MXPA01008257A - Method of continuous production for wallboard tape joint compound - Google Patents

Abstract

A method of continuously producing a cementitious composition such as joint compound includes pre-mixing at least two dry ingredients and pre-mixing at least two liquid ingredients. The ingredients are provided in a continuous mixing apparatus and at least substantially continuously blended.

Description

CONTINUOUS PRODUCTION METHOD FOR A COMPOSITE OF TAPE BOARD FOR WALL BOARD BACKGROUND OF THE INVENTION FIELD OF THE INVENTION The present invention relates generally to the production of cement compositions, and more particularly to the production of compounds for filling and coating joints between adjacent gypsum wallboard sheets, for repairing imperfections in building materials, and for texturing.

DESCRIPTION OF RELATED TECHNOLOGY One of the most common methods today for building interior walls includes the use of inorganic wallboard panels or sheets such as gypsum wallboard, usually referred to simply as "wallboard" or "drywall". The use of a wallboard, contrary to conventional wet plaster methods, is often desired since the installation of the wallboard is ordinarily less expensive and faster than that of conventional plaster. The wall board is conventionally produced by enclosing a core of an aqueous suspension of gypsum and other additive materials, between two large sheets of paper. After the gypsum suspension has been placed and dried, the sheet is cut into standard sizes. Gypsum wallboard is described, for example, in the Kirk-Othmer encyclopedia of Chemical Technology, second edition, 1970, vol. 21, pages 621-24, the description of which is incorporated herein by reference. A wall is generally made by securing, for example, with screws and / or nails, the wall board to a support structure, for example, pieces of wood oriented vertically or horizontally. Since the wall board is typically supplied in sheets or panels of standard size, when a wall is formed from the sheets, there will generally be a number of joints between adjacent sheets. In most wallboard constructions, it is necessary to hide these joints between adjacent panels so that the wall will have a smooth, monolithic finish similar to that obtained with conventional wet plaster methods. It is also necessary, typically, to hide the screws and / or nails used to secure the panels of the wall board to the construction, the projections caused by the screws and / or nails, imperfections in the panels of the wall board, as well as other materials (for example defense) used to form the wall. The prior art discloses a number of compositions of the joint compound (sometimes referred to by applicants as "mud") which can be used to conceal the joints between the adjacent sheets of the wall board. Said compositions can also be applied to other defects in the wall board, for example the defects or depressions caused by the screws or nails used to keep the wall board in place. To hide the joints between the panels of the wall board, the joint compound is typically applied in several layers or coatings. A first layer of the joint compound is placed on the joint between the wall boards with a wallboard knife, or mason's spoon. The first coating is mainly made for the purpose of filling the space between the adjacent wall panels. The tape of the board (for example, made of paper) can then be embedded in the first composite coating of the board. It is conventional to apply the joint compound in many, for example, three, coatings or layers to obtain a smooth finish, and each coating of the joint compound must be allowed to dry before the next coating of the joint compound is placed. (If the above coating is not allowed to dry, problems such as excessive shrinkage and / or cracking may occur). Once it is dry, the treated area is sanded before applying the next finishing coating of the joint compound. The joint compound can be used for other uses, for example, to repair imperfections in various construction materials and to add texture to walls and ceilings. There are many different types of joint compounds. The compounds of the joint can be supplied as a dry powder or in a ready-to-mix form mixed in a mill. They can also be of the "drying" type or a "setting" type. The joint compound can be supplied in the form of a dry powder, to which a quantity of water is added at the work site by the applicants to give the joint compound a suitable consistency. Other gasket compounds, often referred to as "ready to mix" or "already mixed" gasket compounds, are pre-mixed with water and other additives during the manufacture of the product. These joint compounds are usually packaged and sold in a corrugated box or plastic bucket in a form that is suitable for use with little or no water addition at the job site. The already mixed joint compound has many advantages such as providing a consistent product formulation, reducing to eliminate the time necessary to mix the joint compound with water at the job site, and eliminating the need to have water available in the workplace. the work site Among the prior art gasket compound compositions, it is known that a filler (for example, calcium carbonate, calcium sulfate hemihydrate or calcium sulfate dihydrate), thickener, preservative and a binder, as well as other additives are generally used. produce a joint compound. See the patent of E.U.A. No. 5,653,797 whose description is incorporated herein by reference. The general ranges of ingredients used in a very useful conventional weight board compound include the ingredients shown in Table 1 below.

TABLE I Compound of the conventional weight board Ingredient Percent by weight Water 20-37 Preservatives 0.02-1.0 Calcium carbonate 10-100 Mica (filler) 0.5-5.0 Attagel clay (non-leveling agent) 0.5-5.0 Cellulose thickener 0.12-1.0 Latex (binder) 1.0-4.0 Accelerator 0.01-2.0 Many of the compounds of the board are of the "drying" or "setting" type. A large portion of a joint compound of the drying type, comprises calcium carbonate (CaCO3) and / or calcium sulfate dihydrate (CaS0 -2H20). Before use (generally during manufacture), these components and a binder (together with many other known ingredients) are mixed for a specific time with water. After application, when the water dries (ie evaporates) a relatively hard dry cement material is left behind. The calcium sulfate dihydrate and the calcium carbonate may comprise a substantial portion of what is sometimes referred to as the filler component.

