Abstract:
The present invention relates to a composite fiberboard, which is specifically adapted for use as a coverboard in roofing systems. The formulation and physical characteristics of the composite fiberboard of the invention have increased the flexural strength of the board relative the flexural strength of current commercial fiberboards of similar type. In turn, the composite fiberboard is able to meet the Class 90 wind uplift requirements as measured by Factory Mutual FM 4450 Approval Standard for Class I Insulated Steel Deck Roofs.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims the benefit under 35 U.S.C. §119(e) of U.S. provisional application Ser. No. 60/765,708, filed Feb. 6, 2006. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates to an enhanced composite fiberboard especially designed for use as a coverboard in roofing systems. The composite fiberboard of the invention has certain advantages over other types of boards used in roof coverboard systems, such as gypsum-based and perlite-based boards.  
         [0003]     Gypsum-based roofing coverboards, such as the Gypsum-based roofing coverboards marketed by United States Gypsum Corporation under the name “SECURE ROCK” and Georgia Pacific Corporation under the name “DENSDECK”, are commercially available. While these gypsum-based boards perform very well, in terms of flexural strength and compressive resistance, there has remained a need to take weight out of the board, without significantly affecting strength performance.  
         [0004]     Perlite-based composite fiberboards have been used as the installation layer component in roofing systems for decades. These insulation boards, such as the kind marketed by Johns Manville International, Inc. under the name “FESCO”, are typically lower in basis weight and density than the aforementioned gypsum-based boards and, thus, do not have the requisite flexural strength and handleability to be used as the coverboard component of the roofing system. It is generally known in the art that these insulation fiberboards tend to break during installation. Thus, what is needed is a lighter board which meets the desired strength and flexibility performance for a coverboard component of a roofing system.  
       SUMMARY OF THE INVENTION  
       [0005]     The present invention relates to a composite fiberboard, which is specifically adapted for use as a coverboard in roofing systems. The material components of the composite fiberboard of the invention have been available for many years and have been used in numerous products including, but not limited to, acoustical ceiling panels. Surprisingly, beneficial results were obtained by decreasing the perlite content and simultaneously increasing the cellulose fiber content of conventional perlite-based insulation material.  
         [0006]     The composite fiberboard comprises, by dry weight, from about 30% to about 60% cellulosic fibers and from about 20% to about 50% expanded perlite. The fiberboard has a thickness in the range from about 0.475 inches to about 0.70 inches and a basis weight of from about 0.70 pounds per square foot (psf) to about 0.95 psf. The formulation and physical characteristics of the composite fiberboard of the invention provide increased flexural strength such that the composite fiberboard is able to attain a Class 90 wind uplift rating pursuant to Factory Mutual FM 4450 Approval Standard for Class I Insulated Steel Deck Roofs (hereafter referred to as “the FM 4450 test”) as measured against the mode of failure of fastener fracturing.  
     
