초록 ▼

An improved composite material is produced by mixing gypsum and host particles of a stronger substance, such as wood fibers, in a dilute slurry; heating the slurry, under pressure, to convert the gypsum to calcium sulfate alpha hemihydrate; and substantially dewatering the hot slurry before rehydrat

An improved composite material is produced by mixing gypsum and host particles of a stronger substance, such as wood fibers, in a dilute slurry; heating the slurry, under pressure, to convert the gypsum to calcium sulfate alpha hemihydrate; and substantially dewatering the hot slurry before rehydrating the hemihydrate back to gypsum. The resulting material is a homogoneous mass comprising gypsum crystals physically interlocked with the discrete host particles. According to a further aspect of the invention, an improved wallboard, having fire resistance, dimensional stability and excellent strength properties, is produced by compressing the composite mass before hydrating it to a final set.

대표청구항 ▼

1. A process for making a composite material, comprising: mixing ground gypsum with host particles of a reinforcing material and sufficient liquid to make a dilute slurry consisting of at least about 70% by weight liquid; calcining the gypsum, in the presence of the host particles, by heating th

1. A process for making a composite material, comprising: mixing ground gypsum with host particles of a reinforcing material and sufficient liquid to make a dilute slurry consisting of at least about 70% by weight liquid; calcining the gypsum, in the presence of the host particles, by heating the dilute slurry under pressure, to form acicular calcium sulfate alpha hemihydrate crystals; and separating a major portion of the liquid from the calcined gypsum and host particles before rehydrating the hemihydrate back to gypsum. 2. A process for making a composite material, as recited in claim 1, which further includes continuously agitating the slurry while the gypsum is being calcined and the hemihydrate crystals are forming. 3. A process for making a composite material, comprising: mixing ground gypsum and a plurality of host particles together with water to form a slurry, said host particles being generally insoluble in said water but having voids on their surfaces and/or within their bodies penetrable by the slurry menstruum containing suspended and/or solubilized gypsum and said slurry being sufficiently dilute to wet out said host particles with slurry menstruum and to foster the growth of acicular calcium sulfate alpha hemihydrate crystals when heated under pressure; heating the slurry under pressure to a temperature sufficient to calcine the gypsum to calcium sulfate hemihydrate; maintaining the slurry heated and under pressure while allowing the calcium sulfate molecules to nucleate and form crystals in-situ in and about the voids in the host particles; relieving the pressure and dewatering the slurry; and drying the dewatered solids to remove substantially all the remaining free water and stabilize the calcium sulfate while still physically interlocked with the host particles. 4. A process for making a composite material as in claim 3, which further includes maintaining the temperature of the slurry and the dewatered solids at a temperature above the temperature at which the calcium sulfate hemihydrate will rehydrate to calcium sulfate dihydrate until substantially all the excess free water has been removed by dewatering and drying. 5. A process for making a composite material as in claim 3, which further includes continuously agitating the slurry while it is heated and until the calcination of the gypsum is substantially complete. 6. A process for making a composite material as in claim 3, which includes maintaining the temperature of the slurry at about 200° F. until it has been substantially dewatered. 7. A process for making a composite material as in claim 4, which further includes maintaining the temperature of the slurry above about 200° F. until it has been substantially dewatered and dried. 8. A process for making a composite material as in claim 3, wherein the host particles are cellulosic particles from the group consisting of fibers, chips and flakes. 9. A process for making a composite material as in claim 3, wherein the host particles each have penetrable voids over a substantial portion of their bodies. 10. A process for making a composite material as in claim 3, which further includes the step of cooling the dewatered solids at a temperature below that at which the calcium sulfate hemihydrate crystals will rehydrate to calcium sulfate dihydrate and allowing such rehydration to take place before drying the dewatered mass to remove the remaining free water. 11. A process for making a composite material as in in claim 3, further including the step of dewatering the heated slurry to form a filter cake, then wet pressing the filter cake and allowing the temperature of the filter cake to fall below the temperature at which the calcium sulfate hemihydrate rehydrates to gypsum crystals before drying it. 12. A process for making a composite material as in claim 3, further including the step of forming a mat from the heated slurry and, after substantially dewatering the mat, wet pressing the mat to compress the material to a predetermined thickness or density. 13. A process for making a composite material as in claim 12, further including allowing the temperature of the compressed material to fall below the temperature at which the calcium sulfate will rehydrate to gypsum and allowing such hydration to continue until gypsum crystals physically interlocked with the host particles are joined with like crystals to form an integral homogeneous mass and then drying the mass to remove the remaining free water. 