MX2007013364A - Wet gypsum accelerator and methods, composition, and product relating thereto. - Google Patents

Abstract

A wet gypsum accelerator comprising ground product having a median particle size of from about 0.5 micron to about 2 microns and calcium sulfate dihydrate, water, and at least one additive selected from the group consisting of (i) an organic phosphonic compound, (ii) a phosphate-containing compound, or (iii) a mixture of (i) and (ii), is disclosed. Also disclosed are a method of preparing a wet gypsum accelerator, a method of hydrating calcined gypsum to form an interlocking matrix of set gypsum, a set gypsum-containing composition, and a set gypsum-containing product.

Description

WET PLASTER ACCELERATOR AND METHODS, COMPOSITION, AND PRODUCT RELATED TO THE SAME TECHNICAL FIELD OF THE INVENTION The present invention relates generally to gypsum compositions. More particularly, the invention relates to wet gypsum accelerators to accelerate the hydration of calcined gypsum to calcium sulfate dihydrate, as well as to methods, compositions, and products related thereto. BACKGROUND OF THE INVENTION [0002] Wet plaster, comprising calcium sulfate dihydrate, is a well-known material that is commonly included in many types of products. As an example, the set gypsum is the main compound of final products created with the use of traditional plasters, for example, the walls of gypsum with superficial finish, and also of the gypsum boards used in the typical wall construction. dry on interior walls and roofs of buildings. In addition, hardened gypsum is the main composite of products and boards composed of gypsum / cellulose fiber, and is also included in products that fill and smooth joints between the edges of gypsum boards. Typically, such gypsum-containing products are prepared to form a mixture of calcined gypsum, that is, calcium sulfate hemihydrate and / or anhydrous calcium sulfate, and water, as well as other compounds, as desired. The mixture is typically emptied in a pre-determined form or on the surface of a substrate. The calcined gypsum reacts with the water to form a matrix of crystalline hydrated gypsum or calcium sulfate dihydrate. It is the desired hydration of calcined gypsum which allows the formation of an entangled matrix of set gypsum, thereby imparting solidity to the gypsum structure in the gypsum-containing product. In general, the rate of hydration and the percentage conversion rate can impact the final strength and speed of production of the product containing gypsum. Light heating can be used to move the water unreacted to produce a dry product. Regardless of the type of gypsum-containing product that is made, acceleration materials are commonly included in the mixture comprising calcined gypsum and water to increase hydration efficiency, to control the setting time, and to maximize production speed . Typically, an accelerator material includes finely ground dry calcium dihydrate sulfate, commonly referred to as "gypsum seeds". Gypsum seeds increase the nucleation of the set gypsum crystals, thereby increasing the rate of crystallization. As is known in the art, conventional gypsum seed accelerator pads progressively lose their effectiveness as they age, even under normal conditions. In this regard, some throttle efficiency is lost even during grinding, and the gypsum seeds lose power over time during which they are handled or stored. The loss of efficiency in the acceleration of conventional accelerator materials is exacerbated when the accelerator is exposed to heat and / or humidity. In order to combat the loss of efficiency of the gypsum seeds over time, particularly under heat and / or humidity conditions, it is customary to coat the calcium sulfate accelerating material dihydrate with any of the known coating agents, such as, for example, sugars, including sucrose, dextrose and the like, starch, boric acid, or long chain fatty acids, and salts thereof. Conventional heat-resistant accelerator matepals are both ground and provided in dry form in a sufficient manner while the accelerator loses efficiency in contact with moisture, for example, because the acceleration particles undesirably agglomerate and / or due to both the gypsum and the Coating agents are often hygroscopic in nature and as such attract moisture. A wet gypsum accelerator was disclosed in U.S. Pat. No 6, 409,825, commonly assigned. Either way, there remains a need for a wet gypsum accelerator with superior properties as well as new techniques and systems to produce such an accelerator. BRIEF COMPENDIUM OF THE INVENTION The present invention provides a wet gypsum accelerator, a method for preparing a wet gypsum accelerator, a method for hydrating calcined gypsum to form an entangled matrix of set gypsum, a composition containing set gypsum, and a product that contains plaster set. The wet gypsum accelerator of the invention comprises a ground product having particles of medium size from about 0.5 micron to about 2 microns, wherein the milled product comprises calcium sulfate dihydrate. The wet gypsum accelerator further comprises water, and at least one additive selected from (i) an organic phosphonic compound, and (ii) a phosphate-containing compound. The mixtures of (i) and (ii) can also be used. The wet gypsum accelerator is prepared through wet grinding. Water, the additive, and the plaster are combined to form a mixture, with other optional compounds added, as desired. When combined with water, the gypsum may be in the form of calcium sulfate dihydrate, or alternatively, at least some of the gypsum may be in the form of calcined gypsum, that is calcium sulfate hemihydrate and / or anhydrous calcium sulfate. The calcined gypsum is converted at least in part to calcium sulfate dihydrate in the presence of water. Excess water in wet plaster grinding is desirable to facilitate grinding. Preferably, the gypsum is in the form of calcium sulfate dihydrate when grinding is initiated, but the grinding may begin before all the calcined gypsum is converted to calcium sulfate dihydrate. The calcium sulfate dihydrate is ground wet in the presence of the additive (s) to form the wet gypsum accelerator. The wet gypsum accelerator according to the invention is useful for the preparation of a composition containing set gypsum, and for a product comprising the composition containing set gypsum. In particular, the wet gypsum accelerator of the invention must be combined with water and calcined gypsum in any manner to form an aqueous mixture in which the calcined gypsum is hydrated to form an interlaced matrix of wet gypsum. Preferably, the calcined gypsum is first mixed with water and then mixed with the wet gypsum accelerator. According to the present invention, the wet gypsum accelerator comprises a ground product. The milled product comprises calcium sulfate dihydrate. The ground product has medium-sized particles from about 0.5 micron to 2 microns. It has been found that the described wet gypsum accelerator improves efficiency by making compositions and products containing set gypsum by raising the rate of hydration of the calcined gypsum to form an entangled gypsum matrix, which must be measured by time at 50.degree. % of hydration. The invention is useful in the manufacture of any variety of products containing set gypsum formed of calcined gypsum, such as, but not limited to, roofing materials, boards such as plasterboard, gypsum, joint compounds, materials for soil, specialized materials, and the like. The wet gypsum accelerator of the invention can be used in the preparation of set gypsum products prepared by any of the variety of processes known in the art by adding the wet gypsum accelerator to an aqueous mixture of calcined gypsum. A suitable method for introducing the wet gypsum accelerator into the aqueous gypsum mixture is described in the concurrently filed and co-owned application entitled "METHODS OF AND SYSTEMS FOR ADDING TO HIGH VISCOSITY GYPSUM