METALLATES HENRY A. GARDNER Institute of Paint and Varnish Research, Washington, D. C.
A series of metallic compounds of phthalic anhydride have been developed which have distinct possibilities in the pigment field. Tables are presented to show that these compounds, even in white, are practically opaque to ultraviolet light at all wave lengths. Titanium and lead phthalates are referred to in detail. Possibilities of various metallic phthalates are suggested for improving rubber and its derivatives, for increasing the light resistance of viscose films to be used in packaging, for the opaquing and strengthening of various cellulosic products, and for decreasing the chalking tendencies and increasing the tint retention of paints or lacquers. General methods of production and some physical properties of the pigments are indicated.
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ROMATIC polybasic acids, such as phthalic acid, may be combined with metals to form relatively insoluble pigments which heretofore have not been employed in industry. The writer has prepared a number of such products and suggests that they be given the generic name of “metallates.” Most of these metallic salts of phthalic acid are relatively insoluble in water and the commonly encountered organic solvents, and may be incorporated in oil paints, varnish enamels, cellulosic compositions, rubber, and other substances. They may be ground to any desired degree of fineness and seem to have many of the desirable properties of pigmenting materials.
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Methods of Production There are several methods of preparing these products, but the simplest is to dissolve phthalic anhydride in boiling water and add a pigment such as carbonate of lead, leaded zinc, or similar substances. Almost immediate reaction takes place. Carbonates of certain other metals may be used in the same manner to produce white or colored phthalsted pigments. In about 5 minutes the reaction is usually complete on a small batch. In the treatment of basic carbonate of lead, for instance, about 77 grams of pigment and 44 grams or less of phthalic anhydride can be employed, according to the degree of phthalating desired. For the treatment of leaded zinc, as little as 5 grams of phthalic anhydride can be used to 100 grams of the leaded zinc, where only a mild phthalating is desired. As the degree of phthalating is increased, changes in oil absorption and other physical properties will be noted. Thus, starting with a
25 per cent leaded zinc with a specific gravity of 5.9 alld an oil absorption of 10.2, treatment of 100 grams of this product with 10 grams of phthalic acid produced a pigment which shows a specific gravity of 4.5 and an oil absorption of 15.8. Or, when the leaded zinc was treated with as high as 20 per cent of phthalic acid, the resulting pigment had a specific gravity of 3.74 and an oil absorption of 18.7. Whereas the weight per solid gallon of the original leaded zinc was 49 pounds, the weight per solid gallon of the pigment treated with 20 per cent of phthalic acid was 31 pounds. The great bulking value of the latter pigment would be of commercial importance in lowering the actual cost per gallon of paint made from the pigment, because of the lower number of pounds required to deliver a gallon volume. One of the most interesting properties produced by phthalated products is the good consistency which they give to paints. They are of high oil absorption and they produce paints of a thixotropic nature. In another method of procedure the reaction can take place by treating a solution of a metallic salt, such as lead acetate, with a water solution of phthalic acid or sodium phthalate. The resulting pigment is extremely white and has a specific gravity of about 3.12. By this method the writer has also prepared phthalates of copper, barium, cobalt, mercury, cadmium, lithium, silver, manganese, and iron, as well as of some of the rarer metals. The reactions referred to may take place in the presence of a t least one other white or colored pigment, the phthalate being precipitated on the particles of the base pigment in any desired quantity. The phthalates appear to be adsorbed very strongly to the surfaces of pigment particles. Even such pigments as are not reacted upon chemically by phthalic acid, such as titanium or antimony oxides, appear to adsorb definite small quantities of the acid, which then appear no longer soluble in water. In the preparation of titanium phthalate, the reactants are titanium sulfate, neutralized to a desirable pH value, and sodium phthalate. A dense white precipitate is formed under the correct methods of precipitation. More or less titanium hydroxide may occur in such a precipitate. Pigments with a specific gravity as low as 1.72 have been produced by this process. When titanium phthalate is dried a t 105’ C. for a substantial period, the product becomes gelatinous and then has a tendency to form semi-vitreous or horny aggregates. As a rule, therefore, it is desirable to precipitate titanium phthalate upon another pigment, and then dry and grind, or to employ it immediately after precipitation. In the latter instance, removal of the water can be accomplished b y transference to some other medium such as alcohol. This pigment seems to be extremely colloidal in nature, most of the particles being less than 0.1 micron in size. When used in baking compositions, it seems to impart to such compositions some effects noted when the pigment is dried from water solution. Titanium phthalate appears to be of special interest because of its rather unique property of retarding the chalking properties of other pigments such as titanium oxide. When 5 to 10 per cent is precipitated upon a batch of titanium-barium pigment, distinct improvement in weathering properties is noted.
