Document ZnDegkkQVMLz5rmo004D08azZ

594 INDUSTRIAL AND ENGINEERING CHEMISTRY Vol. 21, No. 6 Figure 1--Apparatus for Determining Rate of Evaporation half of which are controlled by a thermostat, supplies the heat. Humidity may be controlled by large evaporating dishes filled with a solution of a definite concentration of sul furic acid. In practice sulfuric acid was found to be unneces sary; The humidity within the cabinet changed so slowly that when using water alone a test could be completed before any appreciable humidity change had taken place. The lower compartment also contains a motor-driven fan to promote air circulation. The upper compartment contains a rotating drum, motor-driven from the outside. A circular shelf is built around the bottom of this drum to hold the test panels. Sufficient panels for a given test are placed on this shelf around the drum, the entire cabinet is brought to the conditions desired, and the panels are then flow-coated with the respective test lacquers through a small hole in the top of the cabinet. The drum is then rotated until the panels are dry and the relative degree of blush is noted. Humidity is calculated from readings of wet and dry bulb thermometers placed in the upper compartment of the cabinet. This ap paratus can be built in any shop at a very small cost. In this apparatus consistent checks can be obtained on a series of lacquers over a range of temperature and humidity. Relative blush resistance of a series of lacquers as determined by this apparatus is the same at varying temperatures and humidities. Relative blush resistance was judged in two ways. The relative degree of blush at a given temperature and humidity was noted and the blush resistance of each member of a series of lacquers under test was noted as tem perature and humidity were gradually increased, and each member in turn blushed. The dew point rather than the humidity is the critical factor in determining whether a given lacquer will blush. Ra t e o f Ev a p o r at io n --The method of determining rate of evaporation makes use of a small air tunnel as shown in Figure 2. At previous meetings the desirability of a standard method for determining rate of evaporation has been men tioned. It is believed that an air tunnel such as this could be developed into a definite standard. Weighed, ground-glasscovered dishes are partially filled with equal weighed volumes of the solvents under test. These dishes are then placed in the air tunnel, the covers removed, and the fan started. At intervals of time the air is turned off, the covers are placed on the dishes and the dishes weighed. The loss is recorded in per cent and refers to either weight or volume. Humidity has practically no effect on rate of evaporation. Temperature has a very decided effect. It was found that when the temperature was kept within =*= 0.5 C. checks could be obtained on a given solvent wdthin a range of 2 per cent. Figure 2--Apparatus for Determining Bluslj Resistance In standardizing this test it would be necessary to use a standard test liquid as a basis of comparison rather than to attempt to build standard air tunnels, A standard test liquid could be such a thing as a carefully purified fraction of butyl acetate. In running this test a constant voltage should be used on the fan motor or a rheostat and voltmeter should be in the line to control voltage. i Effect of Various Driers on Linseed Oil Films during Aging1 P. E. Marling Th e Lo w s Br o t h er s Co mpa n y , Da y t o n , Oh io HIS paper shows the relationship, during aging, of acid as a drier is an increasing function of the drying time; and of T value, iodine number and solubility of linseed oil films containing different concentrations of lead, other experiments5 which attempted to show that the iodine number of linseed oil films during drying bear a general in manganese, and cobalt. It presents a continuation of prevvei rse relationship to the acid value and the concentration, of ously reported experiments,2 in which it was concluded that the cobalt bears a definite relationship to the'decreasing iodine the acid value of linseed oil films containing cobalt acetate number. x Presented under the title "The Effect of Age on the Acid Value and Iodine Number of Linseed Oil Films Containing Various Concentrations of Lead, Manganese, and Cobalt Driers" before the Divirion of Punt and Varnish Chemistry at the 76th Meeting of the American Chemical Society, Swampscott, Mass., September 10 to 