ADDITIVE TO A POST-MIXER AQUEOUS DISPERSION OF CALCINED GYPSUM "(Agent Reference No. 234910), U.S. Patent Application. Do not. . Advantageously, the wet gypsum accelerator of the invention exhibits substantial longevity and maintains its effectiveness over time so that the wet gypsum accelerator can be made, stored, and even transported over long distances, prior to its use. Due to its special nature, the wet gypsum accelerator is considered to be a material resistant to high heat and / or humidity so that it maintains all or much of its effectiveness even on exposure to this. In preferred embodiments, the invention also reduces manufacturing costs because the additives are preferably provided in relatively small amounts and the ratio of water to stucco from the stucco sludge is reduced when the wet gypsum accelerator is used in comparison to the dry gypsum accelerator. . The invention reduces the expense of additional manufacture when a second accelerating material, such as aluminum sulfate or potash, is generally not required because the wet gypsum accelerator maintains its high efficiency over time and on exposure to high humidity. However, the second accelerator materials can be used if desired. The invention also allows the ease and efficiency of manufacturing by allowing wet accelerator blending with calcined gypsum and other compounds used to secure products containing set gypsum, such as, but not limited to, plasterboard or cellulose fiber gypsum board -cast. The wet gypsum accelerator for the production of boards and the production of fiber panels is useful to improve the hydration rate of the stucco, by improving the effectiveness of the stucco, and reducing the manufacturing costs. The effectiveness of the stucco can be measured by the conversion rate. These and other advantages of the present invention, also as additional inventive features, will be apparent from the description of the invention. The invention can be better understood with reference to the following detailed description of the preferred embodiments. DETAILED DESCRIPTION OF THE INVENTION The present invention provides a wet gypsum accelerator comprising a ground product. The ground product is the result of the wet grinding of a calcium sulphate substance in the presence of various additives. Such an additive comprises an additive selected from an organic phosphonic compound; a phosphate-containing compound; and a mixture of an organic phosphonic compound and a phosphate-containing compound. The ground product has particles of medium size from about 0.5 micron to about 2 microns and comprises at least calcium dihydrate and water, and may further comprise one or more additive compounds including during grinding. More than one of each type of additive can be used in the practice of the invention. The measurement range of the average particles of the ground product is believed to be responsible for the wet gypsum mixture that has the manageability necessary to be used in a continuous production process or in batches without an efficient acceleration sacrificed of the hydration of the stucco . The wet gypsum accelerator of the invention is preferably prepared by the wet milling of the calcium sulfate dihydrate in the presence of additives under conditions sufficient to produce a milled product with an average particle size of from about 0.5 microns to about 2 microns. Once prepared, the wet gypsum accelerator of the invention is useful to increase the efficiency in the manufacture of a product containing set gypsum. The wet gypsum accelerator is combined with calcined gypsum and water, as well as other desired compounds, to form a mixture that is emptied into a pre-determined form or on a substrate surface, during the manufacture of the product containing set gypsum. As is well understood in the gypsum specialty, calcined gypsum is hydrated in the presence of water to form crystalline hydrated gypsum. When there is a sufficient amount of calcined gypsum that is hydrated, an entangled matrix of set plaster is typically formed. The inclusion of the wet gypsum accelerator of the invention in the mixture of calcined gypsum and water increases the rate of, and predictably in the time required for, the hydration of calcined gypsum to calcium sulfate dihydrate of the desired product containing set gypsum. It is believed that the wet gypsum accelerator of the invention provides nucleation sites by increasing the crystallization rate of the binding matrix of the set gypsum. The wet gypsum accelerator of the invention can be used in the making of any variety of products containing hardened gypsum, such as, for example, conventional gypsum board or gypsum-cellulose fiber board such as the FIBEROCK® composite panels, available commercially at the USG Corporation, also as roofing materials, flooring materials, joint compounds, plasters, specialty products, and the like. The wet plaster accelerator according to the invention shows a substantial longevity such that it maintains all or much of its effectiveness for long periods of time. Preferably, the wet gypsum accelerator of the invention maintains all or much of its effectiveness for at least several weeks, and more preferably, for at least a few months, for example, three months, and still more preferably, for at least six months. , or even more. As a result, the wet gypsum accelerator can be prepared and then stored and / or transported, even for long distances, before being used. The wet gypsum accelerator of the invention preferably remains effective even on exposure to high temperatures and / or humidity. Also, due to the inventive wet gypsum accelerator which maintains its efficiency over time, even in high humidity exposure, a second accelerating material, such as potassium sulphate or aluminum, is not required in the practice of the invention, although the Second material accelerator can be included for certain applications and practices if desired. The wet gypsum accelerator according to the invention can be used to make products containing set gypsum processed by any dry or wet feed system. For example, a dry feed system to produce drywall, and a wet feed process to make boards composed of cellulose-gypsum fibers. In some modalities, although the wet gypsum accelerator is produced in the presence of water, once the accelerator is produced it can be dried. The wet gypsum accelerator according to the invention is prepared by wet grinding. The gypsum feed material used in the grinding process can have any suitable medium particle size. In some embodiments, the gypsum feedstock has an initial median particle size of 50 microns or larger. In some embodiments, the gypsum feedstock is natural gypsum and has an initial median particle size from about 20 to about 30 microns. In some embodiments, the gypsum feedstock is synthetic gypsum and has and has an initial median particle size from about 40 to about 100 microns. According to the invention, gypsum, water, and at least one additive combine to form the mixture. In some embodiments, the gypsum used to form the wet grind mixture is the calcium sulfate dihydrate. In other embodiments, the plaster may be in the form of calcined gypsum when combined with water. If the gypsum is calcined, it is believed that the calcined gypsum is hydrated by a portion of the water to form calcium sulfate dihydrate. Preferably, the gypsum is in the form of calcium sulfate dihydrate when wet grinding begins, but it is not necessary to convert all the calcined gypsum to calcium sulfate dihydrate at this point. A sufficient amount of water beyond that required to hydrate the calcined gypsum is preferably included in the mixture to accommodate the passage of the wet mill after the calcium sulfate dihydrate was formed. In such cases, the additive is preferably added after most, and more preferably, all of the calcium sulfate dihydrate is formed to maximize the exposure of the additive to the calcium sulfate dihydrate.

