1130
Vol. 36, No. 12
INDUSTRIAL AND ENGINEERING CHEMISTRY
TABLE
OF EXPOSURE TO ULTRAVIOLET LIGHTI N VARIOUS ATMOSPHERES ON I. EFFECT
INTRINSIC
ACETATE AND NITRATE
Relative Viscosity Cellulose Cellulose acetate nitrate
Ex asure $me, Hr.
A. 1.349 1.329 1.308 1.287 1.266 1.261 1.193 1.162 1.130 1.100 1.084
0 10
24 36 48 72 96 120 144 176 200
Intrinsic Viscosity Cellulase Cellulose acetate nitrate
Ultraviolet Light, Air 1.270 1.497 1.422 1.218 1.342 1.162 1,262 1.120 1.179 1.094 1.119 1,064 0,882 1.050 0.751 1.042 0,622 1.039 1.035 0.477 0.403 1.031
B . Stored in Dark a t Room Temperature 1.345 1,266 1.482 1.343 1.265 1.475 1.344 1.261 1.478 1.343 1.258 1.475 1,342 1.258 1.471
0
50 100 150 200
C. Ultraviolet Light, Nitrogen 1.348 1,268 1.493 1.340 1.262 1.463 1.338 1.258 1.456 1.336 1.256 1.448 1.330 1.249 1.426 1.328 1.245 1.418 1.322 1.241 1.396 1.388 1.320 1.234 1.317 1.231 1.377 1.313 1.229 1,312
0
24 48 72 96 120 144 168 192 216
Ex osure &ne, HI.
D. 1.195 0.986 0.751 0.567 0.449 0.310 0.244 0.206 0.191 0.172 0.163
0-1
Na N,
bt7L96-7
Na
6;-120-J ‘---144--,
1.179 1.175 1.160
1.148 1.148
OF
CELLULOSE
Relative Viscosity Intrinsic Viscosity Cellulose Cellulose Celluloae Cellulose acetate nitrate acetate nitrate Ultraviolet Light, Nitrogen and Oxygen Alternately 1.349 1.270 1.497 1.195
bt24-J -81
VISCOSITY
N2
6;-168-J -1927
NS 2 16---’
1.340
1.263
1.463
1 167
1.288
1.138
1.265
0.646
1.281
1.131
1.238
0 626
1.222
1,060
1.002
0.291
1.218
1.066
0.990
0.272
1.172
1.032
0.794
0.157
1.162
1.028
0.751
0.138
1.120
1.021
0.568
0.104
1.118
1.018
0.558
0.089
E. Ultraviolet Light, Air and Nitrogen Alternately 1.187 1.163 1.147 1.139
1.111 1.096
1,080 1.051
1.039 1.031
4’ 0
10
-24-7
1.349
1.270
1.497
1.195
1.329
1.218
1.422
0.986
1.303
1.618
1.323
0.776
1.301
1.168
1.316
0.733
1.262
1.100
1.163
0.476
1.256
1.093
1.139
0.445
1.218
1.088
0.956
0.329
r144--J Air L-l681
1.210
1.059
0.953
0.298
1.179
1.042
0.823
0.206
y 1 9 2 - J Na Air -216
1.169
1.033
0.780
0.162
1,134
1.030
0.628
0.148
Na ~ 4 8 - J Air -72-7 Nt ~ 9 6 - J Air -120A 2
Further experiments of a more exact quantitative nature, with respect to light intensity, and to chemical nature of the degradation products would be useful. ACKNOWLEDGMENT
The encouragement and suggestions of T. S. Carswell are gratefully acknowledged. LITERATURE CITED
R.,and Fenske, M. R., IND.ENQ.CHEM.,ANAL. ED., 10, 297 (1938). (2) Federal Specification LP-4068, Plastics, Organic; General Specifications, Test Methods, Jan. 24, 1944. (3) Hercules Powder Co. Bull., “Effect of Heat and Light on Nitrocellulose Films”, 1935. (4) Hill, J. R,,and Weber, C. G., J . Research Natl. Bur. Standards, (1) Cannon, M.
17, 871 (1936). E.O.,IND.ENQ.CHEW.,30, 1200 (1938).
