COBALT FEEDER DRIER A. C. ZETTLEMOYER, GEORGE W. LOWER, AND ERNEST GAMBLE National Printing Ink Research I n s t i t u t e , L e h i g h U n i v e r s i t y , B e t h l e h e m , P a .
manganese borste. However, because cobalt is a more active drier, attention was focused on insoluble cobalt drier.
Certain printing inks fail to exhibit the expected drying time after being stored. These inks, particularly those containing laked pigments, dry in the required time immediately after manufacture but thereafter show marked increase in drying time. To alleviate this difficulty, a cobalt borate drier was developed. This drier acts on a “feeder” principle whereby more cobalt dissolves in the ink vehicle to replace the soluble cobalt taken up by the pigment. The concentration of soluble cobalt and, consequently, the drying time are kept at a relatively constant level over long periods.
0
PREPARATION OF DRIERS
NE of the problems besetting the printing ink manufac-
turer has been the loss of drying of inks on aging. Certain inks have failed to exhibit the expected drying time after being stored. Some inks with a given drier content dry in the required time immediately after manufacture, but subsequently show marked increases in drying time. The most serious offenders are those inks made with laked pigments or, in some instances, carbon black. When the printing ink industry was canvassed over a year ago, this aging on storing was considered t o be one of its outstanding problems. A considerable number of individuals and paint groups have studied this problem. Several suggestions as to how the problem should be solved have been made recently, but have not been put into practice because of economical reasons or because of lack of sufficient control of the drying time a t a given age. A study made by the Cincinnati-Dayton-Indianapolis-Columbus Paint and Varnish Production Club (2) ascribed the loss in drier effectiveness to precipitation of the drier by acids, alkalies, or base exchange, or t o adsorption and absorption of the drier by the pigment or other solid present. In other words, in most cases interaction of drier with the pigment appears t o be the principal cause of drier loss. Where the pigment was a t fault the C.D.I.C. club stated that loss of drying could probably be avoided by addition of excess drier, pretreatment of the pigment by drier, formation of a protective coating on the pigment particles, or use of driers which are not adsorbed. The Montreal Paint and Varnish Production Club (7) found t h a t pigments which settle rapidly tend t o cause less drier loss. Apparently, less drier was taken u p by the pigment because i t was in suspension a shorter time. After aging, the initial drying rate was partially restored by regrinding which destroyed the flocculates and freed the entrapped drier. I n the case of clear, unpigmented oils the Montreal Club attributed the drying loss t o precipitation and a change of dispersion of the drier in the oil. The problem is more serious for printing inks than for paints. In printing inks the pigments do not settle out as they usually do in paints, and the pigment concentration is generally much greater in inks. Important also is the fact t h a t the drying time is more critical in printing processes. While excess drier is one solution t o the loss of drying problem, i t causes too rapid drying on the press during printing and dangerous generation of heat in the printed paper stacks. The approach examined here was the addition of a material which would supply or L‘fced’’more drier into solution as the drier metal in the varnish was adsorbed. Erikson ( 4 ) found t h a t soluble driers lose their strength much faster than the insoluble manganese borate and cobalt acetate driers. Some work has been done by Bernstein (1) on combinations of lead borate and
The borate, acetate, stearate, hydrate, and carbonate of cobalt were each examined for their effect upon the aging of printing inks. Tests were carried out in unpigmented varnishes and in a tartrazine yellow lake ink which was notorious with respect t o loss of drying. It was felt t h a t if loss of drying was prevented in this ink through the use of feeder driers, then similar results could be expected from inks in which the problem is less serious. The driers were converted into pastes by milling with a linseed oil varnish on a three-roll mill. The stearate, acetate, and hydrate were commercial products, and were milled into the varnish from the dry state. Cobalt carbonate was prepared (8) by adding a n equivalent weight of calcium carbonate to a saturated solution of CoC12.HzO. The mixture was sealed in a test tube and allowed t o react for-18 hours at 150” C. The resulting carbonate was filtered off and milled in the pulp state with one part of N o . l regular varnish. A smooth fluid paste was obtained. Cobalt borate was prepared by a precipitation reaction between aqueous solutions of borax and cobalt