Calcium sulfate dihydrate, either combined with water or after it has been formed in the water of calcined gypsum, is a wet milling in the presence of an additive compound to form the wet gypsum accelerator. Generally, the smaller the average particle size of the resulting milled product, the better the efficiency of the acceleration to make products and compositions containing set gypsum. However, as the average particle size decreases, the viscosity of the wet gypsum accelerator increases so that the sludge becomes increasingly difficult to handle and process. The high viscosity sludge can be diluted after grinding, or in steps subsequent to the grinding steps, with additional water or an aqueous solution to make the handling process easier. Thus, the particle size of the calcium sulfate dihydrate can be as small as desired to allow efficient production of set gypsum. In some embodiments where an additional step of dilution is not carried out, a particle of sufficiently large size can be used to allow the production of a wet gypsum accelerator sludge with a sufficiently low viscosity to allow mud pumps and other wastewater equipment processing effectively handle the sludge during the formation processes of the ground and hardened gypsum. In other embodiments, a small particle is maintained, and the sludge is diluted before use. The mixture comprising calcium sulfate dihydrate, water, and an additive is preferably milled under conditions sufficient to provide a mixture in which the ground product has a median particle size from about 0.5 micron to about 2 microns. Preferably, the ground product has a median particle size from about 1 miera to about 1.7 micras. More preferably, the ground product has a median particle size from about 1 miera to about 1.5 micras. Desirably, the standard deviation of the particle size distribution for the calcium sulfate dihydrate is less than 5 microns. Preferably, the standard deviation is less than 3 microns. The size of the wet gypsum accelerator particles can be measured using laser dispersion analysis and / or other appropriate techniques. The appropriate instruments for dispersed analysis are available by Horiba, Microtrack and Malvern. An Horiba instrument was used for the measurements described in the examples section. Alternatively, the mixture comprises calcium sulfate dihydrate, water, and additive which is desirably milled under conditions sufficient to provide a slurry with a viscosity in the range from about 1000 cP or greater to a temperature in an ambient temperature range from about 65.6 degrees. C (150 degrees F). Typically, the wet gypsum accelerator has a viscosity in a range from about 1000 cP to about 5000 cP. Preferably, the wet gypsum accelerator has a viscosity in a range from about 2000 cP to about 4000 cP. More preferably, the wet gypsum accelerator has a viscosity in the range from about 2500 cP to about 3500 cP. In some embodiments, the viscosity range is from about 2800 cP to about 3200 cP. The highest viscosity ranges are ranges measured in the absence of dispersants or other chemical additives that may have a significant effect on the viscosity or the measurement thereof.

The ground product from the grinding process has been found to be substantially amorphous and irregularly shaped. Calcium sulfate dihydrate formed by the conventional wet mixing process are typically highly crystalline. Wet milling in the presence of an additive antagonizes recrystallization to form defined crystalline gypsum particles. Therefore, the ground product is substantially amorphous which means that the ground product comprises small or undefined crystal forms. Typically, about 60% or more of the milled product is amorphous. Preferably, about 75% or more of the milled product is amorphous. More preferably, about 90% or more of the milled product is amorphous. The milled product may have a surface area of about 20,000 cm 2 / g or more as determined in the laser scattering analysis. Preferably, the ground product has a surface area of about 30,000 cm 2 / g or more, or about 40,000 cm / g or more. Generally, the ground product has a surface area from about 100,000 cm2 / g or less. In a preferred embodiment, the ground product has a surface area of from about 20,000 cm 2 / g to about 80,000 cm 2 / g, or up to about 40,000 cm 2 / g to about 80,000 cm 2 / g. According to the invention, the mixture of calcium sulfate dihydrate, water, and additive is a wet grind in a mill assembly. First, the calcium sulfate dihydrate, water and additives are combined in any order and then pumped into the mill assembly. The mill assembly can be any suitable wet grinding set. Typically, the mill assembly comprises a grinding chamber containing a grinding shaft fitted with discs and spacers and a plurality of beads. The discs and spacers comprise any suitable material, for example, the discs and spacers comprise at least one stainless steel, PREMALLOY®, nylon, ceramics, and polyurethane. The discs and spacers preferably comprise PREMALLOY®. The discs selected for use in the grinding chamber can have any suitable shape. Typically the discs are standard flat discs or discs with pins, in particular the clamped discs that are designed to improve the flow of the media shaft through the mill. The axis of the mill and the corresponding grinding chamber can be oriented horizontally or vertically. In preferred embodiments, the mill axis is oriented horizontally.

Typically, the grinding chamber is jacketed so that it can be cooled with water. Preferably the grinding chamber is cooled with water to maintain a constant grinding temperature. The mill assembly can comprise any suitable counting, for example, balls and / or spheres. The accounts may comprise any suitable material, for example the accounts may comprise one or more metals or one or more ceramics. Suitable metals include stainless steel, carbon steel, chromium alloy steel, and the like. Suitable ceramics include zirconia, aluminum, cerium oxide, silicon, glasses and the like. As shown in laboratory tests, sulfate groups of calcium sulfate dihydrate produce a corrosive environment within the mill. Therefore, it is preferable to use beads or beads resistant to corrosion. The corrosion resistant beads include stainless steel beads or steel beads that are coated with corrosion resistant materials and ceramic beads. Particularly in a preferred embodiment, the beads comprise zirconia stabilized with cerium oxide comprising 20% cerium oxide and 80% zirconia, for example the ZIRCONOX® beads commercially available from Jyoti Ceramic Inds., Nashik, India. The beads used in connection with the mill assembly can have any suitable size and density. Typically the size and density of the beads will determine, at least in part, the size of the calcium sulfate dihydrate particles and hence the viscosity of the wet gypsum accelerator that is produced by the grinding process. To achieve a median particle size of calcium sulfate dihydrate from about 0.5 micron to about 2 microns, it is desirable to use beads having an average diameter of the count from about 0.5 mm to about 3 mm. Preferably, the beads have an average diameter of the bill from about 1 mm to about 2 mm. Desirably the beads have a density of about 2.5 g / cm3 or larger. Preferably, the beads have a density of about 4 g / cm3 or larger. More preferably, the beads have a density of about 6 g / cm3 or greater. In a particularly preferred embodiment, the beads are ZIRCONOX® ceramic beads having a median particle size from about 1.2 mm to about 1.7 mm and a density from about 6.1 g / cm3 or greater. Conveniently the beads are present in the mill assembly in an amount of about 70% volume or greater. Preferably about 70% of the volume up to about 90% of the volume of the beads is present in the whole mill. More preferably about 75% of the volume to about 85% of the volume of the beads is present in the whole mill.

