Method of molding fireproof products containing magnesium oxychloride cement
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of application Ser. No. 194,557, filed Nov. 1, 1971 now U.S. Pat. No. 3,778,304, which is a continuation-in-part of application Ser. No. 811,616, filed Mar. 28, 1969, which in turn is a continuation-in-part of application Ser. No. 589,808, filed Oct. 27, 1966, both now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to a process of fireproofing and the resultant fireproof product. More particularly, it relates to fireproofing with foamed magnesium oxychloride cement. 
     Fireproofing of porous organic materials such as insulating board, fiberboard, and the like has long been a difficult problem. Most chemicals used for fireproofing are expensive in the amounts required, so that the economies of fiberboard are lost in preparation of the commercial fireproof product. Moreover, many of the materials used for &#34;fireproofing&#34; are in fact simply flame retardants, which resist the spread of flames and extinguish the fire by the release of chlorine gas or other extinguishing material. However, fire retardant and flame retardant materials do not prevent the burning of the organic constituents of the porous substrates. In many cases, smoke still is given off through the burning of the cellulose fibers or other organic materials often with the result that severe smoke damage is still possible even though open flames do not break out. 
     Materials which have layers of fireproof materials over burnable organic materials, such as gypsum board, also suffer shortcomings. Gypsum board is not suitable for exterior use because of severe sensitivity to water. In addition, the paper backing in gypsum board is burnable. 
     Materials like asbestos-cement board are fireproof, but they are so expensive and so dense that they have not achieved the wide commercial acceptance possible with low-cost materials. 
     Magnesium oxychloride cement has been known for many years as a flooring material. However, because of its density and lack of porosity, it has not been widely used in other applications. It has previously been suggested to introduce porosity into magnesium oxychloride cement in U.S. Pat. No. 1,429,451 by the inter-mixing of cork or other light material into the cement and thereafter heating to partially decompose the cork particles. Still, the product of this patent is so dense that it has not achieved acceptance in the building and construction trades for walls, roofing, etc. 
     It has been suggested to make building boards and roofing material from magnesium oxychloride cement in U.S. Pat. No. 1,372,118 by forming magnesium oxychloride cement in a foraminous support. However, the product obtained is so dense and heavy that its usefulness is limited. 
     A less dense board is described in U.S. Pat. No. 1,500,207 where a magnesium oxychloride cement surface resembling ornamental stone is coated on fiberboard. However, the cement is only on the surface and fails to thoroughly wet all the fibers in order to render them fireproof. 
     Porous magnesium oxychloride cement is disclosed in U.S. Pat. No. 1,965,538. However, this patent does not relate to fireproofing of burnable products. 
     U.S. Pat. No. 2,702,753 relates to a foamed magnesium oxychloride tile having certain other ingredients. However, the magnesium oxychloride is not intended to fireproof other burnable materials. 
     U.S. Pat. No. 3,050,427 shows the use of fibrous glass in a binder. Of the binders listed in this patent, magnesium oxychloride cement is suggested as a possibility. However, the patent does not relate to fireproofing with foamed magnesium oxychloride cement. 
     SUMMARY OF THE INVENTION AND OBJECTS 
     This invention relates to relatively low density burnable materials which have been rendered non-burnable by the even distribution, throughout the burnable material, of foamed magnesium oxychloride cement. The even distribution of the cement may be accomplished by impregnating a porous substrate with a forthing mixture of the cement of this invention. The cement is foamed by the presence of a frothing agent which produces gas bubbles. The forthing cement may be molded in a wide variety of configurations and may be given different properties by incorporating other materials, such as fiberglass, into the cement. 
     It is an object of this invention to provide an inexpensive, fireproof porous material having high strength properties and low density. 
     It is a further object of this invention to provide an improved process of manufacturing low density fireproof materials. 
     These and other objects of the invention will appear from the following description in which the preferred embodiments of the invention have been set forth in detail. 
