then determined by measuring sag as described in example 2, except that the produced panels were cut into test panels of approximately 1 foot by 4 feet (the 1 foot being in the direction of the production line, i.e. parallel). Sag measurements were performed after subjecting the test panels to a temperature of 90F and a relative humidity of 90% for 24, 48 and 96 hours. Table 5 shows the results for the inventive samples produced with various concentrations of trimetaphosphate ion and the control sample (0% sodium trimetaphosphate) produced immediately before and after the inventive samples were produced.

TABLE 5

Droop of gypsum board in production line

(1 foot X4 inches)Ruler plate)

STMP concentration (% by weight)	Plate sag after 24 hours (inches)	Plate sag after 48 hours (inches)	Plate sag after 96 hours (inches)
				0 (front)	3.45	3.95	5.27
0.004	3.23	3.71	5.19
				0.008	2.81	3.31	4.58
0.016	1.72	1.91	2.58
				0.024	0.96	1.12	1.61
0.04	0.49	0.68	0.82
				0.08	0.21	0.24	0.29
0 (rear)	3.65	4.58	6.75

The data in Table 5 show that as the concentration of STMP is increased, the gypsum boards made according to the invention have progressively increased sag resistance (and thus progressively increased permanent set resistance) as compared to the control boards.

Table 5A further illustrates the sag resistance provided by the compositions and methods of the present invention. More specifically, Table 5A shows the moisture deflection of gypsum boards having sag, i.e., 1 foot by 2 foot dimensions as measured according to ASTM C473-95, on a production line having the same formulation as set forth above in Table 4. Table 5A shows that the sag resistance trend measured according to ASTM C473-95 is the same as the sag resistance trend of feldspathic plasterboard (1 foot x 4 foot) shown in fig. 5.

TABLE 5A

ASTM C473-95 for production line gypsum boards

Results of humidification deviation test

Test number	STMP additive (% by weight)	Dry plate weight lb/MSF	Humidification deflection (inches) for 48 hours
					In parallel	Crossing
			Previous control	0			1590	-0.306	-0.247
1	0.04	1583			-0.042	-0.034
			2	0.08			1609	-0.027	-0.021
3	0.16	1583			-0.015	-0.014
			Subsequent control	0			1585	-0.409	-0.145

Wet 12X 4 foot line gypsum board and final dried 12X 4 foot line gypsum board (as determined according to ASTM C473-95) were also determined to determine their shrinkage in width and length after drying. The more the plates shrink, the poorer their dimensional stability. The results are shown in Table 6.

TABLE 6

Shrinkage rate of gypsum board in production line

STMP concentration (% by weight)	Plate Width shrinkage (inch/4 foot)	Plate length shrinkage (inch/12 foot)
			0 (control group)	0.13	0.38
0.004	0.06	0.38
			0.008	0	0.31
0.016	0	0.25
			0.024	0	0.25
0.040	0	0
			0.080	0	0
0.16	0	0

The data in table 6 shows that the plates prepared according to the invention have better dimensional stability than the control plates. When the amount of the STMP added was 0.04% or more, no shrinkage in length and width was observed.

Example 6

Sag resistance under humidified and condensed conditions (production line plasterboard)

Additional tests illustrate the sag resistance provided by the compositions and methods of the present invention. More specifically, production line ceilings were tested where controlled condensation was performed at a vapor barrier placed between the ceiling and the joist. The procedure for this test is as follows. Small-scale shelving and indoor enclosing walls are built. The top and side spaces of the small joist are insulated and kept cool to obtain controlled condensation at the ceiling. The ceiling area is 8 feet by 8 feet, the door frames are 2 feet by 8 feet in size, and the center-to-center distance (o.c.) is 24 inches. The top and sides of the indoor space are surrounded by a 6 mil polymer (poly) vapor barrier and the humidity of the indoor space is increased to obtain controlled condensation at the ceiling.

Two 4 foot by 8 foot panels of test material (one test article and one control article) were attached side by side to the frame with a 6 mil polyethylene vapor barrier layer directly on top of the panels. The ends of the plates are not fixed. The indoor humidity is improved by the steam humidifier, and the temperature in the rest buildings is reduced by the window type air conditioning device. The vapor output of the humidifier is adjusted until constant condensation occurs at the vapor barrier above the ceiling. Constant temperature and constant humidity were not necessarily maintained throughout the test. Thus, the results should be considered as a relative measure of sag resistance between the test article and the control article, with no attempt to predict the amount of sag under defined conditions.

The sag of the ceiling at three locations (midspan between each pair of frames) was then measured periodically along the panel, giving a total of 6 readings of deflection per article per test. The temperature within the range of the skyscrapers and room enclosures was also recorded at each sag measurement.

For background information, theoretical dew point conditions (assuming room temperature is constant at 70 a) are shown below.

Indoor relative humidity of room temperature and high temperature of the third floor

70_ 50％ 51_

70_ 60％ 56_

70_ 70％ 60_

70_ 80％ 63_

70_ 90％ 68_

The tests were carried out over a period of 19 days using the following materials: 1/2 inches of a production line gypsum board according to the invention; and 5/8 inch Firecode type X gypsum board as described previously. The results are shown in FIG. 4 below and show that gypsum boards made according to the invention consistently have less sag than the control (i.e., the aforementioned 5/8 inch Firecode type X gypsum board).

In this test, the distributed load applied to the midspan between each frame immediately after the 8 th day reading was 1.0 lb/linear foot. This applied load significantly increased the sag of the control panel, but had little effect on the inventive panel. As shown in fig. 4, the gypsum boards made in accordance with the present invention exhibited sag deviations significantly below the human visual range, i.e., less than 0.1 inch per 2 feet of length.

Example 7

Nail pulling resistance of gypsum board of production line

In a typical large-scale production line, another set of paper-faced foamed gypsum boards is prepared in a gypsum board preparation plant. The gypsum boards were prepared with three concentrations of trimetaphosphate ion, and compared to a control board (prepared without trimetaphosphate ion) for nail pull resistance.

Gypsum board is made using methods and components typical of prior art gypsum board manufacturing methods and components, except that trimetaphosphate ions are used in the manufacture of some boards. The composition and weight percent thereof were the same as those listed in table 4 above. The preparation of the plate is described in example 5.

Nail pull resistance was determined according to ASTM C473-95. The results of the inventive samples prepared with various concentrations of trimetaphosphate ion and the control sample (0% sodium trimetaphosphate) prepared immediately before and after the inventive samples were prepared are shown in table 7.

TABLE 7

Nail pulling resistance of gypsum board of production line

STMP concentration (% by weight)	Nail pull resistance (lbs)
		0 (front)	89
0.04	93
		0.08	96
0.16	99
		0 (rear)	90

The results in Table 7 show that gypsum boards made according to the invention have higher overall strength (nail pull resistance) than the control boards.

Example 8

Production line gypsum board paper combines wholeness

In a typical large-scale production line, another set of paper-faced foamed gypsum boards is prepared in a gypsum board preparation plant. The boards were prepared with various concentrations of trimetaphosphate ion, pregelatinized starch, and non-pregelatinized starch, and compared to control boards (without trimetaphosphate ion or pregelatinized starch) for the integrity of the bond between the gypsum board core and its overlay paper (after conditioning to extreme humidity and humidity conditions).

Gypsum board is made using methods and components typical of prior art gypsum board manufacturing methods and components, except for the introduction of trimetaphosphate ions and pregelatinized starch and the modification of the concentration of non-pregelatinized starch in the manufacture of some boards. The composition and weight percent thereof were the same as those listed in table 4 above. The preparation of the plate is described in example 5.

The pregelatinized starch used in the experiments was PCF1000, available from Lauhoff Grain. The non-pregelatinized starch was HI-BOND, a dry-milled acid-modified non-pregelatinized starch available from Lauhoff Grain, Inc.

After the production line made the gypsum board, the board was cut into test specimens measuring 4 x 6 x 1/2 inches (the 4 inches being in the direction of the production line). Each of these small panel samples was then conditioned by holding the front side covering the total area of the outer surface of the paper in contact with a cloth completely saturated with water at a temperature of 90F and a relative humidity of 90% for about 6 hours, then removing the wet cloth and allowing the panel samples to dry slowly under the same conditions until they reached a constant weight (typically about 3 days). A straight score 1/8 inches deep was then scored on the back of the panel sample 2.5 inches from and parallel to a 6 inch edge. The core was then broken along the score without breaking or stressing the paper on the front side of the board, and the larger piece (2.5 x 6 inches) of the board sample was then rotated to apply a force downward while keeping its back side of the small piece upward static and horizontal in order to apply a force to peel the overlay paper on the front side of the lower board from the large board. The force is increased until the two plates are completely separated. The front side of the large panel was then examined to determine the percent surface area where the overlay paper was completely peeled from the core surface (also referred to as "complete peel"). The percentages are shown in table 8, expressed as "% binding failure".

TABLE 8

Gypsum board paper combination failure of production line

H1-BOND concentration (% by weight)	STMP concentration (% by weight)	PCF1000 concentration (% by weight)	Binding failure (%)
				0.60	0	0	87
0.60	0.08	0	97
				0.96	0.08	0	97
0.60	0.08	0.16	42
				0.60	0.08	0.32	0
0.28	0.08	0.32	20
				0.60	0	0	83

The data in table 8 shows the problem of paper-to-core bond failure under extremely humid conditions: STMP makes the problem worse; increasing the concentration of typical non-pregelatinized starch (HI-BOND) did not alleviate the problem; the addition of some pregelatinized starch (PCF1000) reduces or eliminates this problem.

Example 9

Post-treatment of calcium sulfate dihydrate

In some other preferred embodiments of the present invention, cast calcium sulfate dihydrate bodies are treated with an aqueous solution of trimetaphosphate ions in a manner sufficient to uniformly disperse the trimetaphosphate ion solution in the cast calcium sulfate dihydrate body to improve the strength, resistance to permanent deformation (e.g., sag resistance), and dimensional stability of the set gypsum product after re-drying. More specifically, it has been found that treatment of calcium sulfate dihydrate castings with trimetaphosphate ions increases strength, resistance to permanent deformation (e.g., sag resistance), and dimensional stability to a similar degree as achieved by embodiments in which trimetaphosphate ions are added to calcined gypsum. Thus, embodiments of adding trimetaphosphate ions to set gypsum provide novel compositions and methods for making improved gypsum products, including (but not limited to) boards, panels, stucco, tile, gypsum/cellulose fiber composites, and the like. Thus, any gypsum-based product requiring tight control of sag resistance will be advantageously obtained from this embodiment of the invention. The treatment may also increase the strength of the gypsum cast by about 15%. The gypsum casting can be impregnated with 0.04-2.0% by weight (based on the weight of the gypsum) of trimetaphosphate ions by spraying or soaking with an aqueous solution containing the trimetaphosphate ions, and then drying the gypsum casting.