To avoid various drawbacks of the type of drying of the joint compound, the compounds of the "setting type" have been developed. A joint compound of the setting type includes a calcium sulfate hemihydrate (CaSO -1 / 2H2O, also referred to as calcined gypsum). (See U.S. Patent No. 5,653,797, previously incorporated herein by reference). To produce calcined gypsum, one converts calcium sulphate dihydrate from gypsum in raw state to hemihydrate state through a known procedure called calcination. This procedure removes one and one half of the water molecules from the calcium sulfate gypsum dihydrate. The hemihydrated form of calcium sulfate is substantially more soluble in water than the dihydrated form of calcium sulfate. The calcium sulfate hemihydrate may comprise a substantial portion of what is sometimes referred to as the filler component. During use in a compound of the setting gasket, the calcium sulphate hemihydrate is rehydrated to the dihydrate state. This rehydration procedure is usually carried out for a short period of time. Also, it is extremely difficult to produce a joint compound comprising hemihydrated gypsum since the product will be left in its storage container. In this way, the compounds of the joint of the setting type have generally had to be supplied in powder form. The compounds of the setting gasket have the advantage of having generally fast finishing times (setting time) than the compounds of the drying gasket. This is useful for the reasons stated above. In addition, since the compounds of the setting joint form a crystalline lattice in the setting (opposite only to the drying), these compounds typically provide a stronger, more durable bond between the adjacent wallboard sheets than the compounds of the board type of drying. However, since these compounds provide a stronger bond between the adjacent wallboard sheets, the joint compound is often harder to sand for a smooth finish. Although the industry has many types of joint compounds, joint compounds (particularly already mixed materials) are generally manufactured by the same type of process, a batch process. However, using a batch process to make the joint compound creates many drawbacks. First, the use of a batch procedure will limit the maximum production speed due to the longer mixing time and the need to complete one batch before starting the next. Secondly, the residence time in an apparatus used for the batch process can be high, which typically causes relatively longer production times. Third, in the batch mixing procedure, the accumulation of material typically occurs in mixers used for batch operations, resulting in prolonged unproductive times for cleaning, maintenance and contamination. Since the demand for the joint compound in the industry increases, it is desired to produce a joint compound, faster and more efficiently. It is also desired to provide a process for producing a product of the joint compound that does not vary from one batch to another. In addition, it may be useful to provide a more effective process for producing joint compound products that reduces or eliminates the need for certain ingredients, thereby reducing the cost and complexity of the manufacturing process.

BRIEF DESCRIPTION OF THE INVENTION It is an object of the invention to overcome one or more of the problems described above. Also, the invention provides a method for continuously producing a cement suspension, comprising the steps of premixing at least two dry ingredients, premixing at least two liquid ingredients, supplying the mixed dry ingredients and the mixed liquid ingredients in a continuous mixer, and at least substantially continuously mixing the ingredients in the mixer to produce the cement suspension.

Other objects and advantages of the invention will be apparent to those skilled in the art from the following detailed description, which is taken in conjunction with the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a process diagram of the dry powder ingredients used in accordance with the embodiment of the invention. Figure 2 is an alternative embodiment of a process diagram of the dry powder ingredients used in accordance with the invention. Figure 3 is a process diagram of the liquid ingredients used in accordance with one embodiment of the invention. Figure 4 is an alternative embodiment of a process diagram of the liquid ingredients used in accordance with the invention. Figure 5 is an alternative embodiment of a process diagram of the liquid ingredients used in accordance with the invention.

DETAILED DESCRIPTION OF THE INVENTION According to the invention, a method is provided for continuously producing a cement suspension comprising the steps of premixing at least two dry ingredients, premixing at least two liquid ingredients, supplying the mixed dry ingredients and the mixed liquid ingredients in a continuous mixer. , and at least substantially continuously mixing the ingredients in the mixer to produce the cement suspension. According to one embodiment of the invention, the continuous process usefully produces a cement suspension including about 25% to about 35% by weight of water, based on the total weight of the suspension. The cement compositions of the invention are generally produced by combining both dry solid ingredients and wet (liquid) ingredients. According to a preferred method of the invention, two or more of the dry ingredients or ingredients are premixed first in a mixing apparatus or mixer. These dry ingredients described in more detail below may include limestone, perlite, clay, mica, thickeners, binders, talc, gypsum (calcium sulfate dihydrate), stucco and urea. Although the term dry materials or ingredients may be used, those skilled in the art will understand that such materials may include absorbed or chemically combined moisture.

