Source: http://www.google.fr/patents/US4722866
Timestamp: 2013-12-06 05:41:16
Document Index: 184345879

Matched Legal Cases: ['Application No. 2', 'Application No. 77', 'Application No. 76', 'Application No. 78', 'Application No. 77', 'Application No. 76', 'Application No. 2', 'Application No. 77']

Brevet US4722866 - Fire resistant gypsum board - Google�BrevetsRecherche Images Maps Play YouTube Actualit�s Gmail Drive Plus » Recherche avanc�e dans les brevets | Connexion Recherche avanc�e dans les brevets BrevetsA composition useful as the core of fire resistant gypsum board and comprising a major amount of set calcined gypsum and minor amounts of whisker fibers, glass fibers and clay....http://www.google.fr/patents/US4722866?utm_source=gb-gplus-shareBrevet US4722866 - Fire resistant gypsum board Num�ro de publicationUS4722866 AType de publicationOctroi Num�ro de demandeUS 07/046,437 Date de publication2 f�vr. 1988 Date de d�p�t4 mai 1987 Date de priorit�9 avr. 1985�tat de paiement des fraisCaduc Num�ro de publication046437, 07046437, US 4722866 A, US 4722866A, US-A-4722866, US4722866 A, US4722866A InventeursCharles W. Lehnert, Glenn E. Wilson Cessionnaire d'origineGeorgia-Pacific CorporationCitations de brevets (15), R�f�renc� par (37), Classifications (19), �v�nements juridiques (7) Liens externes: USPTO, Cession USPTO, EspacenetFire resistant gypsum boardUS 4722866 A R�sum� A composition useful as the core of fire resistant gypsum board and comprising a major amount of set calcined gypsum and minor amounts of whisker fibers, glass fibers and clay.
We claim: 1. Fire resistant gypsum wallboard having a core sandwiched between facing sheets and comprising the set product of at least about 80 wt. % of calcined gypsum, at least about 0.04 wt. % glass fibers, at least about 0.1 wt. % whisker fibers and at least about 1.5 wt. % clay.
2. Wallboard according to claim 1 having a core comprising the set product of: ______________________________________          Wt. %______________________________________calcined gypsum  about 80 to about 90;glass fibers     about 0.04 to about 1.0;whisker fibers   about 0.1 to about 2.0; andclay             about 1.5 to about 5&#58067;______________________________________ 3. Wallboard according to claim 2 having a core comprising the set product of: ______________________________________          Wt. %______________________________________calcined gypsum  about 83 to about 88;glass fibers     about 0.1 to about 0.4;whisker fibers   about 0.4 to about 1.0; andclay             about 1.5 to about 3.5.______________________________________ 4. Wallboard according to claim 2 wherein the core has a density of about 44 to about 50 lbs/cu. ft. and wherein the amounts and proportions of ingredients comprising the core are such that a core having a thickness of about 0.5 inch has a shrink resistance of no less than 75% and cracks no more than 6 inches/24 sq. in. after heating to about 1800 about 2 hours.
5. Wallboard according to any of claims 2, 3, or 4, wherein said whisker fibers are water-insoluble calcium sulfate anhydrite.
6. Wallboard according to claim 2 having a core wherein said whisker fibers have a testing consistency of about 100 to about 600 grams of water per 100 grams of whisker fibers and a length to diameter ratio of about 400:1 to about 5:1.
7. Wallboard according to claim 6 having a core wherein said whisker fibers have an average length to diameter ratio of about 20:1 to about 30:1.
8. Wallboard according to claim 2 having a core wherein said whisker fibers have a length of about 10 to about 400 micrometers.
9. Wallboard according to claim 8 having a core wherein said whisker fibers have an average length of about 35 to about 45 micrometers.
10. Wallboard according to claim 2 having a core wherein said whisker fibers have a testing consistency of about 200 to about 350 grams of water to 100 grams of fibers and a length to diameter ratio of about 200:1 to about 10:1.
11. Wallboard according to claim 10 having a core wherein said whisker fibers have a length of about 20 to 200 micrometers.
