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Patented Aug. 27, 1946 ' 2,406,472 UNITED STATES ‘PATENT OFFICE 2,406,472 ' MANUFACTURE OF CADMIUM YELLOW ' PIGMENTS i ' Ludwig Francis Nerlinger, Wilmington, Del., as- > signor to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware No Drawing.‘ Application November 23, 1944, Serial N0. 564,899 ' ‘ 5‘ Claims. (01. 106-301) , 2 1 This invention relates to the production of cadmium yellow pigments, and more particularly to a novel improved method for obtaining zinc ‘ method for precipitating and recovering an im proved cadmium sul?de pigment. Additional ob jects of the invention will be apparent from the containing cadmium sul?de pigments in lighter, ensuing description of the invention. greener shades. _ The foregoing and other objects are obtainable Cadmium sul?de pigments are well-known, be in this invention which comprises ?rst preparing ing useful primarily because of their light and a suspension of precipitated zinc sul?de and heat resistance and non-bleeding characteris barium, sulfate and thereafter precipitating cad tics. Due to their brightness, color and resist mium sul?de and barium sulfate in the presence ance to alkali (especially the latter) they are 10 of and upon the surface of said suspended zinc valuable pigments for use in aqueous emulsion » sul?de particles. type paints which have recentlygained consid erable commercial importance. These paints cipitation reaction is conveniently conducted in usually contain casein as a binder which is solu- ' a suitable reaction vessel, such as a conventional _ In practically adapting the-invention, the pre bilized with the alkali. The water phase of the 15 type tank, equippedwith a sweep agitator and to paint is therefore alkaline and the pigment-which which the reactants, in solution, may be added is used must be alkali-resistant. Chrome yellow as desired. To insure proper» agitation at'the'. has been widely used for the production of bright start ofthe action, water'is ?rst added to the yellow paints but is de?nitely de?cient in alkali tank. ‘ Thereafter, a solution of vzinc sulfate (at resistance. Hence, it is not suitable for use in 20 a concentration ranging from about 50-450 g./l.) aqueous emulsion paints. Hansa Yellow pigments together with a chemically-equivalent amountnof are not satisfactory for use in such paints, due to barium sul?de, is added to the tank and until a the tendency of the pigment to migrate to the oil slight reaction for sul?de ions is obtained. Addi phase of the paint. . tion of the chemically-equivalent amounts of Cadmium sul?de pigments range in color from 25 these two reactants provides an aqueous suspen orange to a greenish yellow. Their color depends, sion of raw lithopone pigment (a co-precipitated among other things, on the method of combining mixture of zinc sul?de and barium sulfate). the reactants used in their production, the cal After the adjustment of the end point to provide cination temperature to which the pigment is a slight test for sul?de ions, a solution of, cad subjected, and the amount of zinc co-‘precipi 30 mium sulfate and a further quantity of barium tated with the pigment. The orange shades can sul?de are simultaneously added to the tank in be prepared by co-precipitating cadmium sul?de order to precipitate a cadmium lithopone com andbarium sulfate from solutions of cadmium position upon the zinc sul?de lithopone already sulfate and barium sul?de. Some variations in present in the tank. The cadmium and barium hue can be obtained by proper selection of oper 35 reactants are added in equivalent amounts and ating conditions, but no known method has eX- - isted for obtaining the lighter and greener shades of cadmium sul?de from pure cadmium sulfate solutions. Prior methods vfor obtaining such lighter, greener shades'involve the co-precipita 40 ‘tion of zinc and cadmium sul?des from a mixed sulfate solution. It is among the objects of this invention to pro duce an improved cadmium sul?de-containing pigment, especially a zinc-containing cadmium 45 sul?de pigment of the desired ‘lighter, greener shades. a range of about 6.0 to 8.5 or approaching neu trality. The resulting precipitate, comprising cadmium sulfide, zinc sul?de and barium sulfate, is then adjusted to about 8.6 pH using barium ‘ sul?de solution, is then ?ltered, dried and cal cined at a temperature ranging from about 600 750° C. to develop, essential pigment, properties, including oil absorption, tinting strength,‘ bril liance of color, etc. ‘ Y To a more complete understanding of the in A,particular_.0bject