Fire-resistant gypsum fiberboard

Details Fire-resistant gypsum fiberboard Fire-resistant gypsum fiberboard

1999-05-19

2001-10-09

Morris, Terrel (Department: 1771)

Stock material or miscellaneous articles

Web or sheet containing structurally defined element or...

Noninterengaged fiber-containing paper-free web or sheet...

C428S703000, C428S920000, C428S921000, C106S772000, C106S773000, C106S774000, C106S775000, C106S780000, C106S782000, C106S781000, C052S309170

Reexamination Certificate

active

06299970

ABSTRACT:

CROSS REFERENCE TO RELATED APPLICATIONS
This application is a Continuation application of Ser. No. 07/699,676, filed May 14, 1991 now U.S. Pat. No. 5,155,959, which is in turn is a Divisional application of Ser. No. 07/420,362, filed Oct. 12, 1989 now U.S. Pat. No. 5,171,366,and assigned to the Assignee of the present application, which applications are hereby incorporated by reference.
FIELD OF THE INVENTION
This invention is in the field of building materials, especially fire-resistant building materials which contain gypsum in combination with certain fibrous additives, including paper fiber, as well as methods for producing such materials and to articles which incorporate them, such as fire doors.
BACKGROUND OF THE INVENTION
Various products containing the naturally-occurring mineral, gypsum, have been developed for the building trades. Especially notable are various gypsum wall board products, e.g., sheet materials typically faced with paper. Desirable characteristics of such products include their strength at relatively low density (about 0.7 gm/cm
3
), ease of handling and fabrication, and low cost. In producing gypsum building products, calcined gypsum, i.e., anhydrous or hemihydrate (CaSO
4
.½H
2
O), known also as stucco, plaster of paris, molding plaster, building plaster, and the like, typically in an aqueous slurry, is cast, molded, and dried. During the course of this process, the calcined gypsum is further hydrated, yielding CaSO
4
.2H
2
O.
Although the hydration adds only about 20% to the weight of the calcined gypsum, excess water generally is present in the slurry to decrease the viscosity and facilitate molding. However, the excess water is undesirable in other respects. For example, it must be removed in subsequent processing of the product, at considerable cost. Furthermore, the resultant dried product is of low density and compressive strength. Consequently, it is conventional wisdom in the art that the amount of water should be held to a minimum, and various additives and treatments have been proposed to fluidize the slurry, but minimize the water; e.g., U.S. Pat. Nos. 2,913,308; 4,222,984; and 4,252,568. “Dry” or “semi-dry” processes have been described in which water required for the hydration chemistry is supplied by a water-saturable filler, such as wood 'shavings, wood fiber granulate and bark; e.g., U.S. Pat. No. 4,328,178. In this regard, the article entitled “Inorganically Bonded Wood” by A. A. Moslemi, Chem. Tech., August 1988, pp 504-510, summarizes the state of the art.
A number of building materials have been disclosed in which substantial quantities of cellulosic fillers, including wood particles and fibers, have been included in gypsum-containing products, not only as aids to incorporating the water necessary to hydrate the gypsum, but also to strengthen and otherwise upgrade the mechanical properties of the product. For example, U.S. Pat. No. 3,951,735 discloses a strengthened gypsum wallboard material having a density of 1.1-1.6 gm/cm
3
(obtained by compressing a lamination) which includes calcined gypsum and cellulosic fiber such as paper pulp, but the criticality of also including a substantial amount of asbestos fiber is pointed out. Similarly, U.S. Pat. No. 4,127,628 discloses a multi-layered gypsum product of low density (0.3-0.9 gm/cm
3
) which includes glass fibers and optionally also contains pulp and polyvinyl alcohol, but, in addition, a substantial amount of asbestos fiber. Products which require asbestos to attain superior properties are difficult to justify in view of the environmental and health hazards associated with such products.
U.S. Pat. No. 4,239,716 describes a gypsum-containing building product containing a reinforcing agent which may be wood pulp or glass fibers, together with a binder, such as polyvinyl acetate. However, the disclosure is limited to the use of fibrous alpha-calcium sulfate hemihydrate, a very expensive raw material, requiring special conditions to produce, which is difficult to reconcile if equivalent properties could be obtained in a product which employs common and inexpensive non-fibrous forms of calcined gypsum.
Gypsum building materials generally are held in high regard for use in fire-resistant construction. The spread of fire and the penetration of flame through set gypsum structures is delayed, because impinging heat initially operates to reverse the hydration reaction, recalcining the gypsum, liberating water. The liberated water is an additional energy sink, absorbing its heat of vaporization.
Finally, however, although the gypsum doesn't burn, it shrinks and cracks when heated in a flame. It is known that this tendency to crack can be countered with appropriate additives, such as fiber, especially glass textile fibers, which hold the structure together, and raw vermiculite, which expands when heated, counteracting the gypsum shrinkage. With this knowledge, a number of gypsum-containing products have been developed in which fire-resistance is critical. Such products include fire doors, for example.
Fire doors may be of either the panel or flush types. They include facings on the two major surface, and the core of the door may either be solid or at least partially hollow. Edge banding is included around the door periphery for aesthetic or structural reasons.
Fire doors, as used in residential, commercial and industrial applications, are typically employed in conjunction with fire walls to provide fire protection between different zones of a structure, and particularly to isolate high fire risk areas of a building from the remainder of the structure, such as the garage of a dwelling from its living quarters. Fire doors usually are not capable of indefinitely withstanding the high temperature conditions of a fire but, rather, are designed to maintain the integrity of the fire wall for a limited time to permit the occupants of a building to escape and to delay the spread of the fire until fire control equipment can be brought to the scene.
Various tests have been devised for fire doors and are based on factors, such as the time that a given door would withstand a certain temperature while maintaining its integrity, and hose stream tests which involve the door's ability to withstand the forces of a high pressure water stream. The American Society for Testing Materials (ASTM) has devised tests to establish fire door standards, and these standards are incorporated into building codes and architectural specifications. One such standard, ASTM Method E 152, requires a door to maintain its integrity for periods ranging up to 1.5 hrs. while withstanding progressively higher temperatures and the erosive effects of a high pressure fire hose at the conclusion of the fire exposure.
Considerations in fire door design, in addition to retarding the advance of a fire, include the cost of raw materials and the cost of fabrication. Furthermore, the weight of the door is important, both from the standpoint of ease in handling and the cost of transportation. The strength of the door is also a significant factor, since fire doors must pass the previously noted water stream tests as well as have the requisite structural strength to withstand normal use and abuse.
Fire-resistant doors have been made in a variety of constructions utilizing a number of different materials, including wood, metal and mineral materials. Early forms of fire doors simply comprised wooden cores faced with metal sheeting. Although wood of ample thickness is an effective fire and heat retardant, doors of such construction tended to be heavy and were expensive to fabricate and transport.
Mineral materials have also been employed in the manufacture of fire doors. The core of a commercial metal fire door principally comprises a composition including mineral fibers and a binder. Such doors suffer, however, from a lack of strength, and handling the friable cores results in the production of irritating dust particles during the manufacturing process.
It has also been proposed to make fire doors wherein the core comprises pa

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