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United States Patent Office 2,140,235 W Patented Dec. 13, 1938 2,140,235 UNITED STATES PATENT OFFICE 2,140,235 W. E. GMENT Ekbert Lederle, Ludwigshafen, Max Ginther, w Mannheim, and Rudolf Bri, Heidelberg, Ger many No Drawing. Application March 14, 1935, serial No. 11,164. In Germany March 14, 1934 5 Claims. (C. 134-8) This invention relates to the manufacture of ing one part of the zinc by magnesium. The ad non-charing white pigments containing titan vantages of the zinc magnesium titanate pig ates. ments thus obtained are to be seen in a greater A drawback well known in the paint industry hardness and resistivity of the color film as well is the so-called chalking of paint coatings. The as in a higher white content (albedo), together 5 cause of this is that the paint, or its binding with a better covering power and tinting strength. agent is destroyed which becomes evident in the Furthermore, the tendency of the paint to be Occurrence of loose pigment particles on the film come yellow during drying which is peculiar to Surface. Especially the white pigments show certain binding agents is overcome to a great ex 0 this drawback to a more or less great extent, tent in the pigments containing magnesium. 10 particularly such pigments as contain titanium Further, it has been found that the size of the dioxide. - primary particles of the zinc titanate is of par In accordance with the present invention it has ticular importance for their behaviour when used been found that zinc titanate having the crystal as paint. While the secondary particles deter line structure of spinel and/or Corundum yields mine the pigment-technical behaviour of a pig- 15 excellent white pigments which are distinguished ment (for instance covering power), the size of particularly in that they are fast to chalking the primary particles determines their catalytic and are Weather-proof. This essential advance behaviour (polymerization of the linseed oil, its is due to the particular properties of the zinc destruction by atmospheric influences and the 20 titanate crystals and by the absence of unbound like). The determination of the size of the pri 20 titanium dioxide. Such zinc titanates are zinc mary particles of zinc titanates arrived at by Orthotitanate, Zinc metatitanate and mixed crys X-ray photography has shown that as soon as tals of these tWO compounds. Zinc titanate pig sharp interferences are formed, that is at a size ments are obtained by heating zinc oxide with of primary particles of more than 10 cm. and 2 5 titanium dioxide in the proportion of at least at increased sharpness of the X-ray interference 25 0.9 mol of zinc oxide upon mol of titanium di lines and therewith also increasing size of the oxide at temperatures between 500 and 100° C. primary particles, the paints made with these The mixture is kept at these temperatures until pigments are more resistant to the influence of the whole titanium dioxide is bound to zinc oxide the weather. For obtaining the desired size of 30 in the form of zinc titanate so that then prac the particles it is advantageous to effect the 30 tically no free titanium dioxide is present. When formation of the titanate at temperatures of using more than about 1.5 mols of zinc oxide between about 500 and 80° C. and to heat the upon innol of titanium dioxide exclusively mixed titanate to a temperature of up to 1100 C. crystals of zinc titanate having the crystalline In the manufacture of the non-chalking zinc Structure of spinei are obtained, whereas between titanate or zinc magnesium titanate pigments 35 i and about 1.5 mols of zinc oxide at higher it is possible to start directly with the corre- . temperatures, for instance, 900-1100° C., mix sponding oxides, for instance, zinc oxide Or mag tures of zinc titanate crystals of the spinel nesium oxide and titanium dioxide or titanium Crystalline form with those of the corundum dioxide hydrates. Instead of the zinc- or mag crystalline form, and at lower temperatures, for nesium oxide also such compounds can be used 40 instance, 500-900 C., likewise mixed crystals of which on heating yield these oxides, for instance, the spinel crystalline form are obtained. When carbonates, hydrocarbonates, compounds con using more than 2 mols of zinc oxide upon 1 mol taining sulfur and oxygen etc. - The zinc oxide of titanium dioxide the excess is not bound. used may be obtained by precipitation, for in 4. However, more than 2 mols of zinc should gener stance, in the manufacture of sodium hydrosul 45 . ally not be necessary. The pigments consisting fite from zinc hydrosulfite solutions, or pyrogeni of zinc titanate having the crystalline structure cally. The zinc may also be employed wholly of Spinel or those having the crystalline structure or partially as metallic zinc in a finely dispersed of corundum as well as the pigments consisting form, for instance, zinc dust, whereby