Document gEYbk2J8e1NN3Q2ndxj6bJedq

1961-62 Paint Tachnolcgy Course Glidden iLasfcarn Region WHITE PIGMENTS There are significant differences in physical properties of the various white pigments* The paint formulator must fully recognize these dif ferences in order to use the pigments most efficiently* The low bulking value for lead pigments (W-l* W-104) is an economic disadvantage* since materials for paint are purchased by the pound and sold by the gallon. The high bulk of the titanium-calcium pigment (W-214, W-232, W-179* W-180J is one of the advantages of this material when used in paints which require extender pigments* The oil absorp tion of white pigments, is in the low to medium range* In some respects this situation is fortunate* because a higher per cent of pigment is required for white paints than for colored paints* A very important difference among white pigments is their variation in refractive index and corresponding hiding power. It is well known that hiding power is a function of the difference in refractive index of the pigment and the binder and the particle size of the pigment* Most of the white pigments (especially some titaniums) are produced in the optimum particle size range (0.3 microns) for maximum light scat tering. Smaller particles are transparent* larger particles are hard to grind and give lower gloss. The lead pigments (W-l V-104) are somewhat larger than optimum size* which detracts further from their hiding power* The three white pig ments* white lead carbonate (W-104), zinc oxide (W-33, W-219* W-17 2;* and titanium dioxide (see chart)* illustrate a fundamental property of pigments* namely their degree of chemical reactivity with the ve hicle and with the acidic compounds which form in the film as it dries and ages* White lead and zinc oxide are reactive pigments* titanium dioxide is a non-reactive pigment. The reactive pigments combine with free fatty acids in the vehicle* and with acids* such as formic acetic* and propionic which are formed as oxidation decomposition products in the dry film to produce the corresponding lead and zinc soaps or salts* The non-reactive pigment (titanium; does not combine with the free acids* Reactivity with free acids formed in the paint film affects the hardness* flexibility* coater resistance* gloss* and durability* White house paints are made with combinations of reactive and non reactive pigments to obtain optimum properties* Most architectural white paints and enamels tend to discolor or ''yellow'' to varying degrees on agin. In the dark* this ''yellowing" may be con siderable* The primary cause of yellowing is the formation of color bodies due to oxidation of the oil or other unsaturated components in the binder* About 10# of zinc oxide reduces or delays this yellowing* Zinc oxide gives the best protection of any pigment from the effects of sunlight* - OVER - GLP34576 - Page Two - Extended pigments such as titanium-calcium pigment* although they are used in low cost enamels* are used chiefly in paints like flat wall finishes which require high pigment volume concentration to reduce the gloss* The leaded zinc oxides are used in exterior house paints as an economical source of both lead and zinc* FBR/jfe F. B. ROBINSON C C C L L GLP34577