The liquid ingredients used in the method of the invention are preferably also premixed. In one embodiment, water and latex (eg, in the form of an emulsion) are premixed, although the remaining liquid ingredients (described in detail below) are premixed separately. In another embodiment, all liquid ingredients are premixed together. The liquid ingredients used in the production of the joint compound may include water, latex, glycol, dibutyl phthalate, preservatives, defoamers, and humectants. After the preferred premix step (s), both the dry ingredients and the liquid ingredients are simultaneously fed into a continuous mixing apparatus. This continuous mixing apparatus preferably operates on a scale of about 650 revolutions per minute (rpm) at about 1600 rpm, as described in detail below. The ingredients are mixed in the continuous mixer for a predetermined period (e.g., from about 0.35 to about 2 minutes), to form a uniform paste or suspension that then flows from the mixer. In a particularly preferred embodiment, all ingredients are fed continuously into the mixer, and the uniform paste produced or suspension is continuously extruded from the mixer. Referring now to both Fig. 1 and Fig. 2, the limestone, which can be stored in a silo 10, is transferred to a hopper-scale 12 (a storage or holding container). Limestone, which is the main ingredient in a joint compound of the invention, can be purchased at Georgia Marble of Kennesaw, Georgia, York Limestone of York, Pennsylvania, or Pfizer Limestone of New York, New York. The limestone in the joint compound of the invention preferably comprises at least 50% by weight and more preferably approximately 60% by weight to approximately 70% by weight, based on the total weight of the joint compound. The limestone is transferred from the scale hopper 12 by a pneumatic system 14 which mechanically conveys the limestone to the receiving container 16. The receiving container 16 is not assembled to scale, but preferably can automatically discharge the material on demand. The limestone is preferably transferred from the receiving container 16 to a feed hopper 20 by a second pneumatic system 18. The feed hopper 20 subsequently transfers the limestone to a mixer 22, where it is preferably premixed with other ingredients. The feed rate of the limestone is preferably on a scale of about 45.5 kg / min to about 181.8 kg / min. This feed rate, as well as other feed rates described below, are based on the weight (or mass) of the ingredient fed into a continuous mixing apparatus. Any type of controlled feeder can be used as the feed hopper. However, weight loss type feeders such as the Acrison feeders available from Acrison of Buffalo, New York, are preferred as they provide a feed accuracy of ± 0.5% by weight. In addition, the weight loss type feeders also continuously monitor the actual flow of the dry ingredients while they are discharged from the feeder. Alternatively, less expensive volumetric feeders with an accuracy of ± 2.0% by weight can also be used. These feeders do not monitor the actual power supply, but commercially available devices can be added to monitor the product to be supplied from the feeder. Some ingredients, such as thickeners, are available either in liquid form or in powder form. As described in more detail below, a liquid pump and a measuring system are preferably provided for the liquid ingredients. Computer controls are preferably provided to regulate the amount and speed of feeding the ingredients. Now in relation to other preferred ingredients, pearlite, clay, and mica are generally supplied in bulk bags. Perlite is preferably used in the joint compound to control the density, shrinkage, and cracking resistance of the joint compound. Perlite such as expanded silicon perlite 43-34 available from Silbrico Corp. of Chicago, Illinois can be used. The amount of pearlite used in the joint compound produced according to the invention is preferably on a scale from about 1% by weight to about 6% by weight, based on the total weight of the joint compound. The feed rate of the pearlite is preferably on a scale of about 1.4 kg / min to about 2.7 kg / min. Nevertheless, perlite need not be used in conventional weight-binding compounds of the invention. The clay is preferably used in the joint compound of the invention as a non-leveling agent and / or a thickening agent that controls the viscosity or rheology of the final product. The clay also helps to improve or create the water retention properties of the joint compound. A clay such as Supergel B / Mil White clay available from Mil White of Houston, Texas can be used. The amount of clay used in the joint compound is on a scale of about 1% by weight to about 4% by weight, based on the total weight of the joint compound. The preferred feed rate ranges from about 0.45 kg / min to about 2.7 kg / min. Mica is also preferably included in the joint compound. Mica, which is a mineral of lower overall density is used as a filler, or diluent, and can be purchased from KGM Corp. of Kings Mountain, North Carolina. Mica also improves the crack resistance of the joint compound. The amount of mica used in the joint compound can vary on a scale of 1% by weight to about 4% by weight, based on the total weight of the joint compound, while the preferred feed rate is preferably found in a scale of about 0.45 kg / min to about 1.8 kg / min. Commercially available bulk bag unloaders for pearlite 24, clay 26 and mica 28 are preferably mounted on the floor of the production site to allow direct forklift service. These ingredients are transported to hoppers or retention receivers 30, 32, 34 mounted above the feed hoppers 36, 38, 40, respectively, which subsequently discharge the desired ingredient (s) into the mixer 22. In a preferred operation, the feeders 36, 38, 40 are located in a mezzanine above, and are capable of unloading the ingredients directly into the mixer 22. In another embodiment, the feeders 36, 38, 40 are mounted on the floor, and discharge the ingredients into a conveyor / elevator (not shown in the figures). Said transporter / elevator will then transfer the ingredients to mixer 22 located at another level. With feeders mounted on the floor, the procedure can be more efficient and less intense in terms of work. The other preferred small-quantity dry ingredients that are used in the present invention, such as thickener, binder, talc, and gypsum, are received in bags, totes, or fiber drums in paddles 42, 44, 46, 48. Thickeners they