Drying of Linseed Oil Paint Concentration of Driers DOUGLAS G. NICHOLSON AND CHARLES E. HOLLEY, JR. University of Illinois, Urbana, 111.
T
HE rate of oxidation of drying oil films has been studied in some detail by several investigators. Many methods of attack have been used in this work; a summary of them was given by Currier and Kagarise (J), in which the following variables were observed: ( a ) time required to reach a definite temperature using an oil-soaked cloth (9); (b) measurement of the volume of oxygen absorbed as a function of time (1-5, 7,8, 11), and ( c ) weight, plasticity, or hardness changes as a function of time (6, 10, 12). The latter method was used in this study, the gain in weight of a paint film being the measured variable. This investigation is concerned with the effect of drier concentration upon the weight changes in a film of paint, rather than a film of drying oil. (Preliminary work showed that the oil alone gained weight far more rapidly than did the pigmented oil.) Genthe ( 7 ) and subsequent authors (4, 1 2 ) pointed out the errors resulting from data which do not take into account the volatile products of oxidation. It was assumed in this investigation that the volatile products were a constant factor and, for comparative purposes, were irrelevant. The agreement of the experimental results seems to indicate that this assumption was not without justification.
A method has been devised by which it is possible to follow changes in weight of paint films while out of contact with air. There is a limiting drier concentration above which no further appreciable acceleration of drying is obtained. A high drier concentration produces more rapid initial drying than a low concentration, although the rapidity of weight gain falls off more rapidly when high concentrations are used. In the cases of cobalt naphthenate and cobalt resinate the rate of gain in weight depends upon the concentration of the cation and not upon the anion of the drier material. A film of linseed oil pigmented with titanium dioxide changes in weight much more slowly than does the unpigmented oil (using equal drier concentrations).
A detail of the mechanism controlling the beam and pan releases is given in Figure 2. A system of cog wheels was used to operate the chain, and a n extension on the rod holding the rider finger was used to adjust the rider. According to Rogers and Taylor (11) the use of pure oxygen does not accelerate the drying of linseed oil when the reaction is catalyzed by driers. The use of oxygen was considered justified, however, because through its use the purity and constancy of the atmosphere in and surrounding the balance Experimental Procedure could be assured. The oxygen was bubbled through concentrated sulfuric acid, filtered through glass wool, and introAPPARATUS.The apparatus consisted of a glass plate duced through the outer case into the balance a t a rate (ap10.1 x 13.7 cm. upon which a film of paint 0.011 inch proximately 120 cc. per minute) sufficiently rapid to sweep (0.279 mm.) thick was spread by a “drawing-down” process, out the volatile oxidation products and prevent any inward and a balance to which was connected a gas train. The balance diffusion of air. (Figure 1) of the chain weigh type, was enclosed in a case, so MATERIALS.The paint fitted that weighings up to used consisted of titanium 1.1000 prams could be made dioxide ground in body-Q without opening the case. linseed oil (3.5 pounds of The glass plate used in titanium dioxide per gallon the drawing-down process of paint). It contained no was 0.049 inch (1.245 mm.) drier or volatile thinners. thick. Two flat brass strips The driers used were solid 0.06Oinch (1.524 mm.) thick cobalt resinate and cobalt w e r e p l a c e d beyond the naphthenate containing 2.3 edges of the plate, a few and 10.9 per cent cobalt drops of paint were spread m e t a l , respectively. In on the plate, and a level order to facilitate the inmetallic strip was drawn c o r p o r a t i o n of the driers over in contact with the into the paint, oleic acid brass strips. Thus there s o l u t i o n s of these subwas a clearance space of stances were added to defi0.011 inch between the guide nite quantities of the paint. strip and the surface of the I n this way the drier was glass plate. The films of uniformly distributed paint so prepared weighed throughout the paint withbetween 2.7 and 3.0 out any necessity of heatFIGURE 1. PHOTOGRAPH OF BALANCE AND CASE grams. u
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INDUSTRIAL AND ENGINEERING CHEMISTRY
ing the material.' The weaker drier concentrations were made by diluting the initial drier solution with oleic acid. I n all cases a definite volume of paint was mixed with the same volume of oleic acid; the only variable was the amount of drier present. PLATE
GLASS
RUBBER CqNtENTRKi
CASE
GASKET
TUBES
FIGURE 2. DETAILOF MECHANISM CONTROLLIKG BEAMAND PAXRELEASES
115
Results The results are shown in Figures 3 to 8. Figure 3 shows the total gain plotted against time for several concentrations of cobalt resinate as well as for the paint with no drier added. Figure 4 shows similar curves for cobalt naphthenate. I n each case increased drier concentration resulted in a more rapid initial gain and a shorter induction period, but the total gain a t the end of each trial was less than that obtained with a lower drier concentration. This is in agreement with the theory that drying is a reaction which begins a t the air-film interface and, in cases of high drier concentration, forms an impervious film on the surface of the paint, preventing the inner portion of the film from drying properly. Skinning and wrinkling were quite evident in the paints containing high concentrations of driers. The left-hand curve of Figure 3 connects data points obtained when using two different drier concentrations. This indicates that there is a limit to the concentration of drier which
Since there is some question concerning the mechanism of drying a t elevated temperatures as compared with room temperature (S), this study was carried out a t room temperature (25' f 1O C.) in order that the observations could be made under conditions more nearly those in actual practice. PROCEDURE. The following procedure was followed in conducting each trial: The glass plate was weighed accurately, coated with an even film of paint, wiped clean on the edges, and placed on the balance pan; the case was closed, and the plate plus the film of paint was weighed. Prior to the painting of the plate, the proper number of weights was placed upon the other balance pan, making it possible t o close the balance case immediately upon the insertion of the painted plate. The balance case was not opened again until the determination was completed; all weighings were made from outside the outer case. A stream of oxygen was kept flowing at all times so that the case was flushed free of air. Weighings were then made at 15- or 30-minute intervals while the film gained weight rapidly, and at 30- or 60-minute intervals after the reaction had slowed down. The trial was considered complete when the rate of gain in weight had passed through a maximum and was attaining a fairly constant value. Duplicate trials were made in all cases for check purposes.
