ANTIFOULING COMPOSITIONS S. B. TUWIBER AND D. A. DODGE
METALLIC COPPER
Phelps Dodge Corporation, h T e w York, N. Y.
Paint systems for the protection of underw-ater marine surfaces require formulation to meet a number of important requirements. The diversity of these requirements makes the problem difficult. The primer and top coat must fulfill their functions as well as be mutually compatible in forming a coherent film. In our tests we have employed panels of steel, coated in the field, and allowed a drying period comparable with those permissible in good practice for commercial shipping. Most promising results have been found with paints formulated with pure electrolytic flake copper in one of the class of varnish vehicles with short oil length, con-
ROBABLY no single application of protective coatings holds greater possibility for development than antifouling compositions, and probably in few other fields would a n improved coating have so great value per gallon or per square foot covered. A truly satisfactory antifouling composition should not only retain the integrity of its film, but also prevent the accumulation of plant and animal growths. In case of a large steamship, such an accumulation might increase the consumption of fuel necessary to maintain any given speed by as much as 30 per cent. Dry-dock charges are high, and dollar loss due to a ship being out of service is not inconsiderable. Moreover, during the intervals between applications of paint to the ships’ bottoms, corrosion of the steel hulls may occur to an extent that it too becomes an important item of depreciation or repair. The difficulty of formulating paints for underwater service on ships’ hulls is complicated by the fact that a compromise must be struck between durability, protection against fouling, cost of paint, and cost of application. These factors must be weighed differently for different sizes of vessels, different waters through which the vessel must pass or remain moored, type of surface (i. e., wood or steel), and type of service (i. e., pleasure or commercial). Speed and design of the hull may be of importance as well as the allowed drying time for the primer and top coat. For pleasure craft the cost of the paint may be very high since the price it will bring is affected to a greater degree by personal satisfaction resulting from good performance and because the total number of gallons employed for a job is usually not great. Such paints are usually heavily loaded with expensive mercury compounds, metallic copper, etc. Steel vessels present a different problem from those of wood because of the necessity of using a primer under an anticorrosive undercoat which should have the property of inhibiting corrosion and of forming an adherent bond between the steel and the outer coating of antifouling film. In formulating antifouling compositions, it must be borne in mind that durability is a function of the primer as well as of the top coat, and of the mutual adhesion of the two after being in service. Regarding the other factors, tropical and semitropical waters usually present a greater problem, both from the
P
taining coumarone-indene and phenolic resins. The best appears to be one with a vehicle of 6gallon tung oil varnish based upon three quarters coumarone-indene and one quarter p-phenylphenol-formaldehyde resin. Final failure w-ith this composition in panel tests in Florida waters occurred by softening of the primer, follow-ed by peeling. Until the time of such failure, resistance to fouling was good. The primer contained red lead in alkyd resin vehicle. The antifouling paint ~ h i c hgave best results in the panel exposures was employed with the same primer on a practical scale on the Lake Traverse. Results upon this vessel have been encouraging.
standpoint of resistance t o fouling and film integrity, than do those of the temperate regions. Fouling in these waters occurs a t a more or less uniformly severe rate a t all times of the year, whereas in temperate regions there id usually a more distinct season for maximum growth, particularly of barnacles. Certain organisms such as the teredo, a serious menace to wooden-hull vessels, are not found in colder waters. Harbors are generally more severe from the standpoint of fouling than the high seas. The speed of the vessel and the relative proportion of the service time during which it is moving to that when it is not is also highly important. Seed barnacles may not have a chance to adhere to a surface moving through the water a t sufficient velocity. With some types of paint there is also a tendency for portions of the film to be swept away due t o a chalking action which also releases accumulated growths; however, ability to protect the surface is also lost. IThere there is a tendency for adhesion to become poor, the motion may result in stripping large portions of the paint film.