The following are two methods of post-treating set gypsum:

1) mixing stucco and other additives (dry basis) 2) mixing stucco and other additives (dry basis)

Preparing slurry from water and preparing slurry from water

↓ ↓

Foaming (weight or density reduction) mixing/stirring (wet process)

↓ ↓

Gypsum casting/final set gypsum casting/final set

And drying ↓

↓ post-processing with STMP

Post-treatment with STMP (spray surface)

(spray or soak) ↓

↓ dry gypsum product

Redried gypsum casting body ↓

↓' improved plaster product

Improved gypsum product

In both of the above methods, the aqueous solution of trimetaphosphate ion is preferably provided in an amount and manner sufficient to achieve a concentration of trimetaphosphate ion in the cast calcium sulfate dihydrate body of from about 0.04 to about 0.16% by weight based on the weight of calcium sulfate dihydrate.

The beneficial effect of reducing sag variation (i.e., sag resistance) using the first method described above is shown in fig. 5. The results of preparing 5 boards and testing the sag deviation are shown in fig. 5. The dry weight of the panel was 750-785 g. The control board was not applied with any solution after the gypsum was cast/final set and dried. Marking of the board with Water only application means that only the set and dried gypsum casting is sprayed with water and then dried. The board marked with the STMP solution was prepared by spraying a 1% by weight aqueous solution of trimetaphosphate ion onto the set and dried gypsum cast and then drying. The panels marked with a gypsum-STMP solution are produced by spraying an aqueous mixture saturated with gypsum and containing 1% by weight of trimetaphosphate ions onto the set and dried gypsum casting and drying. In general, it is preferable to spray a solution containing trimetaphosphate ion at a concentration of 0.5 to 2%. The final content of trimetaphosphate ion in the STMP solution boards and the gypsum-STMP solution boards was 0.2% by weight of the mortar used to prepare the gypsum cast and 0.17% by weight of the set gypsum board formed.

Example 10

Treatment of high salt materials

Other embodiments of the present invention relate to the preparation of set gypsum products from a mixture comprising a calcium sulfate material and water in a high concentration of chloride ions or salts thereof (i.e., at least 0.015 weight percent, more typically 0.02 to 1.5 weight percent, based on the weight of the calcium sulfate material in the mixture). The chloride ions or salts thereof can be impurities in the calcium sulfate material itself and in the water used in the mixture (e.g., seawater or brackish ground water) that could not be used to prepare a stable set gypsum product prior to the present invention because of attendant problems such as voids, paper bond failure, end burning, poor resistance to permanent deformation, low strength and low dimensional stability.

The tests in Table 9 relate to gypsum boards prepared and treated in the same manner as described in example 2, except that various levels of chloride ion and various levels of trimetaphosphate ion were added to the mixture. Sag deviations were tested in the same manner as described in example 2.

TABLE 9

With mortars containing different amounts of STMP and sodium chloride

Preparation of Gypsum cube (2X 2)/Board core

Laboratory test results for (24X 6X 0.5) castings

Sodium chloride additive (% by weight)	STMP additive (% by weight)	Dry plate weight (g)	Water absorbed in 90/90 Room (% by weight)	Deflection of 48 hours humidification sag in inches	Compressive Strength of Dry cube (psi)
						0	0	534	0.17	0.445	675
0.2	0	535	0.88	2.086	697
						0.5	0	528	1.91	4.086	603
1.0	0	500	4.74	＞6	448
						2.0	0	481	6.94	＞6	304
0.5	0	530	1.90	3.752	613
						0.5	0.1	526	1.94	0.006	678
0.5	0.2	527	1.92	0.007	684
						0.5	0.3	518	1.95	0.005	662
0.5	0.5	508	1.89	0.003	668
						0.8	0	509	2.93	5.786	477
0.8	0.1	509	3.07	0.014	540
						0.8	0.2	505	2.91	0.007	543
0.8	0.4	501	2.99	0.010	538
						0.8	0.8	500	2.96	0.005	554

The tests in table 10 show that mixtures containing high concentrations of chloride ions or salts thereof can be used by treatment with trimetaphosphate ions. The plates were prepared and treated in the same manner as in example 4, except that various amounts of chloride ion and various amounts of trimetaphosphate ion were added to the mixture. The bond integrity between the gypsum board core and its facing paper was tested in the same manner as in example 8.

Watch 10

Laboratory cast plasterboard (24X 14X 0.5) prepared from mortar

Starch and salts in various STMP, PCF1000 and LC-211

Test results for paper to board core bonding under additives

Salt additive (wt.%)	STMP additive (wt.%)	PC F1000&′LC-211 additive (wt.%)	Dry plate weight (g)	Water uptake after 5 days in 90/90 Room (wt.%)	5 day binding failure (%)	3 hours humidification binding failure (%)	3 days humidification binding failure (%)	Combined moisture and humidification failure (%)
									0	0	0.2&0.2	2271	0.29	0	5	0	2
0.2	0	0.2&0.2	2290	0.81	1	0	0	0
									0.6	0	0.2&0.2	2284	2.12	2	8	0	0
0.2	0.1	0.2&0.2	2269	0.87	0	1	2	1
									0.6	0.1	0.2&0.2	2267	1.95	2	3	0	0
0.6	0.2	0.2&0.2	2271	2.07	3	0	3	2
									1.0	0.2	0.2&0.2	2285	3.61	9	14	3	10

Table 11 shows the high hydrochloride salt content of the boards (sodium chloride content in the mortar 0.08-0.16% by weight) treated with trimetaphosphate ion and PFC1000 starch, the boards were otherwise prepared and treated in the same manner as in example 5 above. As shown in Table 11, the treatment resulted in an increase in nail pull strength (measured in the same manner as in example 4, i.e., ASTM C473-95) and provided similar bonding performance (measured in the same manner as in example 8) as compared to a control panel without sodium chloride added. In addition, the treatment with trimetaphosphate ions significantly improved the wet droop even with hydrochloride additions up to 0.3%.

TABLE 11

Plant test results of high salt experiments in gypsum control devices
Experiment of	NaCl	STMP	Hi-binding	PCF1000	Plate weight	Nail pulling device	Paper to core bond		24 hours humidification sag
										Period of time	Salt additive	Additive agent	Starch	Starch		Strength of	Load(s)	% failure	(1′×4′)
	(wt.％)	(wt.％)	(wt.％)	(wt.％)	(lb/MSF)	(pound)	(pound)	(％)	(inch/4 foot spacing)
1 (control)	0	0	0.52	0	1581	88.7	14.8	13.6	3.25
										2	0	0	0.28	0.24	1586	92.1	13.30	15.3	2.45
3	0.08	0	0.28	0.24	1577	89.3	11.20	13.7	5.25
										4	0.16	0	0.28	0.24	1580	87.7	11.50	22.4	11.5
5	0.3	0	0.28	0.24	1574	89.6	9.00	31.8	＞12.5
										6	0.3	0.08	0.28	0.24	1577	89.2	8.10	30.3	0.25
7	0.16	0.08	0.28	0.24	1567	95.5	11.40	32.8	0.25
										8	0.08	0.08	0.28	0.24	1592	94.5	12.20	19.5	0.25
9	0	0	0.28	0.24	1609	93.6	12.40	15.1	2.85
										10 (control)	0	0	0.52	0	1561	83.9	14.90	11.5	2.25
11	0.3	0	0.52	0	1619	93.4	10.10	25.4	＞12.5

Table 12 shows that the higher (than the high) hydrochloride salt content of the gypsum board treated with trimetaphosphate ion and PFC1000 starch in Table 11 (0.368% by weight hydrochloride in mortar) is the board which has been otherwise prepared and treated in the same manner as in example 5 above. As shown in Table 12, the treatment resulted in an increase in nail pull strength (measured in the same manner as in example 4, i.e., ASTM C473-95) and provided better bonding performance (measured in the same manner as in example 8) as compared to the control board.

TABLE 12

Factory test results of high salt experiments in a plate mill
									Experiment of	% high chloride	Hydrochloride salt	STMP	Hi-binding	PCF-1000	Nail pulling strength	Paper to core bond
Period of time	Synthetic stoneOintment	Concentration of	Additive agent	Starch	Starch		Load(s)	% failure
										(wt.％)	(wt.％)	(wt.％)	(wt.％)	(wt.％)	(pound)	(pound)	(％)
									1 (control)	0	0.032	0	0.4	0	73	14.10	49.0
2	50	0.12	0.16	0.15	0.25	85	16.70	0.0
									3	100	0.368	0.16	0.15	0.25	86	14.40	0.0
4	100	0.368	0.16	0.4	0	89	10.90	34.0
									5	100	0.368	0	0.4	0	77	19.70	0.0
6 (control)	0	0.032	0	0.4	0	75	19.5	10.0

Example 11

Treating calcined gypsum with various reinforcing materials

In an example of the above preferred embodiment, the reinforcing material is trimetaphosphate ion. However, any reinforcing material that generally falls within the general definition of reinforcing material set forth above will have a positive effect (e.g., improved resistance to permanent deformation) in the treatment of calcined gypsum. Commonly used reinforcing materials are condensed phosphoric acids, each containing 2 or more phosphoric acid units; and condensed phosphates or condensed phosphate ions, each containing 2 or more phosphate units.

Specific examples of such reinforcing materials include, for example, the following acids or salts, or their anionic moieties: the molecular formula is (NaPO)₃)₃Sodium trimetaphosphate having 6-27 repeating phosphate units and having the formula Na_n+2P_nO_3n+1The sodium hexametaphosphate (wherein n is 6-27) has a molecular formula of K₄P₂O₇Tetrapotassium pyrophosphate of formula Na₃K₂P₃O₁₀The molecular formula of the trisodium dipotassium triphosphate is Na₅P₃O₁₀Sodium triphosphate of formula Na₄P₂O₇Tetrasodium pyrophosphate of formula Al (PO)₃)₃The molecular formula of the aluminum trimetaphosphate is Na₂H₂P₂O₇Sodium acid pyrophosphate of (i) having 1000-3000 repeating phosphate units and having the formula (NH)₄)_n+2P_nO_3n+1Or ammonium polyphosphate (wherein n is 1000-3000), or having 2 or more repeating phosphoric acid units and having the formula H_n+2P_nO_3n+1Wherein n is 2 or more.