FIGURE 4.
TOTAL G.4IN US. TIMEFOR SEVERAL CONCENTRATIONS O F COB.4LT NAPHTHENATE Symbol
C o in Co N a p h t h e n a t e Yoby weight in paint
X
0.1168
0 0
0 0583 0 0389
A
0,0350 0 0116
+
TIME,
MIN.
FIGURE3. TOTALGAIN us. TIMEFOR SEVERAL COXCENTRATIONS OF COBALT RESINATE Symbol
C o in Co Resinate
% b y weiohl in paint
0" 0 6V
0.1168 0.0874 0.0389 0.0311 0..0194 No drier added
TIME
,
MIN
FIGURE 5 . GAIN IN W E I G H T P E R 15-MINUTE INTERVAL US. TOTALDRYINGTIME FOR SEVERALCONCENTRATIONS OF
COBALT RESINATE
Symbol
C o i n Co Resinate weight in paint 0.0874 0.0389 0.0311 0.0194
70b y 0 0
INDUSTRIAL AND ENGINEERING CHEMISTRY
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OF DRYING OF PIQMENTED OIL AND OF FIGURE 8. COMPARISON OIL ALONE,CONTAINING 0.0116 PER CENT COBALT BY WEIGHT AS COBALT NAPHTHENATE TIME,
0 = paint X = linseed oil
MIN
FIGURE6 . GAININ WEIGHTPER 15-MINUTEINTERVALvs. TOTALDRYINGTIME FOR SEVERALCONCENTRATIONS OF COBALT NAPHTHENATE Symbol
Co in Co Naphthenate
% bg weight in paint 0.1168 0.0583 0.0389 0.0350 0.0116
X 0
0
2
curves show more clearly the change in the rate of drying with variations in drier concentration. Figure 7 is a comparison of cobalt resinate and cobalt naphthenate a t the same cobalt concentration (plotted as in Figures 5 and 6). The difference is not significant, and it may be stated that the rate of drying is dependent upon the metal content and not upon the character or concentration of the anion. These data agree with those reported by Gardner (6) in which linoleate and resinate were compared. Attention is called to the fact that the time required for maximum gain in weight is equal and independent of the anion present. Figure 8 shows graphically how a film of pigmented oil dries as compared with a film of the oil alone.
Acknowledgment Acknowledgment is due the Krebs Pigment and Color Corporation for the preparation of the paint and to the Xuodex Products Company for the cobalt naphthenate drier used in this investigation. The suggestions and criticism offered by J. F. Broeker were of definite aid in this work. 01' J 0 Id0
'
300
'
500
'
TIME,
760
'
'
10' 00
'
'
'
14 'w
I
MIN
FIGURE 7. COMPARISON OF COBALT RESINATE AND NAPHTHENATE AT SAMECOBALT CONCENTRATION OF 0.0389 PER CENTCOBALT BY WEIGHT X
0
--
cobalt resinate cobalt naphthenate
is effective, and above which further increases do not give rise to any appreciable increase in the initial drying velocity. These facts are in agreement with the findings of Rogers and Taylor (11). In Figures 5 and 6 the actual gain in weight per 1Bminute interval is plotted against the total drying time. These
Literature Cited Chataway, H . D., S.SOC.Chem. Ind., 47, 167T (1928). Chatterji and Finch, J. Chem. Soc., 127, 2464 (1925). Chatterji and Finch, S. SOC.Chem. Ind., 45, 333T (1926). Coffey, S., S.Chem. SOC.,119, 1152, 1408 (1921). Currier, A. J., and Kagarise, I. H., IND. ENG. CHEM.,29, 467 (1937). Gardner, H. A,, Drugs, Oils & Painfs, 35, 208 (1919). Genthe, A., 2.angew. Chem., 19, 2087 (1906). Long, J. S.,and Chataway, H. D., IND. ENQ.CHEM.,23, 53 (1931). Mackey, W. M., and Ingle, H., J. Soc. Chem. Ind., 15,90 (1896). Rhodes, F. H., and Chen, K. S.,IND. ENG. CHEM.,14, 222 (1922). Rogers, W., and Taylor, H. S., J . Phw. Chem., 30, 1334 (1926). Wise, Y. E., and Duncan, R . A,, IND.ENQ.CHEM.,7, 202 (1915). RECFJIVED June 28, 1937.