Methods of Testing It is axiomatic that methods of testing protective coatings should, when possible, reproduce all of the significant factors of the service for which the coatings are formulated. For antifouling systems the only tests whose significance cannot be questioned are actual service on ship bottoms. This involves considerable expense and risk, and the condition of the surface cannot be noted except when the vessel is hauled out of the water. Moreover, no two voyages are alike. One important element is found in those occasions when the vessel may have t o move from the sea t o fresh water rivers. Barnacles and other growths may be killed by this treatment although barnacles which have accumulated and established a foothold will not usually slough away. Even when two or more paint systems are applied at the same time and under comparable conditions to the same hull, it is not certain that the order of failure after a second voyage will be the same as that found after the first. Probably a final evaluation will depend upon a statistical comparison after many individual tests. As a preliminary to service testing on ship hulls it is customary to attempt an evaluation of finishes by the more 1 154
INDUSTRIAL AND ENGINEERING CHEMISTRY
September, 1941
economical and systematic testing of small panels placed on racks submerged in harbors. Selection of the site is important. To evaluate finishes intended for ships running from Gulf and South American ports to those on the East Coast, tests in Florida waters are probably significant if not completely reliable. All of the tests reported here were made at Miami upon steel panels prepared according to Gardnerl. Both fouling and destruction of the paint film are more severe in this locality than in most conditions of service. The testing may therefore be said to be accelerated in the same sense that exterior weathering tests on house paints made a t a 45” angle facing south are accelerated compared with the normal exposure on houses. As in all accelerated tests, the various types of film failure (chalking, cracking, s c a l i n g ) a s well a s f o u l i n g ( b a r n a c l e s , fungi, etc.) should be accelerated proportionately. This is an ideal not realized in practice.
1155
VESSELUSED FOR PRACTICAL TESTS
Composition of Primers The primer must not be lifted by the solvents used in the antifouling composition and yet must dry quickly enoughthat is, within 4-6 hours-for application of the top coat. I n a series of antifouling compositions tested, powerful solvents are used and the primer is one of a limited class of formulations in order to meet the necessary requirements. I n our tests we have used a quick-drying red lead paint; the composition of which is 68 per cent pure red lead pigment and 32 per cent alkyd-type vehicle. This paint, while far from ideal, appeared to be the best of a number of proprietary compositions tested.
Composition of Antifouling Paints All of the antifouling compositions contain a copper bronze pigment incorporated in paste form. The paste contains 78 to 80 per cent of electrolytically refined oxygen-free copper coated with a polishing agent of stearic acid and oily matter; the rest is high-solvency petroleum spirits. Each formula tested included 3 pounds of this pigment paste per gallon of paint. The vehicles tested were prepared in small laboratory batches in all cases by heating the oil and resin to 450-460’ F. 1 Gardner, H. A., and Sward, G. G., “Physical and Chemical Examination of Paints, Varnishes, Lacquers and Colors”. 9 t h ed., 1939.
TABLE I. ANTIFOULINGCOMPOSITIONS Panel Length, No. gal. 4 134 4 135 4 136 4 137 4 138 4 139 6 140 141 6 6 142 143 6 144 6 145 6 4 146 4 147 4 148 4 149 150 6 151 6 152 6 6 153
Vehicle Oil Linseed Tung Linseed Tung Linseed Tung Linseed Tung Linseed Tung Linseed Tung Linseed Tung Linseed Tung Linseed Tung Linseed Tung
Resin Coumarone phenolic phenolic phenolic phenolic Coumarone 75 coumarone-257 phenolic 75% coumarone-25% phenolic
in 30 minutes, holding a t this temperature for 15 minutes, and immediately reducing to 50 per cent nonvolatile. In this reduction, 9.2 per cent by weight of the total solvent was o-dichlorobenzene which was added to cut each varnish after the 15-minute period. High-solvency petroleum spirits then followed; two fractions were employed, the higher boiling being 24.0 per cent by weight of solvent and the lighter fraction, 66.8 per cent. Each vehicle contained 0.04 per cent cobalt per gallon in the form of the linoleate.
