MXPA97000683A - Ready-mixed setting-type joint compound, and method of making same - Google Patents

Abstract

A process for the production of a ready-mixed setting-type joint compound includes the use of calciumásulfate hemihydrate, water, and a set-retarding agent. The retarder includes a polymer composition including acrylic acid and acrylamide monomer units, for example a copolymer (or a mixture of copolymers) of acrylic acid and acrylamide or a blend of a homopolymer of acrylic acid and a homopolymer of acrylamide. The joint compound can be combined with an accelerator including a metallic salt. The joint compound of the invention can be formulated either as a lightweight joint compound or as a conventional weight joint compound. The joint compounds provide short setting times, reduced shrinkage, reduced preparation time, and beneficial application properties.

Description

"COMPOSED FOR PREMIXED SETTING TYPE GASKETS, AND MANUFACTURING METHOD OF THE SAME" BACKGROUND OF THE INVENTION FIELD OF THE INVENTION The present invention relates generally to the production and use of cementitious compositions, and more particularly to the production of compounds to be used for filling and coating joints between adjacent pressed gypsum fiber sheets, as well as for repairing other imperfections in construction materials. . The invention further relates to the preparation and use of set-type joint compounds that can be premixed with water and stored over considerable periods of time before being used to hide the joints between adjacent pressed gypsum fiber sheets.

DESCRIPTION OF RELATED TECHNOLOGY One of the most common ways to build interior walls today includes the use of panels or sheets of inorganic pressed fiber such as pressed gypsum fiber which is often referred to simply as "pressed fiber" or "wall" dry". The use of pressed fiber, as opposed to conventional wet mortar methods, is often desirable because the installation of the pressed fiber is generally less expensive than for conventional mortar. The pressed fiber is conventionally produced by enclosing a core of an aqueous slurry of gypsum and other materials between two large sheets of paper. After the thick slurry of gypsum has set and dried, the sheet is cut into normal sizes. The pressed gypsum fiber is described, for example, in the Kirk-Othmer Encyclopedia of Chemical Technology, Second Edition, 1970, Volume 21, pages 621 to 24, the disclosure of which is incorporated herein by reference. A wall or wall is generally manufactured by securing, eg, with screws and / or nails, the fiber pressed into a support structure, for example pieces of wood oriented vertically and horizontally. Because pressed fiber typically provides sheets or panels of normal size, when forming a wall of the sheets, there will usually be a number of joints between the adjacent sheets. In most pressed fiber construction, it is necessary to hide these joints between the adjacent panels so that the wall has a smooth finish similar to that obtained with conventional wet mortar methods. It is also typically necessary to hide the screws and / or nails used to secure the pressed fiber panels in the framework, the imperfections in the pressed fiber panels, as well as other materials (e.g., corner flanges) used to form the wall or wall. The prior art discloses a number of joint compound compositions (sometimes referred to by applicators as "mud") that can be used to hide joints between the adjacent sheets of the pressed fiber. These compositions can also be applied to other defects in the pressed fiber, for example defects or depressions caused by screws or nails used to hold the pressed fiber in place. In order to hide the joints between the pressed fiber panels, the joint compound is typically applied in several layers or hands. A first layer of the joint compound is placed in the joint between the pressed fiber boards with a knife, blade or trowel. The first layer is mainly for the purpose of filling the space between the adjacent pressed fiber boards. The jointing tape (for example made of paper) can then be embedded in the first layer of the jointing compound. It is conventional to apply the joint compound in several coats or layers in order to obtain a smooth finish and each layer of the joint compound should be allowed to dry prior to the placement of the next layer of joint compound. (If the previous layer is not allowed to dry, problems such as excessive shrinkage and / or cracking can occur). Once dried, the treated area is sanded before applying the next layer of joint compound. Because each layer of the joint compound must be almost completely dry before the subsequent layer can be applied, this can cause undesirable delays in completing the wall or wall. The drying times required are often within the range of approximately 24 hours for each layer. A cold humid climate can make it particularly difficult for the joint compound to dry out. Three layers of joint compound are often required to produce satisfactory results. Once dried, the joints and other treated locations are provided with a final sanding to produce a smooth surface similar to a conventional wet mortar wall or wall before painting or applying another finish. The joint compound can be supplied in the form of a dry powder, to which an amount of water is added at the work site by the operator to provide the joint compound with an appropriate consistency. Other joint compounds which are often referred to as "already mixed" or "premixed" joint compounds are premixed with water during manufacture. These joint compounds are usually sold in a bucket or bucket in a form that is suitable for use with little or no addition of water at the job site. Compounds for premixed joints have the advantages of providing a consistent formulation, reducing or eliminating the time necessary to prepare the composition of the joint compound and reducing or eliminating the need for having water available at the site. Among the compositions of the joint compound of the prior art, it is known to generally use a filler or filler (eg, calcium carbonate, calcium sulfate hemihydrate, or calcium sulfate dihydrate) and a binder. , as well as several other components to produce a joint compound. Many of the joint compounds are of the "drying" type. In the drying type joint compound, the filler or filler material essentially comprises calcium carbonate (CaCÜ3). Before use (generally during manufacture), the filler or filler and a binder (together with several other known ingredients) are mixed with water. After application, when the water dries, that is, when it evaporates, a relatively hard dry cementitious material remains. In order to avoid the various disadvantages of the type of joint compound drying, "setting type" compounds have been developed. In composites of the set type, at least a considerable portion of the filler or filler is calcium suflate hemihydrate (CaS04 • la / 2H2 ?, which is also referred to as calcined gypsum). In order to produce the calcined gypsum, the raw gypsum calcium sulfate dihydrate is converted into the hemihydrate state through a known process called calcination. This process removes 1 1/2 molecules of gypsum water from the calcium sulfate dihydrate. The calcium sulfate hemihydrate form is essentially more soluble in water than the calcium sulfate dihydrate form. During use in a setting joint compound, the calcium sulfate hemihydrate is rehydrated to the dihydrate state. This rehydration process usually takes place over a fairly short period of time. Correspondingly, it has been extremely difficult to produce a joint compound comprising hemihydrate gypsum because the product is set in the cuvette. Therefore, joint compounds of the setting type have generally had to be supplied in powder form. The compounds for setting joints have the advantage of having generally faster finishing times (setting time) than the compounds for drying joints. This is an advantage due to the reasons stated above. further, because the setting joint compounds form a crystalline lattice as they set (as opposed to drying only), these compounds typically provide a stronger, more durable bond between the adjacent pressed fiber sheets than the joint compounds drying At least one compound for premixed setting gaskets has been disclosed in the literature. For example, in U.S. Patent No. 4,661,161 issued to Jakacki et al. Discloses a setting joint compound comprising an aqueous slurry of calcium sulfate hemihydrate and a setting retarding agent consisting of two ingredients: a organic protein retarder and a chelating agent, e.g., which is selected from diethylene triamine pentaacetic acid, ethylenediamine tetraacetic acid and salts thereof. However, it is believed that already-mixed setting-type joint compounds have not been used commercially in a satisfactory manner due to the need to find an appropriate retarding agent and an appropriate accelerator to overcome the retarding agent. Others have made known the use of delay agents for certain objects. However, even though different types of retarding agents have been suggested, the object of the retarders, the final product, and the conditions under which the product is used (eg in the manufacture of the pressed fiber board) have differed considerably from the object, production conditions and working conditions of the joint compounds. For example, even though manufacturers of pressed fiber board have used certain types of retarding agents, the object in the application is to prevent immediate water absorption and provide rigidity to the slurry during production as well as to facilitate control of the thick suspension. In the production of pressed fiber board, retarding agents are added to stabilize a thick stucco suspension for only a matter of seconds. It will be understood that the retarding agents are typically used in the production of the pressed fiber board at an extremely low rate, for example of approximately .0007 weight percent (v.gr, in a 635.60 kilogram batch they could typically be added more or less 30 grams of the retarding agent). Accordingly, due to the above-stated reasons, it would be desirable to produce a joint compound of the ready-mix type which is also of the setting type and which is stable during storage for the periods required for commercial use. It would also be desirable to produce a premixed joint compound that provides improved application characteristics, cracking resistance and less shrinkage compared to conventional joint and pre-mix compounds. It would also be desirable to produce a premixed joint compound which allows a reduced time between applications of successive layers and which in some cases can reduce the number of layers required. It would also be advantageous if the aforementioned joint compounds could be produced in the form of compounds for conventional weight joints and of the light weight type. The compositions of the present invention solve or ameliorate each of the deficiencies in the compositions and methods of the prior art described above.

