Document MGKdpo1r85Bomzk5Nko8G22wa

Patented Jan. 25, 1949 NAmttti lAO PiTliiT Otria. - i 2,460,241 UNITED STATES PATENT OFFICE 2,460,241 BASIC LEAD SULFATE PIGMENT Adrian Richard Pitrot, Hempstead, N. Y,, assignor to National Lead Company, New York, N. Y,, a corporation of New Jersey No Drawing. Application February 5, 1947, Serial No. 726,741 7 Claims. (Cl. 106--297) 12 This invention relates to an improved basic plates the formation of an Intimate mixture of lead sulphate pigment and to a novel process for basic lead sulphate and aluminum oxide, or an manufacturing this new pigment. aluminum salt which will yield aluminum oxide Basic lead sulphate has long been known as a on heating, and the subsequent calcination of this paint pigment. It is prepared commercially, gen 5 mixture at a temperature between about 900 and erally by either volatilizing lead sulphide ores, about 1000 C., and preferably about 950 C., to or pig lead and sulphur, in a suitable furnace and form a combined basic lead sulphate aluminum collecting the product as a finely divided sublimed oxide composition having superior pigment prop basic lead sulphate, or adding sulphuric acid to erties. a slurry of lead oxide which contains a small 10 The intimate mixture of aluminum oxide may amount of basic lead acetate, such as is described be obtained by several methods. Aluminum in the patent issued to Alex Stewart, No. 2,249,330, oxide, or an aluminum oxide containing salt may dated July 15, 1941. The composition of basic be finely ground and thoroughly mechanically lead sulphate as made by either of these processes mixed with commercial basic lead sulphate; or is commonly a mixture of monobasic and normal 15 the aluminum oxide may be introduced, as such lead sulphate, and it may contain from 1 to 3 or in the form of an aluminum oxide containing mols of normal lead sulphate for each mol of salt, in some stage of the process used for manu monobasic lead sulphate present. facturing basic lead sulphate so that the product The film forming characteristics of basic lead will comprise an intimate mixture. It is much sulphates are largely dependent on their basicity. 20 preferred, however, to form the mixture by the The more highly basic compounds, however, are novel method to be described in detail below in not generally employed in paints because of their which a sulphate salt of aluminum is reacted with extreme reactivity with drying oil vehicles. For lead oxide to form basic lead sulphate and simul this reason, lead sulphate pigments generally taneously to precipitate aluminum hydrate in tend to contain more of the normal lead sulphate, 25 situ. It is not necessary that the alumina be and as a consequence, are definitely deficient in present in the form of AI2O3 prior to calcination weathering properties compared, for instance, to of the mixture, and it may be convenient to use basic lead carbonate white lead. As a result of a salt such as aluminum hydrate, or aluminum the comparatively poor weathering properties of sulphate which, at the calcination temperature these sulphate pigments, they have been almost 30 employed will decompose to form aluminum exclusively used in mixed pigment formulations oxide. An amount of aluminum salt should be in which their deficiencies are tempered by the used which will give from about 2% to about 10% substantial presence of other pigments. While aluminum oxide in the final product, preferably basic lead carbonate white lead may be used as about 8%. a single pigment in paint formulations and ex 35 In the preferred process of this invention, lead cellent weathering qualities obtained, it has never oxide is first added and mixed with sufficient been heretofore possible to use basic lead sulphate water to make a slurry. A small amount, which alone as the pigment phase because of its inher may be between about 1 to about 5% of the weight ently poor weathering qualities which are gen of the lead oxide and preferably about 3% of erally manifested by early chalking and cracking 40 acetic acid is then added to form lead acetate of the film. in solution and accelerate the reaction. A solu It is, therefore, the principal object of this tion of aluminum sulphate is then slowly added invention to provide a new and improved basic while agitating and maintaining the temperature lead sulphate pigment having superior weather of the slurry between about 55 C. and about 85 ing properties compared to basic lead sulphate 45 C. The amount of aluminum sulphate added is used heretofore. It is a further object of this such that the sulphate portion thereof is sufficient invention to provide a basic lead sulphate pigment to form the desired composition of basic lead sul which may be used alone as the pigment portion phate when combined with the lead oxide. The of a surface coating composition. It is another resulting precipitate is then washed to remove object of this invention to provide a novel proc 50 soluble acetate salts and then is filtered and dried ess for manufacturing this improved basic lead or partially dried, or simply filtered, to form a sulphate pigment. These and other objects of mixture suitable for calcination. It should be this invention will become apparent from the noted that the addition of the aluminum sulphate following description. solution to the lead oxide slurry accomplishes two 0000-NLI-000018981 2,460,341 34 combine? with the PbO to form basic lead sul phate and, second, aluminum hydroxide is pre cipitated in situ resulting in an extremely well dispersed mixture. Table Uncalcined Mixture Same Calcined Same Calcined at 845 C. at 950 C. It will be appreciated that when using the S method described above, wherein aluminum sul phate is added to a slurry of lead oxide, the rela Ti tiling Power1.. 