The present invention relates to a new and improved flame resistant material, a molding compound for producing the same, a fugitive retarder-catalyst system for the molding compound, and a new and improved method of producing inorganic fiber board having a hard surfacing thereon. 
     BACKGROUND OF THE INVENTION 
     A need has long existed for a flame proof wallboard for dwellings, hospitals, and other public buildings to take the place of marble, tile, and other hard fire proof surfacing materials which are now too expensive for general use in the building industry. The usual drywall board comprising gypsum between two layers of paper is not sufficiently fire resistant for hospitals and public buildings, nor is the painted fiber board that is presently available. Concrete materials are not sufficiently strong to resist scratching and they are too porous to meet santitary codes for hospitals. The same is generally true of cement bonded fiber boards, such as masonite, etc. 
     Accordingly, it is an object of the present invention to produce an inexpensive light weight paneling which has a surface which has a very low flame spread rate, that liberates very little smoke when subjected to temperatures of 1,000° F or more, and which contributes practically no fuel to a fire that is contained by the paneling. 
     Another object of the present invention is the provision of a wallboard of the above described type having a smooth dense surface that cannot be scratched by a carbon steel knife. 
     Another object of the present invention is the provision of a new and improved molding compound for producing such fire resistant surfaces. 
     Another object of the invention is the provision of a new and improved retarder-catalyst system for aldehyde condensate resins. 
     A further object of the present invention is the provision of a new and improved method of making a fiber board. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The solitary FIGURE of the drawing is a schematic representation of a preferred method of making wallboard according to principles of the 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     According to the principles of the present invention, it has been discovered that unique fire resistant properties are provided by inorganic fillers that contain aluminum trihydrate when bonded together by an aldehyde condensate resin. It appears that aluminum trihydrate protects the bond which it has with an aldehyde condensate resin and particularly melamine resins in that it gives off water vapors in generally two stages starting as low as approximately 400° F and continuing to a temperature of approximately 570° F. On the other hand, the aldehyde condensate resins, and particularly melamine resins, only slowly oxidize at such temperatures and do not pyrolytically disintegrate at any appreciable rate until it is at a temperature above the water liberation temperature of the aluminum trihydrate. During the first stage of water liberation from aluminum trihydrate, it is converted to a monohydrate which is also crystalline, so that the crystalline structure to which the resin is bonded is maintained until the final stage of liberation of the water vapor. 
     While all of the reasons for the unique combination are not known, it is also believed that at temperatures of about 570° F the nascent aluminum oxide that is produced reacts with the methylol groups, and/or nitrogen compounds to form methoxides and then carbides and when slightly soluble forms of silicate are present, aluminum silicates. 
     According to further principles of the invention, a new retarder-catalyst system is provided for aldehyde condensate resins which will allow the aldehyde condensate resins to thicken at room temperature in a controlled manner following which the retarders are driven off to allow the aldehyde condensate resins to cure. Such a retarder-catalyst system has particular advantages when making sheet molding compound. 
     According to still further principles of the invention, a new and improved method is provided for making surfaced wallboard by taking a layer of the sheet molding compound of the present invention, superimposing it on top of a layer of inorganic fibers containing uncured aldehyde condensate prepolymer as a potential binder, and pressing the sheet molding compound and fiber-binder layers together at elevated temperatures to cure the binder of the surfacing layer while also simultaneously curing the prepolymer of the back-up layer, and bonding the two layers together. 
     Some of the advantages of the present invention will be made apparent by the following examples: 
     EXAMPLE 1 
     A sheet molding compound is made from the following materials in the parts by weight indicated: 
     
         ______________________________________Alumina trihydrate (50-80 micron)                     2400Alumina trihydrate (6.5-9.5 micron)                     2400Powdered silica (-200 mesh)                     4200Quintas quartz            3000A-staged melamine-formaldehyde                     3200 prepolymerAmmonium chloride (catalyst)                     22Zinc stearate (retarder)  352Ammonium hydroxide (retarder)                     90Titanium dioxide (-200 mesh)                     456Water                     2950______________________________________ 
    
