Abstract:
Improved methods for the production of lightweight, rigid, insulative perlite/cement solid articles such as bricks ( 62 ) are provided wherein expanded perlite is first treated with a cement binder followed by application of cement with subsequent mixing and forming. In preferred forms, a continuous belt ( 12 ) is provided with laterally spaced apart stations ( 22 - 28 ) for application of perlite, binder, water and Portland cement, respectively, onto the belt ( 12 ); these materials are then mixed in a drum mixer ( 38 ) to produce a mixture ( 61 ) which is poured into a frame assembly ( 44 ) for final curing/hardening.

Description:
RELATED APPLICATIONS 
   This application claims the priority benefit of a provisional application entitled PERLITE COMPOSITION AND METHOD OF MAKING THE SAME, Ser. No. 60/733,156, filed Nov. 3, 2005, incorporated by reference herein. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention is broadly concerned with improved methods for the production fo highly desirable solid articles (e.g., sheets, panels, bricks, mold pourings) containing expanded perlite and cement. More particularly, the invention is concerned with such methods wherein expanded perlite is first treated by application of cement binder, followed by mixing of cement with the treated perlite to form a castable or formable mixture. 
   2. Description of the Prior Art 
   Perlite is a generic term for naturally occurring siliceous volcanic rock. A distinguishing feature of perlite is that when heated to a suitable point in its softening range, it expands four to twenty times its original volume. This expansion is due to the presence of 2-6% combined water in the crude perlite rock. When quickly heated above 1600° F., the crude rock pops in a manner similar to popcorn as the combined water vaporizes, creating countless tiny bubbles in the heat-softened glassy particles. It is the presence of these tiny glass-sealed bubbles which accounts for the desirable physical properties of expanded perlite. Expanded perlite can be manufactured to weigh from 2-15 lb/cubic foot, making it adaptable for numerous applications in the construction, industrial, chemical, horticultural and petrochemical industries. 
   Expanded perlite has been used in the past in the fabrication of lightweight building materials and artificial stones. Thus, U.S. Pat. No. 4,043,826 describes a process for making artificial rocks wherein latex paint, water, calcium chloride, Portland cement mid horticultural perlite are mixed together and poured into a flexible mold in the shape of a natural rock. U.S. Pat. No. 3,847,633 is directed to the production of building materials wherein Portland cement and perlite are mixed together along with plaster of paris, fly ash and fiberglass reinforcing material. In the process, dry materials are pre-blended, followed by the addition of water and mixing; the resulting slurry is then formed using a specific, two-stage, differential temperature curing regimen. U.S. Pat Nos. 2,858,227 and 4,042,046 describe additional variants of these processes for the production of perlite/cement products. 
   SUMMARY OF THE INVENTION 
   The present invention provides improved methods for the production of highly useful perlite/cement products such as sheets, panels or bricks. Broadly speaking, the methods of the invention involve first providing a quantity of expanded perlite and treating the perlite by applying a cement binder thereto, so as to at least partially encapsulate the perlite with binder. Thereafter, an amount of cement (preferably Portland cement grades I or III) is added to the binder-treated perlite and a mixture is created. This mixture can then be formed and allowed to harden to yield the final solid articles of the invention. The cement binder is normally an aqueous synthetic resin product and may be used in concentrated or dilute forms. Additional water may also be applied to the binder-treated perlite prior to cement addition as necessary. 
   It has been found that the order of addition of the starting materials is important, i.e., simultaneous mixing of perlite, binder and cement does not produce the desired products. Rather, it is preferred to first treat the expanded perlite with binder followed by mixing thereof with cement to form the formable mixture. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an essentially schematic, side elevational view of a preferred apparatus used in the fabrication of solid articles in accordance with the invention; and 
       FIG. 2  is an isometric view of a representative form partially filled with the material of the invention, in the final step of the fabrication process. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Turning now to the drawing,  FIG. 1  illustrates a preferred, in-line apparatus  10  useful in fabricating the solid articles of the invention. Broadly speaking, the apparatus  20  includes a continuous belt  12  trained about endmost rollers  14 , 16  and presenting an upper run  18  and an opposed, lower run  20 . In practice, a belt length of approximately 42 inches has been found to be sufficient. 
   Additionally, located above run  18  are a series of laterally spaced apart ingredient stations  22 , 24 , 26  and  28 . The station  22  is designed to hold a supply of expanded perlite and includes a lower outlet designed to deliver a thin layer  30  of perlite (e.g., from about 1/16 to ½ inches, more preferably from about ⅛ to ¼ inches in thickness) onto run  18 . The station  24  is designed to distribute liquid cement binder onto the upper surface of layer  30 , and preferably is operable to spray the binder through exemplary spray pattern  32 . Preferably, the binder is used at a ratio of about 1 part binder to 34 parts perlite (all parts referred to herein are parts by volume). The binder may be as received from the manufacturer, or may be diluted with water. 
   Although not wishing to be bound by any theory, it is believed that the binder essentially encapsulates the perlite prior to application of cement. Indeed, it has been found that simultaneous mixing of perlite, binder and cement does not produce a satisfactory product. Therefore, the stepwise application of binder and then cement to the perlite is deemed to be important. 
   The station  26  is similar to station  24 , but holds water which is sprayed atop the binder-treated perlite layer  30 . Ultimately, the preferred binder/water ratio, whether derived from a mixture of binder and water and/or application of binder followed by water, is about 10 parts water per part of binder. The preferred application is via an exemplary spray pattern  34 . Finally, the station  28  is adapted to hold a supply of powdered Portland cement and is further designed to distribute an even layer  36  thereof over the previously treated perlite layer  30 . In preferred practice, the cement layer  36  should be applied to achieve a ratio of about 8 parts cement to 34 parts perlite. 