50........................ 90....................... 100. o; 1 A bsorption *. . 28........................ 22.4.................. . 14.2. Color (whiteness). equal u> white better than better than tive proportions of SO< and AI2O3 in the final product are interdependent. When using this PbO (Total). - lead .stand- white lead nrd. standard. 71.26 percent.. 76.2 percent.. white lead standard. 76.20 percent. method for the manufacture of basic lead sul- 10 SOs (Total)-____ AliOj....................... 15.52 percent.. 7.08 percent.. 16.34 percent.. 7.60 percent.. !0.o4 percent. 7.h0 nereenr. phates of ordinary composition, that is those con Combined Water. 5.50 percent... none.................. :io:;i\ taining from 1 to 3 mols of normal lead sulphate for each mol of monobasic lead sulphate present, 1 Determined according to Lilt* method "ivor. of the AI2O3 content will vary from 7,6% to 8.6%. cul and Chemical Examination of Points. Varniriic?. .r.d J/.equrrs.'' by H. A. Gardner and C. G. Sword, 10th edition. M .v, 1040. If the desired product approaches the composition : ft J Determined according to the method civcn on iso of " phys of normal lead sulphate, the alumina content will approach 10%. If on the other hand, the more basic lead sulphate compounds are to be formed, the alumina content will be correspondingly low ered. If it is desired to prepare compositions con- taining high sulphate content and low alumina content, a solution of aluminum sulphate and sul ical and Chemical Examination of Paints. v;r'mshcs -.ad T.acqnci':' " by IT. A. Gardner and C. G. Sword, loth edition, M.i>. 1046. In order that this invention may be clearly understood, the following example? will show -) several methods of producing the product of this invention. Example 1 phuric acid may be used for precipitation to pro 790 grams of litharge bolted wet through a duce a mixture of the desired composition. If 100 mesh screen as added to a vessel containing the more basic sulphates containing high alumina approximately 7,600 ml. of water. Then 19 content are desired, it may be advantageous to trams of (80%) acetic acid was added. The add additional aluminum hydroxide to the mix mixture was agitated sufficiently to keep the ture or to add it dispersed in or mixed with the excess litharge in suspension and then heated aluminum sulphate solution. to a temperature of approximately 70 C. Then The mixture of basic lead sulphate and alumina 3,1 P.11.5 grains of (95%) sulfuric acid was diluted or the alumina containing salt is then calcined with water-to a volume of approximately 500 ml. at a temperature between about 900 C. and about and added slowly over a period of approximately 1000 C,, preferably about 950 C. It will be found 3 hours, with continued agitation and with the that temperatures appreciably lower than this temperatures maintained between 55 C. and are not effective in producing the combination of 89 70 C. Then a siurry of finely divided aluminum the alumina and basic lead sulphate, which is hydroxide weighing 1158 grams and containing the product of this invention. At the same time, 116.24 grams aluminum hydroxide was added temperatures substantially higher than 1000 c. and the mixture stirred for approximately 3 should not be used due to the possibility of melt- hours. ing or volatilizing the lead sulphate. At a tern- TM The slurry was then filtered, washed with about perature in the stated range, it will be found that i liters of water to remove any soluble acetate the alumina reacts in some manner and to some remaining. It was then dried and calcined in extent with the lead monoxide or the lead sul a muffle furnace at 950 C. for 4 hours. phate present in the system. It has been found Some physical and chemical properties of this that when lower calcining temperatures are em substance are: ployed, the product exhibits excessively high oil Tinting power 95 absorption. The sharp drop in oil absorption of Oil absorption 10.3 the pigment when calcined at about 950 C. indi ColorBetter than white lead standard cates some consolidation of surface which sug- 50 PbO (total) per cent., 76.30 gests a chemical or physical reaction. So 16.00 The actual nature of the reaction between the S03 ----- 16.00 alumina and the basic lead sulphate is not clearly AI2O3 7.74 understood. It may be a chemical combination or a physical combination, such as a solid solution 55 Example II of the two components, or both. Since the com 528 grams of litharge, bolted wet through a bination is chemical and/or physical for conven 100 mesh screen was added to a vessel contain ience, it is herein referred to as a chemico-phys ing 4500 ml. of water and 15 g. of 80% acetic ical combination. It will be found necessary to acid solution, forming basic lead acetate. The maintain the pigment at calcination temperature 00 mixture was agitated sufficiently to keep the for from about 3 to about 5 hours and preferably excess litharge in suspension and the slurry about 4 hours, to effect the desired combination. heated to a temperature of about 70 C. Then Since the pigment at this stage is finely divided, 271.4 g. of aluminum sulphate, Ab(S04)3.18H20 total fumacing time of large batches will un dissolved In 1500 ml. of water, was slowly added doubtedly be considerably longer, due to the slow os over a period of about 4 hours with constant heat penetration into this type of mass, as is agitation. The slurry was maintained at a tem well known. However, maintaining all parts of perature of between 55 and 75 C. throughout the the charge at about 950 C. for about four hours reaction period. The precipitate formed was will result in effective calcination, and the de sired combination. The effect of calcination on a mixture pro duced according to this invention is illustrated by the properties given in the following table which 70 then filtered and washed with about 4 liters of cold water to remove soluble acetate salts. It was then dried and calcined in a muffle furnace at `950 C. for 4 hours. The product as made above showed the following properties: compares the same material calcined at different Tinting power ----------------------------------------- 100 temperatures. 