COMPENDIUM OF THE INVENTION An object of the invention is to overcome one or more of the problems described above. Accordingly, the invention provides a process for producing an already mixed jointing compound which includes combining the calcium sulfate hemihydrate, water and a setting retarding agent. Other known ingredients such as fillers or fillers, thickeners and preservatives are also preferably included. The retarding agent includes a polymeric composition including acrylic acid and acrylamide monomer units for example a copolymer (or a mixture of copolymers) of acrylic acid and acrylamide or a mixture of an acrylic acid homopolymer and an acrylamide homopolymer. The joint compound of the invention can be formulated either as a light weight joint compound or as a conventional joint compound. According to a particular feature of the invention, the joint compound of the invention is combined with an activator or accelerator just before being used, v.gr, of its application in a wall or wall or ceiling. The accelerator, which overcomes the effect of the retarding agent, preferably includes a metal salt that provides an acidic cation. According to a further particularity of the invention, the joint compound is used without the addition of an accelerator. In this embodiment, the joint compound acts as a premixed joint compound of the drying type. Other objects and advantages of the invention will become apparent to those skilled in the art and from the following detailed description, which is taken in conjunction with the appended claims.

DETAILED DESCRIPTION OF A PREFERRED MODALITY According to the invention, suitable compositions are provided for filling and coating imperfections in building materials such as joints between adjacent panels of pressed gypsum fiber boards. The invention further provides a method of preparing and using setting-type joint compounds that can be pre-mixed with water by a manufacturer and stored over considerable periods of time before being used to hide the joints between adjacent pressed fiber panels. A joint compound of the ready-mix type can be produced by incorporating a copolymer of acrylic acid and acrylamide as a retarding agent. The joint compound of the invention preferably has a shelf life of approximately two years. As used herein, the term "shelf life" is meant to refer to the time that elapses between the manufacture of the joint compound (including the mixing of calcined gypsum and water) and the point when the dihydrate crystals they have been formed and interlaced at the stage where the composition is not appropriate or finished of superior quality. The term "setting time" is intended to refer to the time that elapses between the initial application of the joint compound and the point when the joint compound has "set" as described above, wherein the compound for together it is essentially dry, the dihydrate crystals are sufficiently formed and interlaced and a subsequent layer of the joint compound can be satisfactorily applied through a previous layer.