The wet gypsum accelerator of the invention can be produced in a batch operation or a continuous operation. In a typical wet gypsum accelerator production system for plasterboard or gypsum board applications, first calcium sulfate dihydrate, water, and additives are mixed in a feed tank. In some modalities, this mixture is directed for about 8 minutes. The mixing time will depend, in part, on the size of the batch and the feed rate. In some embodiments, this mixture is desirable for the calcium sulfate dihydrate to be added to the mill assembly through an automatic feed system. The resulting mixture is then transported to the water-cooled mill assembly by a feed pump. The mixture is continuously ground and recirculated through a closed loop recirculation system from about 10 minutes or more. The current grinding time will depend, at least in part, on the desired size of the final medium particles for the calcium sulfate dihydrate particles and / or the viscosity desired for the wet gypsum accelerator sludge, as well as the size and density of grinding beads used to grind the calcium sulfate particles dihydrate. Typically, the mixture is milled for about 15 minutes to about 50 minutes. Preferably the mixture is milled for about 25 minutes to about 35 minutes. Once the desired median particle size is obtained, the mixture is allowed to exit the mill assembly. In some embodiments, a medium-sized particle is obtained from about 0.5 miera to about 2 micras. For a batch operation, the mixture is transported to a storage tank. When a batch operation has been performed, typically the mixture is ground in multiple steps via the closed loop system through the milling assembly. In some embodiments, about 4 to 5 steps are performed at a flow rate from approximately 37.85 to 56.8 I (10-15 gallons) / minute. In a continuous operation mode, the mixture is transported directly to the board mixer. When a continuous operation is performed, typically the mixture is ground in a single step at a flow rate from about 7.57 to 11.4 I (2 to 3 gallons) per minute. The wet gypsum accelerator of the invention is desirably added to an aqueous mixture of calcined gypsum in an amount effective to accelerate and / or control the rate of conversion of the mixture of calcined gypsum to set gypsum. Typically, the hydration rate is evaluated on the basis of "Time at 50% Hydration". The time at 50% hydration can be shortened by using more accelerator. The gypsum accelerator provides nucleation sites so that more dihydrate crystals are formed and a larger number of thinner gypsum crystals are obtained. Other accelerators, such as potash and aluminum sulfate, cause the gypsum crystals to grow faster, resulting in less, fatter crystals. A larger number of thinner gypsum crystals make a better and stronger matrix compared to less thicker gypsum crystals. Because the hydration of calcined gypsum to set gypsum is an exothermic process, the Time at 50% Hydration can be calculated by determining the temperature increase caused by hydration and then measuring the amount of time required to generate the temperature increase . The midpoint in time has been found to correspond to Time at 50% Hydration, as is known to those with skill in the specialty. Preferably, the wet gypsum accelerator according to the invention results in Time at 50% Hydration of the calcined gypsum of about 8 minutes or less, more preferably 6 minutes or less. Even more preferably, the use of the wet gypsum accelerator according to the invention results in a 50% Hydration Time of the calcined gypsum from about 5 minutes or less to about 4 minutes or less. Time at 50% Hydration can be affected by a number of different factors such as the amount of accelerator used, the amount of calcium sulfate hemihydrate and water used, the initial temperature of the mixture, and the mixing energy used during mixing. When hydration is measured, a control can be directed with fixed variables except for those variables that are being tested such as amount or type of WGA. This procedure allows the comparison of several types of accelerators in general as well as specific types of WGA. The amount of wet gypsum accelerator added to an aqueous mixture of calcined gypsum will depend on the compounds of the calcined gypsum aqueous mixture, such as the inclusion of prepared retarders, dispersants, foam, starch, paper fiber, and the like. By way of example, the wet gypsum accelerator of the invention can be provided in an amount from about 0.5% to about 3% by weight of calcined gypsum, more preferably, in an amount from about 0.5% to about 2% by weight of the calcined plaster. The calcined gypsum used to prepare the calcium sulfate dihydrate included in the wet gypsum accelerator of the invention may be in the form of calcium sulfate alpha hemihydrate, calcium sulfate beta hemihydrate, water-soluble anhydrous calcium sulfate, or mixtures of these various forms of calcium sulfate hemihydrates and anhydrites. Calcined gypsum can be fibrous and non-fibrous. In addition, the wet gypsum accelerator of the invention can be used to accelerate the hydration of the calcined gypsum or any of these forms of anhydrites and calcium sulfate hemihydrates as well as the various forms of anhydrites and calcium sulfate hemihydrates such as the forms fibrous and non-fibrous plaster calcined. While not wishing to be bound by any particular theory, it is believed that, while milling, the desired additives according to the invention are associated with the newly generated external surface of the calcium sulfate dihydrate, providing at least a partial coating. in calcium sulfate dihydrate. It is believed that the additives absorb strongly and instantaneously at active sites on the surface of freshly ground calcium sulfate dihydrate, where unwanted crystallization may occur otherwise. As a result, by absorbing into such active sites, it is believed that the additives protect in size and shape of the active sites to prevent gypsum gypsum crystallization during exposure to water and heat and to protect the gypsum active sites. ground during the wet milling process itself. The organic phosphonic compounds suitable for use in the wet gypsum accelerator of the invention have at least one functional group RPO3M2, where M is a cation, phosphorus, or hydrogen, and R is an organic group. Examples include organic phosphates and phosphonic acids. Organic polyphosphonic compounds are preferred although organic monophosphonic compounds can also be used according to the invention. Preferred organic polyphosphonic compounds include at least two phosphonic acid groups, or at least one phosphate salt or ionic group and at least one phosphonic acid group. A monophosphonic compound according to the invention includes a phosphonate salt or ionic group or at least one phosphonic acid group.

