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PATENT OFFICE 2,177,269 STABILIZATION of SOLUBLE CRYSTALLINE MATERIALS Roy William Sullivan

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PATENT OFFICE 2,177,269 STABILIZATION of SOLUBLE CRYSTALLINE MATERIALS Roy William Sullivan Patented Oct. 24, 1939 ’ 2,177,269 UNlTED STATES PATENT OFFICE 2,177,269 STABILIZATION OF SOLUBLE CRYSTALLINE MATERIALS Roy William Sullivan. Crag-mere, DeL, assignor to E. I, du Pont de Nemours & Company, Wil mington, Del., a corporation of Delaware No Drawing. Application January 4, 1938, Serial No. 183,322 16 Claims. (Cl. 134--58) This invention relates to the treatment of ?t for most practical uses. Their presence is slightly soluble crystalline materials or com especially objectionable in calcium sulfate em pounds useful as pigment extenders, ?llers, sub ployed as an extender for such prime pigments strates or bases, to render the same stable and as titanium oxide, zinc sul?de, etc., or as a sub resistant to, hydration and particle size increase. strate or base for lakes or toner pigment colors, More particularly, the invention involves the because the acicular particles deleteriously affect treatment of pigment-useful alkaline earth metal the texture, tinting strength and hiding power compounds, such as sulfates or carbonates, with of the resultant pigment. a novel type of inhibiting agent which effectively With a view to controlling the formation of 10 prevents the hydration or increase in particle needle-like crystals during gypsum precipitation 10 size of such compounds when contacted with from aqueous media, or retarding the setting of aqueous media. plaster of Paris, certain albuminoids, i. e., glue, In a more speci?c and preferred embodiment, gelatin and egg albumin, have been proposed as the invention relates to the stabilization of cal useful. (U. S. Patent to Wallerstein 879,603; 15 cium sulfate, and especially its anhydrite modi Kolloid Z. 25, 6211919) Traube.) These agents 15 ?cation, in order to effectively and permanently have not proven satisfactory or effective and, eliminate the usual tendency towards hydration since such agents are subject to bacterial de and particle size increase which these compounds composition, their use involves the additional dis exhibit on contact with water. advantage of subsequently giving off offensive‘ 20 The individual particles going to make up the and objectionable odors. 20 crystalline materials or compounds referred to, It is among the objects of my invention to and especially useful for pigment or extender overcome these and other disadvantages which purposes, exhibit an objectionable tendency to the use of prior treating agents has involved, “grow” or increase in size when contacted with and‘to provide a novel and improved type of aqueous media. Calcium sulfate is especially treating or restraining agent which is particu 25 subject to this condition, and, accordingly, the larly effective for inhibiting the hydration and /or invention will be hereinafter exempli?ed and il particle size growth of pigment-useful, slightly lustratively described in connection with its par soluble crystalline materials of the type men ticular adaptation to such type of pigment ex tioned. An additional and particular object in 30' tender or ?ller. cludes the provision of’ a novel treating agent 30 Calcium sulfate occurs in several forms, 1. e., especially adapted to stabilize pigment-useful ex as soluble or insoluble anhydrite calcium sulfate tenders or ?llers when in contact with aqueous (C3304), as the dihydrate, gypsum media, and which effectively inhibits their hy (CaSO42HzO) dration or particle size growth during pigment processing, i. e., when said extenders and ?llers 35 or the hemihydrate, plaster of Paris must remain suspended in aqueous media with a prime pigment during washing, bleaching, (CaSO4.1/;>_H2O) water-classifying, ?ltering or during drying. An Finely-divided naturally occurring or arti?cially especial object of the invention includes the pro 40 prepared insoluble anhydrite is especially useful vision of a restraining agent particularly effec 40 asa pigment extender or ?ller, and is character, tive in stabilizing pigment-useful calcium sulfate ized by a speci?c X-ray diffraction pattern. Its and its insoluble anhydrite modi?cation against particle size may vary to as high as 10 microns, hydration and particle size increase. but for pigment purposes preferably ranges from, These and other objects are obtainable in the say, 0.2 to 2.0 microns. These small particles present invention, which broadly comprises 45 are extremely reactive and this is especially true treating an alkaline earth metal sulfate or car if the product has not been dehydrated at high bonate, useful as a pigment extender, ?ller, sub temperatures. When this ?nely-divided calcium strate or base, with a water-soluble glycolate sulfate comes in contact with water, its particles whereby the same becomes stable and resistant hydrate and “grow” or increase in size, due to against hydration and particle size increase. ' formation of