    
     DESCRIPTION OF THE INVENTION  
       [0007]     Conventional perlite-based insulation roofing material typically contains several of the following ingredients in varying amounts: perlite, cellulose, starch, latex, alum, silicone, bituminous material and mineral wool. Perlite-based insulation roofing material is significantly less strong than the materials used in the coverboard component of the roofing system, e.g. the gypsum-based coverboards described above. An obvious way to increase flexural strength of perlite based insulation roofing material would be to increase the basis weight of the product. However, increasing the basis weight was found to produce a brittle board that was subject to cracking at pressures below 90 psf in the wind uplift test. Surprisingly, it was found that by increasing the basis weight and altering the amounts of the various ingredients of conventional perlite-based insulation fiberboard panels, panels having high flexural strength and a resistance to premature cracking could be produced. In other words, boards having a high energy to fracture when pressure is applied, could be produced without the expected significant increase in weight.  
         [0008]     The composite fiberboard of the invention comprises, by dry weight, from about 30% to about 60% cellulosic fibers, from 0% to about 35% mineral wool fibers, from about 20% to about 50% expanded perlite, from about 5% to about 15% starch binder, from 0% to about 6% latex binder, from 0% to about 1% alum, from about 0.2% to about 0.6% silicone and from about 0.1% to about 0.3% polymer retention aid and preferably from about 40% to about 44% cellulosic fibers, from 14% to about 20% mineral wool fibers, from about 29% to about 33% expanded perlite, from about 8% to about 9% starch binder, from 2% to about 3% latex binder, from 0.4% to about 0.5% alum, from about 0.4% to about 0.45% silicone and from about 0.2% to about 0.25% polymer retention aid. The composite fiberboard of the invention has a basis weight in the range from about 0.70 to about 0.95 pounds per square foot; a thickness in the range from about 0.425 to about 0.7 inches; and a width and length of two by four feet or two by eight feet. Although one of ordinary skill would generally expect an adjustment in basis weight to have an impact on the material&#39;s flexural strength, it has been determined that such an impact on flexural strength does not necessarily equate to an impact of the same magnitude on the material&#39;s ability to resist wind uplift pressures.  
         [0009]     A key component in the composite fiberboard formulation of the invention is cellulosic fiber. The cellulosic fiber improves the strength to the fiberboard, relative conventional boards of comparable thickness, width, length and basis weight, through the hydrogen bonding between the cellulosic fibers and an interfelting of the cellulosic fibers with the expanded perlite particles. More specifically, the cellulose fibers assist in holding the expanded perlite particles in place within the board and also act as a bulking material to maintain the fiberboard within the required basis weight range. Unlike conventional roofing insulation board, such as the aforementioned FESCO insulation board, the fiberboard of the invention does not require bituminous material, such as asphalt, to assist the cellulosic fibers in holding the expanded perlite particles in place.  
         [0010]     In the production of the composite fiberboards of the invention, the aforementioned ingredients are metered into a mixer where they are blended with water and delivered as a slurry to a wet forming apparatus such as a Fourdriner machine. The wet forming apparatus transforms the slurry of ingredients into a wet-laid mat of selected thickness, basis weight/density and percent solids. The wet-laid mat is then passed through a dryer where it is dried into a composite fiberboard. The composite fiberboard is conveyed to a finishing area where the board is cut and trimmed to the desired width and length.  
         [0000]     Wind Up-Lift Test:  
         [0011]     With respect to boards used in roofing systems, a major concern is whether or not the board has the required strength to withstand extreme weather conditions. It is important that a board&#39;s wind uplift resistance be optimized to avoid deleterious effects when the board is exposed to extreme wind conditions. The board&#39;s ability to withstand breaking or fracturing when exposed to pressure is a measure of the board&#39;s resistance to wind uplift.  
         [0012]     In general, wind uplift is the force generated by wind on a roof system resulting from wind-induced pressures. Wind that is deflected around and across the surfaces of a building causes a drop in air pressure immediately above the roof surface (negative pressure); the air in the building will flow beneath the roof deck (positive pressure). The combined uplift pressures tend to lift the roof upward.  
         [0013]     The wind uplift performance of several samples having the aforementioned physical characteristics was tested using the widely accepted and generally available FM 4450 test which is herein incorporated by reference. In brief, the FM 4450 test measures the board&#39;s ability to withstand breaking or fracturing when exposed to pressure. In other words, the test measures the energy that is required for the board to fail upon application of a schedule of pressures in 15 psf increments beginning with 30 psf. Prior to and during attainment of each increment of pressure, the assembly is observed for failure. In order to qualify for Class I-90 as measured against a particular mode of failure, the FM 4450 test requires that the test material resist a minimum uplift pressure of 90 psf without a failure for a duration of one minute. The mode of failure tested in the examples set forth herein was the fracture of at least one fastener.  
         [0014]     Set forth in Table 1 are samples having varying physical characteristics which were tested to determine if the sample possessed the requisite wind uplift resistance. The materials are listed in percent by dry weight.  
                                             TABLE 1                       Physical                   Characteristics   Sample 1   Sample 2   Sample 3                                Cellulose   40.58   40.42   43.93       Perlite   33.47   33.38   28.98       Miner Wool   14.65   14.08   14.46       Starch   7.91   8.30   8.90       Latex   2.43   2.73   2.64       Alum   0.42   0.48   0.46       Silicone   0.37   0.42   0.40       Polymer Retention Aid   0.17   0.20   0.22       Thickness (inches)   0.455   0.47   0.47       Basis Weight (psf)   0.77   0.75   0.76       Density (lbs/board ft)   1.70   1.61   1.62       Density (pcf)   20.40   19.32   19.44                  
 