Preliminary Tests Tests have been made on steel panels exposed in Florida waters at various times since June, 1938. Various vehicles were tried, most of which were found unsatisfactory because of poor durability, poor antifouling qualities, or both. The resins were mainly coal tar and phenolics, and tung oil was used in most of these. Varnish vehicles of 12-gallon length and longer yielded poor results. A number of 6-gallon varnish vehicles were then tried. In the best composition tested, the resin was three fourths dark coumarone-indene resin and one fourth p-phenylphenol-formaldehyde polymer. The oil was 100 per cent tung. Then began a more systematic study. A series of panels were painted with two coats of the red lead primer described above, followed by a Ringle coat of one of the antifouling compositions listed in Table I. Table I1 indicates the condition after each month of exposure up t o 6. In the application of the finishes, 4 hours were allowed between coats and 4-hour drying of the finished coat before immersion. All of these panels were exposed August 21, 1940. The composition used on panel 143, a 6-gallon tung oil vehicle based on three fourths coumarone-indene and one fourth p-phenylphenolformaldehyde, was found to be the best followed by panel 135, a 4-gallon tung-oil coumarone-indene vehicle. The most important factors in rating of panels are blistering, rusting, scaling, and barnacle growth. Moss is less important, while scum accumulation is significant only in that it is sometimes an indication of more serious fouling which may follow. Final failure of the coatings appears to be by disintegration of the primer, resulting in loss of adhesion between it and the top coat, which then peeled away .,rend left no protection against fouling. Rusting occurred t o a minor extent even
INDUSTRIAL AND ENGINEERING CHEMISTRY
1156
Vol. 33, No. 9
TABLE 11. CONDITIOX OF PANELS DURING 6 MONTHSOF EXPOSURE^ Pane NO.
134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153
7 -
1 A A A
i
Blistering after Months: 2 3 4 5 x xx xx xxxx x x X xx x x X xx X xx X xx
;
;
7
6 xxxx xx xxx xx xx
1 A A A A A
2 i
R u s t after M o n t h s :3 4 5 X xx xx X
X
-1
X
X
X
A 9
X X
X X
X
X
x A A A A A
i 7 -
1
x x xx x x xx x xx xx xxx
x x xx x x xx x xx xx xxx
-: :
; 2 i
xx X X
xx X
xx xx xxx
xx xx xx xx xx xx xx xx xx xxx
Barnacles after Months:2 3 4 5
134 136 A A x 136 137 -4 A x 138 A x x 139 -4 x x 140 A A x 141 A A x 142 A A x A x x 143 144 A x x A A xx 145 x; 146 147 148 a A x A A x 149 x x 150 151 ; A x x x 152 x x 153 No change, A ; very slight, x;
i
X X
X
X X
xx xxx xx
X X
x
xx xx xx xx xx xx xx xx xx xxx
X
X
xx
xx
X
X
X X
X X
X X
6 X X X
XX
X
xx xx X X
X
X X X X
X
X
X X
X
X X
xxx ;x:
xxx xxx xx
xxx xxx xx
X
X
X
X
X
X
xx
xx
S X
X
X
X
X X
X X
X
x A x A x x A A x x
X
X X
X X
X X
X
xx
X
xx
xx
xx
X X
X X
X
X
X
X
X X
X
xx
xx
X
X
X
X
x
X
X
X X
X X
xxx
xxx
Scum after Months: 1 2 3 4 5 xx xx xxxxx xxx xxx xx xxx xxxx xxxxx xxxx x xx xxxxx xxxx xxxx x xxx xxxx xxxx xxxx x xxx xxx xxx xxxx x xxx xxxx xxxx xxxx xx xx xxxx xxx xxxx xx xx xxxxx xxxx xxxx xx xx xxxxx xxxx xxxx xxxxx xxxx xx xx xxxxx xxxx xx xx xxxxx xxxx xxxx xxxxx xxxx xx xx xxxxx xxx xx xx xxx xxxxx xxxxx xx xxx xxxxx xxxxx xxxxx x xxx xxxxx xx xx xxxxx xxxxx xxxxx x xxx xxxx xxxx xxx xxxxx xxxxx x xxx xxxx xx xxx xxxx xxxxx xxxxx xxxx xxxx xx xxx xxxx xxx; b a d , xxxx; very bad, xxxxx.