     The above materials were prepared by mixing the ammonium hydroxide in water followed by the melamine-formaldehyde prepolymer. Thereafter, the ammonium chloride is dissolved therein. The fine alumina trihydrate is then added followed by the coarse alumina trihydrate. Thereafter, the fine silica is blended therein, followed by the coarser quintas quartz. After a homogenous slurry is produced, the zinc stearate in powder form is added and dispersed throughout. 
     A sheet molding compound is made from the slurry using the procedure taught in the Davis, Wood, and Miller U.S. Pat. No. 3,615,979. A 20 mil thickness of the slurry is spread onto a first polyethylene carrier sheet, and another 20 mil thickness of the slurry is spread onto a second polyethylene carrier sheet. Twenty-eight grams per square foot of 1/4-inch long chopped fiber strand is delivered evenly to the top of the slurry on the first carrier sheet, and the second layer of the slurry is brought down on top of the layer of chopped strand. The two layers of slurry are forced together to embed the chopped strand generally uniformly throughout the slurry to form a sheet molding compound. The sheet molding compound separated by the polyethylene sheets is cut into sheets and is allowed to thicken from 24 to 96 hours into a handleable and slightly tacky state. 
     The sheet molding compound so produced can be used as a surfacing for any type of substrate, or a number of thicknesses of the sheet molding compound can be pressed together and cured into a dense board. In most instances, however, a light weight wallboard is desired; and according to further principles of the present invention, this is produced in a new and improved way by superimposing five pelts that each comprise a 3-inch thickness of air blow glass fiber wool having a 1/2 pound per cubic foot density that is wetted out with a binder forming solution comprising a phenol-formaldehyde partial condensate containing urea, and dicyandiamide in an amount to provide approximately 30% nitrogen based on resin solids. A layer of the sheet molding compound produced as above described is placed on top of the five pelts and the composite is placed between heated platens of a press and are cured at 350° F and a pressure of 200 psi for 12 minutes. This procedure produces a composite of a substrate approximately 1/4-inch thick of bonded glass fibers having a density of 45  pounds per cubic foot and approximately a 40 mil thick surfacing of the cured sheet molding compound. The surfacing layer is adequately bonded to the glass fiber substrate with only a slight penetration of the sheet molding compound into the surface of the glass fiber substrate. It can be seen that this procedure not only simultaneously cures the binder of the surfacing layer, and the substrate, but also bonds the two layers together at the same time. 
     The above described procedure produces a remarkable material, the surface of which cannot be scratched by a carbon steel knife, and when flame tested according to the ASTM E-84 tunnel test has a flame spread rate of approximately 12, a fuel contribution of approximately 4, and a smoke development of approximately 12. 
     EXAMPLE II 
     The process of Example I is repeated excepting that the melamine-formaldehyde resin is replaced with a phenol-formaldehyde, urea, dicyandiamide mixture that was used for the binder of the glass fiber board. The product produced has substantially the same properties as that of Example I, but differs principally therefrom in that a slight yellow color exists in the surfacing. 
     EXAMPLE III 
     The process of Example II is repeated excepting that the zinc stearate is replaced by aluminum stearate, and the aluminum chloride is replaced with a lignin sulfonate. The wallboard produced has substantially the same properties as that of Example I. 
     EXAMPLE IV 
     The process of Example I is repeated excepting that the zinc stearate is replaced with ammonium palmitate and the wallboard produced has substantially the same properties as that of Example I. 
     EXAMPLE V 
     The process of Example I is repeated excepting that the zinc stearate is replaced with calcium palmitate, and the wallboard produced has substantially the same properties as that of Example I. 
     In general, molding compounds for producing flame resistant surfaces can be prepared within the range of materials given below in parts by weight: 
     
         ______________________________________Ingredients          Parts by Weight______________________________________Alumina trihydrate   from 15 to 80Other inorganic fillers                0 to 50Aldehyde condensate prepolymers                from 15 to 45Fatty acid salts     0 to 4.0Ammonia hydroxide retarder                from 0.1 to 3.0Acid salt catalyst   0.05 to 0.5______________________________________ 
    
     Wall surfaces having a hard white surface, which are the preferred materials of the present invention, can be produced within the range of materials given below in parts by weight: 
     
         ______________________________________Ingredients          Parts by Weight______________________________________Alumina trihydrate     20 to 40Granular silica fillers                  35 to 50Titania                0 to 5Melamine-formaldehyde prepolymers                  15 to 30Fatty acid salts       1 to 5Acid salt catalysts    0.05 to 0.5Ammonia hydroxide      0.5 to 3.0______________________________________ 
    
     In all cases, the most preferred materials will include an inorganic fiber reinforcement, as for example, chopped glass fibers in an amount between 1 and approximately 30% based on the slurry solids. When a large volume of glass fibers is to be incorporated into the molding compound, a larger amount of water than that given in Example I will be used, and the amount can easily be determined by adding water until the proper consistency is reached. 
     Any type of acid salt catalyst can be used, as is known in the art, as for example, ammonium chloride, ammonium sulfate, ammonium nitrate, lignin sulfonate, etc. Ammonium salts are preferred in that a beneficial buffering action is achieved with the ammonium hydroxide. 
     Any type of fatty acid salt can be utilized as the permanent retarder provided that it is generally insoluble, or only slightly soluble in cold water, has increased solubility in warm water, and in addition has its solubility increased by ammonium hydroxide. These salts will include the zinc salts, calcium salts, magnesium salts, etc. 
     The alumina trihydrate liberates water vapor starting at a temperature of approximately 400° F and provides a beneficial affect with respect to prolonging the life of the binder that is generally proportional to the amount that is present. For best results, however, the amount used should be more than approximately 15% by weight of the solids of the molding compound. Other inorganic fillers can be used, and by selecting materials that are harder than steel, a nonscratching surface can be provided. In this respect, one of the most readily available and cheapest materials is silica; and it is believed desirable to use silica in combination with ammonium hydroxide in that it provides a slight amount of soluble silicates for reaction with the nascent alumina that is produced by the dehydration which occurs during a fire. 
     While the invention has been described in considerable detail, I do not wish to be limited to the particular embodiments described; and it is my intention to cover hereby all novel adaptations, modifications, and arrangements thereof which come within the practice of those skilled in the art to which the invention relates.
A scratch resistant, flame resistant material is made by producing a sheet molding compound of a melamine-aldehyde precondensate, silica, alumina trihydrate, slightly soluble soap, ammonium hydroxide and acid salt catalyst. The sheet molding compound is applied to the surface of a pelt of glass fibers containing a heat curable binder and the composite is bonded together under heat and pressure to cure both binders simultaneously and bond the sheet molding compound to the fiber layer of the pelt.