12. Wallboard according to claim 2 having a core which is substantially free from heat-expandable minerals.
13. Wallboard according to claim 2 having a core including at least about 0.5 wt. % vermiculite.
14. Wallboard according to claim 3 having a core including about 0.5 to about 1.5 wt % vermiculite.
15. Wallboard according to claim 4 having a core including about 0.8 to about 1.2 wt. % vermiculite.
16. Wallboard according to claim 2 wherein the clay is kaolin clay.
17. Wallboard according to claim 4 wherein the core comprises the set product of: ______________________________________          Wt. %______________________________________calcined gypsum  about 83 to about 88;glass fibers     about 0.1 to about 0.4;whisker fibers   about 0.4 to about 1.0; andclay             about 1.5 to about 3.5.______________________________________ 18. Wallboard according to claim 4 or 17 wherein said whisker fibers are water insoluble calcium sulfate anhydrite having a testing consistency of about 100 to about 800 grams of water per 100 grams of whisker fibers and a length to diameter ratio of about 400:1 to about 5:1.
19. Wallboard according to claim 2 wherein the core is sandwiched between fiberglass facing sheets.
20. Wallboard according to claim 2 wherein the core is sandwiched between plastic scrim facing sheets.
21. Wallboard according to claim 2 wherein the core is sandwiched between paper facing sheets.
This is a divisional of co-pending application Ser. No. 721,524 filed on Apr. 9, 1985, now U.S. Pat. No. 4,664,707.
FIELD OF THE INVENTION This invention relates to an improved fire resistant composition, and more particularly, to a gypsum composition which is capable of being used as the core of fire resistant gypsum board.
As its name implies, the main ingredient of the core of gypsum board derives from gypsum, which is a naturally occurring mineral typically found in old salt-lake beds, volcanic deposits and clay beds in the form of calcium sulphate dihydrate (CaSO.sub.4.2H.sub.2 O). Gypsum is also formed as a by-product of various industrial processes such as, for example, the manufacture of titanium dioxide and the desulfurization of flue gases. Calcining, that is, heating the mineral to about 120 C. drives off 11/2 molecules of water, leaving behind calcium sulphate hemihydrate (CaSO.sub.4.1/2H.sub.2 O). Anydrous calcium sulfate (CaSO.sub.4) can be produced by heating to a temperature of about 163 "calcined gypsum", is capable of reacting with water to form calcium sulphate dihydrate, which is referred to herein as "set calcined gypsum". Speaking generally, the core of fire resistant gypsum board is made from an aqueous slurry of calcined gypsum which has set to form a hard, fairly rigid product.
Fire resistant gypsum board must have certain basic properties in order to meet accepted standards which dictate whether the board is suitable for commercial use. Such properties are evaluated in fire resistant assembly tests which have been adopted by the industry. When exposed to intense heat, such as that generated by fire in a burning building, the board, which is extensively used for constructing walls and ceilings, is expected to stay in place for a defined length of time where it functions to deter the spread of fire. When subjected to standard fire resistant tests which stimulate conditions in a burning building, it is not unusual for commercially available fire resistant board to remain in place for one to two hours during which time it is exposed to temperatures as high as 1850 resist its tendency to shrink under the influence of heat because, as it shrinks, it progressively pulls away from the fasteners and supports to which it is fastened and eventually collapses. This allows the fire to spread and attack adjacent parts of the building. In addition, the core should resist cracking as it is heated and should also exhibit good strength properties at high temperatures. To summarize, fire resistant gypsum board should have good dimensional stability properties and strength at high temperatures.
REPORTED DEVELOPMENTS There have been a number of developments which have sought to improve the fire resistant properties of gypsum board cores. One of these developments is reported in U.S. Pat. No. 2,526,066 to Croce, which discloses a fire resistant wallboard core comprising set calcined gypsum, unexpanded vermiculite, glass fibers, and/or asbestos fibers. The fibers serve to prevent spalling and cracking of the core as the vermiculite expands when the core is exposed to fire. The expansion of the vermiculite tends to offset the tendency of the gypsum to shrink as the chemically combined water in the gypsum is driven off by heat.
SUMMARY OF THE INVENTION In accordance with this invention, there is provided an improved fire resistant gypsum composition and, particularly, a composition which can be used to excellent advantage as the core of fire resistant gypsum wallboard and which comprises a major amount of set calcined gypsum and minor amounts of glass fibers, whisker fibers and clay. Compositions for use in the present invention can comprise, for example, about 80 to 90 wt. % calcined gypsum; about 0.04 to about 1.0 wt. % glass fibers; about 0.1 to about 2.0 wt. % whisker fibers; and about 0.5 to about 5.0 wt. % clay.
