US 3281252 A
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United States atent 3,281,252 PROCESS OF COATING FIBERBOARD AND RESULTING PRODUCT William P. Fairchild, San Diego, Calif assignor to Kelco Company, San Diego, Calif., a corporation of Delaware No Drawing. Filed Mar. 29, 1965, Ser. No. 443,689 8 Claims. (Cl. 106-15) This invention relates to fire retardant coatings for structural panels of compressed fiber, and to the resulting products.
This application is a continuation-in-part of my application entitled Process of Coating Fiberboard and Resulting Product, Serial No. 148,695, filed October 30, 1961.
A common structural panel or board widely used in building and like construction is formed by compressing vegetable fibers so as to produce a porous but structurally rigid panel member, which may be used as wall board, as thermal and acoustic insulation panels on or in partitions, as sub-flooring, on or in ceilings, and the like. A particular type of this product is punched with a plurality of holes, commonly to inch in diameter, which penetrate one surface to a short distance, and renders the product especially useful in the acoustic treatment of enclosures, where it is desirable to reduce echo.
A wide variety of vegetable fibers is used in the manufacture of panels, boards, acoustical tiles, and like products, all of which are hereinafter occasionally referred to as porous compressed vegetable fiber structural panels. One especially widely used product of this type is made from the refuse of sugar cane refining, known as bagasse. In general, the bagasse is shredded so as to separate the individual fibers of the cane sugar stock, to a greater or less extent, and the matted fibers, with or without the addition of paper pulp, ground newspapers, and the like, are compressed to give a structural panel with flat sides, generally about /2 inch in thickness. Panels for acousticaluse and thermal insulation use are commonly made thicker, as much as one inch. Various bark fibers may also be used such as the bark of redwood, Douglas fir, and like trees. Corn stalks are another source of vegetable fibers for the manufacture of structural panels of the type described. As mentioned, structural panels of this type are porous, that is, they will absorb water, and have some permeability to the passage of air, although this may be rather low. However, they form a distinct class from panel boards made, for example, by admixing sawdust with a binder and treating under high temperatures and high pressures so as to produce an impervious, dense board of even greater density than the original wood from which the sawdust was derived.
As may readily be understood, structural panels of the type described and to which this invention is directed are subject to combustion, and offer no more resistance to fire than wood itself. It is highly desirable to treat porous compressed vegetable fiber structural panels so as to render them fire resistant. A number of treating agents are known for this purpose, applicable to wood, paper, draperies, and the like, and all belonging in general to a class of chemicals, generally salts and especially inorganic salts, which are more or less soluble in water, so that the articles to be treated may be sprayed with or dipped in a solution of the chemical in question, whereupon the water is allowed to evaporate and a fire resistant chemical thereby incorporated in and on the treated article.
It is a fact, however, that surface treatment is of greater importance than treatment in depth, that is, throughout the body of an article such as the porous structural panels described, since before the interior of such an article can burn, it is necessary for the surface to burn first. Thus, save the surface and you save all is highly applicable to the panels in question.
Great difficulty has been encountered in the past in applying fire retardant treatments to porous compressed vegetable fiber structural panels, because the very nature of these articles causes them to soak up the liquid applied, and there is no surface concentration of the fire retardant chemical, but the latter is rather distributed throughout the body of the panel. In order to achieve satisfactory fire resistance, it is necessary to increase greatly the amount of chemical applied, over what would be necessary if the chemical could be concentrated in the surface layer. Not only does this lead to excessive treating costs, but the Weight of the panel is unduly increased because of the burden of treating chemical which it takes up, and moreover its insulating capacity, both thermal and acoustic, is reduced, because of the greater amount of total solids per cubic inch of material.
An object of the resent invention is to provide a fire retardant treating solution and a process of applying the same to porous compressed vegetable fiber structural panels so as to result in a surface concentration of the treating agent.
Another object of the invention is to provide a porous compressed vegetable fiber structural panel having a surface concentration of fire retarding agent.
Other objects of the invention will appear as the description thereof proceeds.
Generally speaking, and in accordance with an illustrative embodiment of my invention, I prepare an aqueous solution of any selected fire retardant chemical, generally making as concentrated a solution as possible, and incorporate with the said solution a modicum, typically to 1%, of a Xanthomonas colloid produced by the bacterium Xanthomonas campestris.