The results of treating calcined gypsum with this type of reinforcement material are shown in tables 13, 14 and 15.

In table 13, calcined gypsum was treated with various reinforcing materials during the preparation of gypsum boards and cubes. The panels were prepared and treated in the same manner as in example 2 above. Cubes were prepared and processed in the same manner as in example 1 above. Except that in both cases, various reinforcing materials were used, rather than only the trimetaphosphate ion. The deflection of the humidified film was measured in the same manner as in example 2. The compressive strength was measured in the same manner as in example 1 above.

In Table 14, calcined gypsum was treated with polyphosphoric acid during the preparation of gypsum boards and cubes. A panel was prepared and treated in the same manner as in example 2. Cubes were prepared and processed in the same manner as in example 1 above. Except that in both cases, various reinforcing materials were used, rather than only the trimetaphosphate ion. The deflection of the humidified film was measured in the same manner as in example 2. The compressive strength was measured in the same manner as in example 1 above.

In table 15, calcined gypsum was treated with ammonium polyphosphate ("APP") during the preparation of gypsum boards and cubes. The panels were prepared and treated in the same manner as in example 2 above. Cubes were prepared and processed in the same manner as in example 1 above. Except that in both cases, various reinforcing materials were used, rather than only the trimetaphosphate ion. The deflection of the humidified film was measured in the same manner as in example 2. The compressive strength was measured in the same manner as in example 1 above.

The results of tables 13, 14 and 15 show that all materials tested within the definition of the reinforcing material described above give a product with a significant resistance to permanent deformation when calcined gypsum is treated with the reinforcing material in the production of set gypsum products, compared to the control group.

Watch 13

Laboratory test results for gypsum cubes (2X 2) and panels (24X 6X 0.5) prepared with mortars having various phosphate and hydrochloride additives

Phosphates or other specialty chemicals	Additive content (wt.%)	Dry plate weight (g)	Delay (-) neutral (0) or Accelerator (+)	Water uptake from 90/90 cell (wt.%)	Sag bias (wt.%) of 10 days humidification	Compressive Strength of Dry cube (psi)
							Sodium trimetaphosphate	0.1	537.0	0/+	0.06	0.016	745
Sodium hexametaphosphate	0.1	538.2	--	0.09	0.019	552
							Sodium chloride and sodium trimetaphosphate	0.5&0.1	527.5	+	1.93	0.008	621
Sodium chloride and sodium hexametaphosphate	0.5&0.1	539.6	-/0	2.08	0.021	498
							Tetrapotassium pyrophosphate	0.1	538.7	-/0	0.11	0.137	560
Trisodium dipotassium triphosphate	0.1	538.8	-/0	0.07	0.201	552
							Sodium tripolyphosphate	0.1	535.1	-/0	0.09	0.286	531
Tetrasodium pyrophosphate	0.1	556.2	-/0	0.18	0.436	544
							Aluminum trimetaphosphate	0.1	536.2	0/0	0.02	0.521	673
Phosphoric acid monopotassium salt	0.1	540.9	0/+	0.11	0.595	657
							Acid sodium pyrophosphate	0.1	547.7	0/0	0.16	1.385	637
Boric acid	0.1	539.4	0/0	0.15	1.425	624
							Trisodium phosphate	0.1	537.0	--	0.13	1.641	537
Control	0.0	546.2	0/0	0.13	1.734	635
							Phosphoric acid	0.1	534.0	+	0.22	1.796	673
Phosphoric acid monosodium salt	0.1	540.9	+	0.19	2.219	679
							Magnesium chloride	0.1	528.2	0/+	0.23	2.875	521
Phosphoric acid monohydrogen disodium salt	0.1	536.6	0/0	0.13	3.126	629
							Sodium aluminum sulfate	0.1	543.0	++	0.24	3.867	686

TABLE 14

Laboratory test results for gypsum cubes (2X 2)/board (24X 6X 0.5) prepared with mortar with polyphosphoric acid additive

Polyphosphoric acid	Content of additives (wt.%)	Dry plate weight (g)	Delay (-) neutral (0) or Accelerator (+)	Water uptake from 90/90 cell (wt.%)	Sag deflection (in inches) for 2 weeks humidification	Compressive Strength of Dry cube (psi)
							No phosphoric acid (control)	0.0	536.5	0/0	0.06	0.683	767
Polyphosphoric acid (first mixed with water)	0.02	539.6	0/0	0.13	0.042	781
							Polyphosphoric acid (first mixed with water)	0.05	535.1	0/0	0.09	0.025	842
Polyphosphoric acid (first mixed with water)	0.1	542.3	-/0	0.15	0.046	708

Watch 15

Laboratory test results for gypsum cubes (2X 2)/board (24X 6X 0.5) prepared with mortar with ammonium polyphosphate additive

