US 2560521 A
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Patented July 10, 1951 PROCESS OF PRODUCING WATER-REPEL- LENT GYPSUM SHEATHING BOARD Thomas P. Camp,
Arlington Heights, 111., assignor to United States Gypsum Company, Chicago, III., a corporation of Illinois No Drawing. Application May 10, 1946, Serial No. 668,785
3 Claims. (Cl. l54=-86) The present invention relates to improvements in waterproof and water-repellent gypsum sheathing board.
The invention relates more particularly to that type of gypsum sheathing board in which the fibrous cover sheets are rendered water-repellent by the expedient of causing the fibers of the cover sheets to adsorb a.water-repellent soft hydrocarbonaceous material, for example, petrolatum or petroleum jelly.
The invention further relates to a gypsum sheathing board comprising a set core of gypsum, the individual crystals of which are coated with a water-insoluble and water-repellent coating consisting either of paraflln alone or composition comprising both asphalt as well as paraflin, and having at least one of the cover sheets rendered water-repellent.
One of the objects of the present invention is the production of a sheathing board having the usual set gypsum core which has been made resistant to and repellent to water by the incorporation therein, during its manufacture and while still in the state of a slurry, of a fusible organic waterproofing material, the core being enclosed by and adhered to strong cover sheets which have been integrally sized with rosin size and which have been previously or subsequently coated with a highly hydrophobic coating which is applied to the individual fibers of the cover sheets, leaving, however, the normal interstices intact.
A further object of the invention is to produce a waterproof sheathing board having a gypsum core and a highly water-resistant surface which, however, is still vapor-permeable.
A further object is to produce water-repellent cementitious boards provided with highly waterproduct, I have described one valuable and emcient method of preparing the gypsum core for I a sheathing board. I have found that the prodproof and water-repellent paper liners, inwhich boards the cementitious core has been rendered water-resistant by the presence therein of a waxy material, but which core can still be dried so as toremove excess water without the necessity of employing excessively high drying temperatures.
One of the serious disadvantages of gypsum sheathing board in the past has been its lack of water resistance when exposed to the elements. A very particular disadvantage was the softening action of the exposed core when moistened with water. This frequently occurred during periods of wet weather when a gypsum sheathing board was exposed in piles at the site of a building operation prior to erection of the board. In a companion application, Serial No. 585,791 now Patent No. 2,432,963, for a water-resistant gypsum uct described in that application can be further improved by treatment of the exterior surfaces of the sheathing board to make them extremely hydrophobic to water. It is advisable that the surface liners of the gypsum sheathing not only be water resistant, but the surface of the liner should not be easily wetted by water. In other words, it should have a negative capillary effect so that water will rapidly run oil the surface. I have discovered that this can be most efliciently and cheaply accomplished by coating the paper liners used for manufacture of the sheathing with petrolatum, which is also known as petroleum jelly.
The paper liners used on both sides of the waterproof gypsum core, thereby forming the sheathing board, are made from chip papers, usually from reworked waste papers, which in their re-formation are heavily sized with rosin size, thereby making them highly water resistant. These papers are usually made in thicknesses of .020" to .030" and weigh about -75 pounds per thousand square feet, and while highly water resistant, nevertheless have a suiilciently open texture so that they will bond completely and satisfactorily with the gypsum core, which usually contains from about 5 to about 10 pounds of farinaceous material per thousand square feet of board.
The application of the water-repellent material, for instance, petrolatum, preferably may be made at the paper machine during the formation of the paper. The best practice is to apply ordinary petrolatum in a liquid state, at a temperature of F. to F., to the outside liner of the paper on the calender stack, using the water boxes which are provided for such calender stacks to serve as the tank supply from which the petrolatum is drawn. Paper of the aforesaid specifications will absorb from about 5 to about 10 pounds of heated petrolatum per thousand square feet of paper at ordinary machine speeds, which amount is found to be highly satisfactory and sufiiciently water-resistant for the purpose. Instead of applying the petrolatum on the calender stack, it may be applied to the paper subsequent to its manufacture by an ordinary paper coating machine.
When preparing the liner paper employed for the manufacture of gypsum sheathing board at the paper mill, as above described, I find that v the petrolatum coating will be most uniformly distributed over the surface of the paper, and after the paper has stayed in storage a week or more the petrolatum will have thoroughly diffused throughout the paper from the front to the back, but while the petrolatum has completely penetrated the paper, nevertheless it will be found that the bond of the gypsum core tothe coated paper liners is not impaired, even though both sides of the paper liner show a marked hydro phobic effect. This is quite an unexpected result, inasmuch as oils and waxes of most any origin will interfere with the proper bonding of gypsum slurries to other surfaces. The oils and waxes, acting usually as a continuous film, are thereby eflicient parting agents preventing bond between the gypsum surface and other surfaces of any type. I would explain this unusual and unexpected result and effect of bonding between the gypsum and the hydrophobic paper liners as being due to the fact that there is no continuous film of petrolatum. That is to say, the interstitial porosity between fibers remains substantially intact and the petrolatum has been absorbed by the fiber itself without bridging the spaces or voids between fibers, thus enabling the gypsum slurry to effect a mechanical bond through the interstitial spaces with the irregular surfaces of the fibers themselves.