75 oil absorption ---------------------------------------- 14-2 * 0000-NLI-000018982 3,460,341 56 Color (white an intimate mixture of finely divided basic lead ness) ___ Better than white lead standard sulphate and an aluminum compound which on PbO (total) ---------------------------per cent.. 76.20 heating produces aluminum oxide in amount as SO3 (total)--_____ ______________do___ 16.34 to produce between about 2% and about 10% AI3O3do_______________________________ 7.60 S aluminum oxide in the mixture and heating the Combined water None mixture at a temperature of between about 900 When alumina is calcined in admixture with lead sulphates in the proportions mentioned above, the product shows improved pigment properties. When the product of Example n, for instance, was incorporated into a linseed oil vehicle, and when 3 coats of the resultant paint were applied to wood, a comparison with 3 coats of a standard formulation of basic carbonate white lead paint showed that after 33 months of outdoor exposure of test fences, the product of this invention had shown little or no signs of chalking, while white lead paint started to chalk at the end of 9 months, and at the con clusion of the test had chalked considerably. Furthermore, there was less chalking and minute cracking in the paint film formulation with the product of this invention than with the standard white lead paint. The two paints described were formulated as follows: 10 10 20 23 C. and about 1000 C. until chemico-physical combination is effected. 4. A process for manufacturing basic lead sul phate-alumina pigment which comprises forming an intimate mixture of finely divided basic lead and an aluminum compound which on heating produces aluminum oxide in amount as to pro duce between about 2% and about 10% aluminum oxide in the mixture and heating the mixture at a temperature between about 900 C. and about 1000 C. for a period of between about 3 and about 5 hours. 5. A process for manufacturing basic lead sul phate-alumina pigment which comprises inti mately mixing finely divided basic lead sulphate with from about 2% to about 10% of alumina, and heating the mixture at a temperature be tween about 900 C. and about 1000 C. until said alumina is chemico-physically combined with said basic lead sulphate. 6. A process for manufacturing basic lead sul phate-alumina pigment which comprises slowly Improved Basic Lead Sulphate Pigment Standard White Lead adding a sulphuric acid solution to a slurry of 30 lead oxide, PbO, containing basic lead acetate, maintaining said slurry at a temperature between Per cent 70.9 29.1 Pit cent. 72.0 28.0 about 55 C. and about 85 C. and continually agitating the same until basic lead sulphate is formed, intimately mixing an aluminum com 100.0 100.0 35 pound which produces aluminum oxide on heat ing with said basic lead sulphate in amount so The vehicle in the aforementioned paints con sisted of 87.6% linseed oil and 12.4% volatile thinner and drier in each case. The basic lead sulphate product of this inven tion has therefore the very great advantage, over basic lead sulphate as heretofore manufac tured, of having definitely superior weathering qualities. As has been shown by the result of the comparison test described, the weathering properties of the product of this Invention are even superior to those of a basic carbonate white lead. While this invention has been illustrated by the examples shown, it is not intended to restrict it specifically thereto and other modifications and embodiments may be used falling within the scope of the following claims. I claim: 1. A pigment consisting essentially of basic lead 40 46 30 53 that between about 2% and about 10% of alumi num oxide will be present in the heated mixture and heating said mixture at a temperature of be tween about 900 C. and about 1000 C. for a period between about 3 and about 5 hours. 7. A process for manufacturing basic lead sul phate-alumina pigment which comprises forming a slurry of lead oxide, PbO, containing a small amount of basic lead acetate, slowly adding to said slurry a solution of aluminum sulphate, meanwhile agitating and maintaining the tem perature between about 55 and about 85 C., to form a mixture containing basic lead sulphate and aluminum hydroxide, washing said mixture to remove acetate salts therefrom, and heating said washed mixture at a temperature between about 900 C. and about 1000 C. for a period be tween about 3 and about 5 hours. ADRIAN RICHARD PITROT. sulphate having from about 2% to about 10% of aluminum oxide physico-chemically combined REFERENCES CITED therewith. The following references are of record in the 2. A pigment consisting essentially of basic file of this patent: lead sulphate having about 8% aluminum oxide 110 chemico-physically combined therewith. UNITED STATES PATENTS 3. A process for manufacturing basic lead sul Number Name Date phate-alumina pigment which comprises forming 2,383,284 BartonAug. 21, 1945 0000-NLI-000018983