The term "open time" as used herein is intended to mean as referring to the time that elapses between (a) the exposure to the atmosphere of a joint compound that is ready to be applied to a wall or wall (v. .gr., the opening of the bucket or bucket containing the premixed joint compound) and (b) the point where the calcined gypsum of the joint compound has reacted sufficiently with the water present so that the joint compound it is no longer satisfactory for application to a press beam joint to produce a superior quality finish. The shelf life, the setting time, and the open time of the joint compounds of the invention can be measured by conventional methods. The joint compound of the invention includes several preferred ingredients or components that combine to form a useful composition. The first ingredient of the joint compound of the invention is calcium sulfate hemihydrate (CaS? 4 * H2?). As is known to those skilled in the art, there are two types of calcium sulfate hemihydrate, the a-hemihydrate form and the ß-hemihydrate form. These two forms are typically produced by different types of calcination processes and differ structurally. For example, when the gypsum is calcined by the wet or pot process, the a-hemihydrate form is obtained. The form of β-hemihydrate can be obtained by calcination in a process referred to as dry calcination, for example, one of the following processes: pot, rotary, kiln, calcidin, mill calcination imp. Caludis Peter, and Holflit. While those skilled in the art will know how to produce both forms of calcium sulfate hemihydrate by dehydrating the weight, the following is a general description of a preferred process for producing a form of α-hemihydrate. The gypsum rock raw material is processed in an autoclave with water spraying and injection of liquid alum (a solution of approximately 0.1 percent) in order to adjust the pH value. The material is subjected to a high pressure of approximately 2.11 kilograms per square centimeter and elevated temperature for about one and a half hours. The a-calcium sulfate hemihydrate (sometimes referred to as "stucco") is formed in this manner.This product is dried at a temperature greater than about 10 ° C in a high speed dryer so that the product Do not re-absorb any amount of free water or environment The dried rock is then milled in a mill to produce a desired particle size of the calcium sulfate hemihydrate and stored in silos for use.It may be advantageous in some applications of the invention use smaller particle sizes of 120 mesh or smaller than 100 mesh (American Society for Materials Testing standard.) The BET surface area of the a-hemihydrate is preferably low, for example within the scale of about 1 to about 2.5 square meters per gram.The ß-hemihydrate, on the other hand has, a much higher BET surface area generally within the scale of about 8 to approximately 12 square meters per gram. The water demand for an a-hemihydrate is within the range of 30 to 45 milliliters per 100 grams, while the water demand for the ß-hemihydrate is much higher within the range of 60 to approximately 85 milliliters per 100 grams. A further description of calcium sulfate can be found in Kirk-Othmer Encyclopedia of Chemical Technolgy, Fourth Edition, 1992, Volume 4, pages 812 to 826 (Petersen et al.) And Karni et al., Materials and Structures, Volume 28, pages 92 a 100 (1995), the exhibits of which are incorporated herein by reference.

The joint compound of the invention can use either the α-hemihydrate form or the β-hemihydrate form of calcium sulfate. The a-hemihydrate form, which has a relatively low water demand, is preferably used in the production of higher strength joint compounds. Because α-hemidrate and β-hemihydrate differ in physical properties (as a result of different manufacturing processes), joint compounds including these forms may have different properties. Those skilled in the art will be able to make modifications based on the disclosure of the invention. The joint compound of the invention may also include one or more secondary filler or filler materials such as mica, talc, and various clays, including pyrophyllite, sericite, and / or diatomaceous earth. The limestone, other filler or secondary filler preferably has a particle size within the range of about 20 to about 25 microns. As stated above, the setting joint compound of the invention includes an agent to retard setting thereof. The retarding agent of the invention is a polymeric composition which includes acrylic acid and acrylamide monomer units, for example (a) a copolymer (or a mixture of copolymers) of acrylic acid and acrylamide or (b) a mixture of a homopolymer of acrylic acid and an acrylamide homopolymer. Thus, when the terms polymeric composition and / or retarding agent are used herein, they are intended to refer to either (a) the copolymer (s) or (b) the aforementioned homopolymer mixture including mixtures of the same. The preferred retardation agent included in the joint compound at a rate within the range of about 0.6 percent to about 4 percent by weight based on the total weight of the calcium sulfate hemihydrate in the joint compound formulation and more preferably within the range of from about 0.6 to about 1.4 weight percent. The preferential retarding agent is included at a rate of at least about 0.8 weight percent based on the total weight of the calcium sulfate hemihydrate in the joint compound formulation, in order to provide the maximum benefits. The preferred retarding agent for the invention is sold under the trade name Colloid 231 by Rhdne-Paulenc Inc., of Danbury, Connecticut, the product data bulletin and the material data security sheets of which are incorporated in the present by reference. Colloid 231 has a molecular weight of about 4300 and a specific gravity of about 1.3 at 25 ° C. A less preferred but useful retarding agent is sold under the trade name Colloid 230 by Rhéne-Poulenc Inc. Colloid 231 is preferred in relation to Colloid 230 due to Colloid 231 having higher potency. Other copolymer solutions include Colloid 211 and Colloid 107 sold by Rhone-Poulenc Inc., as well as Acumer 9141 sold by Rhome & Haas Co. of Philadelphia, Pennsylvania. The molecular weight of the retarder agent copolymer preferably falls within the range of about 1700 to about 6500. The retarding agent including both acrylamide monomer units and acrylic acid (either a copolymer or homopolymer blend) preferably includes from about 50 percent to about 99.9 percent acrylic acid and from about 0.1 percent to about 50 percent acrylamide by weight, and most preferably from about 95 percent to about 98 percent by weight of acrylic acid and about from 1 percent to about 5 weight percent acrylamide and more preferably from about 95 percent to about 98 weight percent acrylic acid and from about 1 percent to about 2 weight percent acrylamide. When the retarding agent is a mixture of an acrylic acid homopolymer and an acrylamide homopolymer, the composition preferably includes (a) low molecular weight polyacrylic acid having a molecular weight in the range of about 1500 to about 5000, and (b) polyacrylamide having a molecular weight within the range of about 1500 to about 7000. Although the invention is not limited to any specific mechanism, it is believed that the retarding agent is absorbed onto the surface of the hemihydrate sulfates avoiding any reaction between the sulfates of the hemihydrate and the water present in the premixed composition. The use of the retarder is also advantageous use in the manufacture it will prevent the mixture of the joint compound from solidifying in the mixer or in the pipe used in commercial operations. It has also been found that the acrylamide portion of the retarder of the invention also provides an initial stiffening effect which helps to improve uniform mixing and rheology of the joint compound both during manufacture and during use of the joint compound. the invention.

Another ingredient of the preferred joint compound of the invention is a non-leveling agent. The non-leveling agents impart certain rheological properties to the joint compound, including thixotropicity. The non-leveling agents also act as viscosity stabilizers. A preferred non-leveling agent is clay attgel, which is included within the range of about 0.5 percent to about 5.0 percent based on the total weight of the composition. Other suitable non-leveling agents are known in the art and include various other clays including bentonite as well as clays mixed with starches. Thickeners such as those described below also function as non-leveling agents. The joint compound of the invention also preferably includes a thickener. Suitable thickeners include methylcellulose, hydroxypropyl methylcellulose, hydroxyethylcellulose, hydroxyethylmethylcellulose and sodium carboxymethylcellulose including combinations thereof. The preferred thickener is Methocel 240S which can be obtained from the Dow Chemical Company of Midland, Michigan. Methocel 240S is a hydroxypropylmethylcellulose. The thickener is preferably included in the composition at a ratio within the range of about 0.12 percent to about 1.0 percent by weight based on the weight of the total composition. The joint compound preferably also includes a plasticizer. The plasticizers provide better adhesion to the substrate in a cold climate and are preferably included at from about 0.02 percent to about 1.0 percent based on the total weight of the composition. Useful plasticizers include dibutyl phthalate which can be obtained from Kalama Chemicals of Seattle, Washington. The dibutyl phthalate is preferably added to the composition of the joint compound within the range of about 0.2 percent to about 0.8 percent, based on the total weight of the composition. A suitable plasticizer is sold under the trade name Benzoplex by Velsicol Chemical Corp. of Memphis, Tennessee. The set premixed joint compound of the invention may also include the following ingredients: defoamers, wetting agents, preservatives, fungicides and binders, in a usual amount from about 0.1 percent to about 50 percent by weight of the composition. As mentioned above, in order to promote or accelerate the setting of the premixed joint compound, a compound or accelerator is added to the compound just prior to use. The amount of the accelerator is generally based on the amount of the calcium sulfate hemihydrate and the retarder in the formulation. Accelerators are preferably added in an amount within the range of from about 0.1 percent to about 5.0 weight percent, and more preferably from about 0.1 percent to about 2.0 weight percent, based on the weight of the hemihydrate calcium sulfate in the composition of the joint compound. It has been found that when 1.0 weight percent of the retarder is used, preferably an accelerator having a concentration of at least about 10 mM (millimoles) is used; more preferably, at least about 12.5 mM or at least about 13.5 mM, and still more preferably at least about 15 mM and especially preferably from about 18 to about 20 mM. Suitable accelerators include metal salts that provide acidic cations, such as aluminum sulfate, potassium sulfate, calcium sulfate, ferric sulfate, and ferric chloride. Aluminum sulfate, Al2 (S0) 3, for example in an aqueous solution having a concentration of about 1 percent to about 47 percent by weight, is the preferred accelerator. Accelerators particularly useful for commercial scale production include the following: (1) aluminum sulfate (also referred to as "paper-making alum", "liquid alum" or (aluminum sulfate liquid), supplied by example, by Peridot Chemicals Inc. of Wayne, New Jersey; Cytec Industries Inc. of West Pattersn, New Jersey; and Industrial Chemical of Armonk, New York; (2) Aluminum potassium sulfate which is a double salt supplied, for example by Holland Chemical Company of Adams, Massachusetts; (3) ferrous sulfate (in powder or liquid form); and (4) ferric chloride (in powder or liquid form) supplied for example by J.T. Baker Chemical Company of Philadelphia, New Jersey. Through the addition of cations such as Al + 3, the calcium sulfate hemihydrate will be converted to the dihydrate form. Although the invention is not limited to any specific mechanism it is believed that the accelerators desorb or neutralize the retarder from the surface of the hemihydrate sulfates, allowing the dihydrate sulfate to react with the water to form calcium sulfate dihydrate, i.e. , the hydrated form of calcium sulfate.

Without the addition of an accelerating agent, the joint compound of the invention will dry just like a conventional premixed joint compound. Therefore, a single formulation of the joint compound of the invention can optionally be used as a joint compound of the setting type or type of drying. Even without the use of an accelerator, the joint compound of the invention has less shrinkage and dries more quickly than conventional drying type joint compounds. See Table VIII below. The general scales of ingredients used in the conventional weight joint compound for all purposes of the invention include the ingredients shown in Table I below.

TABLE I - COMPOSED FOR CONVENTIONAL WEIGHT BOARDS Ingredient% in Weight Water from 20 to 37 Preservatives from 0.02 to 1.0 Retarder from 0.05 to 2.0 Calcium Sulphate Hemihydrate from 10 to 100 Mica (filler or filler) from 0.5 to 5.0 Attagel's Clay (non-leveling agent) from 0.5 to 5.0 to Cellulose Thickener from 0.12 to 1.0 Latex (Binder) from 1.0 to 4.0 Accelerator from 0.01 to 2.0 The joint compound of the invention can also be formulated as a light weight joint compound having a density, for example, within the range of about 960 to about 1320 grams per liter, as opposed to about 1320 to about 1680 grams per liter. liter for compounds for conventional weight joints. Table II below shows the general ingredient scales for preferred lightweight gasket compounds of the invention.

TABLE II - COMPOSITE FOR LIGHTWEIGHT WEIGHTS Ingredient% in Weight Water from 20 to 30 Preservative from 0.01 to 1.0 Retarder from 0.01 to 1.0 Calcium Sulphate Hemihydrate from 10.0 to 100 Limestone (Filling or loading material) from 10.0 to 50.0 Attagel clay (non-leveling agent) from 0.5 to 4.0 Perlite (Filler Material or Light Weight Load) from 1.00 to 10.0 Thickener (s) from 0.10 to 1.0 Latex (Binder) from 1.00 to 4.0 Accelerator from 0.01 to 2.0 Mica from 1 to 4 Talc from 0.5 to 3 It has been found that the joint compound of the invention has reduced water absorption, therefore a smaller amount of water is required to be used in the original mixture when compared to conventional pre-mixed joint compounds. For example, the conventional premix typically uses from about 33 percent to 34 percent by weight of water, while the joint compounds of the invention preferably use from about 29 percent to about 31 percent by weight of water in the original mix This facilitates a reduction in shrinkage of the joint compounds of the invention.

In Table III presented below, two exemplary formulations of the invention are shown that fall within the scales disclosed in the foregoing. The formulation of Example 1 has a density of approximately 13.4 and the formulation of Example 2 has a density of approximately 13.2.

TABLE III Ingredient Example 1 Example 2% by weight% by weight Calcined Plaster (Hemihydrate) 59.77 59.77 Polyvinyl Alcohol 1.0 1.0 Methocel 240S 0.35 0.35 Talc Tc-100 3.0 3.0 Attagel M8113 2.0 2.0 Colloids 231 (Copolymer) 0.5 0.5 Glycol 0.1 0.10 Dicaperl HP 610 0.15 Water 33.2 33.0 The viscosity of the joint compound of Example 1 is within the range of about 490 BU (brabender units) about 550 BU, and the viscosity of the joint compound of Example 2 is within the range of about 550 BU to about 600 BU. (As will be understood by those skilled in the art, the viscosity of the joint compounds is at the lower end of the aforementioned scales after remixing). The viscosity of the conventional weight joint compounds of the invention, generally, they fall within the range of approximately 400 to approximately 700 brabender units, while the viscosity of lightweight joint compounds will generally be within the range of 350 BU to approximately 700 BU. The lightweight filler or filler material used in the lightweight joint compounds of the invention may be an expanded pearlite treated with silicone or silane. The appropriate beads can be obtained from Silbrico Corp., Hodgkins, Illinois and Grefco Inc. of Torrance, California. The lightweight gasket compound preferably also includes talc and / or mica as secondary fillers or fillers.

The binder provides sufficient bond strength and better adhesion of the joint compound to the substrate (e.g., the pressed fiber board). The binder is preferably a latex or polyvinyl alcohol. Preferred latex binders are sold by Air Products and Chemicals Inc. of Allentown, Pennsylvania under the tradenames Airflex 526, Airflex 528 and Reichhold Chemicals Inc. of Research Triangle Park, North Carolina, under the name Reichhold 40716. It can also the polyvinyl alcohol from Air Products and Chemicals Inc. is obtained. Proper latex suppliers also include: National Starch from Bridgewater, New Jersey and Fuller Chemical Company of St. Paul, Minnesota. Mica suitable for use with the invention can be obtained, for example, from Sparton Mica Company of Pacolet, South Carolina and Franklin Minerals of Nashville, Tennessee. Suitable preservatives are sold, for example, under the trade names Troysan 364 and Troysan 174 by Troyu Chemicals of East Hanover, New Jersey. Attagel Clay M8113, a preferred non-leveling agent is supplied from Engelhard Corp. of Iselin, New Jersey. Supergel B obtainable from the Millwhite Company of Houston, Texas is an alternative to Attagel M8113. An example of a preferred embodiment of the invention will now be described in conjunction with the production of a set-type premixed joint compound.

EXAMPLE III In Example III, a joint compound was made in accordance with the method of the invention on a commercial scale. The ingredients used to make the joint compound are shown in Table IV-A, which is presented below.

TABLE IV-A - FORMULATION OF EXAMPLE III Ingredient Weight in kilograms Water 805.85 Troysan 174 1.36 Troysan 364 0.23 Defoamer [Nopco 9201] 1.36 Colloid 231 7.26 Stucco Calibrator 658.30 Limestone 1089.60 Clay 8113 22.70 Mica 5290 45.40 Methocel 240S 9.08 Polyvinyl Alcohol 9.08 Premix of Glycol (10 kilograms) and Flocculant (0.22 kilograms) 10.22 Latex 22.70 TOTAL 2683.14 The defoamer, Troysan 174/364, Methocel 240S (thickener), latex (Ucar 133), polyvinyl alcohol, flocculant, glycol and Colloid 231 (retarder) were pre-weighed and then separated. The pre-weighed amount of the flocculant was added to the pre-weighed glycol followed by mixing for several minutes. Approximately 18,925 liters of water were added followed by mixing for several minutes. In the mixing operation (using a fine dust collection apparatus) 227 liters of water were added to the mixing apparatus while mixing followed by the addition of the defoamer, Colloid 231 and preservation agent to the mixer. The mixing was continued for approximately two minutes.