nitrate. T o obtain as fine a particle size as possible, the precipitation results were studied. Conditions known to affect the size of particles formed in precipitation, such as temperature, concentration, rate of mixing, and use of wetting agents, were varied. The relative particle size of the various precipitates was determined by inspection under a microscope. The method yielding the finest precipitate utilized a Jolibois (6) or Y-mixing tube. Concentrations of 0.1 M nitrate and 0.1 M borax solutions were found to be most effective. The filtered precipitate or pulp was flushed directly into a n oil. When 0.0591, by weight of Aerosol OT wetting agent was added t o the borax solution, a precipitate was obtained which was easier t o grind and flush. Electron micrographs of the cobalt borate pulp revealed t h a t the particles averaged about 0.5 micron in size. Because a very concentrated paste was desired, the minimum amount of varnish which would flush the sample had t o be determined. Using No. 1 regular varnish, a cobalt borateAerosol OT pulp flushed readily at a ratio of 3 parts of varnish t o 1 part of borate pulp (on a dry weight basis). The same pulp prepared without Aerosol O T required a 9 t o 1 ratio. The paste used, then, was made up from a borate containing 24.7% cobalt on a dry weight basis, and the cobalt content of the resulting paste was about 4.570. Pilot plant tests on flushing the wet borate pulp showed improved reeults in t h a t 2 parts of No. 1 regular varnish t o 1 part of cobalt borate on a dry weight basis gave satisfactory flushing action. One type of flushing yielded about a 6% cobalt paste; another system using a higher vacuum produced a paste containing nearly 9% cobalt metal. MEASUREMENT OF DRYING TIME
The action of cobalt borate in a n unpigmented, No. 1 transparent varnish was studied first t o determine the effects of type of varnish and of milling. If a sample was given only a few passes on a three-roll mill, i t developed a n opaque, pink color,
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INDUSTRIAL AND ENGINEERING CHEMISTRY
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Vol. 41, No. 7
ACID NO. 1.6
o ACIDNO. 10.6 e ACIDN0.20.0
8
5 DROP
TIME
4
HRS.
2
0 10
0
A G~E OF INK -
40
30
$DAYS
Effect of Acid Number on Dr?ing Time of Cobalt Borate in Varnish
Figure 1.
DAYS
Figure 2. Drying Loss on Aging a t Various ConcentraLioris of Soluble Cobalt Linoleate i n Yellow Lake Ink
Although the data reported here were obtained on ink films spread on glass strips, some additional work was done t o corrclatc. these drying time results with t,hose obtained from prints 011 paper. The tests on paper substantiated those made on the. glass strips. With tests on paper, however, it, is difficult 1.0 obtain reproducible conditions. All drier proportions used throughout the paper are givcri as per cent of metal on the total weight, of ink. Results showed that there was little difference in the drying rate of 0.3y0cobalt as borate in a varnish made from the KO.3 transparent varnish and pastes in either KO. 1 or No. 3 varnish. The amount of grinding of the paste likewise had little effect on the drying rate. The age of the drier pastes before use, however, affcctcd th(8 initial drying times of varnishes made up with these pastes. Studies indicated that the paste should be aged about 2 weeks. After this period further aging of the paste had no effect. Thi. slower initial drying rate of varnishes made up from the ncww pastes might have been due to the fact t h a t a certain time is required for the maximum amount of cobalt to go into solution in the varnish from which thc paste is prepared.
21
2.
2C
I6
I2
b
4 1.4
m
INSOL.
Q
W
0
I
IO
I
20
I
I
AGE
OF INK
I
I
60
70
EO
DAYS
Figure 3.
Control of Drying Loss on -4ging w-ith Cobalt Borate in Yellow- Lake Ink
apparently due to the presence of water. Repeated passes on the mill resulted in a red, transparent sample. These drier pastes were then rubbed into the No. 1 transparent varnish and tested for drying on a Gardner drying time recorder (6). Drying tests were made a t 68” F. and a relative humidity of 65y0. The ink films were spread on glass strips by a Parks Film-0-Graph. Micrometer measurements a t various places on dried, yellow lake ink films showed them to be 0.001 inch thick. The same thickness was obtained for inks of lvidely different viscosities. a n average thickness of a considerable area of film was also determined by a weight and density method. Drying times were then determined on the Gardner recorder in the usual manner. The “drop time,” the point a t which the last drop appears in the marks left by the wheel of the recorder, was used in this work because it was found to be the most reproducible reading on the films. Drop times could be reproduced within 30 minutes. For other inks, however, the drop time was found difficult to determine; for such inks another method of measuring drying time is necessary.
