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THE INDIA RUBBER WORLD 



April 1, 1921 



PAINT AND RUBBER PIGMENTS 



THE FOLLOWING covcrs the salient features of a talk on paint 

 and rubber pigments given by Frank G. Breyer, chief of the 

 Research Division of the New Jersey Zinc Co., at the March 

 meeting of the New York Section of the American Chemical 

 Society. 



The technical man who directs the purchases of large consumers 

 of both paint and rubber goods is hampered in his judgments of 

 the quality of both, because each is in that peculiar state of matter 

 , which is neither true liquid nor true solid but plastic, and plastics 

 are difficult for both chemist and physicist to deal with. 

 SPECIFICATIONS 

 Rubber, and particularly paint, experts among consumers have 

 been trying to pin down the quality of the product they purchase 

 by specifying what ingredients the producer should use and how 

 he should use them. 



Some success has been obtained by this procedure but the 

 trouble is that the method is calculated to stifle the initiative of 

 the producer whose success, in a large way, depends on the service 

 he renders by his skill in utilizing in his goods either something 

 that gives better properties than the specified ingredients or that 

 gives the same properties at less cost. 



Another trouble with the sort of specification referred to is 

 that it falls short in effect with progressive manufacturers since 

 the latter always occupy an advanced position in knowledge of 

 the technology' of the product. The time may be not far distant 

 when the manufacturers will not state the performance of their 

 tires in terms of mileage but instead will say that they will 

 stand a certain number of blows dealt under an accepted standard 

 method and specified tire inflation. Regarding a tire tread it will 

 be said that it will give a "resistance to wear" index-number 

 higher than a certain figure. That. the temperature of the tire 

 when worked under conditions approximating summer conditions 

 will not rise above a certain point which rapidly increases hard- 

 ening, and that when the tire is artificially aged to the equivalent 

 of a year and a half, the rubber will not harden beyond a given 

 point 



Similarly the paint manufacturer will not say that a paint 

 consists of specified ingredients put together in a prescribed 

 way, but that a sample of the paint as sold will respond to certain 

 exact figures for color and hiding power or surface dirt-obliterat- 

 ing power; that test pieces of a paint film when tested in tension 

 will give certain elastic properties when fresh and show a mini- 

 mum figure for the decrease of elasticity over an artificial aging 

 period. These tests are of exactly the same sort as those under 

 which steel and other metals are specified. 



Such as these, in contradistinction to the "ingredient and meth- 

 od of manufacture" specifications, do not reduce everybody in the 

 industry to the same dead level but leave open the way to in- 

 vention and skill to accomplish the desired result with less labor 

 and with other and cheaper matorials, or to make a better product 

 with materials new to the industry. 



CHEMICAL AND PHYSICAL METHODS 

 The study of any material may be made either analytically or 

 synthetically. While each method has its field, experience shows 

 that the latter method yields the more practical results. Physical 

 tests and analysis of paint and rubber should precede if not 

 supersede their chemical analysis. The great value of physical 

 analysis as applied to pigments for use in the paint and rubber 

 industries was brought out in a very clear and striking manner 

 by means of many microphotographs, charts and special methods 

 of test. 



The paint and rubber manufacturing industries are fortunate 

 that by the exercise of a liberal policy these new methods for 

 physical analysis and instruments for testing will become gen- 

 erally available for determining pigment values and will elim- 



inate the necessity of waiting the results of aging tests requiring 

 months or years to complete. 



PAINT AND RUBBER 



A very interesting and close connection exists between paint 

 and rubber and in each material the function of pigments is the 

 same. This connection between paint and rubber is apparent from 

 tlie following considerations : Each is a suspension of solid 

 particles, five microns' or less in diameter, in a plastic medium. 

 Each in its state of usefulness is employed in an altered form — 

 in paint brought about by the effect of driers, and in rubber, by 

 vulcanizing agents. The usefulness of both paint and rubber is 

 measured chiefly by their elastic properties. 



Linoleum and oilcloth products were classed as of the paint 

 industry. 



IDEAL PIGMENT 



The ideal pigment is characterized by (1) the smallest particle 

 size. (2) These do not form aggregates in the disperse me- 

 dium. (3) They are free from crystallization, (4) exert no 

 injurious but rather a beneficial influence on the mixing. Zinc 

 ixide fulfils all of these requirements and typifies the perfect 

 pigment. 



EFFECT OF ULTRA-VIOLET LIGHT 



By means of ultra-violet light different pigments which are used 

 both in paint and rubber can be quickly identified without chem- 

 ical analysis. 



The destruction of ordinary paint on the outside of buildings 

 is largely due to the effect of ultra-violet light which is present 

 in sunlight, and to moisture. Some of the hardening and conse- 

 quent short life of tires and other rubber goods can be attributed 

 to the same agency. The reflection of ultra-violet light by pig- 

 ments is an important reason for putting them into such goods. 



HEATING OF TIRES 



The effect of certain pigments, on the heating of tires, especially 

 in summer service, was explained as due to the internal friction 

 generated by the movement of pigment aggregates induced 

 by the elastic movement of the plastic rubber. The probability 

 of this occurring can be diagnosed in a tire by making sections 

 and examining them under the microscope. 



Among the many microphotographs of rubber sections exhibited 

 were certain of particular interest such as those showing the 

 even dispersion of zinc oxide in compounded rubber, the tendency 

 of other pigments to form aggregates and the presence of vacuua 

 adjacent to pigment particles in the direction of stretching in 

 rubber under strain as deduced by Schippel in a paper read before 

 the Rubber Section of the American Chemical Society.^ 



PARTICLE SIZE 



Screening methods are ineffectual for the determination of 

 particle size. Only that of aggregates can be so measured, even 

 with a 3S0-mesh opening, since the coarsest pigment particle 

 is five microns, and that of zinc oxide, for example, averages 

 4 micron. 



The usual method of counting dispersed particles in the field 

 of a microscope by means of an eye-piece micrometer is not 

 available for measuring the particle size of pigments. A new 

 method has been developed by Dr. Henry Green which permits 

 particles from 0.3 to five microns diameter, magnified 20,000 

 diameters, to be counted, scaled and tabulated. By this method 

 it has been ascertained that the particle size of zinc oxide is 

 0.4 micron and that one gram of the substance contains five 

 trillion zinc oxide particles. 



^A micron erin.Tl? 1/1000 of n milliinoter. 



•Mectinij of the -Vmerican Chemical Socictv, Philadelphia, Pa., September 

 2 — 6. 1919. Thi Inpia Rutipei! World, October, I?!", pace 20. 



Replete with information for rubber manufacturers — H, C. 

 Person's "Crude Rubber and Compounding Ingredients" and 

 "Rubber Machinerv." 



