A small lump of, the pigment. shown in the upper right-hsod aorner. resembles B nautilus; +reuses are set up dUring the diylng prooe*s by tlie peculiar ehsisctei of titanium plhthala,ts.
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H E original article on metallic phthalates, I m . EYG. CHEM., 28, 1020 (1936), anno~incedt,he developnient of these products and outlined thc methods of pmdiict.ion and some nf the physical and chemical pn>pert,ies. Titanium phthalate precipitate is dense and white. Ihririg the drying process it is converted to semivitreous horny aggregates, resenibling silica gel or a hard resin (Figure 1). Therefore i t is better to precipit.ate it upon anothcr pigment than by itself. For example, it may he precipitated in a suspension of titanium oxide. \Vhen dry, the titanium oxide particles are coated with a seniivitreous shell of titanium phthalate. Oilbase paints, enaniels based on phenolic resin-tung oil varnishes or alkyd varnishes, and nitrocellulose lacquers made with such a treated pigment show much hettrr resistance to chalking and color fading than products made a i t h the untreated pigment. The fact that titanium phthalate ahsorbs substantial amounts of ultraviolet light may be one of the reasons for t.his phenomenon. Also, dry titanium phthalate ahsorbs small amounts of moisture. Hence, it is possiirle that the dura.bility of paints containing this ingredient is due to the flexibility imparted by even very small amounts of absorhed moisture. I'rohably, therefow, titanium phthalate pigments will be used as a light screen, as a surface cementing material, etc., by precipitating 10 per cent or less of it upon titanium oxide or some other basic pigment. An interest.ing phenomenon accompanies the drying of a titanium phthalate pulp. Probably evryone has noted the
Applications of Metallic Phthalates HENRY A. GARDNER Institute of Paint and Varnish Research, Washington, D. C.
irrt ilarity of the cracks produced during the drying of clay or mud, or of wet cakes of pigment pulps. In contrast, whm pulps containing tit,Hniunl phthalate are dried, spiral-shaped cracks (nautilus pattern) are formed (Figure 2). This phenom'enon may have some effect on the properties imparted t,o a paint. Another interesting use of lead phthalatc pigmerit has developed during tlie pest year. It is a very dense, finely divided, white substance. Unlike titanium phthalate it is not gelatinous, but like tidaniurn phthalate i t imparts relatively little hiding power to paints. Therefore, when even relatively small anioiints of this material arc ground int,o a clear varnish (about 8 per cent), tire varnish remains clear and transparent when applied and forms a coating whicli seems to be much more durahle than t,hc dear rarnish aithollt the lead phthalate (Figure 3 ) . This effect probably results hccause the pigment functions as a light Scree11 and thus prcvents passage of ultmriolct light,, which dest,roys most coat,-
ings rapidly. Therefore, t h e r e may be some snbstantial use of lead phthalate in tbis d i r e c t i o n in the future, nia.king it p o s s i b l e t,o use clear, transparent finishes w i t h a greater life expectants than heretofore. Esperitnents are being continuedin the directionof ernpl!J~iIig&tier the metallic phtlralatrs or pignimt,s eo-precipitated with them in ot,tier industries, sue11 a s p a p e r , c e r a m i c s , and fabrics, hut they have not yet hcen develoyd sufficiently f o r t h i s purpose to varrant immediate applic a t i o n . On tlie other hand, whim used in r u I) b e r e o n i p o u n d i ii g , lead pli t ha1 a t e k n d s t,o loI\-er tlie 'i( i s c o s i t y of the compoiind during m i l l i n g and apparently increases tile speed of vnlcarlieation. During the past year the w r i t , e r I t a s f o u n d that plitlralic acid as \rellas tire metallic plrt~halatesh a w a tIist,iiict, effect i n discouraging t li e growth of mildew >Then u s e d i n paints that are exp o s e d in damp. WITH ExmnioR VARNISHAND I:xrossn warm c I i m a t.e s, FOR 6 MONTHS such as that of (Adou,) pmei coated w i t b a clear. untreated rarrrirh. (Abmei panel coated with varnish Florida. Mercury wmtainin$, S m r cent ired phthainte: this aiid copperphthalamount ~d not detract greatly from the clarity of the varnish but did function BS B ates h a v e heen l i g h t shield and add greatly to tile dursbility. f o u n d useful in Compositions for discouraging the attack of teredo and Limnoria upon submerged wood or barnacles upon the steel hulls of ships. These experiments are being carried out in the subtropical maters of Bineayne Bay, aiid it may be some time before qiiantitative data can he reported. R E C ~ Y EMarch ~ 20, 11437. Presented before the Division
oi Paint %lid VarniSh Chemistry s t the 9:3id Xeetina of the Amcriean Chernicsgl POeiCLY. Chapel ITill. N. C . . A ~ n 12 l to 15. 1937.
641
Integration of the Drying Equation at Constant Temperature A. E. MARKUAM 3330 East John Street. Seattle, Wash.
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HE differential drying equation developed in chemical engineering textbooks ( I , 5) for variable conditions using an inert gas, where surface evaporation is the controlling factor, is: -dW 1V
*f") ~
(K~ Il)da
(1)
The integration of this equation becomes possible if the quant,ities bf(u), L, and (Hs - If) are constants or are expressible as functions of W or 6'. For drying a t constant temperabure, ( H , - H ) or A€f is a function of IV, but the relation has not hitherto been expressed in form suitable for fornial integration. Hence the integrated form for this case is:
The left side of this equation has always been evaluated graphically. Such mettiods at best consume considerable time. The object of this paper is t,o show relations between Wand A H xhich make the formal integration possible. The humidity chart (Figure 1) sliovs the nature of this problem when
FILUXE1.
1 I ~ i ~ 1 n Cmnr ir~
the drying operation takes place a t a constant temperature sucli as t. At any point in the dryer, the air has a humidity E-for example, I . At this point the wet-bulb humidity is represented by D, and A H is represented by the segment I N .