In the aforementioned example of my invention employing a Xanthomonas hydrophilic colloid, I referred to such a colloid produced by the bacterium Xanthomonas campestris. This colloidal material is a polymer containing mannose, glucose, potassium glucuronate and acetyl radicals. In such a colloid, the potassium portion can be replaced by several other cations without substantial change in the property of the said material for my purpose. The said colloid, which is a high molecular weight, exocellular material, may be prepared by the bacterium Xanthomonas campestris, by whole culture fermentation of a medium containing 2-5 percent commercial glucose, organic nitrogen source, dipotassium hydrogen phosphate and appropriate trace elements. The incubation time is approximately 96 hours at 28 C. aeroblc conditions. In preparing a Xanthomonas colloid as aforesaid, it is convenient to use corn steep liquor or distillers dry solubles as an organic nitrogen source. It is expedient to grow the culture in two intermediate stages prior to the final inoculation in order to encourage vigorous growth of the bacteria. These stages may be carried out in media having a pH of about 7. In a first stage a transfer from an agar slant to a dilute glucose broth may be made and the bacteria cultured for 24 hours under vigorous agitation and aeration at a temperature of about 30 C. The culture so produced may then be used to inoculate a higher glucose (3%) content broth of larger volume in a second intermediate stage. In this stage the reaction may be permitted to continue for 24 hours under the same conditions as the first stage. The culture so acclimated for use with glucose by the aforementioned first and second stages is then added to the final glucose medium. In the aforesaid method of preparing a Xanthomonas cnmpestris hydrophilic colloid, a loopful of organism from the agar slant is adequate for the first stage comprising 200 milliliters of the said glucose media. In the second stage the material resulting from the first stage may be used together with 9 times its volume of a 3% glucose media. In the final stage the material produced in the second stage may be admixed with 19 times its volume of the final media. A good final media may contain 3% glucose, 0.5% distillers dry solubles, 0.8% d-ipotassium phosphate, 0.1% magnesium sulphate having 7 molecules of water of crystallization and water. The reaction in the final stage may be satisfactorily carried out for 96 hours at 30 C. with vigorous agitation and aeration. The resulting Xanthomonas campestrz's colloidal material which I have found to be particularly suitable for my purpose can be recovered by precipitation in methanol of the clarified mixture from the fermentation. This resulting material may also be designated as a pseudoplastic, heteropolysaccharide hydrophilic colloid or gum produced by the bacterium species 1 X anthomonas campestris.
Other suitable Xanthomonas colloidal material may be prepared by repeating the procedure used for producing the X anthomonas campestri's colloidal material by substituting known Xanthomonas bacterium or organisms, i.e., Xanthomonas carotae, Xanthomonas incanaea, Xanthomonas pz'si, Xanthomonas begoniae, and Xanthomonas malvacearum, for the bacterium, Xanthomonas campestris.
The fire retardant chemicals which may be used are those common in the art, and include boric acid, borax, sodium metaborate (or, what amounts to the same material, equimolar quantities of boric acid and borax), sodium calcium borate, especially as the mineral boronatrocalcite, the native sodium borate known as rasorite, ammonium sulfamate, secondary ammonium phosphate, sodium phosphate, sodium silicate, ammonium sulfate, equimolar mixtures of zinc chloride and sodium dichromate, and like materials. These are all soluble in water, and in general their solubility increases wtih increasing temperatures, so that in order to reduce the amount of water which must be subsequently evaporated off so as to leave a given weight of chemical, it is desirable to use a saturated solution, not merely saturated at room temperature but saturated at elevated temperatures, for example, 60 C. to 100 C. The concentrations of the fire retardant chemicals used thus, it will be clear, will depend upon the particular chemical chosen, its solubility in water, and the temperature at which the solution is prepared.
As mentioned, I use from about to 1% of a Xanthomonas colloid, for example, a Xanthomonas campestrz's hydrophilic colloid, based on a total weight of treating solution, the latter comprising water and the selected chemical or indeed mixture of chemicals.
Like formulations to the above substituting the Xanthomonas colloidal material produced by the other aforementioned Xanthomonas bacterium, produced comparable results in accordance with my invention. However, the quantity of the Xanthomonas colloid should be varied depending upon the species thereof. More particularly, when using a Xanthomonas colloid produced by the organ-isrn Xanthomonas carotae, 1.9 parts of said colloid should be substituted for each part of a colloid produced by the bacterium Xanthomonas campestris. Similarly, when substituting the colloid produced by the bacterium Xanthomonas incanaea, 1.5 parts are required. When substituting Xanthomonas begoniae, 1.65 parts are required. When substituting Xanthomona's pisi, 1.25 parts are required, and when substituting Xanthomonas malvacearum, 1.25 parts are required.
Treating compositions made up in accordance with my invention have the astonishing property of exhibiting minimal penetration into porous compressed vegetable fiber structural panels, when applied to surfaces of the latter. I do not wish to be bound by any theory of operation advanced and indeed I have not'been able to determine all of the factors which contribute to this remarkable property, but it seems to be associated with the nature of the gel formed when the colloid is added, and the fact that the gel nature is unaffected by the presence of the chemicals or even of the combination of the chemicals and the high temperatures which may be and preferably are used.