long, needle-like, acicular gypsum. In one speci?c and preferred embodiment, the 59 During pigment processing the calcium sulfate invention comprises treating ?nely divided cal ?ller or base must contact water for prolonged cium sulfate, and especially insoluble anhydrite, periods of time, especially during the washing with a water-soluble glycolate compound, to ef and ?ltration stages of such manufacture, and fectively inhibit its hydration and particle size 55 ample opportunity is thus afforded for the for increase when subjected to contact with aqueous mation of these acicular gypsum particles. These media. acicular particles are relatively large and coarse Glycolate compounds useful in the present in in nature and very objectionable due to the fact vention comprise the water-soluble variety and 60 that the calcium sulfate is thereby rendered un constitute a new class of compounds, the prop 60 I: 2 2,177,269 erties, characteristics and methods of prepare. of course, that although I have indicated that a tion of which are more particularly described .l% amount of soluble glycolate ( .1 gram per 100 and set out in United States Letters Patents grams of CaSO4) is useful in the invention, it 1,682,292 and 2,060,056. While generally all types will be apparent that smaller or greater amounts of soluble glycolate compounds are useful in my may also be employed and with equally satis invention, those especially adapted and readily factory results. Thus, in my preferred adapta available comprise the alkali metal salts of cel tion, I employ amounts of soluble glycolate com lulose and starch glycolate, which may be pre- , pounds ranging from, say, .05% to 1% (1 gram pared, for example, by the interaction of sodium per 100 grams of CaSOr). While for most prac chloracetate in alkaline suspensions of cellulose, 10 tical purposes this range will prove sufficient, 10 starch or similar compounds represented by the higher concentrations, and up to, say, 10% (10 general formula (Cal-H0091, wherein “x" is a grams per 100 grams of CaSOO may also be em large positive integer. These glycolate com ployed, if desired, and with bene?cial results. pounds will be found to vary in composition and It will be found that the pH of the calcium solubility in water and alkali hydroxide solu 15 sulfate slurry to which the glycolate is added will 15 tions. The amount of polymerization will also have a limiting effect upon its inhibiting proper depend on the conditions'of preparation and will ties. In practice, I have found it advantageous affect somewhat their inhibiting properties. to maintain the pH of the reaction system within Generally, they may be prepared as relatively a range of, say, 4 to 10 or higher. soluble sodium salts, which, as 5% solutions are The speci?c effect which cellulose glycolate 20 quite thick and jelly-like in consistency and on treatment has upon calcium sulfate, as compared dilution with water produce less viscous solu with an albuminoid such as glue, is illustrated tions. These solutions may be dried to produce by the following experiments: a relatively dry material which may be pow A 20% aqueous slurry of freshly precipitated dered, and in such state, directly employed in 25 insoluble anhydrite was adjusted to 7.5 pH with 25 the treatment of the alkali earth metal sulfate or caustic soda and divided into five portions. The carbonate. As indicated, I preferably employ the anhydrite already contained 3.7% of the CaSOr soluble sodium salt glycolate, although this is as gypsum. One part was used as control. A selected for economical reasons only. Obviously, second part was treated with 0.1% glue (based other alkali metal salts, such as those of lithium on CaSO4) and the remaining parts were treated 30 and potassium, may also be employed. Since the with 0.05, 0.1 and 0.4% sodium cellulose glyco compounds potassium cellulose glycolate and late, respectively. It was added as a 2% solution potassium starch glycolate are as useful as the but calculated as the amount of the glycolate corresponding sodium or lithium salts, I desig compound. “I'he various samples were analyzed nate these useful compounds as "alkali metal for gypsum periodically over a period of 75 days 35 cellulose glycolates” and “alkali metal starch with the following results: glycolates,” generically comprehending useful glycolate compounds in the invention, here and in the appended claims, by the term “soluble Days standing glycolate compounds." Sample Treatment In one embodiment of the invention, involving 8 25 44 75 40 the treatment and stabilization of calcium sulfate Per cent Per cenl Per cent Per cent in anhydrite form, an aqueous solution, contain 1 ________ __ Control ___________ ._ 20. 1 92.1 100 ______ __ ing from about .1% to 5% of a water-soluble ' 2 ________ __ . glue ___________ -- l2. 7 48. 4 90. 4 100 3 ________ .. .05% cellulose glyco~ cellulose or starch glycolate compound, may be _____________ __ 5. 2 7. 2 10. l 15. 1 added to an aqueous slurry containing the an 4 ________ __ .l%, cellulose glyco a _____________ _ .
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