WO1992007037A1

WO1992007037A1 - Anti-fouling composition

Info

Publication number: WO1992007037A1
Application number: PCT/AU1991/000466
Authority: WO
Inventors: Arthur Keith Philpott
Original assignee: A.B.O.E. Pty Ltd.
Priority date: 1990-10-11
Filing date: 1991-10-11
Publication date: 1992-04-30

Abstract

The invention provides an anti-fouling composition comprising a selective metal-chelating micro ion exchange resin capable of binding copper, a viscosity-controlled matrix, and optionally one or more components selected from the group consisting of a marine biocide, a film-forming binder, and a pigment. The composition may be used in paints for prevention of fouling of aquatic organisms, or may be incorporated into polymers such as polyester or polyethylene. The polymers may be extruded into filaments in the manufacture of ropes and nets.

Description

ANTI-FOU ING COMPOSITION

This invention relates to an anti-fouling composition for preventing or inhibiting growth of aquatic organisms, especially marine organisms. The composition is suitable for use in anti-fouling paints, or for incorporation into materials such as sheet plate or extruded filament; the latter may be used inter alia in fishing nets.

Background of the Invention Fouling of surfaces which are subject to prolonged or permanent immersion in water is a major problem worldwide. In particular, fouling affects the submerged surfaces of ships and boats, and encrusts fishing nets. As a result, vessels must periodically be hauled out for removal of fouling growths, in order to preserve their hydrodynamic efficiency. Fishing nets hitherto have been discarded when they become encrusted with aquatic growths.

Although these problems can occur both in fresh and in sea water, because of the greater number of vessels operating in the sea the incidence of fouling appears to be greater in this situation.

Fouling of surfaces also occurs as a result of algal growth in vessels retaining large volumes of water over considerable periods of time, such as cooling towers and testing tanks. In these situations, the most common countermeasure hitherto used is chlorination of water, coupled with periodical mechanical cleaning.

In contrast, vessels and structures used in marine or other aquatic environments have been protected by anti-fouling paints or coatings, which are of variable efficacy. The type of protection required depends on the type of fouling expected, which in turn depends on whether the object to be protected is stationary or mobile. The fouling process is one in which aquatic, especially marine organisms endeavour to settle.on or adhere to submerged surfaces. These sessile or seated organisms include:

1. Slimes (bacteria, diatoms)

2. Algae (seaweed)

3. Soft organisms (hydroids, sponges & tunicates)

4. Hard fouling (annelids, bryozoans, barnacles, molluscs) .

Vessel velocity is critical; stationary situations are ideal for barnacle larvae because they can only settle at water flows up to 0.5 knots, while algal spores are capable of settling at flows up to 10 knots. Most fouling however occurs when vessels are stationary.

Anti-fouling compositions are conventionally applied in the form of a paint or coating. The properties required of an anti-fouling coating composition are as follows:

a) It must be able to contain a biocide in as high a concentration as possible; b) Film formation must be satisfactory, ie. a closed uniform film must be formed; c) The applied film thickness must be high enough, eg. at least 50 μm, but preferably higher, and has to be obtained in one coat; d) The adhesion to the substrate, in most cases an anti-corrosive primer, must be satisfactory; e) On drying, after immersion in sea water, the coating film must remain in a good condition, e.g. no coating should occur; and f) The biocide must be able to leach from the coating at a rate high enough to prevent fouling organisms from settling.

The marine anti-fouling paint formulation of this invention meets the above requirements. The majority of anti-fouling paints in use today are effective because toxic ingredients based on heavy metals .re included in their formulation. In use, these heavy metals are leached out at various rates and concentrations from the matrix of the paint. The steady accumulation of these metals in the marine environment has adversely affected marine life, and restrictions have been or are being applied to their use.

Anti-fouling coatings containing organo-leads, organo-mercurials and organo-arsenicals are not acceptable in the U.S.A. The dominant agents commonly used are cuprous oxide, and triphenyl or tributyl derivatives of tin, although restrictions on the use of tin-based anti- foulant paints are now in force in the United Kingdom and France and are under consideration in the U.S.A.

One alternative to a toxic coating is a non-toxic anti-fouling release coating which weakens or eliminates the adhesive bond between fouling organisms and the coating. The fouling would then be dislodged by relatively weak mechanical forces, such as those arising from the motion of the ship through the water.