Examples of my invention will now be given:
Examples To 183 parts of water I added one part of Xanthomonas campestris hydrophilic colloid prepared as described hereinabove. I then heated this to F., and dissolved 16 parts of boric acid therein, to form a treating solution in accordance with the invention. Next, I applied this solution, using a laboratory coating bar, to a porous compressed vegetable fiber structural panel made from bagasse, having a total thickness of /2 inch, and sold under the trade name Celotex. The treated board was all-owed to stand for 72 hours after which time it was dry.
This treated structural panel was then subjected to scorch tests by applying a steel plate thereto heated to 250 C. The scorch resistance of this panel treated in accordance with the invention with the Xanthomonas campestris colloid was very good.
Boric acid solutions of 2%, 5%, and 10% containing 0, 0.1%, 0.3%, 0.75%, and 1% of a Xanthomonas campestris hydrophilic colloid were prepared in the manner described in the example.
These solutions were stored for one week at 140 F. in tightly-capped bottles. They were then used to coat portions of insulating board which had been formed but not dried on the machine during manufacture. That is, the board Was in the same wet condition as is the same board on the machine ahead of the drying section. The coated portions of board were then placed under an infra-red lamp which supplied a surface temperature of 187 C. After 1.5 hours the surface of the board samples was dry. The degree of surface scorch of the various samples was compared with that of uncoated board.
The degree of scorch and fiber toasting was found to be in direct relation to both the concentration of boric acid and the concentration of the Xanthomonas campestris hydrophilic colloid in the coating. For example, at each X anthomonas campestris hydrophilic colloid level scorch decreased with increasing boric acid concentration. Likewise, for a given boric acid level, scorch and fiber toasting decreased with increasing Xanthomonas colloid concentration.
It will be found that when repeating the above examples substituting other Xanthomonas colloids for the Xanthomonas campestris colloid, comparable results will be obtained, particularly when adjusting the quantities in keeping with the disclosure heretofore made in said regard.
While I have described the invention in terms of specific materials, treating agents, treating conditions and the like, it is to be understood that the invention is a broad one, and numerous variations of detail may be made in carrying it out, all within the scope of the claims which follow.
What I claim is:
1. A treating solution adapted for coating porous compressed vegetable fiber structural panels comprising water from about to 1% of a hydrophilic gum colloid produced by a gum producing bacterium of the genus Xanthomonas, and a saturating amount of a fire retardant material selected from the class consisting of boric acid, sodium metaborate, sodium calcium borate, ammonium sulfamate, ammonium phosphate, sodium phosphate, sodium silicate, ammonium sulfate and an equimolar mixture of zinc chloride and sodium dichromate.
2. The composition of claim 1 wherein said hydrophilic colloid is produced by the bacterium Xanthomonas campestris.
3. The composition of claim 1 wherein said hydrophilic colloid is produced by the bacterium Xanthomonas pm.
4. The process of treating a porous compressed vegetable fiber structural panel which comprises applying to at least one surface thereof a treating solution consisting essentially of water, a water soluble :fire retardant material, and a small amount ranging from about to 1% of the treating solution of a hydrophilic colloid produced by a bacterium selected from the group consisting of Xanthomonas carotae, Xanthomonas incanae, Xanthomonas pisi, Xanthomonas begoniae, Xanthomonas malvacearum, and Xanthomonas campestris, said amount of colloid being sufiicien-t to cause the said fire retardant material to concentrate in and adjacent the treated surface of said panel and subsequently allowing the so-treated panel to dry by evaporation of the Water contained in said treating solution.
5. The process of claim 4 wherein said hydrophilic colloid is produced by the bacterioum Xanthomonas campestris.
6. The process of claim 4 wherein said hydrophilic colloid is produced by the bacterium Xanthomonas pisi.
7. The process of claim 4 wherein said fire retardant material is chosen from the class consisting of boric acid, borax, sodium metaborate, sodium calcium borate, am-
References Cited by the Examiner UNITED STATES PATENTS 2,769,729 11/1956 Van de Zande 106-15 XR 2,889,235 6/1959 Campbell et al. 10615 XR 3,000,790 9/ 196-1 Jeanes et al. 3 1 3,020,206 2/1962 Patton et al. 10615 3,054,689 9/1962 Jeanes et al. 106-208 3,096,293 7/1963 Jeanes et al. 106209 XR OTHER REFERENCES Information on Polysaccharide, CA-N-9, September 1959; CA-N-14, April 1961; and CA N-Zl, May 1962, U.S. Dept. of Agriculture Research Service, Northern Utilization Research and Development Div.
ALEXANDER H. BRODMERKEL, Primary Examiner.
J. B. EVANS, Assistant Examiner.