are used to control viscosity, affect rheology, and affect the water retention characteristics of the joint compound produced. Thickeners may include Methocel HPMC-40320 a product manufactured by Dow Chemical of Midland, Michigan, and products sold under the tradenames HEC Nexton-IP5A, IPSA, 3082R by Aqualon Chemical Company of Wilmington, Delaware, a division of Hercules Chemical. The amount of thickener used in the joint compound is preferably on a scale of about 0.1% by weight to about 5% by weight, based on the total weight of the joint compound. More specifically, the amount of the Methocel product used in the joint compound is preferably from about 0.1 wt% to about 1 wt%, based on the weight of the joint compound. The amount of HEC, IP5A, IPA and 3082R thickeners used in the joint compound can be on a scale of about 0.1% by weight to about 5% by weight, based on the total weight of the joint compound. The preferred feed rate of the thickeners is from about 0.045 kg / min to about 0.23 kg / min. The binders are preferably used in the composition of the joint compound for better bonding to the substrate such as the wall board. The binders used may include polyvinyl alcohol available from Air Products of Allentown, Pennsylvania. The binders are preferably included at a rate on a scale of about 0.1% by weight to about 0.4% by weight, based on the total weight of the joint compound, and the preferred feed rate is on a scale of about 0.027 kg / min at approximately 1.36 kg / min. The talc is preferably included in the joint compound to improve the application properties and also as a white diluting pigment. Talc, such as the Talerom or MP 45-26 product manufactured by Barretts Minerals Inc. of Dillon, Montana, can be used in the joint compound. The amount of talc used in the joint compound is preferably on a scale of about 1% by weight to about 4% by weight, based on the total weight of the joint compound, and the preferred feed rate is preferably from about 0.23 kg / min to about 1.36 kg / min. Some of the embodiments of the joint compound of the invention, together with the limestone, also include gypsum (calcium sulfate dihydrate). The amount of gypsum used in the joint compound is preferably on a scale of about 5% by weight to about 60% by weight (based on the total weight of the joint compound), and the preferred feed rate is from about 10 kg / min to about 100 kg / min. The compounds of the gasket of the invention may also include a calcium sulfate hemihydrate (calcined gypsum or stucco) at a preferred rate of about 50% by weight to about 80% by weight based on the total weight of the joint compound. Said joint compound including a calcined gypsum is typically referred to as a compound of the setting type joint, and preferably includes an established retarder as described in US Pat. No. 5,779,786, the disclosure of which is incorporated herein by reference. There are two alternative ways to transfer this small amount of dry ingredients such as thickeners, binders, talc and gypsum into the mixer when feeders are used. In one embodiment, as ilrated in Figure 2, these small amounts of ingredients are fed directly into the mixer 22. Otherwise, as shown in Figure 1, these small amounts of ingredients are transferred to the mixer via the hopper of feed 50, 52, 54, 56 (also referred to as feeders). There are two options in the method for using a feeder to transfer these small amounts of ingredients to the mixer as shown in Figure 1. In one option, the feeders 50, 52, 54, 56 are mounted in a mezzanine above the mixer 22 and discharging the ingredients into the mixer 22. For example, a forklift can place pallet or reel bags of these materials in the mezzanine and an operator can then manually fill the feeders 50, 52, 54, 56 from the bags or drums In another option, the feeders 50, 52, 54, 56 are mounted on a floor below the mixer 22. The small amount of ingredients is transferred from the feeders by means of a conveyor to the mixer 22 located in the mezzanine above the elevators. feeders. Again, in this mode, the operator manually feeds the feeders from the bags or drums. A dry powder mixer 22 is preferably used to pre-mix the dry ingredients before they simultaneously enter the aforementioned mixing apparatus with the liquids. This is done to ensure a homogeneous mixture of very small and large proportions of dry ingredients. Although any conventional mixer 22 can be used, tape mixers are preferred. Several mixers are commercially available. Figures 3 and 4 show two embodiments of the process diagrams of the liquid ingredients according to the method of the invention. Large-volume liquid ingredients such as latex 62, glycol 66 and water 60 are supplied directly from their respective storage tanks to a metering pump 82, 84 and 80, respectively. Glycol 66 is used in the joint compound to provide functional properties to the joint compound such as a wet edge, open time, controlled drying time, and freeze / thaw stability. Glycols 66, such as diethylglycol, manufactured by Dow Chemical Co. of Midland, Michigan, or ethylene glycol or propylene glycol are preferred. The amount of glycol 66 used in the joint compound is preferably on a scale of about 0.1% by weight to about 1% by weight (based on the total weight of the joint compound), while the feed rate preferred is from about 0.045 kg / minute to about 0.36 kg / minute. Latex 62, such as Air Flex 530BP manufactured by Air Products of Allentown, Pennsylvania, or Richhold 40716 manufactured by Rochhold Corp. of Raleigh, North Carolina, may be used in the joint compound. The additional latex that can also be used in the process according to the invention includes ethylene vinyl acetate, polyvinyl acetate emulsion, and vinyl acetate acrylate latex. The amount of latex 62 that is used in the joint compound is preferably on a scale of about 2% by weight to about 2.9% by weight (based on the total weight of the joint compound), while the speed of preferred feed is at about 1.3 kg / minute at about 2.3 kg / minute. The amount of water 60 that is used in the joint compound is preferably on a scale of about 25% by weight to about 35% by weight (based on the total weight of the joint compound), and more preferably of about 30% by weight to about 33% by weight. The amount of water based on limestone and other fillers is preferably on a scale of 30% by weight to about 32% by weight. The preferred flow rate of water is on a scale of about 0.37 liters / hour to about 3.78 liters / hour.