ANALYSES O F DRIER METAL
Drier metal analyses are of considerable importance t o workers in this field. The ink samples were digested with concentrated nitric and perchloric acids. Following t.he procedure of Young, Pinckney, and Dick (9) suitable aliquots were analyzed colorimetrically with nitroso R-salt to develop a characteristic rcd color. Slthough the maximum absorption was found a t 410 millimicrons in a Coleman Universal spectrophotomet,er, the calibration curve obeyed Beer’s law in only a limited concentration range. The maximum difference between the absorption of thc red standard solutions a,nd the yelloiv blanks, however, Tvas found at a wave length of 510 mp. This agrees with the work of Sandell (8). At 510 mp Beer’s law held for concentrations up to 0.3 mg. cobalt per 100 ml. solution. Therefore, absorption was measured at, 510 and not a t 410 mp as recommended earlier. The calibration curves werc standardized against Baker’s C.P. salts which were checked by electrolytic analysis. When the amount of drier in solution in comparison to the amount still left undissolved was desired, petroleum ether was first added to the ink. The mixture was centrifuged immediately, and the analysis of the ether portion was considered to give the amount of soluble drier present in the ink sample.
INDUSTRIAL A N D ENGINEERING CHEMISTRY
July 1949
DROP TIME
HOURS
0
IO
20
AGE O F I N K
60
70
80
90
DAYS
Figure 4. Drying Loss on Aging of Cobalt Borate Feeder Driers Added to Soluble Cobalt Linoleate in Yellow Lake Ink DRYING STUDIES
I n varnish without added pigment, concentration studies indicated the presence of a threshold value for the cobalt borate drier. A concentration of 0.04% cobalt as borate led to a loss of drying, whereas concentrations above 0.0870 did not show this effect. As Table I shows, there is little increase in drying rate with concentrations above 0.08%. Thus, the threshold concentration for this cobalt drier lies somewhere below 0.08% cobalt. Just what inactivates the drier at these low concentrations is not known. It is conceivable that the cobalt linoleate tends to act as a catalyst to form free fatty acids frcm the esters. Such salts of heavy metals are known to be saponification catalysts. According t o this hypothesis, therefore, the presence of free fatty acids causes a retardation in the drying rate and hence causes the aging effect noted in unpigmented varnishes of low cobalt content. As the amount of drier is increased, however, the drying effect of the cobalt may tend to mask the retardation due to the small amount of fatty acids formed.
IN TABLE I. AGINGOF COBALT BORATE
C o Concn., 76
--Drop 1 day
0.04 0.08 0.17 0.28 0.42
3.2 3.0 3.0 2.3 2.5
VARNISH
Time Hours-7 d& 4.6 3.1 2.6 2.7 2.5
25 days 7.5 3.1 2.8 2.6 2.7
For a feeder drier to accelerate drying, it must go into s o h tion in the varnish. The drying time, therefore, should be some function of the amount of drictr in solution. To correlate drying time with amount of soluble drier, simultaneous drying times and analyses of the amounts of soluble cobalt present were made. In a, No. 1 transparent varnish with a total cobalt content of 3.0 mg. per gram of varnish, about 2.5 mg. per gram were found to be soluble after the second day. If t,he feeder drier goes into solution by means of an exchange reaction with the fatty acids present in the varnish, then the acid number of the varnish would be an important factor in determining the amount of soluble cobalt and thus the drying rate. To demonstrate this point, varnishes of acid number 1.6, 10.6, and 20.0 were prepared for drying t'ests. The same amount of borat,e drier, 0.3061, cobalt, was added to each varnish. The varnish with an acid number of 1.6 dried a t a slower rate than the two with higher acid number (Figure 1). The two varnishes of acid number 10.6 and 20.0 have a sufficient concentration of acid to dissolve all of the cobalt present. Theoretical calculations, based on an exchange reaction with a fatty acid, show that 6.05 mg. of cobalt per gram of varnish can be dissolved in a varnish with an acid number of 10.6. Since this is more than the total amount of cobalt (3.0 mg. per gram) present in the two varnishes, both the 10.6 and the 20.0 acid number -varnisheswould be expected to dry a t the same rate.