     A DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Magnesium oxychloride cement (sorel cement) is prepared by the reaction of magnesium chloride, magnesium oxide and water. The literature defines the reaction according to two net equations: 
     
         3 MgO + MgCl.sub.2 + 11 H.sub.2 O → 3 Mg(OH).sub.2.sup.. MgCl.sub.2.sup.. 8H.sub.2 O 
    
     
         5 mgO + MgCl.sub.2 + 13 H.sub.2 O → 5 Mg(OH).sub.2.sup.. MgCl.sub.2.sup.. 8H.sub.2 O 
    
     magnesium oxychloride cement, before it has set, may be made to froth with the addition of frothing agent. By adding a frothing agent during the initial reaction period of the oxychloride cement a continuing froth is obtained which may be impregnated in porous materials. The frothing agent continues to form bubbles in the magnesium oxychloride cement within the porous material until the initial set of the cement takes place, at which time the bubbles are frozen into a low density fireproof product. 
     In preparing magnesium oxychloride cement, I prefer to add water to MgCl 2 .sup.. 6H 2  O to form a mixture having a specific gravity of 22° Baume. In practice, this is approximately a 1:1 ratio with water. The specific gravity is important and should not exceed the range of 21.5° Baume where MgCl 2 .sup.. 6 H 2  O is used. About 41/4 pounds of magnesium chloride is added to water to make a gallon of liquid at 22° Baume. It follows that the range of 21.5° and 22.5° Baume is achieved by roughly the addition of 4 to 5 pounds of magnesium chloride with water to make a gallon. In practice, it is convenient to purchase solutions of magnesium chloride which are commercially available at about 36° Baume. The desired specific gravity may be achieved simply by the addition of water. 
     Where other magnesium chloride hydrates are used or where small amounts of the magnesium chloride are substituted with other cement forming materials (such as magnesium sulfate), the specific gravity may vary slightly beyond the above specified range. Ordinarily, no more than 2 or 3 per cent by weight of the total cement composition of magnesium sulfate should be included, since the water resistance properties are altered and the bubble size and degree of frothing are changed where greater amounts are included. 
     Magnesium oxide is added to the mixture of magnesium chloride in water to commence the reaction to form magnesium oxychloride cement. It is essential to have between 5 and 61/2 pounds of magnesium oxide added per gallon of magnesium chloride solution to form a satisfactory cement. 
     The ratio of magnesium oxide to magnesium chloride is critical for the purposes of this invention. If significantly less than 5 pounds or more than 61/2 pounds of magnesium oxide is added per gallon of magnesium chloride solution at 22° Baume, the strength properties of the resulting product are seriously diminished That is, because of the low density of the foamed magnesium oxychloride cement, insufficient strength remains in the foamed product for commercial purposes if less than 5 pounds or more than 61/2 pounds magnesium chloride is mixed per gallon of 22° Baume magnesium chloride. Since 22° Baume magnesium chloride has approximately 4.25 pounds of magnesium chloride in it, it is convenient to use the ratio of magnesium oxide to magnesium chloride. The preferred embodiment is a ratio of about 51/4 pounds magnesium oxide per 41/4 pounds of magnesium chloride, or a ratio of 1.23. The preferred range of magnesium oxide to magnesium chloride is about 1.23 to about 1.42. 
     However, since most magnesium chloride used in commercial practice of the invention is purchased in liquid form, the foregoing critical range of 5 pounds to 61/2 pounds magnesium oxide per gallon of magnesium chloride at 22° Baume is a useful measure. 
     In practice, it is convenient to maintain a 22° Baume solution of magnesium chloride and water as a liquid component separate from the dry powder which is added to the liquid to commence formation of the cement. The dry powder may include appropriate fillers or solid additives as desired. Substantial amounts of fillers, may be included such as powdered limestone, marble dust, silica flour, and magnesium carbonate, depending upon the density of the final product desired. In molded roofing panels, for example, it is preferred to add 1178  parts insoluble filler per part of magnesium oxide powder. A combination of fillers may be used, such as marble dust in major amount, combined with silica flour and a small portion of pigment. 
     The magnesium oxychloride cement begins the initial set in about two hours. The first stage of setting is concluded in 3 or 4 hours after mixing. Thereafter, the cement continues to harden for a considerable period of time, much like other cements. With faster setting cement, such as is preferred with production molding applications, the initial set may commence in 30 minutes and the pieces removed from the mold in two hours. The cement will not be completely set for 24 hours. 