The following was added to a pig feeder (a hopper that has a screw conveyor that carries the materials to the mixer) in the following order: calcium sulfate hemihydrate, mica, methocel 240S (thickener), polyvinyl alcohol and attagel clay M8113. The pig feeder and the limestone feeder were started. After all the dry ingredients had been added to the mixer, stirring was continued for five minutes. The premix of the flocculant (described above) was then added followed by stirring for an additional three minutes. The latex was added followed by stirring for three minutes. The water was then added to achieve the final desired viscosity (between 400 and 700 BU). The product was then transferred to a holding tank. The joint compound of Example III was found to have the properties listed below.

TABLE IV-B Property Value Density 1584 grams / liter Final Viscosity 650 centipoises Open time 15 minutes (Without Accelerator) Shelf Life approximately two years Setting Time of 10 minutes with Accelerator 120 minutes EXAMPLE IV Another resin formulation was made in accordance with the method described above. The ingredients used to make the resin of Example IV are shown in Table V-A, which is presented below together with the approximate amounts.

TABLE V-A EXAMPLE IV Ingredient Weight in kilograms Water 2618.22 Troysan 174 4.99 Troysan 364 .45 Defoamer [Nopco 9201] 4.54 Colloid 231 23.61 Calibration Stucco 2133.80 Limestone 3541.20 Clay 8118 73.55 Mica 5290 147.52 Methocel 240S 29.51 Polyvinyl Alcohol 29.51 Premix of Glycol (32.70 kilograms) and Flocculant (0.70 kilogram) ) 33.40 Latex 73.55 TOTAL 8713.85 The joint compound of Example IV was found to have the properties listed in the table below.

TABLE V-B Property Value Density 1680 grams / liter Viscosity Final 700 BU Open time 15 minutes (Without Accelerator) Setting Time of 10 minutes a with Acceleration 120 minutes EXAMPLE V Another joint compound was made in accordance with the formulation shown in Table VI, which is presented below.

TABLE VI - EXAMPLE V Ingredient Weight in kilograms Water 2633.20 Troysan 174 2.50 Troysan 364 .45 Defoamer 2.50 Retarder (Colloid 231) 24.52 Calibration Stucco (sieved with 100 mesh) 2065.70 Limestone 3495.80 Clay Attagel 68.10 Mica 136.20 Thickener (Methocel 240S) 22.70 Binder (Polyvinyl Alcohol) 22.70 Glycol 27.24 Flocculant (Separate) 1.38 Latex (UCAR 133) 56.75 TOTAL 8559.72 EXAMPLE VI In order to test the application properties of the invention, two joint compounds were made according to the following formulations. The joint compound of Example VI-A (Table VII) was a conventional weight joint compound and the joint compound of Example VI-B (Table VIII) was a light weight joint compound.

TABLE VII - EXAMPLE VI-A Ingredient% by weight Weight in kg Water 30.1 61.29 Troysan 174 0.05 .10 Troysan 364 0.009 .05 Defoamer 0.05 .09 Retarder (Colloid 231) 0.271 .55 Calcium Sultanate Hemihydrate (Stucco) 24.5 49.94 Limestone 40.0 81.72 Clay (Attagel 8113) 0.85 1.74 Mica 1.70 3.48 Thickener (Methocel) 0.34 0.69 Binder (PVOH) 0.34 0.69 Ethylene glycol 0.38 0.78 Flocculant (Retent) 0.016 .03 TOTAL 98.6 201.15 TABLE VIII - EXAMPLE VI-B Ingredient% by weight weight in kg Diethylene glycol .058 .86 Water 26.85 42.68 Defoamer 0.085 .08 Troysan 364 0.025 .04 Troysan 174 0.05 .06 Retarder (Colloid 231) 0.245 .34 Stucco (mesh -100) 28.57 45.4 Limestone Stone 27.14 43.15 Mica 1.23 1.95 Clay (Attagel 8113) 1.23 1.95 Perlite (Silbrico 42 -23) 3.43 5.45 Thickener (Methocel 40320) 0.48 0.77 Latex 3.65 5.81 Water 6.9 11.08 TOTAL 99.94 159.60 Five batches of each joint compound of Example VI were made according to the invention. The joint compound of Example VI-A was found to have the following properties: viscosity - 630 BU, shrinkage upon setting - 3.0 percent, solids - 67.00 percent and density - 1596 grams per liter. The joint compound of Example VI-B was found to have the following properties: viscosity 490 BU, viscosity after 24 hours - 520 BU, shrinkage upon settling 2.4 percent, solids - 60 percent and density - 1284 grams per liter. In order to test the application properties of the joint compound, the compound was applied to the pressed fiber board by seven different applicators in a fabricated housing plant. The following comments related to the joint report were made during the test: easily mix with the accelerator - it is easy to apply uniform consistency setting time easily set with an accelerator less waste than the dry joint compound current dry working area cleaner high coverage The product was able to provide fast setting times, smooth finish, and more coverage when compared to the powder setting joint compound sold commercially by the dealership of this application. The setting time of the batches was consistently about 10 minutes. No visible signs of cracking or shrinkage were seen for the joint compounds. All applicators preferred the joint compound of the invention in relation to the powder setting joint compound commercially available from the concessionaire. The joint compounds of the invention have several advantages over known joint compounds. It was first found that the joint compound of the invention when used with one of the accelerators of the invention can allow a very fast setting time, for example, of about 10 to 15 minutes, while also providing high strength and stability during the storage.