The liquid raw material ingredients are measured with a measuring pump ("MP") 80, 82, 84, 86, 88, 90, 92, 94 and a flow meter ("FM") 96, 98, 100, 110 , 112, 114, 116, 118 and an impeller (PLC) controlled so that a predetermined measured quantity of liquid is supplied to a continuous mixing apparatus or mixer 58. Since the liquids are mechanically fed, the levels of each liquid are they can precisely control and a high quality product can be manufactured. The measurement is preferably achieved with commercially available progressive cavity type pumps, where each pump is equipped with a magnetic flow meter and the pump system is controlled by a PLC. Each ingredient has its own pump measurement system, as shown in the figures, along with a spare pump operation (not shown) for the small amount of liquid ingredients. Pumps for the small amount of liquids preferably operate at about 0.0063 liters / hour to about 0.315 liters / hour. In one embodiment, as shown in Figure 4, the water 60 and the latex 62 are premixed in a mixer 64 before being mixed in an additional mixer 78 with the other liquid ingredients including giicol 66, di-butyl phthalate 68, preservative (s) 70, defoamer (s) 72, humectant (s) 74, and various optional liquid additives 76 (such as fungicide). Preferably, in the embodiment of Figure 4, the latex 62 is first placed in a bulk tank (not shown). The amount of latex transferred to be premixed with water is measured using a metering pump 82 and a flow meter 98. Likewise, water 60 is first placed in a holding tank (not shown). The amount of water required subsequently is measured using a metering pump 80 and a flow meter 96. The premeasured water and latex are subsequently premixed in the mixer 64 before being mixed with the other liquid ingredients in another mixer 78, as shown in FIG. established previously. The embodiment of Figure 3 does not use the premix of water 60 and latex 62. Generally, with regard to both Figure 3 and 4, the low volume liquid raw material ingredients, such as di-butyl 68 phthalate, conservator (s) 70, defoamer (s) 72, humectant (s) 74, and optional additive (s) 76, are supplied from a totalizer by means of a small receiver tank to be used during the change of the totalizer. One or more preservatives 70, such as Troysan 174 or Troysan 364, manufactured by Troy Chemical of Newark, New Jersey, may be included at a rate on a scale of about 0.005 wt% to about 0.008 wt% (based on total weight of the joint compound), while the feed rate is preferably about 0.0023 kg / min to about 0.0036 kg / min. A defoamer 72, such as the NXZ defoamer 9201A manufactured by Geo Chemical of Clas- trad, New Jersey, may be included at a rate of about 0.118% by weight to about 0.125% by weight (based on the total weight of the joint compound) , while the feed rate is preferably from about 0.045 kg / minute to about 0.057 kg / min. Generally, any hydrocarbon based or silicon based defoamer can be used. Di-butyl phthalate 68 such as K-Flex, product available from Van Water and Roger of Charlotte, North Carolina, may be included at a rate of from about 0.1 wt% to about 0.4 wt% (based on the total weight of the joint compound), while the feed rate is preferably about 0.45 kg / min to about 0.18 kg / min. A humectant 74, such as sorbitol available from Rogette Corp. of Gurnee, Illinois, may be included at a rate of about 0.01 wt% to about 0.05 wt% (based on the total weight of the joint compound), while the feed rate is preferably from about 0.045 kg / min to about 0.36 kg / min. Several additional additives (represented by element 76 in Figures 3 and 4) can also be included in the joint compound. Useful additives include polymeric materials such as low molecular weight polyacrylate sold under the trade name Colloid 231 by Rhodia of Danburry, Connecticut, as discussed in the co-pending US application commonly assigned serial number 08 / 779,938, the description of which is incorporated herein by reference. The amount of additional additive (s) 76 used in the joint compound is preferably from about 0.2 wt% to about 0.8 wt% (based on the total weight of the joint compound), while the feed rate preferred is from about 0.009 kg / min to about 0.36 kg / min. There are two systems for measuring the liquid ingredients that are placed in the continuous mixer 58. In a preferred system, each ingredient is measured with its own intended metering pump, flow meter and controller directly in the continuous mixer. This allows to make changes in the levels of ingredients when a product with different specifications is desired. In an alternative, the less expensive system shown in Figure 5, each liquid of small volume is measured in a mixer 78. With a pump 120 and a measuring system 122, the liquid ingredients are subsequently fed into the continuous mixer 58 In this mode, a second mixing tank, a pump, and a measurement system (not shown) could be available for large batches of production and alterations to differentiate products. Once both the dry ingredients and the liquid ingredients are premixed separately, they are then fed to the continuous mixer 58, as shown in the figures, to produce the joint compound. Various types of continuous mixers 58 can be used in accordance with the method of the invention to produce a composite of the board of the wall board. In general, the inner part of the interior of the mixer 58 defining the mixing chamber may vary from about 10 cm to about 30.5 cm in diameter and from about 61 cm to about 122 cm in length. The mixer volume is preferably at least about 0.056 m 3 and more preferably on a scale of about 0.056 m 3 to about 0.33 m 3. The mixers generally contain stirring means, such as a paddle. The mixers manufactured by Prater of Chicago, Illinois, Munson of Utica, New York, Autocon of Richmond, California, and The Readco Company of York, Pennsylvania are suitable for use in accordance with the invention. The Munson and Prater mixers are horizontal shell mixers with rotating shafts and palette-style mixers attached. The mixing action is the result of both the agitation from the adjustable inclined vanes and the retention time of the product in the mixing chamber. The Autocon mixer has an outer cover and a rotating inner cover with vanes in a vertically oriented configuration. The Readco mixer has horizontal co-rotating shafts with a less than normal tolerance between the pallets and the walls of the pallet resulting in what was described as a kneading and rubbing action. The Readco mixer also has liquid entry points from the multi-location mixing chamber. These continuous mixers can have an exit velocity that can vary on a scale from about 68 kg / min of the final product per minute to about 380 kg / min of the final product per minute.

