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 ______. 4. 9 5. 9 7. 3 8. 9 hydrite, suitable agitation of the slurry being had 5 ______.4% cellulose glyco after addition to intimately associate the gly late. __~ ______. 5. 4 6.1 6. 4 8. 6 colate compound with the suspended anhydrite particles. Glycolate addition is effected, pref Thus it will be seen that the inhibiting effect erably, immediately subsequent to anhydrite for which cellulose glycolate has upon the formation mation. Thus, for example, in processes wherein of gypsum is far more efficient than glue. the calcium sulfate is obtained by dehydrating In another series of experiments handled in a gypsum with strong sulfuric acid, or the anhy similar manner, a comparison of starch and cel 55 drite is prepared by interacting milk of lime lulose glycolate with an albuminoid, such as glue, with sulfuric acid at elevated temperatures, it was made on a freshly precipitated anhydrite LI (A must be separated from the reaction medium by product, after washing free from acid and ad washing, to remove acid, filter pressing and dry justing the slurry to a pH of about '7 with a small ing then being had. In the latter stages of this amount of lime water: 60 processing, during which it may be desirable to blend the anhydrite with a prime pigment, such . Days standing 60 as titanium oxide, zinc sul?de, etc., prolonged No. Treatment water contact is had, during which ample oppor 18 46 74 tunity is afforded for hydration and formation of 65 gypsum crystals. Transformation to gypsum will Per cent Per cent Per cent 1 ______Control ______75. 4 ' 100 ______be preventedif the solution of glycolate is added 2 ______.l% glue ______54.8 100 ______._ 3__.._ _ .l% starch glycolate ...... _ 8. 6 12. 5 17. l to the slurry immediately following anhydrate 4 ______.l% cellulose glycolate...“ 5. 8 6. 9 8. 6 formation. As indicated, relatively small amounts of a Decomposition of the glue was observed to have 70 soluble glycolate compound need be employed for started after samples had been standing for 15 the purpose. Usually about .1%, based on the days. This decomposition not only caused loss of weight of the calcium sulfate present in the the preserving agent but resulted in a most of slurry, or about .25 gram of glycolate per liter fensive odor. of anhydrite suspension, will be su?icient to ef The alkali metal salts of cellulose and starch fect desired stabilization. It is to be understood, glycolate of the present invention do not possess 75 22,197,209‘ 3 this disadvantage. They readily dissolve in water ity, particle size of'sollds. chemical state and to give a very viscous solution and haveexcel-g other deslredlpigmentary properties over periods lent stability. Bacterial decomposition has not. which are sumciently long to assure uniformity been observed'and offensive odors such as are en of product even after prolonged-shelf storage. countered with giue treatmentsare therefore Such assurance could not be had with prior tre'at absent in these solutions. These properties make ing agents, such as glue, even when employed in the glycolate compounds much more desirable greater and excessive amounts, due to the tend than the proteins such as glue. Furthermore, ency of such agents to decompose and thus be these are more powerful and less of the reagent rendered completely ine?ective. , 10 is necessary as is shown by the data above. I claim as my invention: ‘ 10 Although the invention hastbeenexempli?ed l. A process for stabilizing pigment-useful al in a particular embodiment involving the sta kaline earth metal compounds from the group bilization of calcium sulfate, as has been in consisting oi sulfates and carbonates against par dlcated, stabilization and impartation of growth ticle size increase, comprising ‘intimately associat 15 resistant properties to other types of pigment ing said compounds with from about'.05 to 10% 16 useful crystalline materials by treating the same of a water-soluble glycolate. with soluble glycolates is contemplated. Thus, 2. A process for stabilizing pigment-useful al aqueous slurries of other alkaline earth metal kallne earth metal compounds from the group sulfates, such as barium sulfate, strontium sul consisting- oi’ sulfates and carbonates against 20 fate, or carbonates thereof, such as calcium car particle size increase, comprising adding from 20 bonate, barium carbonate or strontium carbonate, about .05 to 10% of a water-soluble glycolate may be similarly treated with a solution of cellu in solution to an aqueous slurry containing said lose or starch glycclate, whereby such compounds compounds. become equally stabilized and growth-resistant. 