We have now unexpectedly found an environmentally acceptable alternative approach: to use the copper already present in sea water by incorporating a regenerable, selective, metal-chelating micro ion exchange resin into a suitable matrix.

In situations, such as cooling towers, which are isolated from the environment, a source of copper may be provided. For example, cooling coils may be made of copper.

Copper is an effective biocide against a broad spectrum of marine life. The standard anti-foulant used in the U.S.A contains cuprous oxide in natural rosin and a vinyl chloride - vinyl acetate copolymer. The anti-foulant mechanism of operation is such that a steady dissolution of resin in sea water creates channels in the paint which allow toxic cuprous oxide to migrate to the surface and dissolve. The rate of migration is controlled primarily by the ratio of vinyl resin to rosin, and the temperature of the sea water. The failure of the coating is usually due to formation over the paint of an insoluble crust of copper compounds rather than to exhaustion of the cuprous oxide biocide in the paint coat. Such controlled release techniques are based on the concept of combining biologically active substances with polymeric materials either by physical combinations in which the polymer acts as a rate controller or chemical combinations in which the polymer acts as a carrier for the agent.

The copper chloride content of sea water is important because leaching stops at 1.3 ppm CuCl concentration and added or extraneous copper leached from conventional anti-foulant coatings is a positive contribution to the increase in sea water copper content. The composition of the present invention and its incorporation into a marine anti-foulant paint overcomes or substantially reduces the problems described above in that:

a) controlled release is not a problem; and b) leaching of copper into the marine environment does not occur.

Summary of the Invention

According to the present invention there is provided an anti-fouling composition comprising a selective metal-chelating micro ion exchange resin capable of binding copper, a viscosity-controlled matrix, and optionally one or more components selected from the group consisting of a marine biocide, a film-forming binder, and a pigment.

The selective metal-chelating micro ion exchange resin functions as a copper reservoir. As the resin is invaded by fouling organisms it loses copper from its structure, and recaptures cupric ions from the surrounding water in a cyclic process of self-regeneration.

In one preferred embodiment of the invention, the composition is an anti-fouling paint, comprising the components referred to above together with a film-forming binder, and the viscosity-controlled matrix comprises a thinner, a plasticizer and a thixotrope. Preferably the film-forming binder is a zinc resinate based on a polymerized resin.

In a second preferred embodiment, the composition of the invention is mixed with polymers, heated, and pressed or extruded to form either sheet plate, fibres or filaments; the latter can be used to form fishing nets, ropes and like products. In this embodiment, the polymer is preferably a high density polyolefin, non-aromatic polyamide, polypropylene or polyester. Normally copper or copper ions destroys the integrity of polyolefins; however, the formulation of this invention shows no deleterious effect of copper or copper ions in the presence of the micro ion exchange resin. A preferred polyamide is nylon. Preferably the marine biocide comprises a general empirical biocide such as zinc oxide, and a broad spectrum biocide such as 2,4,5,6-tetrachloroisophthalonitrile.

Detailed Description of the Invention

A preferred microion exchange resin is sold under the trade name Metpol Copper or Sirorez Cu, which is a selective metal-chelating micro ion exchange resin which functions as a copper reservoir. We have unexpectedly found that it is possible to convert the resin to a finely divided copper-saturated powder form which is insoluble in fresh and sea water. The copper content with respect to the weight of the resin is in the range 1% to

6%, preferably 5%.

A suitable binder is "Ennesin ZR 170", which is a metallic resinate containing 10% zinc and is based on polymerized rosin. The rosin is a carboxylic-acid- functional blend of terpene materials whose major component is abietic acid of the formula C₁₉H₂₉COOH.

The anti-foulant paint of the invention preferably includes zinc oxide as a general empirical biocide, or barium metaborate as an algjσide. The other added biocide component is preferably a broad spectrum microbiocide, 2,4,5,6-tetrachlorisophthal"nitrile, having the formula illustrated below:

This 2,4,5,6-tetrachlorisophthalonitrile has the trade name Napcocide N-96.

A suitable viscosity-controlled matrix for use in this anti-foulant paint is a 3-component blend of mineral turpentine thinner, Hyvis 30 polybutene plasticizer/tackifier and a bentonite type thixotrope, S.D.I.

Other suitable binders, biocides, pigments and matrices are known in the art, and will readily occur to the skilled addressee of the invention.

The paint binders are mixed with the biocide component and the pigment(s) used in the paint. Conventional blending procedures can be used.

The pigment is preferably a sparingly soluble pigment having a solubility in sea water of from 0.5 to 10 ppm by weight, e.g. Zinc oxide which also serves as a general empirical biocide, or barium metaborate which acts as an algicide, and increases stability to ultra-violet radiation exposure. The paint composition in addition may contain a pigment which is not reactive with sea water and may be highly insoluble in sea water (solubility below 0.5 ppm by weight) such as titanium dioxide. Such highly insoluble pigments are preferably used in proportions approximately 40% of the total pigment component of the paint. A suitable pigment is of the type Titanium dioxide RCR6 and as cyprid molluscs show a preference for dark substrates, the light colour obtained with this type of pigment is particuarly desirable. The present invention overcomes or substantially reduces most of the deficiencies existing in the generally accepted anti-foulant paints and compositions.

The crux of the invention is the incorporation of the Metpol Cu which is a selective metal-chelating micro ion exchange resin functioning as a copper reservoir, ie. the resin loses copper from its structure as it is invaded by fouling microorganisms and recaptures cupric ions from sea water to the point of saturation in a process of self- regeneration. Without wishing to be bound by any proposed mechanism for the observed beneficial effects, it is thought that the reaction mechanism would be along the following lines:

-

The ion exchange resin is used as a substrate to hold Cu so that the natural water soluble salts would channel away the Cu⁺⁺ while the regenerable ion exchange was in a fixed accessible site.

Reactions:

Chemical reactions of copper and cuprous oxide in sea water:

CuO + 2C1^" -* C.- 1₂ ^" + e^"

Cu₂0 + 2H⁺ + 4C1^" → 2(CuCl₂-) + H₂0

2Cu₂0 + 0₂ + 6C1^" + 4H₂0 - 3(CuCl₂) + Cu(OH)₂ + 60H^"

Cu₂0 + Cl^" + 2H₂0 + %0₂ → Cu₂(OH)₃Cl + OH^"

Copper in its dissolved form is poisonous to the sessile marine organisms which are responsible for fouling. Sea water diffuses into the paint film, dissolving the cuprous oxide and forming a copper chloride complex (as per the above reactions) in a paint originally containing the copper as cuprous oxide. The Metpol Cu (Sirorez Cu) loses copper from its structure as it is invaded by fouling microorganisms, then recaptures cupric ions from the sea water to the point of saturation in a cyclic operation. This mechanism has many advantages over conventional anti-fouling paints and their mode of operation:

1. There is no copper leaching into the sea water environment, but only a utilization of that already present in a re-cyclable manner;

2. The rate of leaching or exposure to the fouling microorganisms is not dependent on binder formulations; and 3. Formation of insoluble crusts of copper compounds is avoided.

The invention will now be illustrated by way of reference only to the following non-limiting examples. Unless otherwise stated, components are listed in parts by weight.

The copper selective chelating resin herein referred to as "Metpol Cu" is a condensation polymer prepared from phenol, formaldehyde and piperazine by the Mannich reaction, and was found to selectively chelate Cu²⁺ ions, with capacities up to 2.4 mmol/g over a pH range 3- 10.5. The method of preparation of the resin which is described below can be used to synthesize the resin in a suitable form for large-scale use.

Preparation of Sirorez Cu The "Sirorez copper" powder is prepared from poly-12-hydroxy stearic acid/glycidal methacrylate co- methyl-methacrylate 40% solution in butyl acetate/toluene and 0.8% surfactant, such as Dulux No. 498.6890 which is dispersed in 300 ml 75% aqueous ethanol in a 1 litre flask fitted with agitator, thermometer and reflux condenser. Piperazine hexahydrate (67.5g) and 40% formaldehyde solution (60 ml) are added and stirred until dissolved. Phenol (22.5 g) and Bis phenol A (8.4 g) are dissolved in 300 ml of 75% aqueous ethanol and the solution added to the reaction mixture. Mild agitation is maintained and the temperature raised to reflux (approx. 78°C) . Refluxing is continued for 4 hrs after which the condenser is re-set for distillation. After each 200 ml of ethanol/water is collected 200 ml of water is added to the reaction flask to maintain mobility. Distillation is continued until the vapour temperature reaches 100°C (approx. 450 ml distillate is collected) . 20 ml 2N sodium hydroxide is added and the product collected on a Buchner funnel. The yield of dry polymer is approximately 70 g.

The dry polymer is milled to a powder, mixed and agitated with a 5% copper sulphate solution, preferably to saturation point with respect to copper absorption, ie. 5%, although a range of 1-6% is acceptable.

Preparation of Metpol Cu resin

The Sirorez Cu was prepared by mixing and heating the powdered Metpol resin with a 5% copper sulphate solution until the resin was black, indicating complete copper saturation. The Sirorez resin was filtered, washed and ground into a fine powder containing 1-6% copper.

Example 1 Preparation of anti-fouling paint One of the uses of this powder technology involving Metpol Cu is to incorporate it into an anti- foulant paint re arred to as "anti-foul white on ZR 170" in the proportion of 5-25% solids weight basis.

The Metpol Cu is blended with all the other components simply by σrinding all fillers into the solvent matrix to produce a p.int, which can be suitably applied by spray, brush or roller to a surface, such as fibreglass, steel, wood, concrete, or non-ferrous surface. The paint also has the function of an ink. Example 2 Preparation of polymer containing Metpol Cu

The Metpol Cu powder mixed with polypropylene or polyethylene or other polymer can be pelletised, then by the normal method of heating or extruding can be formed into flat sheets or into a filament to be woven into fishing nets, or twisted into ropes.

Example 3 Heat ageing of polyethylene containing Metpol Cu Polyethylene sheets prepared as in Example 2 were subjected to heat ageing at 80°C for a total of 6 months. Samples tested after 10 weeks of 80°C showed a remarkably low degree of change, with an oxidation level lower than a control sample containing no Metpol Cu. The oxidation level decreased slightly as the level of Metpol Cu increased from 5% to 20%. Similar samples of polymer placed in contact with metallic copper became highly oxidized and brittle within 1 week under the same conditions. The trial was continued for a full 6 months, without the samples showing substantial change. Since it is known that oxidation levels provide a very sensitive indicator of physical property changes in polyethylene, the results indicate that polyethylene incorporating Metpol Cu shows excellent long term stability; indeed, the Metpol Cu appears to have substantially improved the properties of the polyethylene host material.

Example 4 Marine immersion trial

A short-term marine immersion trial of Metpol/ZR170 anti-fouling coating was undertaken on a paint test raft in northern Port Phillip Bay, Victoria, Australia. Over the three-month immersion period, test panels coated with this product accumulated a significantly lower biomass of fouling than control panels. The species composition of fouling on the Metpol also differed from that on the controls. Metpol-Ennesin ZR170 anti-fouling paint as described in Example 1 (referred to as Metpol paint) was applied over empirical I pack marine primer system. Two systems were selected:

1. International Marine Coatings - Intertuf JVA003

2. Hempel's Marine Paints - Hempanyl Tar 1628.

Two replicate test panels of each of the following four coating systems were prepared:

Ml: 3 coats Jnte-rtu-f 3 coats Metpol paint

M2: 3 coats Hempanyl Tar 3 coats Metpol paint

M3: 3 coats Intertuf no topcoat M4: 3 coats Hempanyl Tar no topcoat

Systems were applied to both sides of grit- blasted 30 cm x 15 cm mild steel panels. Primers were applied by spray, Metpol paint by brush. 3 coats of Metpol paint yielded a dry film thickness of around 100 um. The 8 painted panels, together with 2 unpainted black acrylic controls, were attached to a single rack on the paint test raft on 20 December 1990. Panels were immersed vertically. One of each of the painted panels was immersed at a depth of approx. 0.5 m, the other at 1.5 m. Acrylic controls were immersed at 1.0 m.

Inspections were made on 16 January and 19 February, and the panels withdrawn on 28 March 1991. During inspection, the extent of fouling was assessed by estimating the percentage of panel surface covered by major fouling types.

After withdrawal, all panels were air-dried. The composition and abundance of marine fouling organisms on Metpol paint-treated panels and acrylic controls were assessed using the frequency method detailed in Australian Standard AS 1580 Method 481.5: Assessment of durability and resistance to fouling of marine underwater paint systems and degree of protection of substrate.

No problems were met in application of Metpol paint and, over the period of the test, no physical defects were observed in the coating, or between the coating and either of the primers. The marine fouling growth of Metpol paint-treated panels differed signficantly in both composition (Table 1) and biomass (Table 2) to that on the uncoated primers and acrylic control panels. The composition and abundance of fouling on the uncoated primers did not appear to differ signficantly from that on the acrylic controls (Table 2) .

Although a diverse array of organisms was present on Metpol paint-treated panels, these were mostly small or encrusting species and the total biomass of fouling was much lower than on the other panels. Settlement of organisms occurred through the immersion period, and was not a sign of paint failure towards the end of the test. Settlement of barnacles (Balanus variegatus & Elminius modes tuε) , erect bryozoans (Bugula spp.), tubeworms (including Ficopomatus enigmatica) and colonial ascidians was greatly inhibited by Metpol paint. These organisms are all major macrofoulers in Port Phillip Bay, and were present in abundance on the other panels.

Table 1 Fouling composition and abundance on panels after immersion. Each value in the table is the mean of frequencies determined for each side of the two replicate panels.

Table 2 Dry weight biomass of fouling (g/dm²) on panels after immersion

System Mean S.D.

(g/dm²)

Ml 1.20 ± 0.66

M2 0.49 ± 0.25

M3 25.6 + 3.4

M4 25.6 ± 8.4

Control 31.6 ± 11.1

Example 5 Extrusion into filaments

One particularly desirable application of the invention is to the manufacture of fishing nets. Currently fishing nets used in aquaculture systems have a relatively short life, since they must be washed using abrasive washers when they become encrusted with aquatic growths, and consequently provide insufficient water flow through and oxygenation. This results in high mortality of the farmed fish. The process is also very labour intensive. For use in nets, it is necessary that the Metpol Cu polymer should be able to be extruded or spun into fine filaments.

Using conventional extrusion techniques, Metpol Cu polymers (polyethylene or polyester) were spun into fine filaments of 500 Denier. In addition to Metpol Cu, as described in Example 2, one set of samples of each polymer also incorporated barium metaborate at 10% by weight with respect to the final polymer as a pigment. Barium metaborate improves stability to ultra-violet radiation, and also has algicidal activity. The results of extrusion trials are shown in Table 3. The filaments were woven into 12-filament strands, and interwoven into panels approximately 1 m x 1 m for marine immersion trials. Table 3 Composition of Metpol-polymer filaments

Polyethylene Filament Polyester Filament 500 Denier 500 Denier

Barium metaborate constituted 10% by weight of the Metpol Cu added.

It will be clearly understood that the invention in its general aspects is not limited to the specific details referred to hereinabove.

Claims

CLAIMS :

1. An anti-fouling composition comprising a selective metal-chelating micro ion exchange resin capable of binding copper, a viscosity-controlled matrix, and optionally one or more components selected from the group consisting of a marine biocide, a film-forming binder, and a pigment.

2. A composition according to Claim 1, wherein the micro ion exchange resin is Metpol Cu, as hereinbefore described.

3. A composition according to Claim 1 or Claim 2, wherein said composition is an anti-fouling paint, and further comprises a film-forming binder, and wherein the viscosity-controlled matrix comprises a thinner, a plasticizer and thixotrope.

4. A composition according to Claim 3, wherein the film-forming binder is a zinc resinate based on a polymerized resin.

5. A composition according to Claim 1 or Claim 2 which further comprises a polymer.

6. A composition according to Claim 5, wherein the polymer is selected from the group consisting of high- density polyolefins, non-aromatic polyamides, polypropylenes and polyesters.

7. A composition according to Claim 6, wherein the polymer is selected from the group consisting of polypropylene, polyester and nylon.

8. A composition according to anyone of Claims 1 to 7 in which the marine biocide is one or more compounds selected from of the group consisting of zinc oxide,2, 4,5,6-tetrachloro-isoόthalonitrile, and barium metaborate.

9. A sheet, plate, fibre or filament comprising a polymer according to any one of Claims 5 to 8.

10. A method of preventing fouling by aquatic organisms comprising the step of applying to a surface subject to such fouling a coating of a composition according to any one of Claims l to 8, and, where the aquatic environment is poor in copper, providing, a source of copper.