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The drying rate of the same concentration of a typical soluble drier, cobalt linoleate, was not affected by the acid number of the varnish within the range tested here. Drying loss studies were made on a commercial tartrazine yellow lake ink consisting of 50% yellow lake pigment and 50% No. 0 litho varnish. The said number of the ink was determined to be about 10. Figure 2 shows the loss of drying on aging with a soluble drier, cobalt linoleate, The drying time could be maintained at about 0.7 hour for a long period by overloading the ink with a soluble drier. At a concentration of 0.56% there was little loss of drying time, but the time was nearly the same as for the 0.84% concentration. Further reduction of drier concentration to 0.28% showed a rapid initial loss from 1 to 3 hours, after which the drying loss curve leveled off fairly well. At a concentration of 0.254 and below, the loss of drying on aging was very great. As Figure 2 shows, the 0.1% concentration dried initially in 1.9 hours, but after 7 days it took 13.2 hours. This represents a rapid loss in drying time. This particular sample required 44 hours to dry after 99 days. The drop time for a printing ink should not be too low, lest the heat produced in the drying reaction be too high, or the ink dry on the press. If, for example, a drop time of 8 hours is required, Figure 2 indicates that i t is impossible t o obtain and maintain this drop time over any considerable period with a soluble drier. Figure 3 gives the drying time-age curves for an insoluble drier, cobalt borate. In the first 5 days there was an initial loss of drying time, but the subsequent loss was very slight. A desired drying time can be obtained and held by varying the concentration of the insoluble drier-that is, any desired drying level can be prescribed and maintained. The ratio of soluble to insoluble drier and the total drier content will vary with the ink and with the drying conditions. Thus, the loss of drying over a long period was relatively small in comparison with a soluble drier a t the same drying level. Although a drying level of 8 to 10 hours could not be obtained with a soluble drier for a period greater than 2 days, with an insoluble drier the same drying time of 8 to 10 hours was held for more than 100 days. Some of the inks containing cobalt borate were actually stored for 6 months without appreciable change in drying time. Figure 3 shows that the effect of increasing the concentration of insoluble drier is twofold: It lowrrs the drop time and lowers the rate of initial loss of drying. Figure 4 presents the result of using a combination of soluble and insoluble driers. The combination not only reduces the drying time but also lowers the initial and subsequent rate of loss of drying. A week or 10 days are necessary for constant drying rate to be attained. Since cobalt stearate is only slightly soluble in linseed oil varnishes, it should also act as a feeder drier, similar to the
DROP TIME HOURS
DAYS
Figure 5. Comparison of cobalt Borate and Stearate for Controlling Drying Loss in Yellow Lake Ink
INDUSTRIAL AND ENGINEERING CHEMISTRY
1504
cobalt borates. T h a t it does so is shown in Figure 5, but for a given concentration of cobalt metal, the stearate was not so effective as the borate. The addition of soluble drier to the stearate increased the drying rate in the same manner as it did with the borates.
OTIIER
Vol. 41, No. 7
i n ~ s
An extension of this work on yellow lake ink to i r i h made with Persian orange and peacocli blue gave similar results. Without the borate drier, however, loss of drying on aging was less for the Persian orange ink tested than for the yellow lake ink, and even less for the particular peacock blue ink tested. Conscquently, less feeder drier was required than for the yellow lake ink used. Cobalt borate feeder drier studies on inks pigmented with carbon black indicatcd that in this case the borate is not a satisfactory means of combating loss of drying. Since much greater amounts of drier are necessary with black inks than with the yellow lalie inks, various drying levels can be maintained through the use of soluble driers alone. Blacks appear to be a special problem. ACKNOWLEDGMENT
The authors wish to acknowledge the assistance 01 I. M. Bernstein in helping to initiate this w o r l ~ LITERATURE CITED
Figure 6.
