Fire Resistant Wallboard

Abstract

A fire resistant wallboard with carbon black and expandable graphite. A carbon black layer is positioned between the conventional cover sheet and a gypsum core with embedded expandable graphite. The carbon black layer may be employed either with one of the cover sheets or with both of the cover sheets.

Claims

1. A fire resistant wallboard comprising in order: a. a front cover sheet; b. a front carbon black layer; c. a core comprising a mixture of gypsum and expandable graphite; and d. a back cover sheet, wherein the front carbon black layer is positioned between the front cover sheet and the gypsum core.

2. The fire resistant wallboard of claim 1, wherein the front carbon black layer is between 8 mil and 15 mil thick.

3. The fire resistant wallboard of claim 1, wherein front carbon black layer dosage is between 0.5 to 5.0 lbs/MSF.

4. The fire resistant wallboard of claim 1, wherein expandable graphite dosage in the core is between 3.0 to 30.0 lbs/MSF.

5. A fire resistant wallboard comprising in order: a. a front cover sheet; b. a front carbon black layer; c. a core comprising a mixture of gypsum and expandable graphite; d. a back carbon black layer; and e. a back cover sheet, wherein the front carbon black layer is positioned between the front cover sheet and the gypsum core and the back carbon black layer is positioned between the back cover sheet and the gypsum core.

6. The fire resistant wallboard of claim 5, wherein the front carbon black layer and the back carbon black layer are between 8 mil and 15 mil thick.

7. The fire resistant wallboard of claim 5, wherein front carbon black layer dosage and back carbon black layer dosage are between 0.5 to 5.0 lbs/MSF.

8. The fire resistant wallboard of claim 5, wherein expandable graphite dosage in the core is between 3.0 to 30.0 lbs/MSF.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] FIG. 1 is a photographic cross-section view of a first embodiment of a fire resistant wallboard in accordance with the present invention.

[0010] FIG. 2 is a photographic cross-section view of a second embodiment of a fire resistant wallboard in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] FIG. 1 shows a cross-section of a fire resistant wallboard 10 that exposes the various layers of the fire resistant wallboard 10 of the present invention. Beginning in order from the front of the wallboard 10 to the back of the wallboard 10, the wallboard 10 includes the following layers. A front cover sheet 12, a front carbon black layer 14, a gypsum+expandable graphite core 16, and a back cover sheet 20.

[0012] The front cover sheet 12 and the back cover sheet 20 are conventional paper cover sheets used in conventional wallboard construction.

[0013] The front carbon black layer 14 is formed of carbon black. The front carbon black layer 14 is between 8 mil (0.008 inch, 0.2032 mm) and 15 mil (0.015 inch, 0.381 mm) thick. The carbon black layer 14 extends over the full length and width of the wallboard 10. The front carbon black layer 14 is Thermax N991, manufactured by CanCarb of Medicine Hat, Alberta, Canada. As shown in Table 1, Thermax in 991 has the following characteristics.

TABLE-US-00001 TABLE 1 ASTM Test Thermax Parameter Method N991 Powder Sieve Residue D1514 325 Mesh % (ppm) max. 0.0250 (250) Magnetics on 325 Mesh % 0.0005 (5) (ppm) max. Nitrogen Surface Area, m2/g D6556 7.0-12.0 Oil Absorption Number D2414 44.0 (OAN) cm3/100 g max. Ash Content % max. D1506 0.20 pH D1512 9.0-11.0 Toluene Extract % max. 0.50 Heat Loss % max. D1509 0.1

[0014] In the process of manufacturing the wallboard of the present invention, the carbon black layer is deposited on the front cover sheet 12 before being married to the gypsum+expandable graphite core 16.

[0015] The gypsum+expandable graphite core 16 comprises a mixture of a conventional gypsum core and expandable graphite evenly distributed throughout the core 16. The core 16 comprises approximately 16 pounds per MSF (thousand square feet) of the finished core 16. Two different grades of expandable graphite, 3494 and 3570 manufactured by Asbury Graphite of North Carolina, Inc. of Lumberton North Carolina, can be used for the core 16. Specifications for expandable graphite 3494 and expandable graphite 3570 are shown in Table 2 and Table 3 below.