The stirring mechanism (e.g. paddle (s)) within the mixing apparatus 58 preferably moves at a speed of at least 600 rpm, more preferably on a scale from about 600 rpm to about 1350 rpm, and more preferably on a scale of about 750 rpm to about 900 rpm. The mixing apparatus 58 preferably has controls that allow the adjustment of these speeds depending on other parameters of the process. While blending occurs, a Nametre viscometer can be used to measure the viscosity of the composition to ensure a consistent product. The viscosity reading should allow to control the amount of water that is added to the suspension, to ensure that the desired viscosity is maintained. The suspension discharged from the mixer 58 is subsequently transferred by a pump to a holding tank. Vacuum processing, if necessary, can be performed at this point in the procedure. Table II shows a summary of the preferred weight percentages (based on the total weight of the gasket compound) and the flow rates of the ingredients used to produce the gasket compounds according to the invention. The percentages by weight are based on the total weight of the final composition. Table III shows the density and flow rate of the ingredients used to produce the joint compound according to the invention in different system capacities.

TABLE II TABLE The method of the invention avoids the above-described drawbacks of the batch process, facilitates the transition between products with little or no contamination from the above products, and provides an cost-effective process with high production speeds.

EXAMPLE 1 Table IV shows a comparison of two procedures for making ready-to-mix light weight gasket compounds, one using a batch process and another using a continuous process of the invention. Each procedure produced 5.31 kg of the joint compound ready to be mixed in accordance with the recipes defined above.

The batch process produced the joint compound in 35 minutes while the continuous process according to the invention produced the same amount of joint compound in only 18 minutes. In addition, as shown in Table IV, the continuous procedure used reduced the levels of Troysan 364, Troysan 174, defoamer, diethylene glycol, Super Gel B clay, mica, talc, methocel, latex, Sil Cel, and water due to uniform mixing at a high intensity and a lower mixing area. Since the method of the invention was able to utilize reduced levels of these ingredients, the process was able to utilize higher levels of low cost limestone filler.

SQUARE IV Formula for batch mixer vs. continuous blender Lightweight blended board compound Quantity in Kg Materials Lot Water Invention 1135 1135 Troysan 364 1.36 0.908 Troysan 174 6.81 5.9 Defoamer 5.45 4.54 Diethylene glycol 49.9 45.4 Limestone 1253 1271 Clay super gel B 96.5 81.7 Mica [52-90] 238 181.6 Talc [45-26] 261 181.6 Metocel [40320] 30.2 25.4 Latex [40716] 276.9 272.4 Perlite-Sil Cel [43-34] 257 254 Limestone 481 635.6 Water 999 999 Water 45.4 Table V shows the changes in viscosity over time of the joint compound manufactured in accordance with Table IV. The viscosity of the joint compound manufactured by the continuous processes of the invention increased from about 500 units of Braebender ("BU") to about 560 BU in 24 hours, while the viscosity of the joint compound manufactured by the process in batch showed a greater increase, from around 450 BU to approximately 600 BU in 24 hours. In this way, the compound of the gasket of the invention had a more stable viscosity.