Important advantages flow from the provision of the present invention. For example, fire resistant wallboard which meets industry-accepted fire resistance tests can be made utilizing whisker fibers, a relatively inexpensive material. The use of whisker fibers also improves the fire resistant properties of the wallboard in that such fibers continue to effectively reinforce the core at temperatures as high as 1900 which is about 600 fibers degrade. Further savings in material costs can be realized from the manufacture of the wallboard core of the present invention by eliminating the use of vermiculite, a commonly used ingredient in conventional fire resistant gypsum wallboard, without sacrificing the fire resistant properties which are expected of commercial wallboard. And such advantages can be achieved by manufacturing gypsum board of the present invention according to conventional techniques utilizing existing equipment.
DETAILED DESCRIPTION OF THE INVENTION The essential ingredients of the fire resistant gypsum board core of the present invention are set calcined gypsum, glass fibers, clay and whisker fibers.
The ingredient present in the core of the invention in the greatest amount is set calcined gypsum, that is, calcium sulfate dihydrate formed by the hydration of anhydrous calcium sulfate or of calcium sulfate hemihydrate, either of which can be formed by calcining gypsum. Hydration is typically effected from a water slurry containing the calcined gypsum and other ingredients comprising the core in accordance with usual gypsum board manufacturing techniques. The set calcined gypsum functions to bind together the core ingredients in the form of a solid continuous mass. The calcined gypsum component should not be so alkaline as to have a degrading effect upon the glass fibers of the core composition. In preferred form, a 100 g sample of the calcined gypsum mixed with an equal amount of water forms a mixture which has a pH of about 7 to about 9, most preferably in excess of 7 and less than 9.
The clay component of the gypsum board core improves the core's ability to resist shrinking upon exposure to heat. Examples of clays which can be used in the practice of the present invention are described in aforementioned U.S. Pat. No. 3,616,173 to Green and Sunberg, the disclosure of which, as it relates to clays, is incorporated herein by reference.
The whisker fiber component of the core functions to reduce cracking and spalling of the core when it is exposed to elevated temperatures, including temperatures at which the glass fiber component loses its functional properties as it melts away. In this connection, the whisker fibers can continue to function at temperatures as high as 1900 or more which is about 600 fibers lose their effectiveness. Whisker fibers are well known in the art. See, for example, the following U.S. Pat. Nos. 4,152,408 (whisker fibers as reinforcement for organic polymeric resins, hydraulic cements, wood pulp and paper products); 4,029,512 (fibrous insoluble calcium sulfate anhydrite as reinforcement for hydraulic cement matrices such as Portland cement and organic polymeric matrices such as polyester and polypropylene; 3,961,105 (waterproofed whisker fibers, no disclosed use); and 3,822,340 (whisker fibers as replacement for asbestos for insulating and fireproofing of buildings; use in structural units such as beams, sheathing, flooring and the like; as reinforcement for glass fibers; use in a fire resistant 100% whisker fiber molded board product). Additionally, the following publications disclose various types of whisker fibers and applications thereof: U.K. Patent Application No. 2,053,874A (fibrous calcium sulfate useful in construction materials such as panels, heat insulating material, and core material); Japanese Patent Application No. 77-63755 (incombustible gypsum fiber-board comprising a major amount of bulky needle crystals of calcium sulfate hemihydrate, and minor amounts of glass fibers, paper pulp, polyacrylamide and silicon); Japanese Patent Application No. 76-80937 (calcium sulfate hemihydrate needle crystals, no use disclosed); Japanese Patent Application No. 78-61474 (acicular gypsum crystals as reinforcement for thermoplastic resins such as polypropylene); Japanese Patent Application No. 77-48667 (bulky acicular calcium sulfate anhydrite crystals, that is, gypsum whiskers as material for non-flammable building material such as sheeting and boards and as a filler for plastics); and Japanese Patent Application No. 76-137037 (needle-like crystal fibers of calcium sulfate hemihydrate as filler material for synthetic resins, paint lacquer and the like). It is evident from the foregoing that whisker fibers have been used in a wide variety of applications but their use in the core of fire resistant gypsum board, as described herein, has not heretofore been known.
The manufacture of whisker fibers is well known in the art. See, for example, the following U.S. Pat. Nos.: 3,822,340; 3,961,105; 4,029,512; and 4,152,408. Additionally, the following publications disclose the manufacture of "needle crystals" and fibers of calcium sulfate which may also be used in the practice of the present invention: U.K. Patent Application No. 2,053,874A; and Japanese Patent Application Nos.: 77-63755; 76-80937; 78-61474; 77-48667; and 76-137037.