TABLE-US-00002 TABLE 2 Expandable Graphite 3494 General Product Description Minimum Maximum % Moisture 0 3 % ExpCarb 80 100 % +50 Mesh (300 Micron) 0 5 % 200 Total (75 Micron) 0 25 Expansion Ratio X:1 70 130 pH 1 6

TABLE-US-00003 TABLE 3 Expandable Graphite 3570 General Product Description Minimum Maximum % Ash 0 10 0 10 % Moisture 0 2 0 2 % ExpCarb 90 100 % +100 Total (150 Micron) 85 100 Expansion Ratio X:1 215 300 pH 5 10

[0016] A control formula for a gypsum core wallboard contains 60 lbs./MSF of vermiculite VCX 204 supplied by Specialty Vermiculite Corp. of Enoree, South Carolina. The specification for the vermiculite is shown in Tables 4, 5, and 6.

TABLE-US-00004 TABLE 4 Typical Properties of VCX Vermiculite Property Typical Value Color Dark greenish brown to golden brown Shape Flake Angle of Repose 27-45 Solubility Insoluble in water Aspect Ratio 20-40 Surface Area (a) 0.5-1.0 (m.sup.2/gm) Mohs Hardness 1.5-2.0 (Nonabrasive) Specific Gravity 2.4-2.8 Bulk Density 40-65 (lbs/ft.sup.3) 640-1,041 (kg/m.sup.3) Refractive Index = 1.52-1.57 , y = 1.54-1.61 Moisture Content 6.5% (heated to 250 F., 110 C.) Total Ignition Loss 8.0-20.0% (at 2000 F., 1100 C) pH (in water) 6-8 Expansion 10X (Volume Change) Expansion Temperature 1100-1800 F. (580-970 C.) Sintering Temperature 2100-2200 F. (1150-1200 C.) Fusion Point 2200-2400 F. (1200-1300 C.) Cation Exchange Capacity 50-100 (m. ./100 g) (a) B.E.T. values obtained by nitrogen adsorption technique

TABLE-US-00005 TABLE 5 Chemical Formula (Mg, Ca, K, Fe.sup.II).sub.3 (Si, AI, Fe.sup.III).sub.4 O.sub.10 (OH).sub.24H.sub.2O Typical Chemical Analysis .sup.(b) Element.sup.(b) % by Weight SiO.sub.2 36-46 MgO 16-24 AI.sub.2O.sub.3 11-16 Fe.sub.2O.sub.3 8-13 K.sub.2O 4-6 CaO 1-3 TiO.sub.2 1-3 MnO 0.1-0.2 Cr.sub.2O.sub.3 0.05-0.2 Na.sub.2O 0.1-0.3 Other 0.0-0.5 .sup.(b)Elements are expressed as oxide

TABLE-US-00006 TABLE 6 Typical VCX Particle Size % Weight Retained On Each Screen Vermiculite Grade U.S. Screens Mm VCX 203 VCX 204 VCX 205 8 2.36 12 1.70 0-10 16 1.18 10-35 20 0.85 25-40 30 0.60 20-40 0-1 40 0.425 2-14 24-40 50 0.30 0-8 24-38 0-20 70 0.212 0-7 10-20 100 0.15 0-15 30-76 100 pan <0.15

[0017] A small-scale fire test that is reflective of full furnace ASTM E119 tests involves cutting out a 7.5 inch7.5 inch size of the test wallboard 10, locating the exact center point of the front cover sheet 12 of wallboard 10, and then affixing a thermocouple to the back (unexposed) cover sheet 20 at the center point location. A blowtorch flame is directed to the center point on the front cover sheet 12 (at a predetermined distance from the front cover sheet 12), and the temperature readings of the thermocouple located on the back cover sheet 20 of the side opposite of the flame are monitored.