The organic group of organic phosphonic compounds binds directly to the phosphorus atom. Suitable phosphonic compounds for use in the invention include, but are not limited to, compounds characterized by the following structures: In these structures, R refers to an organic portion containing at least one carbon atom directly attached to a phosphorus atom P, and n is a number from about 1 to about 1,000, preferably a number from about 2 to about 50 Organic phosphonic compounds include, for example, aminotri (methylene phosphonic acid), 1-hydroxyethylidene-1,1-diphosphonic acid, diethylenetriamine penta (methylene phosphonic acid), hexamethylenediamine tetra (methylene phosphonic acid), also as any suitable salt thereof, such as, for example, the pentasodium salt, the tetrasodium salt, trisodium salt, potassium salt, sodium salt, ammonium salt, calcium salt or magnesium salt of any of the preceding acids, and the like, or combinations of salts and / or preceding acids. In some embodiments, DEQUEST® phosphates commercially available from Solutia, Inc., in San Luis, Missuouri, are used in the invention. Examples of DEQUEST® phosphates include DEQUEST® 2000, DEQUEST® 2006, DEQUEST® 2016, DEQUEST® 2054, DEQUEST® 2060S, DEQUEST® 2066A, and the like.

Other examples of suitable organic phosphonic compounds are found, for example, in U.S. Pat. No. 5,788,857. Any suitable phosphate-containing compound providing a benefit to the invention can be used. By way of example, the phosphate-containing compound can be an orthophosphate or a polyphosphate, and in addition, the phosphate-containing compound can be in the form of an ion, salt, or acid. Suitable examples of phosphates according to the invention will be apparent to those skilled in the art. For example, any suitable orthophosphate-containing compound can be used in the practice of the invention, including, but not limited to, monobasic phosphate salts, such as monoammonium phosphate, monosodium phosphate, monopotassium phosphate, or combinations thereof. the same. A preferred monobasic phosphate salt is monosodium phosphate. The polybasic orthophosphates can also be used according to the invention. Likewise, any suitable polyphosphate salt can be used according to the present invention. The polyphosphate can be cyclic or acyclic. Examples of cyclic polyphosphates include trimetaphosphate salts, including double salts, that is, trimetaphosphate salts having two cations. The trimetaphosphate salt can be selected, for example, from sodium trimetaphosphate, potassium trimetaphosphate, calcium trimetaphosphate, sodium calcium trimetaphosphate, lithium trimetaphosphate, ammonium trimetaphosphate, aluminum trimetaphosphate and the like, or combinations thereof. Sodium trimetaphosphate is a preferred trimetaphosphate salt. Also, any suitable acyclic polyphosphonic salt can be used in accordance with the present invention. Preferably, the acyclic polyphosphate salt has at least two phosphate units. By way of example, suitable acyclic polyphosphate salts according to the present invention include, but are not limited to, pyrophosphates, tripolyphosphates, sodium hexametaphosphate having about 6 to about 27 repeating phosphate units, potassium hexametaphosphate having near from 6 to about 27 repeating phosphate units, ammonium hexametaphosphate having from about 6 to about 27 repeating phosphate units, and combinations thereof. A preferred acyclic polyphosphonic salt according to the present invention is commercially available as CALGON® from Solutia, Inc., San Luis, Missouri, which is a sodium hexametaphosphate having about 6 to about 27 repeating phosphate units. further, the phosphate-containing compound may be in the acid form or any of the preceding salts. The acid can be, for example, a phosphoric acid or a polyphosphoric acid. Preferably, the phosphate-containing compound is selected from the group consisting of tetrapotassium pyrophosphate, sodium acid pyrophosphate, sodium tripolyphosphate, tetrasodium pyrophosphate, sodium potassium tripolyphosphate, sodium hexametaphosphate salt having from 6 to about 27 units of phosphate, ammonium polyphosphate, sodium trimetaphosphate, and combinations thereof. The ingredients in the wet gypsum accelerator of the invention can be provided in any suitable amount. For example, the calcium sulfate dihydrate can be provided in an amount of at least about 20% by weight of the accelerator, preferably at least about 30% by weight of the accelerator. The calcium sulfate dihydrate may be present, for example, in an amount from about 35% to about 45% by weight of the accelerator, more preferably, in an amount from about 38% to about 42% by weight of the accelerator. Generally, lower solids contents provide greater efficiency but also significantly increase the grinding time resulting in a decrease in the rate of yield and / or production. The additive is preferably provided in as low a quantity as possible to minimize costs, while still achieving the desired benefits of increasing longevity, so that the wet gypsum accelerator maintains its efficiency over time and withstand exposure to water. water and heat. Preferably, the additive compound, either a single additive or a combination of additives, is provided in an amount of from about 0.1% to about 10% by weight of the calcium sulfate dihydrate, more preferably, in an amount from about 0.1% to about 2% by weight of the calcium sulfate dihydrate, and still more preferably, in an amount of about 0.1% by weight of the calcium sulfate dihydrate. In preferred embodiments, at least one organic phosphonic compound is used as an additive. Organic phosphonic compounds are generally superior in accelerator efficiency increase, even though they are included in relatively small amounts. More preferably, at least one phosphate-containing compound is used in combination with at least one organic phosphonic compound. For example, it is believed that, depending on the size and shape of several active sites, the organic phosphonic compound may increase nucleation at some active sites while the phosphate-containing compound may act at other sites so that the combination is desirable. In addition, in preferred embodiments, the phosphate-containing compound, particularly cyclic compounds such as a trimetaphosphate compound, including at least one ion and / or salt, is added in conjunction with the organic phosphonic compound to increase aging resistance. It is believed that the inclusion of a phosphate-containing compound stabilizes and maintains the wet strength of the accelerator to improve the aging properties of the wet gypsum accelerator. In embodiments of the invention comprising more than one additive, each additive is preferably included in a suitable amount to achieve longevity and / or the desired 50% Hydration Time, but preferably, the total amount of additive falls within the ranges previously described. For example, in embodiments where at least one compound having phosphate is used in combination with at least one organic phosphonic compound, the organic phosphonic compound is preferably included in an amount from about 0.05% to about 9.95% by weight of the calcium sulfate dihydrate , and the phosphate-containing compound in the same manner is preferably present in an amount from about 0.05% to about 9.95% by weight of the calcium sulfate dihydrate. In some modalities, the additive is present up to 10% by weight of the calcium sulfate dihydrate. In some embodiments, the additive is presented up to about 0.05% to about 4.95% by weight of the calcium sulfate dihydrate. Particularly in a preferred embodiment, the additive is a mixture of about 0.5% pentasodium salt of aminotri (methylene phosphonic acid) by weight of the calcium sulfate dihydrate and about 0.5% of sodium trimetaphosphate by weight of the calcium sulfate dihydrate. As a further benefit of the invention, the wet gypsum accelerator can be used as a means to provide an organic phosphonic compound and / or an inorganic phosphate compound as a pretreatment to increase the various properties of the composition and the product containing gypsum. resulting setting, for example, plasterboard or gypsum board, roof plates, and the like, such as, for example, strength, dimensional stability, resistance to permanent deformation, and the like, as described in the patent application of US Pat. USA Serial No. 08 / 916,058 of common cession (abandoned) and in US patents. Nos. 6,342,284, 6,409,824, and 6,632,550, of common assignment, incorporated herein in their entirety by reference. The following examples further illustrate the present invention but should not be construed in any way limiting its scope. EXAMPLE 1. HYDRATION RATE This example illustrates the preparation of the wet gypsum accelerator and demonstrates the increase in the rate of hydration of the calcined gypsum and the efficiency resulting from the use of the wet gypsum accelerator of the invention compared to the dry gypsum accelerators. . To prepare each wet gypsum accelerator (WGA), a Premier HM45 wet mill bed fitted with PREMALLOY discs and spacers was used for the initial wet milling of calcium sulfate dihydrate from the plant of the United States Gypsum Company plant Galena Park in the presence of of one or more additives. Calcium sulfate dihydrate as starting material has an initial median particle size of about 55 microns. Specifically, 189.3 I (50 gallons) of processed water, 181.4 kg (400 pounds) of calcium sulfate dihydrate, and 0.5% by weight, based on the weight of the calcium sulfate dihydrate, each of aminotri (methylene phosphonic acid), salt Pentasodic (Dequest® 2006) and sodium trimetaphosphate (NaTMP) were combined and ground for 10 minutes, 20 minutes, and 25 minutes, respectively, at a flow rate of 49.2 to 56.2 I (13-15 gallons) per minute, recirculation of 4-5 Steps, in a spiral corrugated stainless steel grinding chamber containing 75 to 82% volume of ZIRCONOX® ceramic beads having a diameter of 1.2 mm at 1. 7 mm and a density of 6.1 g / cm3. The longer the grinding time for the WGA composition, the smaller the size of the medium particles of the ground product. The resulting size of the medium particles for each WGA composition is shown in Table 1. Each WGA sample was tested to determine the rate of hydration. For each test, 300 grams of calcium sulfate hemihydrate from the United States Gypsum Company Southard plant was combined with 300 milliliters of tap water at -1.1 degrees C (70 degrees F). One gram of dry weight bases of WGA were added to the calcium sulfate hemihydrate mixture and the mixture was allowed to soak for 10 seconds followed by mixing for 7 seconds at low speed with a Waring blender. The resulting mixture was poured into a polyethylene foam cup, which was then placed inside an insulated container with polyethylene foam to minimize the loss of heat to the environment during the hydration reaction. A test temperature probe was placed in the middle of the mixture, and the temperature was recorded every 5 seconds. Since the reaction of the preparation is exothermic, the degree of the reaction was measured by the increase in temperature. The Time at 50% Hydration was determined to be the time to reach the temperature halfway between the minimum and maximum temperatures recorded during the test. The results are provided in Table 1.