Ammonium polyphosphate ('APP')	Additive content (wt.%)	Dry plate weight (g)	Delayed (-), neutral (0) or procoagulant (+)	Water uptake from 90/90 cell (wt.%)	Sag deflection (in inches) for 2 weeks humidification	Compressive Strength of Dry cube (psi)
							Control	0.0	540.7	0/0	0.35	0.694	912
APP powder (first mixed with water)	0.01	532.5	0/0	0.35	0.045	937
							APP powder (first mixed with water)	0.03	536.3	0/0	0.37	0.020	924
APP powder (first mixed with water)	0.05	539.7	0/0	0.37	0.005	901
							APP powder (first mixed with water)	0.1	541.3	0/0	0.28	0.005	956
APP powder bundle (first mixed with water)	0.2	546.7	0/0	0.30	0.003	967
							APP powder (first mixed with water)	0.4	538.2	0/0	0.33	0.005	998
APP powder bundle (mixing mortar first)	0.05	533.5	0/0	0.35	0.005	907
							APP powder (mixing with mortar first)	0.1	546.9	0/0	0.30	0.006	948
APP powder (mixing with mortar first)	0.2	538.3	0/0	0.31	0.006	998
							APP powder (mixing with mortar first)	0.4	537.4	0/0	0.35	0.002	1017

Example 12

Treatment of calcium sulphate dihydrate castings with various reinforcing materials

In general, any reinforcing material falling within the general definition of reinforcing material set forth above will have a positive effect (e.g., increased resistance to permanent deformation and increased strength) during the processing of the cast calcium sulfate dihydrate body. Commonly used reinforcing materials are: phosphoric acids, each containing 1 or more phosphoric acid units; condensed phosphates or condensed phosphate ions, each containing 2 or more phosphate units; a monobasic salt or monovalent ion of orthophosphoric acid.

The results of treating the calcium sulfate dihydrate cast bodies with these reinforcing materials are shown in table 16.

In table 16, various materials were used to treat the coagulated and dried calcium sulfate dihydrate in the form of plates and cubes. A panel was prepared in the same manner as in example 2 above, and was further processed in the same manner as in example 9. Cubes were prepared in the same manner as in example 1 above and further processed in a similar manner to example 9. Except that in both cases, various reinforcing materials were used, rather than only the trimetaphosphate ion. The deflection of the humidified film was measured in the same manner as in example 2. The compressive strength was measured in the same manner as in example 1 above.

The results in Table 16 show that all materials tested within the above definition of reinforcing material provide significant resistance to permanent deformation and significantly improved strength in the resulting articles when used to treat solidified and dried cast calcium sulfate dihydrate compared to the control.

TABLE 16

Laboratory test results for post-treated gypsum cubes (2X 2)/boards (24X 6X 0.5) prepared with mortar with various phosphate and hydrochloride additives

Phosphates or other special chemicals	Additive content (wt.%)	Dry plate weight (g)	Water uptake from 90/90 cell (wt.%)	Sag deflection (in inches) for 10 days humidification	Compressive Strength of Dry cube (psi)
						Sodium trimetaphosphate	0.4	537.0	0.5	0.016	725
Sodium hexametaphosphate	0.4	538.2	0.9	0.019	697
						Tetrapotassium pyrophosphate	0.4	538.7	0.3	0.017
Tetrasodium pyrophosphate	0.4	556.2	0.6	0.011
						Acid sodium pyrophosphate	0.4	542.1	0.4	0.012
Phosphoric acid monosodium salt	0.4	545.6	1.5	0.025	710
						Phosphoric acid monopotassium salt	0.4	487.5	0.2	0.029	708
Phosphoric acid	0.4	534.7	0.4	0.065	624
						Sodium tripolyphosphate	0.4	540.5	0.6	0.123	657
Boric acid	0.4	486.6	0.1	0.345	611
						Control	0.0	543.9	0.2	0.393	576
Phosphoric acid monohydrogen disodium salt	0.4	541.3	0.7	0.674	724
						Trisodium phosphate	0.4	532.8	0.6	1.082	754
Magnesium chloride	0.4	559.9	2.3	1.385	567
						Sodium chloride	0.4	539.4	7.7	6.385	521

Those skilled in the art will recognize that a wide pH range, i.e., greater than or equal to 3.5, can be used in the manufacture of set gypsum products according to the invention.

In the manufacture of gypsum board according to the invention, the pH operating range is preferably from about 5.0 to about 9.0, more preferably from about 6.5 to about 7.5.

Example 13

Overcome slow coagulation and strength reduction

In the pre-setting treatment of the calcium sulphate material according to the invention, it has also been found that some reinforcing materials will hinder the rate of hydration at which set gypsum is formed and adversely affect the strength of the set gypsum product. It has been found that this hindrance and the negative effect on strength can be alleviated or even overcome by introducing an accelerator in the mixture in a suitable amount and manner. This is shown in table 17 below. A slurry was prepared according to example 1 above, using sodium hexametaphosphate as the reinforcing material. A portion of the slurry was tested using ASTM C472 to determine the time required to achieve 98% hydration of the set gypsum. Another portion of the slurry was used to make cubes according to example 1 to test the compressive strength. For this purpose, any of the known materials that can be used to accelerate the rate of formation of set gypsum can be used. The preferred setting accelerator for this purpose is the one defined in example 1 above.