The reduced setting time (and drying) of the joint compound is one of the main advantages of the invention. The short setting time of the joint compound of the invention, makes it especially suitable for use in fabricated home construction plants, throughout the setting time of the joint compound, is particularly crucial. The short setting time also allows multiple layers of the joint compound to be completed at the work site in one day, while prior art drying joint compounds may require delays of hours or days between the layers. There is also a considerable decrease in the time required for drywall finishing and many jobs can be completed in a single day. In addition, the joint compound of the invention is less brittle and more flexible than many prior art joint compounds. This property also makes the invention particularly suitable for use in building manufactured houses because the transportation of frequently manufactured houses can result in cracks in the application areas of the joint compound. When changing or transporting fabricated houses having walls fabricated with the joint compound of the invention, there must be little or no cracking.

Other advantages of the joint compound of the invention include improved application characteristics, excellent adhesive properties, excellent coating properties and reduced shrinkage compared to conventional dry powder setting compounds and conventional premixed joint compound. The application properties (including wet tack and stability) of the joint compounds of the invention have been found to be excellent. Because the adhesive joint compound of the invention can be made to harden quickly, not only is there a considerable decrease in the time required for drywall construction of gypsum, but there is also less shrinkage, especially that of the associated delayed type with the use of conventional pre-mixed joint compounds. This significantly reduces the cost and time required to re-finish or re-decorate surfaces when these problems are encountered. The shrinkage of the joint compound of the invention is often about 2 weight percent. The following table compares the typical shrinkage properties of the premixed setting gasket compound of the invention as compared to already mixed gasket compounds for all commercially obtainable purposes. The shrinkage varies with the different conditions, such as the drying temperature, humidity, particle size of the filling or loading materials and properties of the raw material.

TABLE IX - SHRINKING PROPERTIES Invention with the Invention without the use of an accelerator accelerator ELEVATED 4 percent by weight 15 percent by weight AVERAGE 3 percent by weight 14 percent by weight LOW 2 percent by weight 12 percent by weight TABLE IX (CONTINUED) Ready mix Conventional conventional dry powder type of commercial setting ELEVATED 20 percent by weight 15 percent by weight AVERAGE 18 percent by weight 12 percent by weight LOW 16 percent by weight 10 percent by weight The joint compound of the invention can also serve to reduce the number of layers of the joint compound required to complete a job, for example, by reducing from 3 to 2. The setting time of the joint compounds of the invention falls within the scale from about 10 minutes to about 120 minutes depending, for example, on the specific formulation and the ambient conditions. A joint compound having a setting time of less than 10 minutes can be formulated from the disclosure of the present invention; however, these setting times are usually not required in the application of the commercial joint compound. The open time of the joint compounds of the invention depends on whether an accelerator is used. The accelerated joint compound should be used, however, within the setting times discussed herein. The non-accelerated joint compounds of the invention have open times similar to conventional mixed joint compounds, e.g., 10 to 20 minutes. Because it is already mixed, the joint compound of the invention reduces mixing time, improves quality control of the product at work sites and reduces the time required for on-site applicator consultation. The soaking time of the dry powder setting compound (the time in which it is generally required to wait between mixing the dry powder and using it) is likewise eliminated. The joint compounds of the invention also provide a bond or bond superior to the substrate when compared to conventional joint compounds. The joint compound formulations disclosed herein can be used either as a mixed-type joint compound or can be easily mixed with the accelerator without the need for additional water. Even when the joint compound is used as a drying type joint compound without the accelerator, the joint compound can provide good crack resistance with low shrinkage. The foregoing detailed description is provided for clarity of understanding only and unnecessary limitations should not be understood, since modifications within the scope of the invention will be apparent to those skilled in the art.

Claims (32)

R E I V I N D I C A C I O N E S:

1. A composition of the joint compound of the ready-mixed setting type suitable for use to hide joints between the edges of adjacent pressed fiber panels, the composition of the joint compound comprises: (a) calcium sulfate hemihydrate; (b) sufficient water to adjust the viscosity of the composition to make the composition suitable for use to hide joints between the edges of adjacent pressed fiber panels; and (c) a setting retarding agent comprising a polymeric composition including acrylic acid and acrylamide monomer units.

2. The composition according to claim 1, wherein the polymer composition is a copolymer of acrylic acid and acrylamide.

3. The composition according to claim 1, wherein the polymer composition is a mixture of an acrylic acid homopolymer and an acrylamide homopolymer.

The composition according to claim 1, wherein the setting retarding agent is present in an amount from about 0.6 percent to about 4.0 percent by weight based on the weight of the calcium sulfate hemihydrate.

The composition according to claim 4, wherein the setting retarding agent is present in an amount from about 0.

6 percent to about 1.4 percent by weight based on the weight of the calcium sulfate hemihydrate. The composition according to claim 1, wherein the setting retarding agent has a molecular weight in the range from about 1700 to about 6700.

7. The composition according to claim 1, further comprising an agent to accelerate the setting of the composition, the agent comprises a metal salt consisting of acidic cations.

The composition according to claim 7, wherein the accelerating agent is present in an amount from about 0.1 percent to about 2.0 percent by weight, based on the weight of the calcium sulfate hemihydrate.

The composition according to claim 1, further comprising: limestone, a non-leveling agent, a thickener, a plasticizer, a preservative and a binder.

The composition according to claim 1, further comprising: (1) a lightweight filler or filler material comprising treated expanded pearlite particles and (2) mica; and the composition has a density of about 1320 grams per liter.

The composition according to claim 1, wherein the composition has a setting time of about 20 minutes or less.

The composition according to claim 1, wherein the composition shrinks upon setting at about 10 volume percent or less.