     The preferred frothing agent is powdered magnesium, which reacts with the oxychloride cement to continuously produce small bubbles. The precise chemistry of the reaction is not understood, but it is believed that the reaction gives off hydrogen gas. It is known that the powdered magnesium continues to generate gas bubbles until it is consumed. The mere entrainment of air bubbles is not satisfactory because the air invariably escapes to the atmosphere before the cement is set. Moreover, entrained air cannot generally be forced into the pores of a porous substrate. That is, when a liquid having air entrained therein is applied to a porous fiberboard or cellulose foam, for example, the porous material will sift out the entrained bubbles while only the liquid impregnates the porous material, making a dense product. On the other hand, by frothing the magnesium oxychloride cement with an internal foaming agent, bubble formation continues until the cement sets. It continues to form bubbles within the pores of the porous substrate so that a low density honey-combed product is obtained that is still fireproof. 
     In order to control the size of the bubbles generated by the reaction of the foaming agent and the magnesium oxychloride cement, I prefer to include a small amount of surfactant. Inasmuch as magnesium oxychloride cement system is basic, the surfactant should be anionic, although it is believed that certain non-ionic surfactants are also suitable. The preferred detergent is a surfactant known as Rohm &amp; Haas &#34;S-100&#34;, defined by the manufacturer as isooctyl phenoxy polyethoxy ethanol containing 10 mols ethylene oxide. Other surfactants, such as GAF 5360, said to be a nonylphenoxypoly (ethyleneoxy) ethanol, or &#34;Duponol ME&#34; a fatty alcohol sulfate, are also highly satisfactory. The surfactant serves to control not only the size of the bubbles but also the amount. 
     Depending upon the particular surfactant, approximately 1/2 percent may be added based on the weight of the cement mixture. When smaller amounts of detergent or surface active agents are employed the amount of bubbles and the size of the bubbles is accordingly reduced. The surfactants vary greatly in ability to produce bubbles, so the weight of added surfactant must depend upon the material used. The range is generally from 0.01 to 1% of the weight of the mixture. 
     While the surfactant controls the size and amount of bubbles, it does not in itself contribute gas bubbles. In other words, the surfactant controls whether many small bubbles or few large bubbles will be produced by the frothing agent in the cement. In order to increase frothing, I have discovered that the addition of a small amount of lactic acid renders the froth much more reactive. Where vigorous foaming is desirable, I prefer to add about 0.1% lactic acid (based on the weight of the mixture) to the aqueous magnesium chloride component. When magnesium is the frothing agent added to the magnesium oxide component, a vigorous reaction commences upon mixing the components. 
     Lactic acid is believed to react with magnesium powder, which in turn reacts with the magnesium chloride. Frothing is increased about fourfold by the addition of 0.1% lactic acid. This increase in frothing may permit a decrease in the amount of magnesium required. Moreover the lactic acid serves as a cure control in that the reaction is exothermic. By increasing the temperature the time of curing the cement is reduced. Whereas normal curing of magnesium oxychloride cement takes about 2 hours for the initial set, the addition of a small quantity of lactic acid can reduce this time to less than 1 hour. Shortening of the curing time is important where the frothing mixture is introduced in the drying sequence of an existing line, as in the case of fireproofing fiberboard. The normal drying and compression period in making fiberboard is relatively short, so cure control by lactic acid permits flexibility in accommodating operation of existing capital equipment. In other applications, such as forming molded products, the higher temperature may not be desirable, so lactic acid may be omitted. 
     The frothing agent, such as powdered magnesium, may be added at any time after mixing of the cement ingredients and before the initial setting. In fact, the frothing agent may be combined with the dry magnesium oxide and packaged and stored. Then, when the magnesium oxide is added to the magnesium chloride in water, the mixture immediately begins to froth as well as to react to form a magnesium oxychloride cement. Where powdered magnesium is the frothing agent, it is preferably added in the amount of about 0.1% or less of the weight of the cement. It has been found that magnesium in an amount between 0.05 and 0.2  of the weight of the cement may be added to give satisfactory frothing. 
     The surfactant is conveniently added along with the powdered magnesium, although it may be added separately. Also, the surfactant may be packaged and stored with the magnesium oxide and powdered cement to make simple, two-part recipe which simply requires the addition of water. 
     When the frothing combination of magnesium chloride, magnesium oxide, powdered magnesium, detergent and water is prepared, it is ready for coating, impregnating laminating, or molding. These steps must take place before the initial set commences. In the absence of any additives, magnesium oxychloride cement sets about 120 minutes after the ingredients are mixed when ordinary commercial grades of calcined magnesium oxide are used. However, where calcining of the magnesium oxide takes place at a lower temperature and under appropriate conditions, the initial cure of the cement may be commenced much sooner. For most purposes, a 40 minute cure is highly satisfactory since it permits thorough impregnation and working of the product before the initial set and still does not require undue periods of waiting for curing during the processing step. 
     Insoluble fillers may be added where desired. For example, insoluble calcium carbonate, such as powdered limestone or marble dust, silica flour, magnesium carbonate, and other insoluble materials may be introduced. Ordinarily, soluble salts should be avoided because they can be leached out and reduce the strength of the foamed cement. 
     In certain instances, the material used as a filler may also have ingredients contained therein which also functions as a frothing agent. For example, black slate from the Chili Bar Quarry in Placerville, California, has the following analysis upon calcining: 
     
                       Table 1                                                     
______________________________________                                    
SiO.sub.2           59.70%                                                
TiO.sub.2           .79%                                                  
Al.sub.2 O.sub.3    16.98%                                                
Fe.sub.2 O.sub.3    .52%                                                  
FeO                 4.88%                                                 
CaO                 1.27%                                                 
MgO                 3.23%                                                 
K.sub.2 O           3.77%                                                 
Na.sub.2 O          1.35%%                                                
CO.sub.2            1.40%                                                 
FeS.sub.2           3.82%                                                 
Carbon              .46%                                                  
Sundry others and water                                                   
present below 110°C.                                               
                    .70%                                                  
______________________________________                                    
 
    
     While it is not precisely understood what components of slate having the foregoing analysis serves as a foaming agent, it has been determined in practice that the addition of a foaming agent is unnecessary where substantial amounts of finely divided slate of the foregoing analysis is used in the manufacture of foamed products according to the present invention. 
     The slate may be added in a variety of amounts depending on the product desired. Preferably, in manufacturing simulated roofing shakes, between 10 and 25 pounds of slate is added per gallon of MgCl 2  solution. 
     Magnesium oxychloride cement is at least four times as strong as Portland cement so that products fireproofed with oxychloride cement according to the present invention retain substantial strength along with low density. Moreover, Portland cement is moisture absorbent, while magnesium oxychloride is not. These properties permit utility in aircraft, for example, for soundproofing and insulation. 
     The cement products of this invention may be made of even lower density by the addition of light-weight materials. For example, mixing the cement with polystyrene beads and molding the combined product gives a light-weight construction material that will not support combustion. The individual beadss will vaporize in heat, but there is no spread of flame and the product is very low in density. Other normally burnable materials, such as cellulosic substances, plastics and organic compositions, may thus be incorporated in the cement to greatly upgrade the fireproof properties of conventional materials. Glass fibers are heat-degradable and are completely consumed in the heat of a butane torch. By incorporating glass fibers in the cement, no distruction of the glass takes place. Other materials which melt or give off noxious gases upon the application of the heat normally encountered in a building fire may also be upgraded as to fire-proofing properties by this invention. 
    
    
     EXAMPLE 1. 