TABLE 17

Action of coagulation accelerator in overcoming retardation and strength reduction

Accelerator addition amount (% by weight)	Amount of SHMP added (% by weight)	Time (minutes) for the set gypsum to reach 98% hydration	Dry cube strength (PSI)
				0	0	23.3	558
0	0.08	31.1	358
				0.05	0.08	18.7	660
0.10	0.08	15.9	739
				0.25	0.08	13.1	808
0.50	0.08	12.2	907

Example 14

Imparting desired shape to gypsum board

It has also been found that gypsum boards having the desired shape can be made in accordance with the teachings of the present invention. Prior to the present invention, the change in shape of a regular gypsum panel generally weakened and made the gypsum panel more flexible by wetting the panel with water, then changing the shape of the gypsum panel as desired, and then waiting for the gypsum panel to dry. However, this prior art technique suffers from a number of manufacturing and installation disadvantages, since the wetting required to weaken the gypsum board and make it more flexible so that it can be changed to the desired shape takes a significant amount of time, i.e., at least 1 hour or more, 12 hours is not uncommon. Furthermore, this prior art technique is not readily used to easily change gypsum panels to the desired shape. If the gypsum board is not properly weakened, it is difficult to change the shape of the gypsum board as desired, i.e., more force is required to change the shape of the gypsum board as desired, and if too much force is applied, the gypsum board will break. Thus, methods and compositions that reduce wetting time and improve the ease of manufacture and installation of gypsum boards of desired shapes are highly desirable.

According to a preferred embodiment of the invention, for example, a gypsum board can be weakened and made more flexible by spraying the gypsum board with an aqueous chloride solution containing any reinforcing material (as described in the examples above and in the summary of the invention). The weakened and more flexible gypsum board can then be easily changed to the desired shape with less force than in the prior art, and will retain the desired shape of the deformed board after drying, because of the advantageous effect of the reinforcing material, in particular the resistance to permanent deformation.

More specifically, for example, it has been found that regular gypsum panels of 5/16 ", 3/8", and 1/2 "thickness can be so weakened to change to a desired shape by spraying gypsum board with a mixture of a hydrochloride solution containing the above-mentioned reinforcing materials or various hydrochloride solutions (e.g., sodium chloride, calcium chloride, magnesium chloride, potassium chloride, aluminum chloride, etc.). To achieve the most preferred results, wetting agents (such as tergitol NP-9 sold by Union Carbide Chemical & plastics Company, Inc.; Neodol _1-7 and Neodol _1-5 sold by Shell Chemical Company, and Icono TDA-6 and Iconol DA-6 sold by BASF Corporation) may be used to achieve the rapid and effective weakening treatment. Starches such as Stapol580 and Stapol630 sold by a.e. staley manufacturing company can be used to improve the final paper to core bond and to increase the strength of the reshaped panel. If foaming is a problem due to the foaming properties of the wetting agent, a defoaming agent may be included in the salt solution.

In a preferred embodiment, the above-described salt solution and other treatment materials are applied to one side of the gypsum board, while the other side is untreated to maintain tensile strength on the untreated side of the gypsum board to prevent the gypsum board from cracking during its shape change.

The treated board may be, for example, any typical paper-faced gypsum board, and any typical additives and gypsum formulations for such boards are used. In a preferred embodiment, the gypsum board has internal reinforcing materials, such as dispersed fibers (e.g., glass, paper, and/or synthetic fibers).

Gypsum boards of any size and thickness can vary in shape according to the invention. According to a preferred embodiment of the invention, the shape of 5/16 ", 3/8" and 1/2 "paper-faced gypsum board can be changed by treating one side of the board with a" curved "solution containing (based on the total weight of the solution) 0.05% by weight sodium chloride, 0.05% by weight sodium trimetaphosphate, 0.05% by weight Tergitol NP-9 surfactant (wetting agent), and 0.025% by weight Stapol580 (modified corn starch). Thistle board of 4 'x 4' USG SHEETROCK — brand wallboard of various thicknesses was sprayed with the preferred bending solution described above in a manner sufficient to saturate 5/16 "boards with about 2 pounds of bending solution, 3/8" boards with about 4 pounds of bending solution, and 1/2 "boards with about 6 pounds of bending solution. The test was conducted by treating one side of the treated gypsum wallboard, and the results were the same whether the treated side was the front side or the back side. The results are shown in Table 18.

As shown in Table 18, the shape of gypsum wallboard of various thicknesses can be changed as desired after treatment according to the present invention. As shown, the time required between application of the bending solution and bending of the plate is only a few minutes, rather than the hours required by the prior art.

The minimum bend radius (i.e., a measure of the degree of bend that can be obtained; the smaller the radius, the greater the degree of bend that can be obtained) for each sheet thickness is shown in table 18. In each case, the minimum radius is significantly smaller than that obtainable in the prior art. Generally, the gypsum board can be bent further in the inherently weaker width direction.

A preferred method of handling and assembling the gypsum board at the construction site is as follows.