The results in Table 1 demonstrate that Time at 50% hydration decreases and Acceleration Efficiency, shown as a normal percentage of efficient Galena Park heat resistant dry accelerator (HRA), increases as medium-sized particles of calcium sulfate dihydrate decrease. The highest standard deviation of the size of the medium particles means a distribution (wide range) of the size of the large particles. Because the feed material is narrow-range synthetic gypsum (~ 50 microns), the median size of the WGA product particles will normally have a large particle size distribution with a high standard deviation.

Generally, the longer the grinding time, the narrower the size distribution of the final particles with a smaller standard deviation for the WGA product. EXAMPLE 2: HYDRATION RATE This example illustrates the preparation of the WGA and demonstrates the increase in the hydration rate resulting from the use of the WGA of the invention. To prepare each WGA, a Premier HML-1.5 wet bed mill (super laboratory mill) was used for the initial wet milling of eight different calcium sulfate dihydrate supplements from the plants of the United States Gypsum Company in the presence of one or more additives. The calcium sulfate dihydrate starting materials had impurities that varied in a range of gypsum extracted with high impurities to pure synthetic gypsum. Specifically, 4000 milligrams of tap water, 3000 grams of calcium sulfate dihydrate (43% solids), and 0.75% by weight, based on the weight of the calcium sulfate dihydrate, each of the aminotri (methylene phosphonic acid), salt pentasodium ( Dequest® 2006) and sodium trimetaphosphate (NaTMP) were combined and ground at .27 I (0.6 gallon) per minute, from 4 to 5 steps, in a spiral corrugated stainless steel grinding chamber containing 75 to 82% volume of ZIRCONOX® ceramic beads having a diameter of 1.2 millimeters to 1.7 millimeters and a density of 6.1 g / cm3. The relationship between grinding time and viscosity is shown in Table 2 for each wet gypsum accelerator formulation.