(5) Xrsemer,
(6) Lawton, T. S.,and Nason, H. K., Modern Plastics, 22, No. 2. 145 (1944).
(7) Merrill, L. R., and Myers, C. S., A.S.T.M. Bull. 113, 19 (1941). ( 8 ) Mitchell, J., IND. ENO.CEBM., ANAL.ED., 12,390 (19.40). (9) Montonna, R. E.,and Winding, C. C., IND. ENO.CHEM.,35. 782 (1943). (10) Stillin&R.‘A., and Van Nostrand, R. J., J. Am. Chem. Soc.. 66,753 (1944).
PREEENT~D before the Division of Paint, Varnish, and Plastics Chemietry at the 108th Meeting of the AMWRZCAN CHEMICAL S o c ~ m u New . York, N. Y.
ANTIFOULING PAINTS Effect of Inert Pigment on Antifouling Action
A
PREVIOUS article in this series ( 1 ) showed that the antifouling efficiency of copper-containing paints is a direct
function of their copper content, and that copper loadings of a t least 6 pounds per gallon are required for highly effective performance in short41 vehicles. Because a simple increase in copper content results in a corresponding increase in pigmentbinder ratio, it has seemed advisable to investigate the antifouling behavior of a series of experimental paints in which pigment-binder ratio is the independent variable. Such a study can throw light on the still open question as to whether the ideal antifouling paint should function primarily by exfoliation (underwater “chalking”) or by acting simply aa a reservoir of soluble compounds toxic to embryonic marine life. A series of formulations in a &gallon tung oil cumar V-3
short-oil varnish was used; the pigmentations consisted of varying proportions of leafed copper powder, barytes (an inert), and mixtures of the two. Freshly sandblasted steel panels were primed with two brush coats of a chromate-type phenolio anticorrosive paint, and finished with two brush coats of the several experimental antifouling paints. The paint compositions appear in Table I.
G . H . Young, W . K . Schneider, and G . W . Seagren MELLON INSTITUTE, PITTSBURGH, PA.
INDUSTRIAL AND ENQINEERING CHEMISTRY
December, 1944
1131
barytes, with corresponding observable exfoliation and erosion, gave no beneficial antifouling action. The formulation of ----;Exfoliating, - - - - - - - -etniaP , co per Paints highest pigment/varnish ratio (code 1) was so “short” in vehicle Code p ~ Pigment ~ compn., ~ %~ Code ~ Kigment, ~ ’Ib./gal. as t o offer brushing difficulties; nevertheless, this formula fouled no. ratio Cu Inert no. cu Inert as severely as did the clear finish. An exception to this gener0 100 1 6 6 None alization was its behavior toward Bryozoa; against these organNone 6 10 6/1 0 100 2 4/1 100 7 6 6 isms the excessively pigmented finish seemed to show some 3 2/1 0 8 6 12 4 Clear varnish 9 None 12 inhibitive action (Tables I1 and 111). Observations on the series of TABLE 11. FOULING RATINGSON NONTOXIC EXFOLIATINQ PAINTS -Bryoeoacopper-containing formulations Panel TubeEqorustFilaAlgae Composite c o n f i r m e d t h e earlier study: No. P/V Ratio Barnacles Mollusks w o r m Hydroids tng mentous Scum Rating While all of the formulations After 1 Month p e r f o r m e d satisfactorily (the 1 7 9 9 7 6 10 4 7.5 poorest rating 7 or better dur7.6 2 7 9 9 7 6 10 8 ing 7-month exposure), the ex10 9 7 6 10 6 8.0 7 3 261 8.6 4 6 10 10 8 6 10 10 pected increase in over-all performance with increase in copper After 4 Months 4 8 6 6 8 8 6 6.0 content was again established. 1 2 3 4 7 6 7 6 3 2 a 2 3 2 5 3.7 4 3 Of greatest significance was the 3 4 4 7 8 4 6 6 2 5.3 observation that addition of inert After 7 Months pigment to copper-containing 2 7 5 6 4 4 8 6 0 formulations further increased 1 2 1 8 3 4 3 3 8 4.3 their antifouling efficiency. This 3 2 7 K 3 1 1 2 3.0 observation bears directly on the 4 2 6 4 4 2 2 2 3.0 probable mechanism of antifouling action of toxic-containing TABLH~ 111. FOULING RATING6 ON COPPER-INERT PAINTS paints.