The composition according to claim 1, wherein the composition shrinks on setting at less than about 5 volume percent and has shelf life of at least one year.

14. A kit having component parts capable of producing a composition of the joint compound of the ready-mix type, the kit consisting of: (a) a premixed composition comprising (1) calcium sulfate hemihydrate; (2) sufficient water to adjust the viscosity of the composition to make the composition suitable for use to hide joints between the edges of adjacent pressed fiber panels; and (3) a setting retarder agent comprising a polymer composition including acrylic acid and acrylamide monomer units; and (b) an agent for accelerating the setting of the composition (a), the accelerating agent comprises from about 0.1 percent to about 5.0 weight percent of the weight of the calcium sulfate hemihydrate.

15. A method for producing a composition of the joint compound suitable for concealing joints between the edges of adjacent pressed fiber panels, the method comprising the steps of: (a) combining, to provide a cementitious composition of a premixed setting type, (1) a first material comprising calcium sulfate hemihydrate; (2) sufficient water to adjust the viscosity of the cementitious composition to make the cementitious composition suitable for use to hide joints between the edges of adjacent pressed fiber panels; and (3) a setting retarding agent comprising a polymeric composition including acrylic acid and acrylamide monomer units; and (b) combining an accelerating agent to accelerate the setting of the cementitious composition with the product of step (a), the accelerating agent comprising a compound selected from the group consisting of aluminum sulfate, potassium sulfate, calcium sulfate , ferric sulfate and ferric chloride; and wherein: the set retarding agent is present in an amount from about 0.6 percent to about 4.0 percent by weight based on the weight of the calcium sulfate hemihydrate.

The method according to claim 15, wherein: the accelerating agent comprises from about 0.1 percent to about 5.0 weight percent of the weight of the calcium sulfate hemihydrate.

17. A composition of the premixable joint compound suitable for use to hide joints between the edges of adjacent pressed fiber panels, the composition of the joint compound comprising: (a) calcium sulfate hemihydrate; (b) sufficient water to adjust the viscosity of the composition; (c) a setting delay agent comprising a polymeric composition including acrylic acid and acrylamide monomer units; and (d) an accelerating agent comprising a metal salt consisting of acidic cations.

18. The composition according to claim 17, wherein the polymer composition is a copolymer of acrylic acid and acrylamide.

The composition according to claim 17, wherein the set retarding agent is present in an amount of 0.6 percent to about 4.0 percent by weight based on the weight of the calcium sulfate hemihydrate.

The composition according to claim 17, wherein the setting retarding agent is present in an amount from about 0.6 percent to about 1.4 percent by weight based on the weight of the calcium sulfate hemihydrate.

The composition according to claim 17, wherein the setting retarding agent has a molecular weight within the range of about 1700 to about 6700.

22. The composition according to claim 17, wherein the accelerating agent is present in an amount from about 0.1 percent to about 5.0 percent by weight based on the weight of the calcium sulfate hemihydrate.

The composition according to claim 17, wherein the accelerating agent comprises a compound selected from the group consisting of aluminum sulfate, potassium sulfate, calcium sulfate, ferric sulfate and ferric chloride.

The composition according to claim 17, further comprising: limestone, a non-leveling agent, a thickener, a plasticizer, a preservative and a binder.

The composition according to claim 17, further comprising: (1) a lightweight filler or filler material comprising treated expanded pearlite particles and (2) mica; and the composition has a density of about 1320 grams per liter or less.

26. The composition according to claim 17, wherein the composition has a setting time of about 20 minutes or less.

27. The composition according to claim 17, wherein the composition shrinks when set at a rate of about 10 volume percent or less.

28. A method for hiding seams between the edges of adjacent fiberboard panels, the method comprising the steps of: (A) providing a cementitious, screeable composition comprising: (1) calcium sulfate hemihydrate; (2) water; and (3) a setting delay agent comprising a polymeric composition including acrylic acid and acrylamide monomer units; (B) combining the cementitious composition with an amount of an accelerating agent to accelerate the setting of the cementitious composition, the accelerating agent comprising a metal salt including acidic cations and the amount remaining within the range of about 0.1 to about 5.0 percent by weight based on the weight of calcium sulfate hemihydrate; and (C) applying the product of step (B) to one of the edges.

29. The method according to claim 28, wherein the setting retarding agent comprises from about 0.6 percent to about 4.0 percent of the weight of the calcium sulfate hemihydrate.

The composition according to claim 28, wherein the setting retarding agent has a molecular weight within the range of about 1700 to about 6700.

31. A method for producing a suitable joint compound composition to hide together between the edges of adjacent pressed fiber panels, the method comprises the steps of: (a) combining to provide a pre-blended settable cementitious composition, (1) calcium sulfate hemihydrate; (2) sufficient water to form a slurry with the calcium sulfate hemihydrate; (3) a filler or filler material that is selected from the group consisting of limestone, calcium sulfate dihydrate and mixtures thereof; and (4) a setting retarder agent comprising a polymer composition including a copolymer of acrylic acid and acrylamide; and (b) combining an accelerating agent to accelerate the setting of the cementitious composition with the product of step (a); and wherein: the setting retarding agent is present in an amount of from about 0.6 percent to about 4.0 percent by weight based on the weight of the calcium sulfate hemihydrate and the accelerating agent is present in an amount of about 0.1 per cent. 100 to about 5.0 weight percent based on the weight of the calcium sulfate hemihydrate and comprises a compound selected from the group consisting of aluminum sulfate, potassium sulfate, calcium sulfate, ferric sulfate and ferric chloride.

32. The composition according to claim 31, wherein the setting retarding agent has a molecular weight within the range of about 1700 to about 6700.