Each formulation of WGA was then tested to determine the rate of hydration. For each test, 300 grams of calcium sulfate hemihydrate were combined from the plant of the United States Gypsum Company's Southard with 300 milliliters of running water, -1.1 degrees C (70 degrees F). One gram of dry weight basis of WGA was added to the mixture of calcium sulfate hemihydrate and the mixture was allowed to soak for 10 seconds followed by a mixture of 7 seconds at low speed with a Waring blender. The resulting mixture was poured into a polystyrene foam cup, which was then placed inside an insulated container with polyethylene foam to minimize the loss of heat to the environment during the hydration reaction. A temperature probe was placed in the middle of the mixture, and the temperature was recorded every 5 seconds. Since the reaction of the preparation is exothermic, the reaction point was measured by the increase in temperature. The Time at 50% Hydration was determined to be the time to reach the average temperature between the minimum and maximum temperatures recorded during the test. The results are provided in Table 3.

The results in Tables 1-3 clearly show that the Time at 50% and 98% hydration decrease as the viscosity increases and as the size of the medium particles of milled product decreases. Generally, the longer the grinding time, the finer the size of the medium particles of ground WGA, the higher the viscosity of the WGA, and the higher the efficiency of the acceleration. EXAMPLE 3: EFFICIENCY This example illustrates the preparation of the WGA and demonstrates the efficiency increase resulting from the use of the WGA of the invention. (0056) To prepare each WGA, a Premier HML-1.5 wet bed mill (super laboratory mill) was used for the initial wet milling of calcium sulfate dihydrate from the plant Southard from United States Gypsum Company in the presence of one or more additives. Specifically, three WGA formulations comprising (1) 43% solids, (2) 33% solids, and (3) 22% solids were tested. Formulation (1) comprises 4000 milliliters of tap water, 3000 grams of calcium sulfate dihydrate, and 0.75% by weight, based on the weight of calcium sulfate dihydrate, each aminotri (methylene phosphonic acid), pentasodium salt (Dequest® 2006) and sodium trimetaphosphate (NaTMP). Formulation (2) comprises 4690 milliliters of tap water, 2310 grams of calcium sulfate dihydrate and 0.5% by weight, based on the weight of calcium sulfate dihydrate, each aminotri (methylene phosphonic acid), pentasodium salt (Dequest® 2006) and sodium trimetaphosphate (NaTMP). The formulation (3) comprises 5460 milliliters of tap water, 1540 grams of calcium sulfate dihydrate, and 0.5% by weight, based on the weight of the calcium sulfate dihydrate, each aminotri (methylene phosphonic acid), pentasodium salt (Dequest® 2006) and sodium trimetaphosphate (NaTMP). Each WGA formulation was combined and ground by specific time intervals, to take WGA samples for viscosity measurements and efficiency tests, at 2.27 I (0.6 gallons) per minute with 4-5 steps in a corrugated stainless steel grinding chamber spiral containing 75 to 82% of the volume of ZIRCONOX® ceramic beads having a diameter of 1.2 millimeters to 1.7 millimeters and a density of 6.1 g / cm3. The relationship between grinding time, viscosity, hydration time, and efficiency is shown in Table 4 of each WGA formulation.

The results of Table 4 demonstrate that the WGA formulations according to the invention having a low solids content can have exceptional efficiencies without sacrificing the workability of the sludge. Either way, the production yield of WGA is significantly decreased with low solids content. Therefore, a solids content of at least about 30% is desirable to optimize the WGA production rate, efficiency in operation, and workability. In some embodiments, the solid content is from about 38% to about 42%. All references cited herein, including patents, patent applications, and publications, are incorporated herein in their entireties by reference. While this invention has been described with an emphasis on the preferred embodiments, it will be apparent to those of ordinary skill in the art that variations of the preferred embodiments may be used and that the invention is intended to be practiced in another manner than that it is specifically described here. Accordingly, this invention includes all modifications encompassed within the scope of the invention as defined in the following claims.

Claims (38)