heating 5 C of the mixtures mentioned above, i. e. having is to be effected in the presence of an oxidizing 50 Crystalline Structure Selected from the group Con agent, for instance, air. Thus, any zinc Or mag sisting of corundum and spinel are distinguished nesium compound, or even the metals themselves by a pure white color and are fast to chalking. which on heating to a temperature within the The pigment-technical properties of the pig range stated above yield the corresponding oxides ments may be considerably improved by replac may be used in the practice of our invention and ; 2 2,240,285 in this description and in the claims appended In order to remove the last traces of unbound hereto, we have enployed the terms 'reactive zinc Zinc or magnesium oxide, the pigments may be compound' and “reactive magnesium compound' lixiviated with ammoniacal ammonium salt solu to designate Such compounds. Instead of titani tion, whereupon the product which is freed front. 5 um dioxide also other titanium compounds, for Zinc and magnesium oxide is heated again if instance, titanium sulfate may be employed, desired. whereby the quantity of zinc or magnesium oxide It is known that zinc orthotitanate (Zn2TiO4) in the manufacture of the starting materiai in Crystallizes in the form of spinel and such prep every case must be calculated on the quantity of arations have already been preared for detect 20 titanium dioxide contained in the compound. ing the spinel formation by way of X-ray pho 10 The process of manufacturing white pigments tography. However, it was impossible to pre is advantageously performed in such a manner pare zinc orthotitanate which is free from that the starting materials, eventually with the unbound TiO2, since either the calcining tem addition of water, are well mixed and are then peratures Were too low, or the time for calcining 5 heated in a rotary kiln either in the wet or dry was too short, or the calcining temperatures from 5 state. The reaction time required may easily be the beginning were too high, this bringing about established by testing the mixture from time to incomplete reaction or the formation of non time during heating and by determining the reactive titanium dioxide. Occasionally zinc quantity of the not yet bound zinc oxide by ex oxide has been added to titanium dioxide pig 20 traction with ammoniacal ammonium salt solu ments with the intention of neutralizing acid tion. From the difference between consumed and residues still present and render them innocuous. free zinc oxide, the quantity of the bound zinc These processes have nothing in common with Oxide and thereWith also the bound titanium di the present invention since in all these cases a oxide is obtained. By the addition of mineraliz considerable excess of titanium dioxide is present 25 ers, as for instance, alkali metal sulfate or chlo in the pigment, whereas according to the present 25 ride, if desired also by the addition of substances, process it is just the presence of unbound titanium such as borates, wolframates, vanadates or the dioxide which has to be prevented. Zinc meta like the duration of the reaction can be decreased. titanate (ZnTiO3) was hitherto unknown either in By the term "mineralizer' as used in this descrip Corundum crystalline form or in spinel crystalline 30 tion and in the claims appended hereto, we mean form. Surprisingly it has been found that zinc 30 Substances, for example, those just enumerated Ortho and zinc metatitanate both having the which, acting as a flux, produce a slight sintering crystalline structure of spinel are able to form action during the heating of the reactive zinc mixed crystals though they are chemically dif compound with the titanium dioxide. When us ferent. The complete transformation to zinc ing mineralizers in the practice of my invention titanate and the absence of free titanium dioxide 35 it will be understood that the quantity employed is detectable by X-ray analysis and in connection should not be so great as to bring about a fusion therewith also chemically. All zinc titanates of the reaction mixture. Mixed crystals from when treated with ammoniacal ammonium salt zinc-meta-titanate and zinc-ortho-titanate of Solution only give off the unbound zinc oxide to the Spinel type may be prepared by mixing zinc the said reagent. Pigments which are fast to 40 titanates with various zinc contents and by unit chalking and being weather-proof, however, are ing them to form a uniform product by means obtained when according to the present inven of a calcining process. tion at least 0.9 mol of the zinc oxide calculated The starting mixture required for effecting the upon TiO2 are insoluble in ammoniacal am reaction may be produced by means of precipi monium Salt solution, for the pigments are then tation, for instance, by precipitating from zinc practically free from unbound TiO2.
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