Generally speaking, whisker fiber manufacture begins by heating an aqueous slurry of calcium sulfate dihydrate (gypsum) under pressure. Whisker fibers usually form from the slurry as elongated thin crystals of calcium sulfate hemihydrate (CaSo.sub.4.1/2H.sub.2 O), although recovery of whisker fibers in the dihydrate form is reported in aforementioned Japanese Patent Application No. 77-63755. Once recovered, the whisker fibers may be treated further by heating to drive off the remaining chemically bound water. This leads to the formation of soluble anhydrous calcium sulfate whisker fibers. Heating still further renders the fibers insoluble in water. Thus, whisker fibers may be recovered in a dihydrate form (CaSO.sub.4.2H.sub.2 O), a hemihydrate form (CaSO.sub.4. 1/2H.sub.2 O), a soluble anhydrite form (CaSO.sub.4), and an insoluble anhydrite form (CaSO.sub.4). Preferred whisker fibers for use in the practice of the present invention are insoluble calcium sulfate anhydrite whisker fibers.
Whisker fibers which are otherwise soluble in water may be coated with various materials which waterproof or otherwise render the coated fibers insoluble in water. Examples of such materials include waxes, hydrolyzed proteins, and polycarboxylic acids.
The components comprising the core can be mixed according to known methods and gypsum board and the core thereof formed according to known techniques. Speaking generally, this initially involves metering the dry ingredients and water into a mixer and forming an aqueous mixture therefrom. The density of the core can be controlled by adding to the aqueous mixture foam formed from a dilute aqueous solution of a surface active material, for example, ammonium or sodium lauryl sulfonate. The dilute aqueous solution can be foamed utilizing air pressure. The quantity of foam added to the aqueous mixture determines the amount of voids or cells present in the resulting core inasmuch as the foam displaces with air other of the core ingredients to form cells or voids in the core. The foam, water and other ingredients are mixed thoroughly to form a pourable aqueous slurry which is dispensed through one or more outlets at the bottom of the mixer onto a moving facing sheet or cover sheet. Another facing sheet is placed on top of the slurry to sandwich it between two moving facing sheets which are the paper facings of the resultant gypsum board. Facing sheets are usually paper but may also be of non-woven or woven fiberglass mats, plastic scrims and the like.
With respect to the amounts and proportions of ingredients comprising the set composition of the present invention, as mentioned above, calcined gypsum comprises at least 50 wt. % of the set composition, with the other ingredients being present in minor, but functional amounts. In fabricating cores of fire resistant gypsum board in accordance with the present invention, it is recommended that the core comprise the set product of at least about 80 wt. % of calcined gypsum, at least about 0.04 wt. % glass fibers, at least about 0.1 wt % whisker fibers, and at least about 0.5 wt. % clay. (The term "wt. %" means weight percent based on the total weight of the dry ingredients prior to the addition of water to form a settable slurry.) Recommended ranges of amounts are set forth below.
______________________________________Ingredients     Broad Range, wt. %                    Preferred Range, wt. %______________________________________calcined  about 80       about 83 to about 88gypsum    to about 90glass fibers     about 0.04     about 0.1 to     to about 1.0   about 0.40whisker fibers     about 0.1      about 0.4 to about 1.0     to about 2.0clay      about 0.5      about 1.5 to about 3.5     to about 5.0______________________________________
If vermiculite is included in the core, it will generally be advantageous to include at least about 0.5 wt. %, for example, about 0.5 to about 1.5 wt. % and preferably about 0.8 to about 1.2 wt. %. Other additives such as accelerating agents, dispersing agents (for example, sodium lignosulfonate) and core adhesives (for example, corn starch) are generally added in addition to the above ingredients in amounts well-known in the art in order to impart desirable properties to the gypsum board and/or to facilitate the manufacturing thereof. In general, the amounts of such additives generally comprise collectively about 0.5 to about 2.0 wt. % of the core.
Operating within the above parameters, it is possible to form an improved fire resistant gypsum core having a density of about 44 to about 50 lbs./cu. ft. and the amount and proportion of ingredients comprising the core being such that a core having a thickness of about 0.5 inch has a shrink resistance of no less than about 75% and cracks no more than about 6 inches/24 square inches after heating to about 1800 2 hours.
EXAMPLES Examples which follow are illustrative of the fire resistance properties of various gypsum board cores within the scope of the present invention. Comparative examples are included also. Two fire resistance properties were measured for all core samples tested: shrink resistance and cracking.
