Gypsum product and method therefor

A method for making a gypsum product water resistant, the method comprising adding a suspension of a hydrophobic substance to a gypsum slurry.

FIELD OF THE INVENTION

The present invention relates generally to gypsum products, and particularly to a method and system for making a gypsum product water resistant, such as with the addition of a suspension into the production line of the gypsum product.

BACKGROUND OF THE INVENTION

Gypsum (calcium sulfate dihydrate or hemihydrate) is a well-known material used in making industrial and building products, especially gypsum wallboard. It is a plentiful and generally inexpensive raw material, which, through a process of hydration may turn into slurry, which may be cast, molded or otherwise formed to useful shapes, and dried to a final product. Gypsum wallboard generally consists of a rehydrated gypsum core sandwiched between multi-ply paper cover sheets, and is used largely for interior wall and ceiling applications.

However, gypsum products, e.g., wallboard, tile, block, casts and the like, have relatively little resistance to water. When ordinary gypsum wallboard, for example, is immersed in water, the board may quickly absorb a considerable amount of water, lose a great deal of its strength, and distort or swell in different places. Many attempts have been made in the past to improve the water resistance of gypsum products by adding waterproofing materials within the gypsum slurry. The most common waterproofing material in use today is a hydrophobic emulsion, usually an emulsion of wax, paraffin, asphalt or a silicone compound, e.g., silanes and siloxanes.

It is important to define clearly the difference between an emulsion and a suspension. An emulsion is defined as a dispersion of one liquid in a second immiscible liquid. One well-known example of an emulsion is milk; another is certain kinds of paint. A suspension, on the other hand, is defined as a dispersion of fine solid or liquid particles in a fluid (liquid or gas), the particles being supported by buoyancy.

Some emulsified silicone compositions used to make gypsum products water repellent may contain an emulsion of polysiloxane and some parts by weight of a liquid suspension of colloidal silica and other parts by weight of an emulsifier stabilizer. However, the silicone composition that is actually added to the gypsum slurry is an emulsion, not a suspension.

Other methods have been proposed in the prior art to improve the water resistance of gypsum products by coating the finished gypsum product with water resistant films or coatings. Another method involves spraying molten paraffin, wax, asphalt, and the like, into the aqueous gypsum slurry.

SUMMARY OF THE INVENTION

The present invention seeks to provide an improved gypsum product and process therefor. In the present invention, contrary to the prior art, the gypsum product is made by adding a suspension of a hydrophobic (that is, water repelling or resisting, the terms being used interchangeably) substance, such as but not limited to, paraffin, wax and the like. Adding a hydrophobic suspension to the gypsum slurry may provide several advantages Emulsions have to be stored at the site where the gypsum product is produced, and have a limited shelf life. The manufacture of emulsions uses a lot of energy and is relatively costly. In contrast, the raw materials for making the suspension are much cheaper and are much more stable. Production of certain water repellent suspensions requires heat. The suspension may be manufactured at the site where the gypsum product is produced. The excess heat of the gypsum production process may be used as part of the manufacturing process of the suspension. Making the suspension at the site where the gypsum product is produced, and introducing the suspension on-line to the gypsum slurry, may provide significant savings in energy, storage, manpower, etc.

There is thus provided in accordance with an embodiment of the present invention a method for making a gypsum product water resistant, the method comprising adding a suspension of a hydrophobic substance to a gypsum slurry.

In accordance with an embodiment of the present invention the suspension is added to the gypsum slurry on-line at a production line where a gypsum product is produced.

Further in accordance with an embodiment of the present invention, the hydrophobic substance may be stored in a first storage container, a liquid may be stored in a second storage container, and the suspension may be formed by dispersing the hydrophobic substance in the liquid in a mixing device.

Still further in accordance with an embodiment of the present invention the suspension may be added directly from the mixing device to the gypsum slurry.

In accordance with another embodiment of the present invention the suspension may be fed from the mixing device to an auxiliary mixing device, and the suspension may be added from the auxiliary mixing device to the gypsum slurry.

Further in accordance with an embodiment of the present invention the flow of the suspension to the gypsum slurry may be controlled with a control feeder valve.