TABLE V Control values Lot Invention Viscosity -Mixer 450 ± 10 BU 500 ± BU -Pack 550 ± 50 BU 500 ± 50 BU -24 Hours 600 + 50 BU 560 + 30 BU EXAMPLE 2 Table VI similarly shows a comparison of the ingredients used in the processes for manufacturing the two ready-to-mix ready-mix board compounds, one using a batch process and the other a continuous process in accordance with the present invention.

TABLE VI I Quantity in Kg Formula Batch Invention Water 1489 1489 Troysan 364 1.36 0.91 Troysan 174 6.81 5.9 Defoamer 19.8 2.7 Glycol 34 22.7 Attapulgite clay 175 136 Mica 363 272 Talc-MP 45-26 340 113.5 Metocel 40320 36.8 31.8 Polyvinyl all 7.0 4.76 Sorbitol 1.6 1.6 Limestone 1610 1700 Latex 40716.00 159 153 Water 527 527 Limestone 1610 1700 Water 527 454 Limestone 1610 1700 Water (fixer) 220 EXAMPLE 3 This example illustrates a preferred method for manufacturing a joint compound in accordance with the present invention. First, the operator selected a desired program model from a computer control screen, and confirmed the accuracy of all the points established in relation to the desired product.

Next, the operator adjusted the set points for the mixer amps of the limestone dry additive and latex amps. When all the start parameters were set to the correct specifications, the operator turned on a continuous mixer by pressing the start button on the mixer. After the mixer was operated, the operator pressed the master switch to operate the liquid and dry additive system. The liquid ingredients were continuously fed to a continuous mixer using a PLC control. The viscosity of the composition leaving the mixer was continuously monitored by an in-line viscosity, and the rate of water addition was adjusted by automatic control to produce the desired viscosity. The mixer mixed dry and liquid ingredients at a high intensity mixing rate for about 35 seconds to about 5 minutes, depending on the type of the product.

An in-line viscometer installed in the transfer line measured and recorded the viscosity of the finished products. The continuously produced ready-mix compound was then transported to a holding tank, where a pump transferred the product to a packing line. Table VII shows a summary of the properties of a composite of the representative continuous joint produced in accordance with the invention, compared to the joint compound produced by a batch process.

CUADRÓ VII The continuous process according to the invention provides any advantage. A continuous process of the invention produces a consistent high quality joint compound faster and more efficient than the traditional batch process. The method of the invention saves time in both cleaning procedures and operations. In addition, the continuous process allows more processing flexibility as well as allows the production of a product of consistent quality, without the variations that are generally found with batch operations. More specifically, in the continuous process of the invention, the residence time is generally shorter (from about 1 to about 2 minutes) than the residence time in a batch process (usually from about 25 to about 45 minutes). The reduced residence time in the continuous process according to the invention is partly due to the high intensity mixing used by the invention measured as at the highest revolutions per minute ("rpm") of the continuous mixer as compared to a mixing in batch While a batch mixer typically operates only at around 45 to about 70 rpm, the continuous mixer according to the invention is capable of operating from about 650 rpm to about 1650 rpm. It has surprisingly been found that because the continuous mixer operates at a higher rpm than that of a batch mixer, there is a better dispersion of the solid particles in the liquid component, which contributes to a shorter residence time in the continuous process of the invention. Batch mixers used in conventional processes can not effectively produce the joint compound at the same high rpm as that of the continuous mixer. If operated at a high rpm, a batch mixer will allow a substantial amount of air to enter the compound of the joint to be manufactured. Air in the joint compound is not desired, for example, as it creates problems at the work site in the finished drywall, such as surfaces marked with pustules (empty spaces of air on a dry surface of the finished joint. It has also been found that another factor contributing to allow a shorter residence time in the process of the invention is the narrow preferred space of the blades in preferred continuous mixers, which create higher heat transfer coefficients. additional residence time The reduced residence time of the invention in this way increases the speed of production of the joint compound In addition, due to the low residence times, the continuous process according to the invention can use less energy than a typical batch procedure to produce the same amount of joint compound, resulting in advantage s cheaper The efficiency and speed of production of the process according to the invention is further improved since the continuous mixer can be cleaned more easily than a batch mixer. This is due to the fact that there is less accumulation of material in a continuous mixer than a batch mixer. This self-cleaning action of a continuous mixer avoids the accumulation of material inside the mixer and can reduce the cleaning time by more than 90%. In this way, there is less unproductive time for cleaning when a continuous mixer is used. Another advantage of the continuous process according to the invention is that the process may require small amounts of several ingredients, or completely eliminate the need for some materials conventionally used to produce the joint compound.