T A B LI.~ COMPOSITION OF
EkFOLIATINQ AND CoppBR PAINTS
84G
Panel
No.
-Lb./Gal.Cu
Inert Barnacles Mollusks
Tube-
worms
Hydroids
-BryosoaEnpmting
After 1 Month
6
6 10
8 9
6
6
7
6
0
6
6
7
lo6
6 8 9
6 0
lo 10
O 0
6 12 12 0 0
9 lo7 10 10
6 12 12
10 10 10 10
8
10
10 10 9 10
4
7
6 6 7
6 10
0 0 6
7 8 8
9 10
8 9
6 0
12 12
10 2
10 7
6
7
10 10 10 9
10 10 10 10 7
After 4 Months 7 7 9 9 6 6 9 10 6
a
10 10 10 lo 6
10 lo 10 10 2
After 7 Months 7 6 8 8 3 6 7 8 6 3
7 8
9
a1
These panels were exposed a t Daytona Beach, Fla., from April through October, 1942. Monthly comparative ratings on the 0-10 basis previously described (9) conclusively demonstrated that at no time during the life of the test did the fonnulations containing only inert pigment show any superiority i n antifouling efficiency over the clear varnish control. Thus, a variation in pigmentation from 0 to 12 pounds per gallon of
Exposure Time
(toxic exhousted)
Figure 1. Theoretical Toxic Losses from Antifouling Paints
Filamentous
Algae & Scum
Composite Rating
PROBABLE MECHANISM O F ANTIFOULING ACTION
If a vehicle is employed with permeability high enough to offer no impedance to diffusional processes, the limiting factors 6 on amount of soluble toxic arriving at the paint-water interface 10 6 8.6 are simply the rate of solution 10 6 9.1 of toxic (or its saturated solution 10 6 7.8 10 6 9.3 solubility if this is low), its con2 2 3.7 centration in the film, and the film thickness. The state of 7 7 7.2 affairs for such a paint is set 8 7 8.1 6.9 forth in Figure 1, curve A (the 9 6 8 8 8.6 initial slope for A is required by 1 2 8.0 Fick’s law, as the toxic is drawn from deeper within the film of finite thiokness). As vehicle permeability is decreased, a series of curves results which finally inflect the other way a t the point where permeability controls the amount of toxic to reach the interface. The limiting case is shown by curve B. Both these curves are displaceable up and down the concentration axis by the specific solubility of the toxic and its intiel concentration in the film. An idealized formulation is presented as curve C. If, superimposed on the above simple considerations, we introduce exfoliation or chalking characteristics in a highly permeable vehicle, the effect (if this is great) is to eliminate film thickness as a control; the toxic is released at the (retreating) interface solely as a function of its solubility and concentration in the film. This fact is shown by curve D,which will be displaced up arid down the concentration axis by the solubility and concentration of the toxic. By proper control of variables, it should be possible to select permeability, chalking rate, and toxic concentration so as to combine curves C and D into a formulation which wastes no toxic initially and releases i t a t a fairly constant rate to yield interface concentrations above the lethal threshold value. The only limitation on such a hypothetical system is how much paint 10 10 10 10 10
8 8 9 8
9.7 9.7 9.7 9.7 8.0
1132
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
could be applied and still stay on. For practical thicknesses (10 mils) this figure implies a finite life expectancy of several years. As the actual paint departs from the ideal (for understandable and independent reasons), its life expectancy is shortened correspondingly. Thus purely theoretical considerations reveal that no paint system can be devised with an infinite antifouling life. During the course of these studies we have had occasion to make comparison exposures of a variety of commercially available bottom paints. The disappointingly short service life of the majority of these products (4-6 months) appears to be attributable, not so much to a deficiency of toxic agents, as to improper balancing of vehicle permeability with the specific toxics employed. A few such paints were significantly improved by the
VOl. 36, No. 12
simple addition of celite, which imparted higher diffusion rate8 to the films. The majority, however, gave too high permeabilities and wasted toxic throughout the early months of exposure. It seems probable that definite improvement in antifouling paint performance would result from quantitative studies of vehicle permeabilities as a function of added pigments other than the toxic agents themselves. LITERATURE CITED
(1) Young, G . H., Gerhardt, G. W., and Schneider, W. K., IND.ENO. CHDM., 35, 432 (1943). (2) Young, G. H., and Schneider, W. K., Ibid., 35, 436 (1943).