Resistance to Ultraviolet Light The most active factor in destroying protective coatings is ultraviolet light. Pigments which transmit this light allow it to destroy the linseed oil or other binder in which the pigment, is ground. On the other hand, if paints contain pigments which do not transmit substantial amounts of ultraviolet light, chalk resistance and tint retention should 1020
~5lWl'fiMBEli,1936
INDUSTKIAI, A X I ) KNGINEEHIU(~(:REMISTKY
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out the phthalate pigments yellowed, cracked, and flaked until final disintegration occurred. Those containing a small amount of titsniurn plrthalate were still in fairly good condition. This result indicated the possibilities of these salts in pigmenting integrally or surface-lacquering the cellulose xanthate films that are nsed for wrapping butter and other foodstuffs such as are made rancid rapidly through the action of light. Similarly, in the preparation of filaments from cellulose xanthates or cellulose acetate, there may first be added varioils metallic phthalates, dispersed either in water, dilute alkali, or in organic liquids. The resnlting filaments prodneed from such mateextrusion, are 'Oft and have a ri' .~, .*, .~, OF < . SMALL ~ AHOUNTof TITANIUM PIFI.I$ALATE IN DECKEA~INQ CHALK- rial, dehintered appoarance. The metallates may INQ PHOPBRTIBS AND LENCXWENINQ L I F ~OF TITANXIM OXIUEPAIWC also find a use as light shields in compounding ocnt titxtiium dioxide and lo per oeni Paint applied t o left-hsnd p+ made W i t h 00 titanium hthslste. It i s still in good condition. Paint appbed t o right-han? ornei w a cellulosic mat.erial or vinyl resin sheets for non,itR 100 per Oenttitanium dioxide. 1% hna chalked x.eiY mprdly. d d o s l n g the wood surfaa9. shatter glass. Small amounts of the metallates will n o t greatly reduce the transparency of the sheets to ordinary light but will greatly minimize the ultraviolet transnlission. Similarly, in rubber lie good. Some of tlie measurements which have previorisly or its derivatives, the metallates decrease the effect of light heerr reported for the transmission of light by rarious white which ordinarily destroys rubber and make it possible to pigments I i o w widely cmplnyed in the paint iiidiistry are JtR follows:' predict the use of this material for exterior purposes heretofore not jmssible. The use of phthalates in rubber tire stock 1,iZilt 'T,Ilillilli*li"ii of Pigriierit Lnser lI.llllU92 hlin. Thick appears to increase strength. For instance, in some recent Piu",ent man A . mi A. : m 5 A. 3%" A. 31:31 A. :+023A. tests wibh a compound made with 300 parts by weight of uaaic lehd earbonxte 0B BR 01 57.5 53 34 rubber, 10 parts of zinc oxide as an activator, 3 parts of 1,itlLop""a 36 52 I3 3% IS 5 Titanium-barium stearic a.cid as a softener, 9 parts of sulfur as a vulcanizer, niliinent :$!a S!I IX 13 I2 11 2 18 0 I, i Titanium dioxide si a:! 2.4 parts of moreaptobenzothiazol as an accelerator, and Zinc oxide 44 a* u U I1