14, 1928, * Evans, Marling, and Lower, In d . En g . Ch e m., 18, 1229 (1926). Experimental Procedure The refined linseed oil that was used in these experiments had the following constants: * Evans, Marling, and Lower, In d . En g . Ch &m., 19, 640 (1927). June, 1929 INDUSTRIAL AND ENGINEERING CHEMISTRY 595 Add value......................................................... Iodine number (Wijs).............. .............. .. Molecular weight................................... .... Refractive index at 20 C..................... Specific gravity at 16.6 C........................... 2.8 176.0 730.0 1.4816 0.933 The linseed oil was heated in Pyrex beakers to 270 C. and the drier was added slowly. The temperature was held at 265-270 C. for 30 minutes, in order that the drier might be completely dissolved. The prepared oils were poured into glass bottles, tightly stoppered, and allowed to age for 1 week before the films were prepared. The treated oils were brushed on glass plates (37 X 50 cm.) and one coat was applied to each glass. The approximate weight of oil for each surface was 4 grams. The coated plates were placed approximately 1 inch (2.5 cm.) apart in wooden racks in a glass-covered box and free circulation of air was supplied from an air-presBure line. The box was located near a west window in the laboratory. Only diffused light reached the films and the temperature ranged from 20 to 30 C. during the 3 months of aging. No attempt was made to regulate the humidity of the test cabinet. Similar films were exposed to a 15-cm. mercury arc light at a distance of 75 cm. from the arci the temperature of the cabinet being 40 to 50 C. The oil films were removed from the glass plates with a safety-razor blade and digested in a solution of 2 parts toluene and 1 part alcohol by volume. The digestion was continued for from 1 to 5 hours, according to the solubility of the film. The digestion was made in Pyrex flasks and heated over a hot-water bath. The insoluble material remaining at the end of 5 hours was measured by filtering through fine cotton cloth and washing with toluenealcohol solution. The residue was dried to constant weight in an electric oven and weighed. The acid value was calcu lated on the soluble portion of the film. The free acid was titrated from the toluene-alcohol oil film solution with 0.1 N alcoholic potash, using phenolphthalein as the indicator. The end point was very indefinite, and the alcoholic potash was added at a regular rate until a pink color showed in the solution. This reading was recorded. Then 0.2 cc. was added and if the color was a deep' red the previous reading was taken as the end point. The iodine number was deter mined by the Wijs method for shellac. The solubility was fairly satisfactory, although the films did not completely dis solve in a few instances. Discussion The results are given in Tables I to IV. In Table I the acid values and iodine numbers have pro gressive changes until the fiftieth day, after which they re main constant. The lower lead concentration attains a 30 per cent insolubility, while the higher lead concentration has only a trace of insoluble at the ninety-fourth day of aging. In Table II the acid values increased to the end of the aging period, while the iodine numbers reached the minimum value earlier. The insoluble portion was greater in the lower manganese concentration than the higher, at the end of the aging period. The films of both concentrations at the end of the aging period gave a semi-paste condition and had enough flowing properties to determine the refractive indices. These values are 1.4885 for the lower concentration and 1.4875 for the higher. These values are lower than the refractive index of heavy heat bodied linseed oils.4 Table III shows the higher cobalt concentration to have a higher acid value, lower iodine number, less insoluble, and greater flowing properties than the lower concentration at the end of the aging period. The refractive index of the higher cobalt concentration was 1.4900, while the low cobalt < Frishkorn, Larsen, Marling, and Shepherd, Paint Mfrg.' Assocn, U. S., Tech Circ. 341 (November, 1928). Table I--Linseed Oil Films Containing Lead Acetate as Drier Ac e Ph y s ic a l Ap p e a r a n c e o p Fil m Ac id Va l u e In s o l u b l e in To l u e n e - Al c o h o l So l n . Io d in e Nu mb e r Days 0.2 PEE CENT LEAD Per cent 1 Wet 20.0 None 82.0 2 Set, slightly tacky 41.0 None 46.0 3 Dry, slightly tacky 48.0 None 40.0 23 Dry, slightly