of the invention is " ‘ vention, the following speci?c examples are given, to provide a novel method for obtaining such im proved form of insoluble cadmium yellow pig ment. While the pH of the solution is maintained within An additional object is to provide a cad mium yellowpigment of improved; brightness of each of which is merely illustrative of- and not‘ to be construed as limiting the invention: Example I '_ _ V tint’and which possesses excellent alkali resist ance to render it advantageously useful in the 200 volumes of water and 60 volumes of a zinc sulphate solution analyzing 400 grams of zinc . manufacture vof ?at, aqueous, emulsion-type paints‘; A further object is to provide a novel sulphate per liter were placed in an agitated‘ tank. and to this was added sufficient 20° Baumé bari- " 2,406,472 r 3 I ‘ ‘um sulphide solution to give a slight excess of ‘ sulphide ions. To the resultant slurry a cadmi‘ um sulphate solution analyzing 97 grams cadmium per liter was added in a small stream while ‘ simultaneouly adding an equivalent amount of 5 ‘ barium sulphide .as _a_20.° Bé. solution... This 51-, ‘ multaneousraclditionewas continued until 'Z50rvol‘ umes of cadmium sulphate solution were added and while maintaining the pH at approximately... . i resorted to herein, the quality of the resulting product demonstrates the existence of a clear advance in the art, the resulting pigment being eminently suited for use in aqueous emulsion paints wherein alkali resistance and brilliance of colorlare ofprime importance.v Wi-l'ileia-zinc sul?de or'zinc sul?de-containing precipitate comprises a preferred type of mate rial upon which the cadmium sul?de is pre '7.(). At the end of the addition of these re-“IQ 'cipitated, other insoluble zinc compounds, such ' agents, the end point was adjusted: to; 8;6.' pH-f ass-the? oxide, carbonate, silicate, or phosphate, f and the suspension ?ltered, dried and calcinedl? " may be suspended in aqueous media for intimate ' ‘e at a temperature of 700° C. with the usual pre.-. association, withv the cadmium sul?de subsee ‘ cautions to prevent oxidation duringicalcinationi ,7 quentlyipreoipitated‘ in said suspension- These The resulting pigment was compared? ,withlai L115, Zinc materials need not be prepared in the reac ‘ pigment produced by the same amount ' of‘ the I tion tankused for the precipitation of the cad reagents but by adding the zincisulphatezsolutionr“ ‘ miunrlithoponaibut may be precipitated in a V 7 i to the cadmium sulphate solution prior torpree-lv separate vessel if it is found more convenient to 1 cipitation. The ?rst sample returned thetsame. do so.. Thus, in the case of the use of zinc litho ‘ hue as the second sample,».but exhibited de?nitely“ “Z0 pone as'a starting material, raw zinc lithopone ; superior brilliance of color, ‘having a brightness liquorfrom normal zinc lithopone operations ‘ value‘ (in.;%, reflectance) may‘ be, conveniently used. of 7315, as com-l ' ‘ paredwith a‘ value of 71.9 for a‘productiobtained" . '25 present at the start of the react-ion,'in order that f in accordance: with the "priorart. Example H In the practice of ' the invention, however?it' is, necessary and ‘6S sentiali that the insoluble zinc compound’ be ' ’_ ‘ > Y- the cadmium lithopone can be effectively pre 1 400* volumes of water‘ and-55 volumes-j of? atzi'no ‘ sulfatev solution ana1yzing=7400 grams" of" Z'nOs ‘ per liter were placed in- an agitatedtanli» and- cipitated upon and intimately associated‘, there with. Mere-‘addition of the insoluble zinc com pound: to a suspension of precipitated cadmium , su?icient 20°: Baumé barium sulphide solution-en lithopone, followed ‘by-?ltration, drying andcal 1 was run in to givea slight excess of'su'lphideions; To the resultant slurry ‘750i volumes of‘ a cad- h cination, will not yield the-superior product ob- 7 tallied-i by a practice of this inventionr I10I‘_.Wi,1l. ‘ mium sulphate solution containing QV-‘graa'ms the c0-_-precipitation of’ the zinc sul?de with the‘ , ’ cadmium> per liter‘was added; in a small stream cadmium; as contemplated in priorpractice, yield“ ' while; simultaneously adding an equivalent f435_ a~ pigment exhibiting superior brillianceof color amount of'barium» sulphide solution to maintain,’ j , ‘ ‘ ; a temperature'4of7d0‘C. 1 possessed by the product of this invention. the pH at approximately 7.0‘. ' At the end ofP-the ‘ The‘ brightness values referred toherein were addition of‘ these'reagents the end point-was-adlf determined- by-rwell-known tests involving the, justed to‘ 8.6‘ pH and the suspension ?ltered} preparation-of a