   The overall apparatus  10  further includes a drum mixer  38  positioned adjacent the output end of belt  12 . The schematically depicted mixer  38  includes a inlet hopper  40  and an outlet  42 . The purpose of the mixer  30  is to thoroughly mix, aerate if desired, and render essentially homogeneous the perlite, binder, water and cement deposited on belt  12 . Although a variety of mixers may be used for this purpose, it has been found that a simple drum provided with internal, helical vanes and powered for rotation via a motor and drive is perfectly suitable. In such a device, the vanes repeatedly lift the material and drop it back towards the base of the drum. Normally, a mixing sequence comprising several material “drops” is adequate to achieve thorough mixing and aeration. 
   The apparatus  10  also has a form assembly  44  positioned adjacent and below outlet  42 . In the example illustrated, the assembly  44  includes a planar base  46  such as a wood or composition panel, with a sheet of flexible plastic  48  positioned atop the base  46 . An upright, rigid, wood or metal frame  50  sits on the sheet  48  and may be provided with internal form walls  52 , 54  so as to define form cavities  56  of desired shape and dimensions. 
   In the practice of the invention, the expanded perlite may be derived from a number of commercial sources, and would normally have densities corresponding to either horticultural or commercial grade perlite. 
   The binder is a conventional cement binder, usually in the form of an aqueous dispersion containing a synthetic resin polymer, such as a vinyl acetate/ethylene copolymer and a vinyl alcohol polymer. One commercial product found useful in the context of the invention is QUIKRETE® bonding adhesive, which is a milky white liquid having a melting point of 32° F., a specific gravity from about 1.0-1.2, a boiling point of 212° F., and a vapor pressure of 17 mm Hg at 68° F. Depending upon the desired characteristics in the final mixture, the binder may be applied as received, or can be diluted with water. Current practice is to dilute the binder at a ratio of 1 gallon binder/10 gallons water for use in the station  24 . The binder is normally applied to the expanded perlite at a level of from about ¾ to 1½ parts binder per 34 parts of expanded perlite, and more preferably from about 1 part binder per 34 parts. 
   A variety of cements may be used in the station  28 . For reasons of cost and availability, Portland cement is preferred, and usually grade III Portland is used. The cement should be deposited onto belt  12  dry, i.e., not premixed with water. The cement is added to the treated perlite at a level of from about 3-18 parts cement per 34 parts untreated perlite, and more preferably from about 8 parts cement to 34 parts untreated perlite. 
   As shown in  FIG. 1 , water may be added with and/or subsequent to application of the binder. Additionally, another application of water may be made downstream of the cement station  28 ; thus, it will be appreciated that the precise locations where water is added, alone or in combination with the binder, is unimportant, so long as adequate water is used. However added, water should be present at a level of from about 4 to 12 parts of water to 34 parts of untreated perlite, more preferably about 10 parts of water to 34 parts of untreated perlite. 
   The final forming step permits the initially perlite/binder/water/cement mixture  61  to harden and cure and thereby form the desired final article. As illustrated in  FIG. 1 , the mixture  61  may have small “clumps” therein, but is generally homogeneous. This is normally accomplished by permitting the formed mixture to cure in ambient air, without any application of pressure. For many products, the curing period will extend for a period of from about 1-4 days, more typically from about 2-3 days. Curing agents can be added to accelerate the curing process, and/or heat drying systems may be used for the same purpose. At the end of the cure period, the completed solid articles can be readily detached from the frame  50 . Although the form  50  depicted in the drawing is designed to produce brick-like articles  62 , it will be appreciated that the invention is not so limited. Thus, the form  50  can be designed to produce structural panels or shower stall components, or for that matter essentially any solid article. 
   It will also be appreciated that the concrete/perlite/water mixtures of the invention may be partially or fully premixed and then delivered to a construction site where the mixture may be poured and cured on-site to produce desired articles. 
   Although not specifically illustrated in the drawing, it will be appreciated that various reinforcing material can be used in fabricating the finished articles of the invention, Such reinforcing materials can be of various types and amounts, such as polyester, fiberglass and/or metal. When used, the reinforcing materials are normally placed within the form cavities  56  prior to or shortly after filling thereof with the mixture  61 ; alternately, these materials may be added during formulation of the curable cement/perlite/water mixture. 
   The final products of the invention have a number of highly desirable qualities. Such products are self-insulating owing to the presence of expanded perlite therein, and moreover can withstand direct butane torch flame (approximately 1750° F.) without burning or spreading. As manufactured, the products are normally solid color, but are readily paintable or stainable. The products can be readily cut using hand or power saws, and will accept fasteners such as nails, screws or bolts. The products are moreover easy to repair using conventional filler products. 
   Products in accordance with the invention in the form of sheets or blocks can be used as internal or external walls, flooring, roofing, counter tops, mantles and fireplace surrounds, shower stalls (walls, floor), columns, pool table slabs, fountains, statuary, urns, swimming pool decking and sheathing, for example. When multiple sheets are used to form walls for buildings, the sheets can be connected using conventional ties, and the cavity between the joined sheets can be filled with concrete, rebar, or additional thermal insulation. The finished walls can then be surfaced inside or outside with hardeners, stucco, cement and/or waterproofing agents, or drywall on interior surfaces. Alternately, the cured articles can be left with their natural surfaces. 
   The products can also be conformed during the molding process to achieve varying degrees of smoothness and shape. For example, coarser grades of perlite with minimal fines creates a less-dense product, whereas finer perlite gives a denser product and a different surface.