ESect of Age on Amount of Soluble Cobalt from Cobalt Borate i n Yellow Lake Ink
Cobalt acetate, carbonate, and hydrate would not accelerate drying in yellow lake ink. -4pparently these compounds dissolve too slowly to be effective. For an o.84y0 cobalt metal concentration, the borate dried yellow lalie ink in 3 hours, whereas the samples of the same ink containing 0.847, cobalt in these compounds were still wet after 24 hours. In conjunction with the aging studies of the feeder driers, concurrent drier solubility tests w r e run with several pigmented inks during aging. The solubility studies were expected to support the conclusion t h a t drying rates are dependent on the amount of soluble drier present. As was anticipated from the drying plots, aging exhibited a pronounced effect upon the amount of soluble cobalt in inks containing borate drier. Figure 6 shows the trend of solubility with aging for a yellow lake ink with 0.84y0 cobalt (as borate) content. The attainment of a n equilibrium amount of cobalt in solution after several days is in excellent agreement with the stabilized drying time of this ink.
Bernstein, I. M., private communication. C.D.I.C. Paint & Varnish Production Club, AVatZ. P a i n t , V a r n i s h & Lacquer Assoc., S c i . Sect., Circ. 629, 273-314 (1941); Oficial Digest Federation P a i n t 6 V a r n i s h Production Clubs, 1941, 21-61. De Senarmont, Ann. chim. p h y s . , [3] 30, 137 (1850). Erikson, G. L., unpub. summary of expti. work on “Effect of Age on Drying of Printing Inks,” February 1946. Gardner and Sward, “Physical and Chemical Examination of Paints, Varnishes, Lacquers and Colors,” 10th ed., p. 149, 1946. Jolibois, P., C o m p t . rend., 169, 1095 (1919). Montreal Paint 8z Varnish Production Club, Paint, Oil C h e m . Rev., 101, NO. 23, 119-21, 130 (1939): Tech. Proc. Federation Paint & V a r n i s h Production Clubs, Annual Meeting Chicago, Oct. 25, 1939; Am. P a i n t J . , Convention D a i l y , Oct. 25, 1939, 1318; NatZ. P a i n t , V a r n i s h , & Lacquer Assoc., S c i . Sect., Circ. 546, 307 (1937); 568, 407 (1938); I b i d . , 629, 337 (1941); Oficial Digest Federation P a i n t & V a r n i s h Production Clubs, 1941, 121; 1942, 489; 1944, 7. Sandell, E. B., “Colorimetric Determination of Traces of Metals,” p. 202, New York, Interscience Publishers, 1944. Young, Pinokney, and Dick, IND. Esc. CHEW.,ANAL.ED., 18, 474 (194G).
RECEIVED J u n e 1, 1948. Presented before t h e Division of Paint, Varnish, and Plastics Chemistry a t the 113th Meeting of t h e ~ ~ C E R I C ACHEHICAI, N SOCIETY, Chicago, Ill.
Partial
ressulre Measurements System drogen Fluori
er
PAUL A. MUNTER, OTTO T. AEPLI, AND RUTH A. KOSSATZ Pennsylvania Salt Manufacturing Company, Wyndmoor, P a .
O?;TIXUATION of the aesemblv of basic data ( 4 ) pertinent to the manufacture of pure anhydrous hydrogen fluoride showed that vapor pressure data are lacking for the industrially important system hydrogen fluoride-water. This is particularly true for concentrations of hydrofluoric acid above 30%. Fredenhagen and Wellmann (2) report,ed partial pressure measurements for this system a t a single temperature of 25’ C., and for concentrations from 0 to 35y0 hydrogen fluoride. Khaidoukov, Linetzkaya, and Bognovarov (3) gave vapor pressure measurements for the system hydrogen fluoride-water from 25 ’ to 75” C. for concentrations from 5 to 3970 hydrogen fluoride. Since the completion of the experimental work described in this paper, Brosheer, Lenfesty, and E more ( 1 ) have reported partial
pressure measurements for the system hydrogen fluoride-water at concentrations from 2 t o 30% hydrogen fluoride, over the range 25’ to 75 C. The present paper describes partial pressure measurements by the dynamic method for solutions of 10, 20, 30, 50, and 70% hydrofluoric acid, a t temperatures from 0 ” to 70” C. O
APPARATUS
The apparatus as finally assembled for these measurements is shown in Figure 1. It consisted of a constant-temperature bath, A ; a source or inert gas, B , and a gas flow regulator, C; a gas purification train, D; a heat exchanger, E , for the entering gas stream; a set of silver preaaturators, F , and a final saturator,