Cracking, as used herein, of a gympsum board core is a measure of the total length of cracks which develop in a core sample heated to a defined temperature over a defined period of time. The extent to which a core crack is when it is subjected to heat is an indication of how well the gypsum board will serve as a barrier to the spread of fire.
______________________________________COMPONENTS   DESCRIPTION______________________________________calcined gypsum        commercially available calcined        gypsum, generally comprising about        90% calcium sulfate hemihydrate and        the remaining 10% comprising various        impurities such as, for example,        limestone, shale, sand and clayglass fibers strands of drawn textile glass fibers,        the fibers having a diameter of about        0.00065 to about 0.0007 inch, the        strands having a length of about 0.5        inch and loosely bonded together by        starch and sold by Owens Corning        Fiberglasswhisker fibers        insoluble calcium sulfate anhydrite        whisker fibers having a length to        diameter ratio within the range of        about 200:1 to about 10:1, a length        within the range of about 20 to about        200 micrometers and a test consis-        tency of about 200 to about 350 ml of        water per 100 grams of whisker fibersclay         ASP 602, a water washed kaolin clay        having an average particle size of 0.8        micron, a specific gravity of 2.58,        and sold by Minerals and Chemical        Phillip Corporation of America______________________________________
In particular, tests to determine skrink resistance and cracking were conducted by preparing core samples having a length of 8 inches, a width of 3 inches and a thickness of 1/2 inch. Samples were prepared by mixing the dry components comprising the core, adding the premixed components to a quantity of water sufficient to achieve a core density of about 46 lbs. per cubic foot, and then mixing for one minute with mechanical agitation. The resulting mixture was poured into a mold and when sufficiently hardened, the cast was removed from the mold and cut into four samples, each of which was 3 inches wide, 8 inches long and 1/2 inch thick. After being thoroughly dried at 110 cast were positioned within a muffle furnace, each sample being placed upright therein on its 8-inch long, 1/2-inch thickness edge in such a way that the samples did not touch each other and roughly defined the sides of an 8-inch by 8-inch square.
The oven and samples were at room temperature when the samples were placed therein. The furnace was then turned on and set to 1800 two hours, the furnace was turned off and allowed to cool undisturbed until the next day. The samples were then removed and evaluated for shrinkage and cracking.
Mean skrink resistance and cracking values are set forth in the table below for the core compositions of Example Nos. 1 to 8 which are illustrative of the invention. The same type values are set forth in the table for the comparative core compositions of Example Nos. 1-C to 4-C. All values expressed represent the average of values from 4 samples. The density of each of the cores of the examples was approximately 46 lb./cu. ft.
______________________________________CORE INGREDIENTS,wt. %Ex-  Cal-            Whisk-     TEST VALUESam-  cined           er         Shrinkple  Gyp-    Glass   Fi-        Resis-   CrackingNo.  sum     Fibers  bers  Clay tance (%)                                    (inches)______________________________________1-C  100     0       0     0    73.5 .+-. 1.0                                    10.1 .+-. 1.82-C  99.78   0.22    0     0    71.5 .+-. 1.0                                    6.9 .+-. 1.83-C  99.12   0       0.88  0    72.5 .+-. 1.0                                    6.7 .+-. 1.84-C  99.5    0.1     0.4   0    72 .+-. 1.0                                    6.0 .+-. 1.81    99.27   0.05    0.14  0.54 73 .+-. 1.7                                    7.6 .+-. 2.72    99.09   0.22    0.14  0.55 73 .+-. 1.7                                    4.0 .+-. 2.73    97.61   0.05    0.14  2.2  83 .+-. 1.7                                    7.7 .+-. 2.74    97.44   0.22    0.14  2.2  84 .+-. 1.7                                    1.4 .+-. 2.75    98.85   0.05    0.55  0.55 74 .+-. 1.7                                    3.9 .+-. 2.76    98.68   0.22    0.55  0.55 71 .+-. 1.7                                    2.7 .+-.  2.77    97.21   0.05    0.54  2.2  82 .+-. 1.7                                    2.0 .+-. 2.78    97.03   0.22    0.55  2.2  80 .+-. 1.7                                    1.3 .+-. 2.7______________________________________
EXAMPLE 9 A core of fire resistant gypsum board illustrative of a preferred formulation of the invention and having a density of about 46 lbs./cu. ft. and a board weight of about 1850 lbs./sq. ft. may be prepared from the set product of the following components (of the same description as set forth for the preceding examples) in the amounts indicated.
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