Usually this bond is the result of re-crystalization of the calcined gypsum used for producing the board core into the form of calcium sulfate dihydrate which latter material has a tendency to form long needle-like crystals. These crystals are interlaced in the core, but a great many of them penetrate into the interstices of the cover sheets, thereby mechanically interlocking the cover sheets with the core, thus producing a very strong bond. This bond is further protected by the presence of some form of cooked carbohydrate, such as cooked starch, in the core material, which farinaceous material, during the drying of theboard, migrates to the interface between the core and the cover sheets, thereby surrounding the gypsum crystals at this critical point; therefore, when the board is dried after the core material has set, the drying being at temperatures which would normally re-calcine the gypsum, the crystals are protected from recalcination by this farinaceous water-holding layer. While it would not have been expected that a gypsum core could be made to bond on waterproof paper, I have found that, contrary to this expectation, paper containing the amounts of petrolatum or similar soft hydrocarbonaceous material will nevertheless bond, undoubtedly due to the fact that the interstices of the papers have not been appreciably impaired by the treatment with the water-repellent materia1.
Moreover, during the drying of the board, the vapor formed from the residual water in the boards may escape through the cover sheets by passing in vapor form through the interstices of the otherwise water-repellent cover sheets. The fact that the individual fibers of the cover sheets are not wettable by water prevents physical water from penetrating through these sheets, mainly because the porosity is overcome by the negative capillarity of water relative to the petrolatum coated fibers.
I have found such paper liners to perform very satisfactorily on the gypsum sheathing forming machine, and subsequently to go through the dryers at high temperatures without blowing. blistering or otherwise disturbing the sheet and without appreciably retarding the rate of moisture elimination from the core, which is highly important in the production of such products. I find that while the porosity of the liners is reduced somewhat and conversely the vapor resistance of the finished sheathing is increased, neither of those values is sufliciently altered to markedly interfere with the characteristics of the finished sheathing.
Gypsum sheathing made in accordance with the present invention is highly water-repellent and may therefore be freely used in place of ordinary wooden sheathing.
I have not deemed it necessary to describe in detail the manufacture of a suitable gypsum core or the details of the manufacture of the gypsum sheathing board, as all this is carried out in machinery which is well known in the art, and fully familiar to gypsum board manufacturers and producers. The core consists of calcined gypsum in admixture with the proper amounts of retarders and accelerators, fibers, and-usually also of a foam which advantageously may be made from a low viscosity starch containing a suitable foam producing agent. Such a method of making a board is fully described in my Patent No. 2,207,339, and the manufacture of a suitable water-repellent gypsum core board is also shown and fully described in the patent to King and Camp No.'2',19 8, 776, and in my already mentioned patent No. 2,432,963.
Reserving to myself such equivalents as will occur to those skilled in the art into which this application falls, I claim as my invention:
1. Process of producing water-repellent gypsum sheathing board which comprises impregnating heavy paper with an amount of petrolatum insufficient to close the interstices of said paper, and thereafter applying a slurry of calcined ypsum thereto which upon eventual setting will bond itself to the thus treated paper.
2. Process of producing water-repellent gypsum sheathing board which comprises applying to one side of a heavy sheet of paper an amount of petrolatum insuflicient to close the interstices thereof, storing the thus treated paper to permit diffusion of said petrolatum through to the other side of said paper, and thereafter applying a slurry'of calcined gypsum thereto, which upon eventual setting will bond itself to the thus treated paper.
3. Process of producing water-repellent gypsum sheathing board which comprises impregnating heavy paper with melted petrolatum in an amount of from about 5 to 10 pounds per 1000 square feet thereof, thereby rendering it waterrepellent but not vapor resistant; thereafter placing a slurry of calcined gypsum containing water-proofing agents disposed therein between two layers of said thus treated paper; and drying the resulting laminated structure.
THOMAS P. CAMP.
REFERENCES CITED The following references are of record in the file of this patent:
UNITED STATES PATENTS Number Name Date 1,295,466 Farmer Feb. 25, 1919 1,325,883 Sexton Dec. 23, 1919 1,784,993 Mason Dec. 16, 1930 1,793,810 Sexton Feb. 24, 1931 1,903,787 Lodge Apr. 18, 1933 2,319,116 Dodge May 11, 1943 Certificate of Correction Patent No. 2,560,521 July 10, 1951 THOMAS P. CAMP It is hereby certified that error app-ears in the printed specification of the above numbered patent requirlng correction as follows:
Column 4, line 29, for No. 2,198, 776 read No. 2,198,776; line 58, for the word disposed read dispersed and that the said Letters Patent should be read as corrected above, so that the same may conform to the record of the case in the Patent Ofiice. Signed and sealed this 4th day of September, A. D. 1951.
THOMAS F. MURPHY,
Assistant Oommz'ssioner of Patents.