Abstract:
An improved fiber reinforced material for use in the manufacture of gaskets is produced by impregnating a nonwoven fabric with an aqueous dispersion of a rubber and filler. The water is then evaporated out of the impregnated fabric. The final product is formed by curing the rubber under heat and pressure.

Description:
BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     The present invention relates to the manufacture of a fiber reinforced compressible material and particularly to a material useful in the manufacture of gaskets. The present invention is also directed to a gasket material comprising fibers and a rubber. Accordingly, the general objects of the present invention are to provide an improved material and method of manufacture thereof. 
     (2) Description of the Prior Art 
     In order to meet government regulations regarding the emissions of certain gases, such as hydrocarbons and halogens, gaskets in mechanically jointed flanges must be able to maintain their seal and prevent leakage of fluids and gases even when subjected to an extremely severe operating environment and undesirable mechanical conditions. Thus, these gaskets must be able to function even though the flanges are either poorly designed or poorly machined and must maintain the ability to seal the flange and prevent leakages even under high operating temperatures and high internal pressures. Gaskets produced from many prior art materials either leak or blow out when exposed to the aforementioned conditions and environments. 
     Accordingly, it is one of the many objects of the present invention to produce a gasket material which exhibits desirable sealability, creep resistance and blow out resistance characteristics. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes the above-discussed disadvantages and other deficiencies of the prior art and provides a novel and improved fiber reinforced rubber material for use in the manufacture of gaskets. 
     The improved fiber reinforced rubber material in accordance with the present invention is produced by impregnating a nonwoven fabric with an aqueous dispersion of rubber and filler until saturated. The aqueous dispersion may further contain varying amounts of inorganic particulate fillers, compounding agents or other materials necessary to impart the desired characteristics to the final product. The impregnated fabric is heated, to evaporate out the water, and is then pressed at a temperature which is sufficiently high to cure the rubber. The final product may be used to form gaskets. 
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The improved fiber reinforced rubber material of the present invention is formed by first impregnating a nonwoven fabric comprised of natural or synthetic fibers with an aqueous dispersion of either a natural or synthetic rubber until saturated. The aqueous dispersion also contains varying amounts of inorganic particulate fillers, such as mica, silica, calcium carbonate, carbon black or clay, and will typically also include compounding agents such as accelerators, curatives, and antioxidants, in order to achieve the desired saturate rheology and final product characteristics. This saturation is accomplished by dip coating, knife coating, roll coating or other coating techniques well known to those skilled in the art. The saturation of the nonwoven fabric should be sufficient enough to achieve the desired rubber content in the final product. 
     The next step involves heating or drying the now saturated nonwoven fabric to evaporate out all the water. The temperature should range from the lowest temperature required to evaporate out the water, depending upon the dispersion content and the thickness of the nonwoven fabric, to below the melting or degrading temperature of the fibers used, preferably between 150° F. to 450° F. 
     Forming the final product requires a curing of the rubber by subjecting the fabric to a pressure between 50 and 3000 pounds per square inch and a temperature between 250° F. and 450° F. Preferably, this curing step utilizes hot platens to press the fabric. 
     Table 1 illustrates the acceptable and preferred ranges of the quantities of the ingredients in an aqueous dispersion useful in the practice of the present invention expressed in percentages by dry weight in the final product. 
     
                       TABLE I______________________________________             Acceptable                       PreferredIngredients       Ranges    Ranges______________________________________Elastomeric Binder             10-80     25-50Inorganic Filler  10-80     40-70Compounding Agents              2-10     3-7______________________________________ 
    
     The present invention may also include extenders, plasticizers, pigments antioxidents, curatives, release agents and other processing aids as necessary. 
     The nonwoven fabric may be comprised of natural or synthetic fibers with cellulose, fiberglass, polyolefin, polyamide, polyester, polyimide and polyacrylic fibers being representative examples of such fibers. Elastomeric binders useful in the practice of the present invention may include natural or synthetic rubber, such as chloroprene, nitrile, isoprene, acrylic or styrene-butadiene rubber or blends of these types of rubbers. 
     The nonwoven fabric should be saturated with an aqueous dispersion of between 30% to 60% solids, these solids being the elastomeric beinder, inorganic filler and compounding agents, so that between 70-90% by weight of the final product will be made up of the solids and 10-30% by weight will be made up of the fibers comprising the nonwoven fabric. If the aqueous dispersion comprises less than 30% solids then it would be difficult to obtain a final product having at least 70% by weight of the solids and if the dispersion comprises more than 60% solids there will be flow problems. 
    
    
     An example of the present invention was prepared by impregnating a nonwoven fabric, of three denier polyester fiber, which had an approximate weight of 4.65 ounces per square yard, with an aqueous dispersion of chloroprene rubber latex and a filler until saturated, as established when 34% rubber content or an 85% weight increase was obtained. The aqueous dispersion contained the following solids: Chloroprene rubber, 50 grams; C3000 mica, 50 grams; zinc oxide, 7.5 grams; sulphur, 2 grams; nickel butyl carbonate, 5 grams; antioxident, 2 grams; and phenolic resin, 10 grams. 
     The saturated fabric was dried in a circulating oven at 230° F. and the rubber was then cured by pressing the fabric between hot platens, at 2000 pounds per square inch and at 320° F., for two minutes. 
     The final product demonstrated the following qualities: 
     
         ______________________________________Parameter                Results______________________________________Thickness, in.           .022Density, g/cc            1.55C D Tensile, psi; per ASTM F 152                    4,100Sealability, ml/hr; per ASTM F37, Fuel A                    .96250 psi, 30 &#34;HgA Creep, %; per ASTM F38B, 22 hrs,                    15.7105° C., 3000 psiB Creep, %; per ASTM F38B, 20 hrs,                    22.4150° C., 2500 psiCompressibility @ 5000 psi, %; per                    8.7ASTM F36, Type 1 materialRecovery, %; per ASTM F36, Type 1                    62.7materialElmendorf tear, gms; per ASTM D689                    721______________________________________ 
    
     Two other examples, and the demonstrated qualities, are as follows. 
     EXAMPLE II 
     
         ______________________________________Ingredient      % Total of Saturant______________________________________Nitrile LCG61C Latex           12.7Neoprene 735 Latex           12.7ABS DSC-44B Latex           12.7Calcium Carbonate           57.1Zinc Oxide      3.1Sulfur          1.1Antioxident     .6______________________________________ 
    
     A nonwoven fabric, of three and six denier one &amp; one-half inch polyester fibers, having a 3.2 ounce per square yard web weight, was impregnated with the above saturant until saturated. The now saturated web was dried at a temperature of 250° C. for 20 minutes and the rubber cured, by pressing the fabric between hot platens, which were compressed at 2000 psi and at a temperature of 300° F. for 5 minutes. 
     The finished product demonstrated the following qualities: 
     
         ______________________________________Parameter                Results______________________________________Thickness, in.           .031Density, g/cc            1.85Tensile, psi; per ASTM F 152                    2500Sealability, ml/hr; per ASTM F37, Fuel A                    .1250 psi, 30 &#34;HgA Creep, %; per ASTM F38B, 22 hrs,                    29.105° C., 3000 psiCompressibility @ 5000 psi, %; per                    20.0ASTM F36, Type 1 materialRecovery, %; per ASTM F36, Type 1                    70.0materialElmendorf tear, gms; per ASTM D689                    560______________________________________ 
    
     EXAMPLE III 
     
         ______________________________________Ingredient       % of Saturant______________________________________Nitrile LCG61C Latex            18.5Neoprene 736 Latex            18.5Calcium Carbonate            55.6Zinc Oxide       1.9Sulfur           .7Antioxident      1.1Stabilizer       3.7______________________________________ 
    
     A nonwoven fabric, of 3 and 6 denier one and one-half inch polyester fibers, having a 3.2 ounce per square yard web weight, was impregnated with the above saturants until saturated. The now saturated web was dried at a temperature of 255° F. for 30 minutes and the rubber cured by pressing the fabric between hot platens, which were compressed at 1750 psi and at a temperature of 300° F. for 3 minutes. 
     The finished product demonstrated the following qualities: 
     
         ______________________________________Parameter                Results______________________________________Thickness, in.           .040Density, g/cc            1.75Tensile, psi; per ASTM F 152                    1750Sealability, ml/hr; per ASTM F37, Fuel A                    5250 psi, 30 &#34;HgA Creep, %; per ASTM F38B, 22 hrs,                    29.3105° C., 3000 psiCompressibility @ 5000 psi, %; per                    25.0ASTM F36, Type 1 materialRecovery, %; per ASTM F36, Type 1                    60.0materialElmendorf tear, gms; per ASTM D689                    818______________________________________ 
    
     While preferred embodiments have been shown and described, various modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it must be understood that the present invention has been described by way of illustration and not limitation.