14. A process for making a board of composite material, comprising: mixing ground gypsum and host particles together with sufficient water to form a slurry, said host particles each having voids on its surface and/or within its body penetrable by the slurry menstruum containing suspended and/or dissolved gypsum and said slurry being sufficiently dilute to substantially wet out the penetrable voids in the host particles and to foster the formation of acicular calcium sulfate alpha hemihydrate crystals when heated under pressure; heating the slurry in a pressure vessel, with continuous agitation, to a temperature sufficient to calcine the gypsum to calcium sulfate alpha-hemihydrate, and maintaining the slurry at such temperature until at least some calcium sulfate hemihydrate has substantially crystallized in and about the voids in the host particles; discharging the heated slurry onto a flat porous forming surface and removing a substantial portion of the water from it to form a filter cake; pressing the filter cake to form a board and to remove additional water therefrom before the temperature of the board falls below the temperature at which the calcium sulfate hemihydrate will rehydrate to gypsum; cooling the board to below the rehydration temperature and allowing the calcium sulfate hemihydrate to rehydrate to gypsum; and drying the board to remove the remaining free water. 15. The process as in claim 14, wherein the dilute slurry comprises ground gypsum and discrete ligno-cellulosic host particles, said celulosic particles each having voids penetrable by the slurry menstruum over a substantial portion of their bodies. 16. The process as in claim 15, wherein the host particles are wood fibers selected from the group consisting of: chemically refined wood pulp, mechanically refined wood pulp, thermo-mechanically refined wood pulp and combinations of the foregoing. 17. The process as in claim 16, wherein the solids in the slurry comprise about 0.5-30% by weight wood fibers. 18. The process as in claim 17, wherein the solids in the slurry comprise between 10-20% by weight wood fibers. 19. The process as in claim 15, wherein the dilute slurry comprises at least about 40-95% by weight water. 20. The process as in claim 14, wherein the dilute slurry comprises at least about 70-95% by weight water. 21. The process as in claim 14, wherein the slurry is heated in the pressure vessel to a temperature between about 285° F. and about 305° F. 22. The process as in claim 14, wherein the temperature of the heated slurry is maintained at a temperature above about 200° F. until it has been substantially dewatered and wet pressed into a board. 23. The process as in claim 22, wherein about 90% of the uncombined water is removed from the slurry by the combined dewatering and wet pressing steps. 24. The process as in claim 22, wherein the board formed by pressing the heated filter cake is cooled to a temperature on the order of 120° F. to effect rehydration of the calcium sulfate hemihydrate before it is finally dried. 25. The process as in claim 14, wherein the board is dried at a sustained temperature between about 110° F. to about 125° F. 26. The process as in claim 14, wherein the dewatered filter cake is pressed to form a board, which after hydration and drying, has a density between 40-50 pcf. 27. A method of making a composite material which includes the steps of calcining gypsum under heat and pressure in a liquid medium containing suspended host particles having voids on their surfaces and/or within their bodies penetrable by said medium under conditions which foster the nucleation and growth of acicular calcium sulfate alpha hemihydrate crystals in-situ in and about voids in such host particles. 28. A method of making a composite gypsum and wood fiber material which includes the steps of a) suspending a mixture of ground gypsum and wood fibers having hollows, fissures, pores, pits and/or other irregular surfaces over a portion of their body in a continously agitated aqueous medium; b) adding an amount of soluble gypsum in excess of that required to saturate the aqueous medium, wherein a portion of the gypsum is solubilized and a portion is suspended in the continuously agitated medium; c) heating the aqueous medium under pressure to precipitate the solubilized gypsum from solution as calcium sulfate alpha hemihydrate; and d) maintaining the reaction condition of step (c) for a sufficient period of time such that the growth of acicular calcium sulfate alpha hemihydrate crystals in, on and about the hollows, fissures, pores, pits and/or other irregular surfaces of the wood fibers is fostered. 29. A composite material, comprising: a host particle of non-gypsum material and having voids on its surfaces and/or within a portion of its body; and calcium sulfate acicular alpha hemihydrate crystals at least some of which have been formed in-situ in and about the voids in the host particle, forming a calcium sulfate crystalline matrix physically interlocked with the host particle. 30. A composite material as recited in claim 29, wherein the host particle is in the form of a chip, a flake or a fiber. 31. A composite material as recited in claim 29, wherein the host particle is a ligno-cellulosic substance. 32. A composite material as recited in claim 31, wherein the host particle is a wood fiber. 33. A composite material comprising: a plurality of host particles of cellulosic material, each particle having voids on its surface and/or within a portion of its body; and calcium sulfate alpha hemihydrate crystals at least some of which have been formed in-situ in and about a significant portion of the voids in the host particles, whereby the host particles are physically interlocked with the calcium sulfate crystals. 34. A composite material as in claim 33, wherein the calcium sulfate hemihydrate crystals are acicular crystals. 35. A composite material as recited in claim 33, wherein the host particle is a wood fiber.