tacky 57.0 None 30.0 36 Slightly soft 60.0 None 28.0 50 Slightly sticky 63.0 None 27.0 59 Slightly sticky 64.0 Trace 27.0 73 Slightly sticky 64.0 19 27.0 94 Considerably sticky 66.0 30 27.0 S.O PER CENT LEAD 1 Set 2 Dry, slightly tacky 3 Dry, slightly tacky 23 Dry, slightly tacky 42 Slightly soft 50 Slightly sticky 59 Slightly sticky 73 * Slightly sticky 94 Slightly sticky 36.0 45.0 48.0 60.0 65.0 66.0 66.0 66.0 66.0 None None None None Trace Trace Trace Trace Trace 60.0 48.0 44.0 34.0 27.0 26.0 26.0 26.0 26.0 Table II--Linseed Oil Films Containing Manganese Acetate as Drier Ag e Ph y s ic a l Ap p e a r an c e o p Fil m Ac id Va l u e In s o l u b l e in To l u e n e - Al c o h o l So l n . Io d in e Nu mb e r Days Per cent 0.02 PER CENT MANGANESE 1 Set 2 Dry, slightly tacky 7 Dry, slightly tacky 20 Slightly soft 38 Slightly soft 58 Very soft 79 Semi-paste 34.0 40.0 56.0 90.0 98.0 108.0 110.0 None None Trace Trace Trace 4 6 70.0 60.0 28.0 23.0 20.0 16.0 16.0 0.20 PER CENT MANGANESE 1 Set 2 Dry, slightly tacky 7 Dry, slightly tacky 20 Slightly soft 28 Considerably soft 38 Considerably soft 58 Very soft 79b Semi-paste 38.0 42.0 65.0 100.0 110.0 118.0 134.0 140.0 None None Trace Trace Trace Trace Trace 1 60,0 54.0 30.0 12.0 12.0 12.0 12.0 12.0 <* Retractive index at 20 C., 1.4886* i Retractive index at 20 C., 1.4876. Table III--Linseed Oil Films Containing Cobalt Acetate as Drier AOS Days 1 2 3 14 27 33 50 64 84 In s o l u b l e Ph y s ic a l Ap p e a r a n c e o p Fil m Ac id Va l u e in To l u e n b Al c o h o l So l n . Per cent 0.016 PER CENT COBALT Set Dry, slightly tacky Dry, slightly tacky Dry, slightly tacky Dry, slightly tacky Slightly soft Slightly tacky Slightly sticky Slightly sticky 61.0 76.0 77,0 82.0 82.0 83.0 * 84.0 84.0 88.0 None None Trace Trace Trace Trace Trace 8 20 I ODIN NUMBBK 36.0 28.0 27.0 26.0 20.0 18.0 18.0 18.0 18.0 0.80 PER CENT COBALT 1 Set . 75.0 2 Dry, slightly tacky 92.0 3 Dry, slightly tacky 98.0 14 Dry, slightly tacky 112.0 33 Slightly soft 123,0 40 Very soft 130.0 50 Very sticky. 136.0 64 Very sticky 142.0 84 Semi-paste 144.0 None Trace Trace Trace Trace Trace Trace Trace Trace 81.0 26.0 23.0 17.0 13.5 13.0 13.0 13.0 13.0 * Refractive index at 20 C., 1.4900. Table IV--Linseed OH Films Exposed to Mercury Arc Light, without Drier and with Two Concentrations of Cobcut Acetate Ag e Ac id Va b d b In s o l u b l e in To l u e n e -Al c o h o l So l n . Io d in e Nu mb e r Bows Per cent WITHOUT DRIER 2 27.0 None 61.0 4 40.0 Trace 45.0 8 16 48.0 60.0 4 34.0 24 24.0 0.015 PER CENT COBALT 2 4 38.0 54.0 None 2 49.0 35.0 8 16 68.0 86.0 19 30.0 33 22.0 0.80 PER CENT COBALT 2 4 8 16 46.0 78.0 110.0 123.0 None 10 33 34 46.0 26.6 20.0 18.0 596 1 INDUSTRIAL AND ENGINEERING CHEMISTRY Vol. 21, No. 6 concentration was not soft enough to make a refractive index determination. Table IV gives the comparison of linseed oils films without drier and with' two concentrations of cobalt in the mercury arc light. All these films show an increasing acid value and decreasing iodine number during the 16-hour exposure period. The acid value of the lower cobalt concentration reached 86 in 16 hours, while the same cobalt concentration required 84 days in the indoor aging test to reach an acid value of 88. Also the insoluble portion was greater in the mercury light exposure. The insoluble portion was greater in the higher cobalt concentration. This condition was reversed in the indoor aging tests. The iodine numbers reach a lower limit and the acid values reach a higher limit in the higher cobalt concentration than the linseed film without drier or the lower eobalt concentration during the same time period. Summary 1--linseed oil films containing two concentrations of lead, manganese, or cobalt drier increased in acid value and de creased in iodine number during indoor aging. 2-- Linseed oil films containing the higher concentration of cobalt or manganese gave the highest acid values and the lowest iodine numbers; these films also showed the greatest flowing at the end of the aging period. The two lead con centrations reached a similar acid value and iodine number; these films showed no evidence of flowing properties. 3-- The lower drier concentration of linseed oil films with lead, manganese, or cobalt had the greater insoluble percent age in a toluene-alcohol solution at the end of the aging period than the higher concentration of the same drier. 