1. CLAIMS 1. A wet gypsum accelerator, characterized in that it comprises: (a) a milled product having a median particle size of from about 0.5 micron to about 2 microns, wherein the milled product comprises calcium sulfate dihydrate; (b) water, and (c) an additive selected from a group consisting of: (i) an organic phosphonic compound; (ii) a phosphate-containing compound; and (iii) a mixture of (i) and (ii).
2. 2. The wet gypsum accelerator of claim 1, characterized in that the ground product is substantially amorphous.
3. 3. The wet gypsum accelerator of claim 1, characterized in that the ground product has a median particle size from about 1 miera to about 1.7 microns.
4. 4. The wet gypsum accelerator of claim 1, characterized in that the ground product has a median particle size from about 1 miera to about 1.5 micras.
5. 5. The wet gypsum accelerator of claim 1, characterized in that the additive is present in an amount from about 0.1% to about 10% by weight of the calcium sulfate dihydrate.
6. The wet gypsum accelerator of claim 1, characterized in that the additive is a mixture of at least one organic phosphonic compound, and at least one phosphate-containing compound, wherein the organic phosphonic compound is present in an amount from about 0.5. % up to about 9.95% by weight of the calcium sulfate dihydrate, and wherein the phosphate-containing compound is present in an amount from about 0.5% to about 9.95% by weight of the calcium sulfate dihydrate.
7. 7. The wet gypsum accelerator of claim 1, characterized in that the additive is a mixture of about 0.5% of pentasodium salt of aminotri (methylene phosphonic acid) by weight of calcium gypsum dihydrate and from about 0.5% sodium trimetaphosphate by weight of calcium gypsum dihydrate.
8. 8. The wet gypsum accelerator of claim 1, characterized in that the calcium sulfate dihydrate is present in an amount of at least 20% by weight of said accelerator.
9. 9. The wet gypsum accelerator of claim 1, characterized in that the calcium sulfate dihydrate is present in an amount from about 35% to about 45% by weight of said accelerator.
10. 10. The wet gypsum accelerator of claim 1, characterized in that the viscosity of the wet gypsum accelerator is from about 1000 cP to about 5000 cP.
11. 11. The wet gypsum accelerator of claim 1, characterized in that the viscosity of the wet gypsum accelerator is from about 2000 cP to about 4000 cP.
12. The wet gypsum accelerator of claim 1, characterized in that the organic phosphonic compound is selected from a group consisting of aminotri (methylene phosphonic acid), 1-hydroxyethylidene-1,1-diphosphonic acid, penta diethylenetriamine (methylene phosphonic acid), tetrahexamethylene diamin (methylene phosphonic acid), a pentasodium salt, trisodium salt, tetrasodium salt, sodium salt, ammonium salt, potassium salt, calcium salt, or magnesium salt of any of the preceding acids, and combinations thereof.
13. 13. The wet gypsum accelerator of claim 1, characterized in that the phosphate-containing compound is selected from the group consisting of orthophosphates, polyphosphates, and combinations thereof.
14. 14. The wet gypsum accelerator of claim 11, characterized in that the phosphate-containing compound is selected from a group consisting of tetrapotassium pyrophosphate, sodium pyrophosphate acid, sodium tripolyphosphate, tetrasodium pyrophosphate, sodium potassium tripolyphosphate, sodium salt sodium hexametaphosphate having from 6 to approximately 27 units phosphate, ammonium polyphosphate, sodium trimetaphosphate, and combinations thereof.
15. 15. The wet gypsum accelerator of claim 1, characterized in that the accelerator, when added to a mixture comprising calcined gypsum and water used to form an entangled matrix of set gypsum, allows Time to 50% Hydration of the gypsum Calcinated from about 6 minutes or less.
16. The wet gypsum accelerator of claim 13, characterized in that the accelerator, when added to a mixture comprising calcined gypsum and water used to form an entangled matrix of set gypsum, allows Time to 50% Hydration of the gypsum Calcinated be from about 5 minutes or less.
17. 17. A method for preparing a wet gypsum accelerator, characterized in that it comprises: (a) calcium sulfate wet milled dihydrate, water, and at least one additive selected from the group consisting of (i) an organic phosphonic compound; (ii) a phosphate-containing compound; and (ii) a mixture of (i) and (ii); and (b) wet milling the gypsum in the presence of an additive to form said wet gypsum accelerator to form a wet gypsum accelerator comprising a ground product having a median particle size from about 0.5 micron to about 2 microns.
18. 18. The method of claim 17, further comprising: providing a mill assembly comprising an axis of the mill and beads, wherein the beads have an average diameter of account from about 0.5 to about 3 millimeters and a density from approximately 2.5 g / cm3 or greater.
19. The method of claim 18, characterized in that the beads have an average diameter of account from about 1 millimeter to about 2 millimeters.
20. The method of claim 18, characterized in that the beads are ceramic beads.
21. 21. The method of claim 18, characterized in that the beads comprise zirconia stabilized with cerium oxide.
22. 22. The method of claim 18, characterized in that the calcium sulfate dihydrate is added to the mill assembly through an automatic feeding system.
23. 23. The method of claim 18, characterized in that the wet mixture is made in a single pass through the beads of the mill assembly.
24. 24. The method of claim 18, characterized in that the wet mixture is made in multiple passes through the bead mill assembly.
25. 25. The method of claim 17, characterized in that the wet gypsum accelerator comprises a milled product that is substantially amorphous.
26. 26. The method of claim 17, characterized in that the wet gypsum accelerator comprises a milled product having a median particle size from about 1 miera to about 1.7 microns.
27. 27. The method of claim 17, characterized in that the wet gypsum accelerator comprises a ground product having a median particle size from about 1 micron to about 1.5 micron.
28. The method of claim 17, characterized in that the calcium sulphate Dihydrate is present in an amount from about 35% to about 45% by weight of said accelerator.
29. 29. The method of claim 17, characterized in that said organic polyphosphonic compound is selected from a group consisting of aminotri (methylene phosphonic acid), 1-hydroxyethylidene-1,1-diphosphonic acid, pentadiethylenetriamine (methylene phosphonic acid), tetrahexamethylenediamine (methylene phosphonic acid) ), a pentasodic salt, trisodium salt, tetrasodium salt, sodium salt, potassium salt, ammonium salt, calcium salt, or magnesium salt of any of the preceding acids, and combinations thereof.
30. The method of claim 17, characterized in that the phosphate-containing compound is selected from a group consisting of orthophosphates, polyphosphates, and combinations thereof.
31. The method of claim 30, characterized in that the phosphate-containing compound is selected from a group consisting of tetrapotassium pyrophosphate, sodium acid pyrophosphate, sodium tripolyphosphate, tetrasodium pyrophosphate, sodium potassium tripolyphosphate, sodium hexametaphosphate salt having from 6 to about 27 units of phosphate, ammonium polyphosphate, sodium salt of sodium trimetaphosphate, ammonium salt, calcium salt, magnesium salt and combinations thereof.
32. 32. The method of claim 17, characterized in that the additive consists of a mixture of about 0.5% pentasodium salt of aminotri (methylene phosphonic acid), calcium sulfate dihydrate and about 0.5% sodium trimetaphosphate by weight of calcium sulfate dihydrate .
33. 33. A method for hydrating calcined gypsum to form an interlaced matrix of set gypsum characterized in that it comprises: forming a calcined gypsum mixture; water, and a wet gypsum accelerator, said wet gypsum accelerator comprises a ground product having a median particle size from about 0.5 micron to about 2 microns, wherein the milled product comprises calcium sulfate dihydrate, the accelerator further comprises water, and at least one additive selected from a group consisting of: (i) an organic phosphonic compound; (i) a compound containing phosphate; and (iii) a mixture of (i) and (ii).
34. 34. The method of claim 33, characterized in that the Time at 50% Hydration of the calcined gypsum is from about 6 minutes or less.
35. 35. The method of claim 33, characterized in that the Time at 50% Hydration of the calcined gypsum is from about 5 minutes or less.
36. 36. A composition containing set gypsum characterized in that it comprises an entangled matrix of the set gypsum formed of at least calcined gypsum, water, and an accelerator comprising calcium sulfate dihydrate having a median particle size from about 0.5 miera to about 2 microns, water, and an additive selected from a group consisting of: (i) an organic phosphonic compound; (ii) a phosphate-containing compound; and (iii) mixtures of (i) and (ii).
37. 37. The hardened gypsum-containing product comprising the composition of claim 36.
38. 38. The hardened gypsum-containing product of claim 36 characterized in that the product is a board or panel.