[0018] The control wallboard containing vermiculite experienced a net shrinkage of 5/1000 inch, and when heated by way of the blow torch fire test, the back cover sheet of this control wallboard required about 60 minutes to reach 670 F. Table 7 shows these results, along with results for various levels of expandable graphite being added to the paper/core slurry and separately, to the gypsum core slurry. Table 7 shows that a mixture of 1.3 lbs./MSF of expandable graphite Grade 3538 (supplied by Asbury Graphite) in the paper/core layer and 9.3 lbs./MSF in the core displayed both lower shrinkage and a longer time to get to 670 F. than the control wallboard. The dosage range of expandable graphite in the core is 3.0 to 30.0 lbs/MSF (based on total dosage of gypsum in the wallboard)

TABLE-US-00007 TABLE 7 Paper/ Core Gypsum Time Layer Core to reach Dosage Dosage Shrinkage 670 F Raw material in lb/MSF in lb/MSF 1/1000 in (min) Vermiculite VCX 204 0 60 5 60 (control) Asbury EG Grade 3538 1.3 0 42 176 Asbury EG Grade 3538 2.0 0 63 66 Asbury EG Grade 3538 1.3 0 97 131 Asbury EG Grade 3494 0 12.2 Asbury EG Grade 3538 1.3 0 4 84 Asbury EG Grade 3494 0 9.3

[0019] Table 8 shows results of gypsum wallboards which were made by dosing the paper/core slurry and the core with various levels of carbon black and expandable graphite. The dosage range of carbon black in the carbon black layer is 0.5 to 5.0 lbs/MSF (based on total dosage of gypsum in the wallboard).

[0020] Table 8 shows that the mixture of 2.6 lbs./MSF of Thermax N991 carbon black in the paper/core slurry along with 16 lbs./MSF of expandable graphite Grade 3494 had superior performance in both shrinkage and thermal transmission than the control vermiculite wallboard.

TABLE-US-00008 TABLE 8 Paper/ Core Layer Gypsum Core Time to Dosage in Dosage in Shrinkage reach 670 F. Raw material Lb/MSF Lb/MSF 1/1000 in (min) Carbon Black Thermax N990 2.6 0 41 30 Carbon Black Thermax N991 2.6 0 41 52 Carbon Black Thermax N991UP 2.6 0 41 38 Vermiculite VCX 204 0 30 31 34 Carbon Black Thermax N990 2.6 0 Vermiculite VCX 204 0 30 33 48 Carbon Black Thermax N991 2.6 0 Vermiculite VCX 204 0 30 31 44 Carbon Black Thermax N991UP 2.6 0 Vermiculite VCX 204 0 30 30 38 Carbon Black Thermax N991 2.6 0 12 120 Asbury EG Grade 3538 0 65 Carbon Black Thermax N991 2.6 0 1 68 Asbury EG Grade 3570 0 10 Carbon Black Thermax N991 2.6 0 8 90 Asbury EG Grade 3494 0 16 Carbon Black Thermax N991 2.6 0 6 115 Asbury EG Grade 3494 0 16 Vermiculite VCX 204 0 60 5 60

[0021] Turning to FIG. 2, the construction of the fire resistant wallboard 110 is in most regards the same as fire resistant wallboard 10 of FIG. 1 in that elements 110, 112, 114, 116, and 120 of FIG. 2 correspond to and are the same as elements 10, 12, 14, 16, and 20 of FIG. 1. The fire resistant wallboard 110, however, has an additional carbon black layer 118 between the back cover sheet 120 and the gypsum+expandable graphite core 116. The additional carbon black layer 118 has the same characteristics as the carbon black layer 14 shown in FIG. 1. The additional carbon black layer 118 provides additional insulation between any flames at the front cover sheet 112 and temperatures experienced at the back cover sheet 120.

[0022] While this invention has been described with reference to preferred embodiments thereof, it is to be understood that variations and modifications can be affected within the spirit and scope of the invention as described herein and as described in the appended claims.