4-- Linseed oil films containing manganese as a drier gave a more plastic film at a low concentration than either lead or cobalt at the end of the aging period. The higher cobalt concentration gave a more plastio film than the higher lead concentration. 5-- Linseed oil films without drier or with cobalt drier in mercury-arc light exposure showed an increase in acid value and decrease in iodine number during the 16-hour period. This agrees with the results of the linseed oil films of similar cobalt concentration in indoor aging. Reflection Factors of White Paints1 F. H. Rhodes and J. V. Starr Co r n e l l Un iv e r s it y , It h a c a , N. V. WO of the most impor The effects of the addition of known amounts of T tant optical properties of a paint are its carbon black, Prussian blue, and aluminum powder upon the brightness and the hiding power of white brightness and its opacity orpaints are measured. Small amounts of carbon black reflected. The total amount of light reflected from an opaque film may be termed the "ultimate brightness" of hiding power. Both prop or of Prussian blue decrease the brightness only slightly the paint. erties are dependent upon and increase the hiding power markedly. With larger The ultimate brightness is the color and the particle amounts of the colored pigments the decrease in the a function of the opacity of size of the pigment, upon the brightness becomes relatively more pronounced. With the paint and of the trans ratio of the refractive index very small amounts of Prussian blue the ratio of the parency of the pigment and of the pigment to that of the increase in hiding power to the decrease in brightness the vehicle of which the paint vehicle, and, to a lesser ex is greater than with carbon black. The addition of is composed. Of truly white tent, upon the oil absorption aluminum powder greatly increases the hiding power, paints made from transpar and the structure of the pig but lowers the brightness and causes the dry film to ent pigment and transparent ment particles. There is, have a flecked appearance. The use of aluminum vehicle, those which are the however, no necessary and powder in undercoats for white finishing coats is of most opaque will show the universal relationship be advantage. highest brightnesses. The tween opacity and brightness. addition of a dark or colored Colored paints are usually more opaque than white ones pigment decreases the brightness but increases the opacity. although the white paints reflect a larger fraction of the in When only small amounts of the dark pigment are added, cident light. In the true white paints high reflecting power is there is usually a very marked increase in hiding power ac usually associated with high hiding power. companied by relatively small decrease in brightness. In When a beam of light falls upon the surface of a paint film, certain cases where extremely high brightness is notrequired-- a portion of the light is reflected from the surface of the film as, for example, in undercoats for white finishing coats--the itself. For any given paint the fraction of the light thus re addition of a small amount of dark pigment should make flected at the film surface is constant and independent of the it possible to increase the opacity and thus to decrease the thickness of the film. The amount of this "surface reflection'' amount of paint required to hide the underlying surface. depends upon the roughness and the texture of the surface; The investigation described in this article was undertaken paints which dry to a glossy film show less surface reflection for the purpose of determining quantitatively the effects of than do "flat" or "eggshell" paints. small amounts of dark pigments upon the brightness and the A portion of the light which actually enters the film is re hiding power of a few typical white paints. flected at the interfaces between the pigment and the vehicle while the remainder penetrates to the underlying base surface. Experimental Work The amount of light reflected from within the film increases with the film thickness up to the point at which the film be comes so thick that it is opaque; further increase in thickness of film produces no further increase in the amount of light Ma t e r ia l s Us e d --Pure refined linseed oil from North American seed was used. The pigments were tLthopone, zino oxide, white lead (basic carbonate, by Dutch process), white lead (basic carbonate, by Carter process), sublimed white lead * Received December 7, 1928. (basic sulfate), barytes (ground native barium sulfate),