paste of therigment in oilfand' The. precipitate was then dried and? calcined‘ at‘; 4o examining-$131111; using‘ a Hunter reflectometer 7 7’ ~ and with a, green light ?lter. A‘, similar pigment was prepared by addingithex I?la‘im' as my invention: zinc sulfate solution to the cadmium sulfate‘ 1 solution prior to- precipitation, using‘ the; same; '1- A- process tf'orproducing an improvedcad mium sul?de pigment which'comprises; precipi , amount'ofthe'reagents; Because of the‘ smaller,’ ~f tating cadmium sul?de by reacting sulfate with ba'rium- sul?de in- the presencev of an aqueous ratio’ of‘ zinc‘ to cadmium, these‘ pigments‘; were," ‘ slightly'lessgreen than the pigments ofiExamp'le- slurry‘ suspension of raw lithopone pigment; con I.I However, the sample prepared according-to; sist-ing Of‘a (BO-precipitated miXtlll‘e' ofezinc' Sul?de ‘ tliisinventiongwas again found to exhibit deii=and barium“ sulfate, and then recovering andcal- . Y .nit'el'y superior brillianceof color, givinga bright? 5.3. Ciriing the resulting" zinc-rcontaining cadmium ' nessavalue'of 6913 ascontrasted with-a value‘gof" sul?de product" at a temperature ranging from 642.8‘ for theprior art product; p _ '_ 600-750? C‘. The order of addition of the various reagents p . V I. 2". Aprocess for producing animproved cad: in the invention'has'been found‘ to be quite'immium sul?de pigment which comprises pre'oime ' portantl in- and critical‘ to the production- of: 5-, tatin-g cadmium lithopone in the presence of zinc, brilliant’and uniform colors in accordancewith' lithopone by Simultaneously/adding to a 5118 the invention. As outlined‘ above, the‘ ‘zinc 3 sul?de is ?rst precipitated and suspended3 in: pended’ aqueous slurry of Said ,ZinC lithoponc sol'utionsof cadmium sulfatev and barium sul?de, ‘ aqueous slurry, following which precipitation» of’ ' and then recovering and calcining the resulting. the cadmium- sul?de is effected. This order‘ of‘ (13 cadmium lithopone pigment.v , precipitation is essential and critical to theiin-é '' ‘ 3. A process for obtaining an improved cad.‘ ‘ vention and has been found necessary in 010‘ ta-iningthe marked‘ improvements which the? mium sul?de pigment which comprises. initially suspendingraw lithopone pigment consi‘siting of 1 present: invention affords; especially over the V a co-pre'cipitated, mixture of zinc. sul?de. andv ‘ prior art method of‘ co-precipita-tion, wherein 65 barium sulfate, in an aqueous slurry,. and there-7 3 the zinc‘ and cadmium sulfate» solutions have ‘after simultaneously adding to the-resulting, sus Vbeen ’ combined; before? the precipitation takes ‘ , place- Therefore, it will be understoodv that the ‘ ‘ improved method'of this invention comprises the I pension’ solutions. of cadmium sulfate and barium sul?de, in order to precipitate cadmium lithe-V pronev upon said suspended rawv lithoponaand j precipitation of cadmium lithopone-in the pres- 70 then recovering. and calcining theiresulting zinc. ‘ ence of zinc lithopone by: used the simultaneous addition of the cadmium sulfate and barium V containing cadmium sul?de product." 7 4. 'A process,- for obtaininganr improved cad: " sul?de, reactants to a- zinc lithopone slurry. mium. sul?de. pigment/which comprisesreacting While it vi'sinot fully understood why. thefunexe cadmium sulfate. with barium sul?de in an’ 7 . peoted results accrue by reason of the procedures .75 aqueous/slurry. suspension of an, insoluble- in; 5 2,406,472 organic zinc compound to precipitate cadmium sul?de upon said suspended zinc compound, and then recovering and calcining the resulting zinc containing cadmium sul?de product. 7 5. A process for obtaining an improved cad mium sul?de pigment which comprises reacting cadmium sulfate with barium sul?de in an 6 aqueous slurry suspension of zinc sul?de to pre cipitate cadmium sul?de upon said suspended ’ zinc sul?de, and then recovering and calcining the resulting zinc-containing cadmium sul?de 6 product. LUDWIG FRANCIS NERLINGER. Patent No. 2,406,472: I ' Certi?cate of Correction I LUDWIG FRANCIS NERLIN GER August 21,‘ 1946. " , “It is hereby certi?ed that errors appear in the printed speci?cation of the above numbered Jpatent requiring correction as follows: Column 2, line 18, for “action” read reaction; column 3, line 28, for “Z1104” read ZnSO4; column 4, line 45, claim 1, before “su1fat'e'm-in‘sert cadmium; and line 63, claim 3, for ‘,‘consisiting” read consisting; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Of?ce. ~ Signed and sealed this 29th day of October, A. D. 1946. LESLIE FRAZER, First Assistant Oomxmz'ssz'oner of Patents.