3. A process for treating pigment-useful al-~ 25 The invention is also particularly e?ective kallne earth metal compounds from the group when the pigment-useful extenders or ?llers, and consisting of sulfates and carbonates to render especially insoluble anhydrite, are used-in‘ (2on7 them stable and resistant _to particle size in junction with a prime pigment ‘for employment crease, comprising adding a .l—5% solution of a in aqueous vehicles, such as casein or water water-soluble glycolate to an aqueous suspension 8-0 paints, or in any system that permits the ex of said compounds. tender or ?ller to come into contact with-appra 4. A process for stabilLzing pigment-useful al ciable amounts of water for prolonged periods. kaline earth metal compounds from the group Likewise, the treatment afforded by the ‘present consisting of sulfates and carbonates against hy invention is equally valuable in many other aque dration and particle size growth, comprising con 36 ous compositions containing pigment-useiul crys _ tacting said compounds while in aqueous suspen talline materials, such as in shoe polishes and son with about 05% to 1% of a water-soluble paper pigmentation suspensions. In such in glycolate. stances hydration of the soluble crystalline ma 5. A process for stabilizing anhydrite against terial, and especially calcium sulfate, occurs and hydration and particle size increase, comprising ultimately proceeds to completion. This hydra adding about 05% to 10% of a water-soluble (it tion can be effectively delayed and prevented by glycolate to ail-aqueous slurry containing the an pretreatlng the extender or ?ller with any of hydrite. the water-soluble glycolates of the present in 6. A process for stabilizing anhydrite against vention, the glycolate apparently becoming ad hydration and particle size increase, comprising sorbed on the individual particles ‘of the ex adding a .l-5% solution of a water-soluble glyco tender or ?ller, thereby forming a protective ?lm late to an aqueous suspension containing said against rehydration and remaining with the ex anhydrite whereby from about .l-5% of said tender after drying. As a result, the composi glycolate becomes intimately associated with said tion then becomes more resistant to chemical and anhydrite. - ‘ physical changes than without the treatment 7. A process for stabilizing anhydrite to ren a?orded by my invention. ‘ , der the same stable and resistant towards hy similarly, it will be found that the bene?cial dration and particle size increase, comprising e?ects a?‘orded by my novel method of treat adding a .1-5% solution of a water-soluble glyco ment do not cease when the pigment is dried late to an aqueous slurry substantially immedi and packaged. The treated pigment continues to ately following formation of the insoluble an 55% exhibit improved resistance to hydration when hydrite in said slurry whereby from about .1—5% suspended in water, provided it has not been of said glycolate becomes intimately associated heated to an unduly high temperature during with said anhydrite. , drying. In order to avoid decomposition of the a. A process for stabilizing anhydrite against organic treating agent, it will be found prefer hydration, comprising contacting the anhydrite able to conduct the drying operation at relatively - with an aqueous solution of from .05% to 1% of low temperatures, such as under vacuum or by a water-soluble glycolate. steam drying. 9. A process for stabilizing anhyclrite against As will be seen, without the use of my novel hydration, comprising contacting the anhydrlte inhibiting agents in calcium sulfate or similar with an aqueous solution of .1 gram to 1 gram 65 extender or ?ller production, a'dlstinct tendency of a water-soluble glycolate per 100 grams of towards formation of long, needle-like gypsum calcium sulfate. particles exists, these particles being very un 10. A process for stabilizing anhydrite against desirable because of their tendency to rapidly hydration, comprising contacting the anhydrite settle from a vehicle or liquid and act as coarse with .05% to 10% of a solution of a water-soluble 70 gritty components in the composition, when ap glycolate, based on the weight of said anhydrite. plied or used on a particular surface. In con 11. As a new composition of matter, an al trast to this, compositions containing pigments kaline earth metal compound from the group and extenders treated in accordance with my in consisting of sulfates and carbonates, and about vention will be found to maintain the same ?uid .05 to 10% of a water-soluble glycolate, said com 4 23,177,269v / V position, when in contact with aqueous media, composition when in contact with water being being stable and resistant against hydration and stable and resistant against hydration. particle size increase. 15. As a new composition of matter, anhydrite 12. As a'new composition of matter, anhydrite' and .05% to 1% of a water-soluble alkali metal and about .05 to 10% of a water-soluble glyco salt of cellulose glycolate, said composition when late, said composition when in contact with in ‘contact with water being stable and resistant ‘ aqueous media being stable and‘ resistant against against hydration. - hydration. ‘ 16. As a new composition of matter, anhydrite 13. As a new composition of mater, anhydrite and .05% to 1% of a water-soluble ‘alkali metal 10 and 0.5% to 10% of a water-soluble glycolate, salt of starch glycolate, said composition when 10 said composition when in contact with water in contact with water being stable and resistant being stable and resistant against hydration, against hydration. 14. As a new compositionof matter, anhydrite and .05% to 1% of a water-soluble g1ycolate,.said ROY WILLIAM SULLIVAN. '