     In this example simulated roofing shakes were prepared using molds having the configuration of wooden shakes in two courses of several shakes per course. 72.2 pounds of 20 mesh slate having the analysis indicated in Table 1 was blended with 24.8 pounds of magnesium oxide and 3 pounds of iron oxide pigment. After these ingredients are thoroughly mixed, 21.4 pounds of the blended mixture is added to one gallon of 22° Baume magnesium chloride liquid. The liquid and powder are thoroughly mixed and the mixture is sprayed onto plastic molds simultaneously with the application of chopped fiberglass strands at the rate of 0.8 ounces per square foot of mold area. The slate reacts with the cement ingredients to foam the cement in the same manner as magnesium powder does. The fiberglass strands are cut into lengths between 1 and 2 inches and applied to the molds at the same time as the mixture is sprayed to give simultaneous application. The sprayed molds are stacked and held for two hours until they are hard enough to be removed. They are then trimmed and packaged for shipment. The molded product has the appearance of wooden shakes and can be easily applied as a roofing material with hammer and nails. The product is completely fireproof, as contrasted to wooden roofing shakes. 
     EXAMPLE 2. 
     In the preparation of the froth, 191/4 pounds of magnesium chloride were added to 41/4 gallons of water. The specific gravity was measured and additional magnesium chloride was added to adjust the specific gravity to 22° Baume. The combined total makes about 5 gallons. 200 grams of lactic acid were added to the aqueous mixture. Magnesium oxide was then measured in an amount equal to 5.5 pounds magnesium oxide to each gallon of magnesium chloride in water. Then, 32 grams of powdered magnesium, which is about 0.1 percent of the dry weight of the magnesium oxychloride cement mixture and 100 grams of surfactant (Rohm &amp; Haas X-100) were added to the magnesium oxide component. The surfactant constituted about 0.5 percent of the dry weight of the total mixture. Chopped glass fibers, in an amount equal to 3% of the total were added to the dry component and mixed thoroughly. The dry magnesium oxide component was added to the aqueous magnesium chloride component and the mixture immediately began to froth. It was poured into the female part of a mold having a decorative configuration for a building ornament. The male part of the mold was closed over the female part and the cement permitted to set. After 2 hours the molded fireproof product was removed from the mold. 
     EXAMPLE 3. 
     Fireproof products according to the present invention may be molded in a desired configuration. Wooden roofing shakes were simulated by forming a mold by vacuum drawing synthetic resin over wooden shakes laid in courses as in roofing. The inside dimensions of the mold were 30 inches × 30 inches and resembled two courses of cedar shakes. Commercially available aqueous magnesium chloride was diluted with water to 22° Baume. For each gallon of this liquid, 15 pounds of magnesium oxide mixture having the following composition was added: 
     
         371/2%       magnesium oxide (50 Min. set)                                
30%          limestone dust - 80 mesh                                     
7%           limestone dust - 200 mesh                                    
10%          silica flour                                                 
21/2%        asbestos fibers                                              
4%           diatomaceous silica                                          
11/2%        pigment (brown and black)                                    
71/2%        waterproofed vermiculite                                     
0.01%        foaming agent                                                
 
    
     The frothing agent mixture was sprayed through an airless spray gun into the mold to completely cover the bottom of the mold. Simultaneously with the spraying of cement, chopped glass fibers were sprayed into the mold in an amount equal to 1/2 ounce fibers per square foot of mold. Since the bottom of the mold had an irregular surface to resemble the shakes, the frothing cement tended to form in the depressions to a greater extent than on the raised portion, but the mold was completely covered to about 1/4 inch. The rovings had a length from about 3/4 inch to about 11/2 inch. The fiberglass provides resiliency and strength, so care was taken to make certain that a uniform layer throughout the area of the mold is provided. The mold was variable in depth from about 1/4 inch to about 11/4 inch. It was filled with the fibers and cement and permitted to set for two hours. After the panel had thoroughly set, it was removed from the mold to give a strong, light-weight panel resembling wooden shakes but was completely fireproof. 
     The weight of the panel was approximately 15 pounds, and had an average thickness of 1/2 inch. It could be nailed onto conventional roofing surfaces and was completely incombustible upon heating to 1350° F. For molded products simulating wood, a density of between 30 and 40 pounds per cubic foot should be obtained. For most purposes, a density of 35 pounds per cubic foot is optimum for ease of manufacture and for resembling wood product density. 
     The products of this invention are relatively low in density while very high in fire resistance, making them suitable for use in construction of buildings.