Still further in accordance with an embodiment of the present invention the suspension may be added to the gypsum slurry in a production line, and the production line and the control feeder valve may operate in a closed control loop.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Reference is now made toFIG. 1, which illustrates a method and system for making a gypsum product water resistant, in accordance with an embodiment of the present invention.

A hydrophobic substance10, such as but not limited to paraffin, wax, asphalt and the like or any combination thereof, may be stored in a storage container12. Hydrophobic substance10may be in the form of liquid, particles, flakes, pellets and other shapes, of any size. Storage container12may comprise a mixer14. Dispersing aids (not shown) may be added to hydrophobic substance10in storage container12. Mixer14may be used to reduce hydrophobic substance10to particles of any desired size. Provision may be made for controlling the temperature of the contents of storage container12, such as, but not limited to, to a temperature range of 60-98° C.

Another storage container16may be provided for storing therein a liquid18, such as but not limited to, water, which will be used to disperse therein hydrophobic substance10to form a suspension. Storage container16may also comprise a mixer20. Dispersing aids (not shown) may be added to liquid18in container16. Provision may be made for controlling the temperature of the contents of storage container16, such as, but not limited to, to a temperature range of 60-98° C.

The contents, or any portion thereof, of storage containers12and16may be fed via tubing22and24, respectively, to a batch mixing device26, where hydrophobic substance10is dispersed in liquid18to form a suspension27. Control valves28and30, respectively, may control the flow of material from storage containers12and16to batch mixing device26. Batch mixing device26may comprise a mixer32, which may be any suitable dispersing mixer, such as but not limited to, a propeller, a stirrer, or dissolver moving at any suitable rate to form or maintain suspension27. A control unit34may be provided that controls operation of batch mixing device26, such as but not limited to, the weight or volume of the substances being mixed, the pressure or temperature of batch mixing device26, and the time duration of mixing. Dispersing aids (not shown) may be added to the suspension in storage container26. Provision may be made for controlling the temperature of the contents of storage container16, such as but not limited to, to a temperature range of 60-98° C.

Suspension27may be added directly, if desired, from batch mixing device26to a gypsum slurry mixer41. Gypsum slurry40may flow along a production line42for making a gypsum product44, such as but not limited to, pre-cast gypsum products, e.g., wallboard, tile, block, casts and the like. The addition of suspension27may impart water resistance to the final gypsum product44. The amount of suspension27added to gypsum slurry40and the rate of its addition thereto may be functions of various factors, such as but not limited to, the speed of the production line42, the type of the gypsum product, the desired quality or thickness or other property of the product, the ratio of hydrophobic substance10to liquid18in suspension27, etc. A control process feeder valve50may control the flow of suspension27to the gypsum slurry mixer41in production line42. The production line42and control process feeder valve50may operate in a closed control loop, wherein the rate of production line42automatically controls the feeding of suspension27to gypsum slurry mixer41.

Instead of adding suspension27directly from batch mixing device26to gypsum slurry40, suspension27may first flow from batch mixing device26to an auxiliary mixing device46via tubing48. A control batch feeder valve50may control the flow of material from batch mixing device26to auxiliary mixing device46. Auxiliary mixing device46may also comprise a mixer52, which may be any suitable dispersing mixer, such as but not limited to, a propeller, stirrer, or dissolver moving at any suitable rate to form or maintain suspension27. Provision may be made for controlling the temperature of the contents of storage container16, such as but not limited to, to a temperature range of 30-98° C. A control unit54may be provided that controls operation of auxiliary mixing device46, such as but not limited to, the weight or volume of the substances being mixed, the pressure or temperature of auxiliary mixing device46, and the time duration of mixing. A control process feeder valve56may control the flow of suspension27, via tubing58, to the gypsum slurry mixer41in production line42. The production line42and control process feeder valves50and56may operate in a closed control loop, wherein the rate of the production line42automatically controls the production and feeding of suspension27to gypsum slurry mixer41.

It is noted that any of the mixing devices (e.g., “batch” or “auxiliary”) may comprise provision for mixing discrete batches or continuous mixing of substances.

It will be appreciated by person skilled in the art that the present invention is not limited by what has been particularly shown and described herein above. Rather the scope of the present invention is defined only by the claims that follow: