WO1988001284A1

WO1988001284A1 - Antifouling paint compositions and method

Info

Publication number: WO1988001284A1
Application number: PCT/US1987/001932
Authority: WO
Inventors: Erith T. Clayton
Original assignee: Clayton Erith T
Priority date: 1986-08-11
Filing date: 1987-08-11
Publication date: 1988-02-25
Also published as: US4835050A; ZA875907B; AU7789187A

Abstract

An antifouling composition employing a multiplicity of voltaic cells formed therein by a mixture of two components having differing electrochemical potentials. Also diclosed is an article of manufacture employing the antifouling composition of the present invention as well as a method of using the antifouling composition of the present invention to prevent fouling. The antifouling composition may be incorporated into a paint, a galvanic coating, or applied to a unitary structure which is then attached to the substrate which is to be protected from fouling.

Description

_ _

ANTIFOULING PAINT COMPOSITIONS AND METHOD

FIELD OF THE INVENTION

The present invention relates to compositions for preventing fouling on surfaces exposed to aquatic environments.

BACKGROUND OF THE INVENTION

From very early times it was believed that anti-fouling paints had to be put in a vehicle which permitted poisonous ions to migrate through the vehicle to the paint-water interface. The presence of the poisonous ions at this interface of the paint and water prevented fouling. Thus, in order for present anti-fouling paints to be effective they must leach toxic elements into the seawater environment. This leaching of toxic elements is highly undesirable since it pollutes the seawater environment. Also, present anti-fouling paint compositions are unsatisfactory since, when the toxic elements us'ed to prevent fouling^" leach out of the paint film, the paint quickly becomes depleted. These anti-fouling paints, which are in use today, are thereby good for only one or two growing seasons and must be repainted quite often. Also, these leachable paints are badly scratched and damaged by sand when boats are dragged on a beach. Such damage will permit fouling to take hold.

The leaching of soluble copper salts, and tributyl tin compounds, into navigable waters from pleasure crafts, nuclear power plants and other ships is of great concern to state and federal authorities, especially in areas of high boat concentrations. Present antifouling paints employ such poisonous ingredients and are a major cause for such concern. A world famous authority on antifouling paints explained that tests had been made with superimposed alternating current, superimposed direct current and - 2 - a combined alternating-direct current and that all such experiments had been entirely unsuccessful in preventing fouling. He also pointed out that years of experience had shown that all antifouling paints, to be effective, had to be formulated in a leachable vehicle so that toxic ions could be released into the water in the immediate vicinity of the antifouling surface and that a non-leachable vehicle had no chance for successfully preventing fouling.

SUMMARY OF THE INVENTION

The present invention relates to a composition of matter capable of surpressing the growth of fouling organisms in an aquatic environment. The composition of matter comprises a mixture of at least two components having different electrochemical potentials. This mixture is capable of generating voltage ^"at any location therein when it is contacted with an electrolytic material.

The present invention also relates to an article of commerce comprising a substrate, and a composition of matter capable of surpressing the growth of fouling organisms in an aquatic environment, on said substrate. The composition on the substrate includes a mixture of at least two components having different electrochemical potentials such that the mixture is capable of generating voltage at any location therein when contacted with an electrolyte.

Yet another embodiment of the present invention relates to a method of preventing fouling of a substrate in an aquatic environment. The method comprises the step of applying an antifouling composition to the substrate. The antifouling composition includes a mixture of at least two components having different electrochemical potentials - 3 - such that the mixture is capable of generating voltage at any location therein, when contacted with an electrolyte.

It is the primary object of the present invention to provide an inexpensive, long-lasting antifouling composition for use on aquatic vehicles of all sorts.

It is a further object of the present invention to provide an antifouling composition that does not leach toxic substances into the aquatic environment.-

It is yet a further object of the present invention to eliminate the need to repaint antifouling paints on an annual basis.

BRIEF DESCRIPTION OF THE DRAWINGS

GRAPH #1 shows the results of a comparative test on wood panels between paint composition in accordance with the present invention and a commercially available antifouling paint.

GRAPH #2 shows the results of a comparative test on steel panels between paint compositions in accordance with the present invention and a second commercially available antifouling paint.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention relates to a composition of matter capable of surpressing the growth of fouling organisms in an aquatic environment which includes at least two components which, in combination, are capable of generating voltage upon contact with an electrolyte. The basis for the present invention is electromotive force which is the driving tendency behind an electric current. Electromotive force is measured in volts. The electromotive force (EMF) of a battery is the potential difference between its terminals when no current flows through the battery. This potential - 4 - difference, called voltage, serves to produce an antifouling structure which inhibits the growth of animal marine life such as barnacles and sea worms, as well as vegetative marine life. This property of the composition, similar to a voltaic cell, functions much like batteries of all kinds.

There presently exists a variety of voltaic cells, but most of them are designed to be batteries. Single fluid cells such as the Leclanche cell using a dry cell with zinc as the negative pole, ammonium chloride solution and carbon with manganese dioxide as a depolarizer, has an EMF of 1.53. Another type of cell is the lead, lead peroxide storage type of voltaic cell such as used in car batteries. The negative pole is lead, the electrolytic solution is sulfuric acid having a density of 1.1 and the positive pole is lead peroxide. The cell has an EMF of 2.2. In addition, there are other types of standard cells such as the Weston normal and-Clark standard and double fluid cells, some of which are Bunsen, Daniell and Grove. Most of these use amalgamated zinc as the negative pole, platinum as the positive pole and two solutions of sulfuric acid and nitric acid having densities of 1.136 and 1.33 respectively, as the electrolytes.

All of the foregoing are called voltaic cells but practically they are essentially used as batteries and in general describe the type of EMF generators which can be used in the practice of the present invention. However, in the present invention, the most useful type of EMF generator consists of small particles which are suitable for incorporation into antifouling paints and coatings which can be used to coat substrates. These particles may consist of metals and non-metals such as zinc and graphite or of metals selected from the EMF table such as aluminum and tin - 5 - added as separate metal powders or in the form of composite metal particles in which each individual particle may consist of one metal completely encapsulated by another metal. An example of such a particle is zinc encapsulated in copper. The particle size of such particles may range from 4 to 15 microns on the average which is usually small enough to make a good paint or coating. The following is a table of the EMF series of metals:

ELECTROMOTIVE SERIES OF THE METALS

Lithium Sodium Chromium Lead Mercury (ous>

Rubidium Magnesium Iron HYDROGEN Silver

Potassium Baryllium Cadmium ^Antimony Palladium

, Barium Aluminum Cobalt /Arsenic Mercury (ic)

Strontium Manganese Nickel \Bisrauth Platinum

Calcium Zinc Tin Copper Gold

Thus, in. its broadest aspect, the invention relates to paints or-coatings which store a voltage, the paints or coatings consisting of a large multiplicity of very small particles of two components having different potentials which are capable of producing an EMF.

The most preferred embodiment of the present invention is a mechanical mixture of two metal powders. The mechanical mixture provides contact between the two components to thereby provide a multiplicity of voltaic cells throughout the composition which are capable of generating voltage when contacted with an electrolyte. The powders should be extremely fine to thereby increase the surface area of the powders. Such a mechanical mixture, when incorporated in a suitable vehicle, makes a good antifouling composition. When it is applied to a zinc coated steel surface or a wood - 6 - surface, it will, when immersed in an electrolyte such as seawater, provide millions of small individual batteries that act to prevent the attachment of marine animals such as barnacles, tunicates, oysters, clams and other organisms. This composition will also serve to retard vegetative growth on the substrate for months or years at a time.

The compositions of the present invention may be formulated in a leachable vehicle, a non-leachable vehicle or in the form of a coating to be applied galvanically. Since the compositions of the present invention do not rely on leaching toxic elements into the environment, they may be formulated successfully in a non-leachable vehicle. However, it is essential in a non-leachable vehicle that the vehicle solids be kept to a minimum, consistent with paintability, by adding a paint solvent to the system that will make painting feasible and that will evaporate leaving behind the solid contents of the vehicle. The -vehicle solids must be kept to a minimum to thereby permit contact between the two components of the antifouling composition in order for the voltaic cells to function effectively. If the vehicle solid content is too high within the paint, contact between the two components will be lost within the paint film. If contact is lost within the paint film, then the voltaic cell will no longer function and no voltage will be produced as a result of contact with the electrolyte.

However, it is desirable to have a thin barrier film across which a voltage will flow. This barrier film will prevent leaching of the components out of the composition and thereby extend the useful life of the composition. Thus, it is apparent if the composition includes sufficient vehicle to prevent contact between the two components or alternatively - 7 - includes a film thick enough to prevent voltage from flowing therethrough, then all antifouling activity will be lost. This problem is most apparent with non-leachable vehicles since non-leachable vehicles tend to contain a higher content of vehicle solids.

Since no material is leached from a non-leachable vehicle, a paint embodying the present composition in a non-leachable vehicle will continue to act as an antifouling agent for years at a time. The non-leachable vehicle creates a hard, durable paint film which will withstand dragging of a rowboat on a beach over rough abrasive sand without damage.

An important advantage of the present antifouling compositions is that they do not pose a toxicity problem. In one embodiment, toxic materials may be incorporated into a non-leachable vehicle within the scope of the present invention as long as the toxic materials are bound solidly into the paint and will not leach therefrom. In^"another embodiment, a leachable vehicle may be used with non-toxic components to formulate a paint within the seope of the present invention. Finally, non-toxic components can be used .in a non-leachable vehicle to thereby extend the useful service life of the paint by preventing leaching of the active ingredients, which create the voltaic cell, from the paint.

The antifouling compositions of the present invention may be applied to several different substrates including wood, steel and fiberglass. Also, the antifouling compositions may be applied to irregularly shaped objects such as pilings, propellers and the like.

Adequate steps must be taken to prevent the antifouling composition of the present invention from rusting a steel substrate. One such preventive - 8 - measure is the use of a proper protective barrier which must be applied to the steel surface prior to application of the antifouling composition. Such a barrier would prevent contact between the steel and the antifouling composition and thereby prevent corrosion of the steel. Another means for preventing corrosion of the steel is to choose components which are anodic to steel.

The compositions of the present invention substantially reduce the corrosive galvanic action of such metals as copper on a ferrous base. These compositions also permit the replacement of toxic metals such as copper by safe, inexpensive substitutes while maintaining the requisite level of antifouling effect. Moreover, these compositions provide very attractive paints with low brush friction when non-metals such as graphite are employed. These graphite paints may include graphite, activated carbon and straight carbon. The graphite functions better if it is dried prior to incorporation into the paint. Alsc the graphite may be combined with any of the metals from the electromotive table included herein to form a composition in accordance with the present invention.

In another embodiment of the present invention the antifouling composition is incorporated into flexible forms that can be releasibly adhered to a surface which is to be protected from fouling. In this embodiment, a flexible surface such as a woven fiberglass mat is coated with the antifouling composition of the present invention. Then, this mat is adhered to any surface which needs protection from fouling. An advantage of this embodiment is that these mats may be removed for cleaning and repair at any time. Also, these mats may be fabricated in different sizes and shapes to conform to the needs of specific situations. For instance, tubes used for water cooling nuclear reactors may be coated with a series of fiberglass mats of this type in order to prevent fouling of the inner surfaces of the cooling tubes.

The components of the voltaic cells of the present invention may be selected from the table of the electromotive series of metals included herein, or alternatively the two components of the present antifouling composition may be selected from any other materials having differing electrochemical potentials. An alternative embodiment of the present invention employs zinc and copper encapsulated within one another. For example, zinc may be encapsulated into copper or copper may be encapsulated into zinc to produce a bi- etal flake. These bi-metal flakes are useful since they produce voltage in the presence of an electrolyte.

An antifouling paint incorporating, for example carbon or graphite in combination with zinc would not only eliminate the toxic materials from the composition but would also drastically cut the cost of raw materials. The Leσlanche cell, consisting of zinc, carbon, ammonium chloride as the electrolyte and a depolarization agent such as manganese dioxide constitutes the basic cell for the average small battery for flashlights, etc., in use for decades around the world. Example 7 shows that the antifouling composition of the present invention can be created without toxic materials and that, in fact, the battery effect is responsible for antifouling regardless of how the battery is composed provided that there is a large multiplicity of battery cells created by contact between the components of the composition - 10 - Non-toxic formulations of nickel and graphite, aluminum and graphite, zinc and graphite, and tin and graphite may be used to generate EMF. Other non-toxic formulations are also possible. The only limitation being that the two components must have differing electric potentials. Further, a non-toxic formulation may be used as a metallurgically integrated metal coating on the substrate. A coating such as zinc-tin can be applied using the portable galvanizer described in U.S. Patent 4,293,584 (Clayton), issued on October 6, 1981. These intimately mixed, non-toxic elements may also be incorporated into a porous matting or the like to provide a renewable antifouling blanket.

Table #1

TABLE SUMMARIZING RESULTS OF THREE EXPOSURE TESTS ONLY THOSE PANELS HAVING RATIOS OF 9⁺, 9 AND

8 ARE SHOWN

Duration of Anti-Fouling Exposure Type ^• .-Picrment Vehicle

* Ratinα F.R.9 plus-

2.15 yrs_j Wood Zn on Cu Polystyren Emulsion

8-1/2 months Wood Zn on Cu Glyptal 245 (1 coat)

8-1/2 months Wood C on Zn Glyptal 245 (1 coat)

8-1/2 months Wood CU on Zn Glyptal 245 (2 coats) Ratinσ F.R.9

401 days Steel Zn on Cu Glyptal (2 coats)

8-1/2 months Wood CU on Zn Glyptal (2 coats)

8-1/2 months Wood Zn on Cu Glyptal - 11 - Rating F.R.8 plus and F.R.8

401 days Steel Zn on Cu (2 coats)

8-1/2 months Wood Cu on Zn 2.15 yrs. Wood Cu on Zn

The following examples are provided to illustrate the present invention:

Example #1:

Steel panels 4" X 12". Steel protected by zinc flake paint. Panel exposed in North Carolina. Duration of test: 8-1/2 months exposure in North Carolina. Test location: Dock E-6.

Paint vehicle: A Polystyrene Rating: 0 - Complete fouling (10 means no fouling) . Panel no mark: 1 coat zinc flake encap- Rating: 9+ sulate^'d on copper flake.' Duplicate of above. 9+

Panel #1 1 coat copper on zinc. 9+ Duplicate of above. 9+

Panel #2 2 coats copper on zinc. 8 Duplicate of above. 5

Comments: A second coat it is believed tends to leave more vehicle solids in or on the surface layer.

Panel #3 Copper mixed with zinc as separate powders

Duplicate of above. 9

Panel #4 2 top coats Copper coated 9 zinc flake. - 12 - Example #2

Panels exposed at North Carolina Test Station for 401 days. Vehicle Alkyd Resin.

Panel no mark: Zinc on copper. " 9 Duplicate of above. " 9

Panel #1 1 coat copper on zinc. " 5 Duplicate of above. " 7

Panel n 2 coats copper on zinc. " 3 Duplicate of above. " 1

Panel #3 2 coats mixture of copper " 8 flake and zinc flake.

Duplicate of above. " 9

Panel #4 2 top coats copper coated " 4

_* zinc composite flake.

- Duplicate of above. ^' " 5

Panel #5 2 coats zinc coa ed copper. " . 8+

Duplicate of above. (only 1 rust spot)

Panel #6 2 coats of copper (100% rusted) 0 flake

Duplicate of above. (100% rusted) 0

Comments on above:

1. Zinc flake encapsulated on copper is almost always better than the reverse copper plated on zinc.

2. Application of 2 coats is almost always worse than a single coat, believed to be due to slight excess of vehicle in second coat.

3. The mixture of the flakes separately, that is one is not physically encapsulated by the other — the flakes are manually mixed was almost as good as composite flakes. The separate mixture was equal to - 13 - the copper on zinc but the zinc on copper was slightly better.

4. The polystyrene vehicle of Example 1 appears better than alkyd resin of this example.

5. Exposure from June 19 to July 24 the following year encompassed a major part of the growing season, which are probably fairly longer in North Carolina.

6. All samples in this test were on steel panels.

Example #3:

Exposed at station in North Carolina. Duration 2.15 years.

Panel #1: Wood copper on zinc. Paint is free of blisters and appears in good condition. Rating: 7 Panel #2: Wood zinc on copper flake. Paint film is free of blisters and appears to be in very good condition. Rating: 9+ Panel #3 Wood zinc on copper flake. Paint film is free of blisters and appears to be in very good condition. Rating: 9+

Panel #4 Wood Duplicate of above,

Rating: 9+

Panel #5 Wood 5 Panel #6 Wood 8

Comments:

1. 2 steel panels were very badly rusted after 2.15 years and had rating of 3 and 0.

Example #4:

A/F EXPOSURE RESULTS OF TAINTON BI-METALS ON PRIMED

STEEL (International Paint 1607 Vehicle Was Used.)

These tests were exposed in Florida on stationary panels for a period of 6 months, starting in April and - 14 - ending in October. Sandblasted steel panels were used, prepared in the following manner.

1st Coat Wash Primer - 1 hour dry

2nd Coat Silver Primocon - 2-4 hours dry

3rd Coat Silver Primocon - Overnight dry

4th Coat Silver Primocon - Overnight dry

All of the above were spray applied

5th Coat Test Paint - 8 hours dry 6th Coat Test Paint - 24 hours dry

5th and 6th coats were brush applied. Results are as follows:

Ratings

Time Exposed (months) 1- 2 3 4 5 6

Month May Jun Jul Aug Sep Oct

50 Zinc on 50 Copper 91 88 78 74 61 55

50 Copper on 50 Zinc 92 89 80 •74 52 46

40 Copper on 60 Zinc 93 83 80 69 12 0

40 Aluminum on 60 Copper- .82 71 65 46 0 6

33 Aluminum on 67 Copper 88 ^• 60 47 36 0 0

1607 Standard 93 79 81 75 33 29

From the above ratings the Zinc on Copper and the Copper on Zinc show promise. Further work will be done on these two Bi-Metals.

Pigment to Vehicle Ratio in Dried Film

Name Pigment Vehicle Remarks

50 Zinc on 50 Copper 36.2 63.8

50 Copper on 50 Zinc 36.2 63.8

40 Copper on 60 Zinc 36.2 63.8

40 Aluminum on 60 Copper 36.2 63.8

33 Aluminum on 67 Copper 36.2 63.8

1607 Standard 47.0 53.0 21% Active Copper - 15 - Example $5 :

A/F RESULTS - TAINTON BI-METALS ON WOOD

These tests were tried on wood and self-primed. They we started in May and ended October, a total time of immersion 5 months.

Ratings Time Exposed (months) 1- 2 3 4 5_

Month Jun Jul Aug Sep Oct

50 Zinc on 50 Copper 100 100 94 94 94

50 Copper on 50 Zinc 100 100 100 86 92

40 Copper on 60 Zinc 92 87 77 77 74

Cl) 40 Aluminum on 60 Copper 71 0 0 0 0

(2) 33-1/3 Aluminum on 66-2/3 Copper 83 31 37 0 0

(3) 50 Copper on 50 Nickel 88 89 91 86 86

694 Singapore Standard 100 100 90 85 100

1. Chipping in first month. ^• .

2. Rust Nodules ^'in first month. 3.- Chipping in first month.

SUMMARY:

From the above results 50 Zinc on 50 Copper and 50 Copper on 50 Zinc, show the most promise when combined with 49 vehicle. All of the rest of the Bi-Metals show no promise, therefore should be discontinued. 49 vehicle is a product of International Paint Company.

Cost of the above two mentioned should be calculated and compared versus 49 and 694. If cost is favorable, further tests should be conducted.

Pigment to Vehicle Ratio in Dried Film

Name Pigment Vehicle Remarks

50 Zinc on 50 Copper 74 26

50 Copper on 50 Zinc 74 26

40 Copper on 60 Zinc 74 26 - 16 -

40 Aluminum on 60 Copper 51. 5 48 . 5 Any higher pigmen ation would be impossible to app

1/3 Aluminum on 2/3 Copper 51. 5 48.5 same

50 Copper on 50 Nickel 74 26

694 Standard 74 26 Cuprous Oxide & Mercury

Example #6: A/F TESTS OF TAINTON BI-METALS IN ALKYD RESIN VEHICLE

The above tests were conducted in Florida on wood starting in June and ending in October for a total time of immersion of 4 months. These panels were all self-primed.

Ratings

Time Exposed (months) 1 2 3 4

Month Jul Aug Sept Oct

50 Copper on 50 Zinc 100 77 12 0

50 Zinc on 50 Copper 100 94 56 8

SUMMARY:

Both tests blistered in one month. Contact type of pigmentation is of little value of right vehicle is not used. Above tests show little value in using an alkyd as an A/F vehicle. This type was recommended by Tainton:

PIGMENT TO VEHICLE RATIO IN DRIED FILM

Name Pigment Vehicle

50 Copper on 50 Zinc 81% 19%

50 Zinc on 50 Copper 81% 19%

Dry times: 15-24 hours between coats . 24 hours before immersion. - 17 - The above results should be compared with the 401 days of exposure using an Alkyd resin in Example #2.

Example #7:

50 parts by weight of fine zinc powder were thoroughly mixed with an equal number of parts of fine Graphite powder. These were incorporated into a paint with outdoor Urethane varnish diluted with mineral spirits. The paint was applied to small zinc coated steel panels and exposed in a small salt water creek in mid April. The panels were examined in early July. The zinc apparently had largely dissolved leaving a black crust that had bubbles in it. There was no sign of any fouling, either vegetable or animal. breaking the bubbles shows the shiny zinc basecoat. Portions of the crust were scraped off to show the zinc priming coat underneath that was still bright and shiny._* The panels were replaced in the water. One month later when they were re-examined there was still no fouling but the steel was showing some red rust around the edge. From the above it was evident that the quantity of graphite may have been too large or the bubble may have been due to water included in the graphite. Fresh panels were made up using 90% zinc and 10% graphite. On other panels the zinc was replaced with tin, nickel or aluminum to vary the voltage generated by these cells. The results were most encouraging. No fouling had occurred after one month of exposure. Not a single barnacle was present anywhere on the panels but there were plenty of large barnacles on nearby wood.

Example #8:

A 16-foot trihull fiberglass runabout was painted with a mixture of zinc dust and graphite with urethane outdoor varnish. The boat bottom was divided into - 18 - sections with different amounts of dilution of the varnish. With the least dilution there were a few large barnacles six to ten inches apart. With the greater dilution of non-leachable vehicle the number of barnacles were substantially reduced.

This test was repeated the following year with similar results.

Note the inclusion of the graphite makes a most excellent smooth paint.

* * * * *

From the above, it may follow that in a non-leachable vehicle that a barrier exists between the cells and its electrolyte, the sea water, in which case no current should flow but voltage is present. If the voltage is sufficient to provide the antifouling then a non-leaching vehicle should last for years because there would be minimal flow of electric_, current to deplete the antifouling elements.

This would appear to be the case because on wood panels after 2.15 years exposure to severe fouling conditions, readings of nine plus were obtained (ten being perfect) . These tests were discontinued at a rating of nine plus leaving the possibility open that they may have lasted much longer, perhaps years longer. This is perhaps confirmed by the five year life on a wooden row boat.

On the other hand, there may be some current flow at a low level that would be slow enough to provide a long life to the paint and enough flow to prevent fouling.

If the applied voltage is sufficient (usually with the average battery is 1.0 to 1.5 volts) any electrical insulation thick enough to block the voltage will cause the whole system to collapse and absolute complete fouling would result (zero rating) . This appears to be in accordance with observed facts 88/0128

- 19 - in which it is well established that any thick layer of insulating material will be completely fouled. To be effective the voltage of the individual cells, the zinc graphite for example, must break through any supernatant "films".

Increasing the E.M.F. (voltage) to a higher level subsequently improves antifouling properties. This was done with the zinc-graphite combination in which there was no trace of vegetation and no trace of any animal growth. If there was any constant electric current flow the zinc would dissolve anodically as a result of increased voltage.

Example #9: An Example of Non-Toxic Elements in a Non-Leachable

Vehicles Exposed The panel were of steel, four inches by 6' inches. The steel was protected on both sides by a substantial zinc coating applied by the portable galvanizer of

U.S. Patent 4,243,584. The metal powders, except the zinc, were five to seven microns, were hydrogen reduced, and purchased from Fusion Alloys Co. The zinc powder was Federated #1 zinc dust and the graphite was purchased from a local store.

Seven panels in all were exposed, including samples of aluminum-tin, zinc-tin, nickel-zinc, zinc- graphite, aluminum-zinc. All sample panels were of steel and all were protected by a substantial zinc coat.

The dry powders were mixed together very thoroughly. The vehicle was a non-leachable urethane varnish, outdoor grade. The samples were exposed for 2.5 months during the height of the growing season.

All of the samples gave most encouraging results, but in this test two were outstanding: the 50-50 zinc-tin and the 90% zinc and 10% graphite. Both samples were completely free of all growth, both animal and vegetative and there was no slime giving them a rating of 10. Most of the other samples were almost free of barnacles, and if there were barnacles they were very tiny especially in comparison with barnacles growing on the wooden frames which were on average about 20 times as large.

Aside from the size, some of the very tiny barnacles had died and dropped off.

The 90% zinc, 10% graphite was also completely free of all barnacles, thee was no grass and no slime. The coating was clean and bright to the touch and was an excellent mix for painting. It rated below the zinc-tin because thee were some bubbles in the graphite. It was learned later that this was probably due to absorbed water in the graphite.

The utility of the non-leachable vehic'le in a non-toxic formulation was considered to be^" confirmed by this test and others that preceded it. The 90% zinc 10% graphite was better than a previous ratio of 50/50 zinc-graphite.

The combination of the zinc with a non-metal was striking and further validates the voltaic cell principle.

Claims

- 21 - WHAT IS CLAIMED IS:

1. A composition of matter capable of suppressing the growth of fouling organisms in an aquatic environment which comprises a mixture of at least two components having different electrochemical potentials such that said mixture is capable of generating voltage at any location therein when contacted with an electrolyte.

2. A composition in accordance with Claim 1 wherein said composition is a coating.

3. A composition in accordance with Claim 1 wherein said composition is incorporated into a paint.

4. A composition in accordance with Claim 3 wherein said paint comprises a non-leachable vehicle.

♦5. A composition in accordance with Claim 1 comprising at least two components selected from the group consisting of nickel, zinc, graphite, aluminum, tin, lead and copper.

6. An article of commerce comprising a substrate, and a composition of matter capable of suppressing the growth of fouling organisms in an aquatic environment on said substrate, said composition comprising a mixture of at least two components having different electrochemical potentials such that said mixture is capable of generating ^'voltage at any location therein when contact with an electrolyte. - 22 -

7. A method of preventing fouling of a substrate in an aquatic environment comprising: applying an antifouling composition to the substrate, said composition comprising a mixture of at least two components having different electrochemical potentials, said mixture being capable of generating voltage at any location therein when contacted with an electrolyte.

8. A method in accordance with Claim 7 wherein said composition comprises a paint and said step of applying said composition comprising spraying, dipping or brushing.

9. A method in accordance with claim 7 wherein said composition comprises a coating and said step of applying said composition comprises galvanizing.

•

10. .A method in accordance with^" claim 7 wherein said^{^}galvanizing comprises mechanical galvanizing at ambient temperature.

11. A non-toxic composition of matter capable of providing long-lasting suppression of the growth of fouling organisms in an aquatic environment which consists essentially of a vehicle selected from leachable and non-leachable vehicles, and at least two components dispersed in said vehicle, said components having different electrochemical potentials such that said composition is capable of generating a voltaic current.

12. A composition of matter as claimed in claim 11 wherein said vehicle comprises a durable non-leachable vehicle.

13. A composition of matter as claimed in claim 11 wherein said vehicle comprises a leachable vehicle

^'and said at least two components consist essentially of non-toxic components. *

14. A composition of matter as claimed in claim 11 wherein said at least two components are selected from the group consisting of zinc, carbon, aluminum, tin, and nickel.

15. An article of commerce comprising a substrate, a layer of a composition of matter capable of -ong-lasting suppression of the growth of fouling organisms in an aquatic environment adhered to at least one surface of said substrate, said composition consisting essentially of a mixture of at least two components having different electrochemical potentials such that said composition is capable of generating a voltaic current and a thin barrier layer of a material selected from plating medium and leachable or non-leachable paint vehicle on the surface of said antifouling layer.

16. An article of commerce in accordance with claim 15 wherein said antifouling layer comprises a metallic coating and said thin barrier layer comprises plating medium.

17. An article of commerce in accordance with claim 15 wherein said antifouling layer comprises a paint and said barrier layer comprises a vehicle selected from leachable and non-leachable vehicles.

18. A method of providing long-lasting suppression of fouling of a substrate when exposed to an aquatic environment comprising: applying a non-toxic antifouling composition to a substrate which will be exposed to fouling conditions, said composition comprising a mixture of at least two components having different electrochemical potentials.

19. A method in accordance with^" claim 18 wherein said composition comprises a paint vehicle selected from leachable and non-leachable vehicles and said step of applying said composition comprises spraying, dipping or brushing.

20. A method in accordance with claim 18 wherein said step of applying said composition comprises metal plating.

21. A method in accordance with claim 18 wherein said step of metal plating comprises mechanical plating at ambient temperature.

22. A method in accordance with claim 19 wherein said composition comprises a leachable vehicle and said components consist essentially of non-toxic components.

23. A method in accordance with claim 19 wherein said composition comprises a non-leachable vehicle.

24. A method of providing long-lasting suppression of fouling of a substrate when exposed to an aquatic environment comprising: incorporating a non-toxic antifouling composition into the substrate, said composition comprising a mixture of at least two components having different electrochemical potentials.