For example, less water is needed to produce a joint compound in the continuous process of the invention than in a batch process. In the continuous process, from about 25% by weight to about 35% by weight of water is used to make the joint compound, while from about 36% by weight to about 45% by weight of water is typically needed in a batch process to make the same amount of joint compound. Not only is it more expensive and efficient in terms of time, the use of less water but also this produces a high quality joint compound. When there is less water in the joint compound, this improves the drying of the joint compound, it is less prone to shrink or break. In addition, less water in the joint compound creates a joint compound that has a viscosity more consistent with time compared to the joint compound produced in a batch process. In addition, the use of surface treatments in thickeners and potassium carbonate can be eliminated, since the process eliminates the need for a surface treatment in water-soluble polymers (for example Methocel 2405, Methocel 40320, etc.). In a conventional batch process, water-soluble polymers, such as hydroxypropylmethylcellulose (HPMC) and hydroxyethylcellulose (HEC) are used as thickening agents. To avoid the formation of lumps during the mixing cycle, these water-soluble polymers are surface treated with glycolol. After the water-soluble polymers are mixed in a suitable manner, potassium carbonate is subsequently used to hydrate these thickeners and remove the surface treatment. In the continuous process according to the invention, since the continuous mixer operates at high RPMs, the thickeners are capable of dispersing in their entirety through the mixture without any formation of lumps and rapidly hydrate. In this way, untreated thickeners can be used and subsequently potassium carbonate is not required. In addition, the amount of mica used can be reduced to about 10% compared to a batch process. The amount of other ingredients, such as ervatives, defoamer, glycol, clay, talc, thickeners, latex, and perlite can also be reduced. The above detailed description is given to clarify the understanding only and should not be understood as unnecessary limitations thereof, since modifications within the scope of the invention will be apparent to those skilled in the art.

Claims (22)

NOVELTY OF THE INVENTION CLAIMS

1. - A method for continuously producing a cement suspension, comprising the steps of: (a) pre-mixing at least two dry ingredients; (b) pre-mix at least two liquid ingredients; (c) supplying said mixed dry ingredients and said mixed liquid ingredients in a continuous mixing apparatus; (d) at least substantially continuously mixing said ingredients in said mixer to produce said cement suspension.

2. The method according to claim 1, further characterized in that step (d) comprises mixing with a stirrer moving at a speed of at least 600 rpm.

3. The method according to claim 2, further characterized in that the agitator comprises a pallet.

4. The method according to claim 2, further characterized in that the speed is on a scale of about 600 rpm to about 1350 rpm.

5. The method according to claim 1, further characterized in that said dry ingredients are selected from the group consisting of limestone, perlite, clay, mica, talc, and gypsum.

6. - The method according to claim 1, further characterized in that the liquid ingredients are selected from the group consisting of water, latex, glycol and dibutyl phthalate.

7. The method according to claim 1, further characterized in that said cement suspension comprises from about 25% by weight to about 35% water, based on the weight of the composition.

8. The method according to claim 1, further characterized in that said cement suspension is a composite of the joint comprising from about 55% by weight to about 75% by weight of limestone, based on the weight of the suspension.

9. The method according to claim 1, further characterized in that it comprises producing at least about 9080 kg of said suspension at least substantially continuously.

10. The method according to claim 1, further characterized in that it comprises: (e) continuously removing said suspension from said apparatus.

11. The method according to claim 1, further characterized in that said cement suspension is a compound of the board and said pre-mixed dry ingredients comprise calcium sulfate dihydrate and calcium carbonate.

12. The method according to claim 1, further characterized in that said cement suspension is a compound of the joint and said pre-mixed dry ingredients comprise calcium sulfate hemihydrate and a retarder.

13. The method according to claim 6, further characterized in that the water flow rate is on a scale of about 0.37 liters / hour to about 3.78 liters / hour.

14. The method according to claim 5, further characterized in that the flow rate of the limestone is on a scale of about 45.5 kg / min to about 181.8 kg / min.

15. A product produced by the method according to claim 1.

16. A suspension of cement suitable for use as a composite of the joint of the wall board, comprising: (a) at least about 50% by weight of a component comprising an ingredient selected from the group consisting of calcium sulfate dihydrate and calcium carbonate; (b) from about 25 to about 35% by weight of water; and (c) a binder.

17. The cement suspension according to claim 16, further characterized in that it comprises from about 25% by weight to about 35% by weight of water, based on the weight of the suspension.

18. The cement suspension according to claim 16, further characterized in that it comprises about 4% by weight or less of clay, about 4% by weight or less of mica, and about 5% by weight or less of a thickener.

19. The cement suspension according to claim 16, further characterized in that it comprises around 55 to 75% by weight of limestone, based on the weight of the suspension.

20. A method for continuously producing a cement suspension, comprising the steps of: (a) combining ingredients comprising (1) a filler selected from the group consisting of calcium sulfate dihydrate and limestone; (2) water; and (3) a binder; (b) continuously mixing said ingredients with a mixing apparatus having a stirrer moving at a speed of at least 650 rpm; and (c) continuously removing the product from step (b) of said mixing apparatus.

21. The method according to claim 20, further characterized in that the agitator comprises a blade.

22. The method according to claim 20, further characterized in that said speed is on a scale of about 600 rpm to about 1350 rpm.