Taking hydrochloride, starch, reinforcing material, wetting agent and required water quantity

↓

Gently mix them together to obtain a homogeneous curved solution

↓

Spraying a bending solution on one side of a gypsum board

↓ waiting for 5-25 minutes

Bending the plasterboard to a desired curvature, assembling the plasterboard, and allowing the plasterboard to dry naturally

Amount by weight of solution: 0.05-1% of a hydrochloride salt; 0.05-0.3% of wetting agent; 0.05-0.5% of a reinforcing material; 0.025-0.2% of starch. In addition, if desired, defoaming agents (such as the FoamMaster sold by Henkel Corporation) may be included in the bending solution in an amount of 0.01-0.05% by weight of the solution.

The hydrochloride salt, wetting agent, and reinforcing material may be applied to the gypsum board separately, in combination, or in several portions at any time prior to drying of the gypsum board to obtain the advantages of the present invention.

Watch 18

Gypsum board of various thicknesses treated with the bending solution of the invention

Latency and minimum bend radius of

Sheet thickness (inches)	Approximate wait time between solution application and plate bending	Longitudinal minimum bend radius (inches)	Transverse minimum bend radius (inches)
				5/16*	5 minutes	20*	16*
3/8*	15 minutes	24*	20*
				1/2*	25 minutes	36*	28*

The invention has been described in detail hereinabove, particularly with reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

Claims (21)

1. A method of producing a shaped gypsum board comprising:

preparing a homogeneous aqueous solution comprising water, at least one hydrochloride salt, a wetting agent and one or more reinforcing materials selected from the group consisting of: phosphoric acids, each containing 1 or more phosphoric acid units; condensed phosphates or condensed phosphate ions, each containing 2 or more phosphate units; and a monobasic salt or monovalent ion of orthophosphoric acid, and

applying the homogeneous aqueous solution to the gypsum board in an amount sufficient to weaken the gypsum board, such that the shape of the gypsum board can be altered,

the shape of the gypsum board is changed according to the requirement,

drying the gypsum board to produce a shaped gypsum board,

the amounts of the hydrochloride salt, the reinforcing material or materials, and the wetting agent applied to the gypsum board are such that an altered shape of the formed gypsum board is obtained in a shorter period of time and the formed gypsum board has a higher resistance to permanent deformation than if the hydrochloride salt, the reinforcing material, and the wetting agent were not applied to the gypsum board.

2. The method of claim 1, wherein the applied solution further comprises a pregelatinized starch.

3. The method of claim 1, wherein the applied solution further comprises a defoaming agent.

4. The method of claim 1, wherein the solution is applied at a hydrochloride concentration of 0.05 to 1.0% by weight of the solution.

5. The method of claim 1, wherein the wetting agent concentration of the applied solution is 0.05-0.3% by weight of the solution.

6. The method of claim 1, wherein the applied solution has a reinforcement concentration of 0.05 to 0.5% by weight of the solution.

7. A method according to claim 2, wherein the starch concentration of the applied solution is 0.025-0.2% by weight of the solution.

8. A method according to claim 3 wherein the applied solution has a concentration of the antifoam agent of from 0.01 to 0.05% by weight of the solution.

9. The method of claim 1, wherein the gypsum board is a paper facing sheet.

10. The method of claim 1 wherein the homogeneous aqueous solution is applied to only one side of the gypsum board.

11. A method of producing a shaped gypsum board comprising:

a homogeneous aqueous solution containing water and a wetting agent is applied to the gypsum board,

applying to the gypsum board a homogeneous aqueous solution comprising water and at least one hydrochloride salt,

prior to drying the gypsum board, applying a solution comprising one or more reinforcing materials selected from the group consisting of: phosphoric acids, each comprising 1 or more phosphoric acid units; salts of condensed phosphoric acids or condensed phosphate ions, each comprising 2 or more phosphate units; and a mono-or monovalent ion of orthophosphoric acid,

the shape of the gypsum board is changed according to the requirement,

drying the gypsum board to obtain a shaped gypsum board,

the amounts of the hydrochloride salt, the reinforcing material or materials, and the wetting agent that have been applied to the gypsum board are such that the altered shape of the formed gypsum board is achieved in a shorter period of time and the resistance to permanent deformation of the formed gypsum board is greater than if the hydrochloride salt, the reinforcing material, and the wetting agent were not applied to the gypsum board.

12. The method of claim 11, wherein a solution containing pregelatinized starch is also applied to the gypsum board prior to drying of the gypsum board.

13. A method according to claim 11, wherein a solution containing a defoaming agent is also applied to the gypsum board prior to drying the gypsum board.

14. A method according to claim 11, wherein the hydrochloride salt concentration of the applied hydrochloride salt containing solution is 0.05-1.0% by weight of the solution.

15. The method according to claim 11, wherein the wetting agent-containing solution is applied at a wetting agent concentration of 0.05 to 0.3% by weight of the solution.

16. A method according to claim 11, wherein the applied solution containing the reinforcing material or materials has a reinforcing material concentration of 0.05 to 0.5% by weight of the solution.

17. The method according to claim 12, wherein the starch concentration of the applied starch-containing solution is 0.025-0.2% by weight of the solution.

18. The method of claim 13, wherein the applied defoamer-containing solution has a defoamer concentration of 0.01-0.05% by weight of the solution.

19. The method of claim 11, wherein the gypsum board is a paper facing sheet.

20. The method of claim 11 wherein the hydrochloride salt, the reinforcing material or materials, and the wetting agent are applied to only one side of the gypsum board.

21. A shaped gypsum board made according to the method of claim 11.