         [0015]     The FM Approvals Uplift Pressure Apparatus is a steel pressure vessel arranged to supply compressed air pressure to the underside of the test panel at pre-established schedule. The pressure vessel measures 9 feet long×5 feet wide×2 inches deep. Each of the above samples was cut to 4′×8′. Each sample was mechanically fastened with a diamond-in-square fastening pattern to a 5′×9′ flat steel deck. A “diamond-in-square fastening pattern” is widely known and accepted by those skilled in the art. The results of these tests are set forth in Table 2.  
                                                     TABLE 2                           Pressure   Sample 1   Sample 2   Sample 3       Time (min)   (psf)   (Pass/Fail)   (Pass/Fail)   (Pass/Fail)                                0:01 to 1:00   30   Pass   Pass   Pass       1:01 to 2:00   45   Pass   Pass   Pass       2:01 to 3:00   60   Pass   Pass   Pass       3:01 to 4:00   75   Pass   Pass   Pass       4:01 to 5:00   90   Pass   Pass   Pass       5:01 to 6:00   105   Pass   Fail*   Pass       6:01 to 7:00   120   Pass   —   Pass       7:01 to 8:00   135   Fail**   —   Fail**                 *Fastener fracture occurred at 20 second mark during 105 psf interval.            **Fastener fracture occurred on approach to 135 psf interval.             
 
         [0016]     In the following example, the formulation was altered to illustrate the impact such alteration would have on the wind uplift performance. In particular, the amount of cellulose was deceased to be more in-line with conventional fiberboard formulations.  
                             TABLE 3                       Composition   Comparative       (% by dry weight)   Sample                                Cellulose   19.9       Perlite   61.9       Miner Wool   0.0       Starch   15.0       Latex   2.40       Alum   0.30       Silicone   0.40       Polymer Retention Aid   0.10       Thickness (inches)   0.50       Basis Weight (psf)   0.89       Density(lbs/board ft)   1.69       Density (pcf)   20.3                  
 
         [0017]     The results of the FM 4450 test are set forth in Table 4.  
                                     TABLE 4                           Pressure   Comparative       Time (min)   (psf)   Sample                                0:01 to 1:00   30   Pass       1:01 to 2:00   45   Pass       2:01 to 3:00   60   Pass       3:01 to 4:00   75   Pass       4:01 to 5:00   90   Fail*       5:01 to 6:00   105   —       6:01 to 7:00   120   —                 *Fastener fracture occurred at the start of the 90 psf interval.             
 
         [0018]     As illustrated in Tables 3 and 4, the formulation for the Comparative Sample has two material percentages outside of the critical material ranges set forth above, namely 19.9% cellulose and 61.9% perlite and such sample was unable to withstand 90 psf for the required one minute time interval. This, in turn, is evidence of the criticality of the composition, and, in particular, the requisite amount of cellulose.  
         [0019]     It will be understood by those of skill in the art that variations on the embodiments set forth herein are possible and within the scope of the present invention. The embodiments set forth above and many other additions, deletions, and modifications may be made by those of skill in the art without departing from the spirit and scope of the invention.