6 xxx xxxx xxxx xxx xxx xxx xxxx xxxx xxxx xxxx xxxx xxxx xxxx xxxxx xxxxx xxxxx xxxx xxxxx xxxxx xxxxx
a 4
xx
xxx
r -
xxx xx
X
A x x A A A -4 A
X
X X X X
xx
X
A
X
6 xx
X
definite, xx; medium,
in cases where parts of the steel surface were exposed; red lead appeared to have inhibited rusting until it was almost entirely eroded away. Barnacle growth on most of the panels was very slight for the entire 6 months. To illustrate the effect of the season of the year upon the behavior of these finishes, two panels primed and coated with the same compositions according to the same schedules used for panel 143 were exposed June 11, 1940, a t the same location. Fouling after 4 months was no more severe upon these panels than on panel 143. Softening of the primer, however, had progressed to a degree worse than for panel 143 after 6 months of exposure. These results show that, although a paint made from a 6-gallon tung oil vehicle, based upon three quarters coumarone resin and one quarter p-phenylphenol-formaldehyde,resisted fouling both through the summer months and those of fall and winter, disintegration of the primer is particularly severe during the warmer periods of the year.
Practical Testing To prove that the combination of a primer consisting of red lead in an alkyd vehicle and a top coat of pure metallic flake copper in a 6-gallon tung vehicle, based upon three quarters coumarone resin and one quarter p-phenylphenolformaldehyde, was practical for commercial shipping in coastal service, a large-scale test is being made. During the week of May 19, 1940, the Lake Traverse, which had been recently bought and was being reconditioned by the \Test Indies Steamships, Inc., was painted a t River Rouge, Mich. This vessel is a freighter of approximately 3000 tons, 250 feet long, with a 40-foot beam. The steel hull was sanclblasted to remove old paint and rust thoroughly. The surface was very clean after this treatment but was marred by numerous pits approximately inch deep. Three coats of
-~ 1 A A
A A .A A A A A A A A A A A A A A A A
--
1 A A -4 A A A A A A A A
iA A A
-4
h
Scaling after Months:-3 4 5 xx xxx xxx -4 A x K A A x xx A A x X A A x xx A A x X x x xxx xxx A A xx xx x xx xx xx A x X X x x X xx A x xx xx x xx xxx xxx A x xx xx x xx xx xxx x xx xx xxx A x xx xxxx x x xx xxx x xx xxx xx xxxx xx xxx xxxx 2 x
Moss after 3 x x x A A A x A A -4 x A x A A .A A A x A x A x -A A A A
2 A A A A A A A A A
i i i
AIonths:--. 4 5 A xx x xx -4 xx A xxx x xxx x xxx . I xx h xxx A xx A xxx A xx x xxx x xxx x xxx X
X
4
X
A
Y
x
,"
X X
x
6 xxxx xxx xxxxx xxxx XXXLX
xxxxx xxxx xxx xxxxx xx xxxx xxxx xxxx xxx xxx xxxx xxxx xxxx xxx xxxx 6 xxx xxxx xx xxx xxx xxx xxx xxxx xxx xxx xxx xxx xxx xxx xx xx xxx xx xx xx
the red lead alkyd primer were applied by spraying, each coat being allowed to dry overnight. Two coats of the metallic copper antifouling paint were then applied, the same composition being used as for panel 143. The surface, approximately 20,000 square feet, required 60 gallons of red lead for the first coat, 50 for the second, and 45 for the third. Fiftytwo gallons of copper paint were used for each coat. The top coats leafed perfectly and gave the appearance of a brilliant sheet of metallic copper. After launching, the boat inimediately sailed for the Atlantic, engaging in its usual business of carrying general cargo from the R'est Indies and South American ports t o various ports on the East Coast. After 5 months of operation the ship had scraped her side badly and required dry-dock servicing in Boston in October, 1940. The hull was in perfect condition with no sign of fouling of any kind and complete absence of film failure, except for the scraped portions which were retouched by spot priming with the same red lead primer used initially; the. entire hull was given a single coat of copper antifouling paint. The ship was then put into charter service in Caribbean. waters. At the t'ime of this writing (March 6, 1941), it is still giving service with no increase in fuel consumption for maintaining regular speed.
iicknowledgment The authors are indebted to the officers of Phelps Dodge Corporation for furnishing the facilities used in this investigation, and for permission to publish. TiUiam H. Osborn, Director of Research, has directed the work, which is continuing. The authors acknowledge the splendid cooperation received from the West Indies Steamships, Inc., and especially the help and advice of 5.11.1. Erickson. before t h e Division of Paint, Varnish, a n d Plastics Chemistry a t h e lOlst Meeting of t h e American Chemical Society, St. Louis, M o . PRmsENTen