CONTRIBUTION from the Multiple Fellowship of Stoner-Mudge, Inc.,
at
Mallon Institute.
Infrared Radiant Heat Baking of Enamels Comparison between the drying behavior of enamels baked in radiant heat and convection ovens at equal panel temperatures showed no significant differences. Absorptivities were determined for black, green, red, yellow, and white gloss enamels. An analysis was made of the distribution of energy in heating these enamels with radiant heat. The influence of convection currents and thermal conduction on radiant heat baking is discussed. The influence of the percentage of polymerizing material in a series of film-forming compositions upon the rate of hardening when baked with radiant heat was determined. The experimental results illustrate the adaptabilityof polymerizing coatings t o the high-temperature short-schedule baking conditions attainable with radiant heat lamps.
T
HE widespread utilization of radiant heat baking by industrial concerns has given impetus to the study of the underlying theory of radiant heating. Contributors (6, 7, 18) to the literature have gradually removed many of the false impressions prevalent in the early days of this new tool. The establishment of the theory and performance principles of the radiant heat lamp is essential for its judicious adaptation in promising fields. Moreover the complete understanding of these principles by the makers of protective coatings will aid in the development of materials designed to use the advantages offered by radiant heat baking to the fullest extent. When radiant heat lamps were first introduced industrially, startling claims were made for their applicability and advantages in the baking of paint films. Baking schedules of paint products were shortened considerably, and it was a t first thought that infrared radiation had a catalytic effect on the drying of paint films. This belief had no sound theoretical basis, and several articles soon suggested methods for disproving the theory. Bennett and Haynes (1) advocated that a time-temperatuie curve he determined for a specimen under a radiant heat lamp and the baking conditions then be duplicated in a convection oven. They stated that no difference would be found between two such baked films. They also suggested that the shortened baking schedules encountered with radiant heat lamps were probably due to the ilttainment of higher temperatures in a shorter time. However, no experimental results were given. I n many cases the short haking times were due to the use of new synthetic enamels that baked more quickly than previous types.
K. C . Ernst and E. F. Schumacher UNIVERSITY OF LOUISVILLE, LOUISVILLE, ICY.
The present experimental investigation has the following objectives: to compare the results obtainable with radiant and convection heating to use existing theory for the determination of absorptivities, and to determine the effect of enamel composition on film hardness. RADIANT HEAT THEORY
Goodell (3) and Tiller and Garber (13) subjected the results obtained in radiant heat baking to mathematical analysis by thermodynamic principles. The derived equations are essentially the same in both cases, with the exception that the final heating equation given by Goodell is valid strictly only for the condition where the temperature of the air surrounding the object being baked is equal to the initial temperature of the object; this condition is not likely to prevail under actual conditions. The final form given by Tiller and Garber holds for all conditions of baking. The theory applying to baking by radiant heat is essentially the same as that underlying the measurement of radiant energy with a radiometric instrument (10). The development of equations for the heating of objects by radiant heat is based upon the principle that the heat absorbed by the receiver is divided between the heat retained by the stock as sensible heat reradiation and the convection losses to the surrounding atmosphere. Although the energy source is entirely radiant heat, conduction and convection effects materially influence the temperature rise obtained in the object. Important considerations in the industrial practicability of radiant heat baking are the absorptivities of coatings being baked, and the percentages of energy distributed among reflection, convection losses, and useful energy during the baking process. The theoretical equations developed for radiant heat baking make possible the determination of absorptivities as well as an analysis of energy distribution. The equations and nomenclature given by Tiller and Garber (12) are used in thia paper with the exception of intensity which is expressed as B.t.u./ (hr.)(sq. ft.) rather than watts/sq. ft.; the equations essential for calculations are briefly restated.
