EP0762955A4

EP0762955A4 - Anti-fouling coating

Info

Publication number: EP0762955A4
Application number: EP95910145A
Authority: EP
Inventors: James R Griffith; Stephen L Snyder
Original assignee: US Department of Navy; US Department of Health and Human Services
Current assignee: US Department of Navy; US Department of Health and Human Services
Priority date: 1994-05-31
Filing date: 1995-01-31
Publication date: 1998-01-07
Also published as: EP0762955A1; KR970703398A; JPH10501272A; WO1995032862A1

Abstract

A silicone coating system containing a 3-isothiazolone biocide, an article comprising a substrate and the coating system thereon, and a method for controlling fouling by marine organisms of an underwater substrate characterized by the step of coating the substrate with the coating system.

Description

ANTIFOULING AND FOUL-RELEASE COATINGS

Field of the Invention This invention pertains to controlling of fouling of a substrate by marine organisms using a silicone coating system containing an effective amount of an organic biocide.

Background of the Invention Fouling marine organisms attach to structural substrates submerged in water and cause various problems. The problems that the fouling marine organisms cause include decreased heat transfer, increased friction and the consequent increase in the power to move the substrate through water, and general degradation of the surface due to the accumulation of the organisms thereon.

It is a routine practice to coat or paint the substrate in order to prevent attachment of the organisms thereto. In the past, organotins have been admixed with paints to provide antifouling performance to the substrates coated with such paints. Organotins used for antifouling purposes are toxic and the use thereof has been banned or restricted in many countries. For that reason, the boat and ship owners have fallen back to the use of the technically inferior but less toxic copper oxide in place of the organotins.

Recently, organic biocides of the type described herein have been incorporated into copper-based antifouling paints to improve their performance or to reduce the copper loading required to achive effective antifouling. There are, however, no effective antifouling paints on the market which do not employ organotins or copper as the principle antifouling agent.

Due to excellent release properties, fouling control paint systems based on silicones have been known since the early 1970s. Silicones are polymers that have a backbone silicon- oxygen-silicon atoms linked together. This structure accounts for the general inertness of silicone rubbers to many deteriorating influences such as ozone, chemicals, weathering and radiation.

U.S. patent application entitled "Nontoxic Antifouling Systems" filed March 6, 1992 on behalf of inventor Griffith, discloses an antifouling silicone system tightly adhering to a substrate. The system includes a silicone rubber bonding layer bonded on one side to a substrate and on the other to a silicone rubber release layer. This application is hereby incorporated by reference. U.S. Patent 4,127,687 pertains to prevention and inhibition of fouling of marine structures by fouling organisms common in sea water. According to the patent, marine structures are coated with a non-silicone paint containing an effective amount of a 3-isothiazolone biocide and a co-biocide. At bottom of col. 2 and at top of col. 3 of this patent, the term "paint" is defined as a coating that does not include silicone- based paints.

Summary of the Invention It is an object of this invention to provide, on a substrate submersible in seawater, a silicone-based coating that is antifouling and foul-release;

Another object of this invention is to coat a substrate with a silicone-based system containing an isothiazolone; Another object of this invention is a substrate coated with a silicone-based system containing an isothiazolone which rapidly biodegrades upon leaching out of the silicone-based system, rapidly metabolizes, and has negligible bioaccumulation. These and other objects of this invention are attained by a silicone coating system containing a 3-isothiozolone as the sole biocide.

Detailed Description of the Invention This invention pertains to a silicone coating system containing a silicone material and an isothiazolone as the sole biocide, to an article comprising a substrate and the coating system thereon, and to a method for controlling fouling of a coated substrate by marine organisms. This technology is based on the mutual compatibility of the silicone material and the biocide. Together, these materials form an homogeneous solution or dispersion which subsequently cures to form a solid silicone elastomer in which there is an homogeneous distribution of the biocide throughout the coating system.

The silicone coating system comprises a silicone material and a 3-isothiozolone biocide distributed therein. In a preferred embodiment, the coating system is duplex and comprises a bonding layer and a release layer, with the bonding layer bonded, on one side, to a substrate and on the other, to the release layer.

The silicone coating system of this invention can be in sheet form or in liquid form. Silicone materials are based on organopolysiloxanes which can be represented by the formula

where n is an integer, greater than 1, corresponding to the degree of polymerization and R and R substituents are organic radicals, individually selected from lower alkyl (C, to C₆₎ radicals such as methyl, propyl, butyl and hexyl; aryl radicals of at least 6 carbon atoms such as phenyl, diphenyl and naphthyl; alkaryl radicals of at least 7 carbon atoms such as tolyl, xylyl and ethylphenyl; haloaryl radicals such of at least 6 carbon atoms such as chlorophenyl, tetrachlorophenyl and difluorophenyl; and alkenyl radicals of at least 2 carbon atoms such as vinyl. In a preferred embodiment, R and R substituents are lower alkyl groups of 1 to 6 carbon atoms, such as methyl groups, which typically constitute at least 50%, preferably 70-90%, of the total number of organic groups attached to silicon atoms by carbon-silicon linkages. Such organopolysiloxanes are typically hydroxy terminated polydimethylsiloxanes or polydimethylsiloxane-polyether copolymers.

The hydroxy-terminated organopolysiloxanes used in the practice of this invention may also be prepared from cyclic organopolysiloxanes such as hexamethylcyclotrisiloxane, octa ethylcyclotetrasiloxane and decamethylcyclopentasiloxane. Mixtures of these cyclic organopolysiloxanes may be employed as long as the number of silicon-bonded methyl groups constitutes a major proportion of the total number of organic groups.

Suitable biocides herein are selected from 3-isothiazolones represented by the following formula:

wherein Y is (1) an unsubstituted alkyl group of 1-18 carbon atoms, typically 4-10 carbon atoms,

(2) a substituted alkyl group having at least one hydrogen atom replaced by hydroxy, halo, cyano, alkylamino, dialkylamino, phenylamino, halophenyla ino, carboxy, carbalkoxy, alkoxy, aryloxy, morpholino, piperidino, pyrrolidonyl, carba oxy, or isothiazolonyl, wherein the total number of carbon atoms in the substituted alkyl group does not exceed 18,

(3) an unsubstituted or halo-substituted alkenyl group of 2-18 carbon atoms. (4) an unsubstituted or halo-substituted alkynyl group of 2-18 carbon atoms,

(5) an unsubstituted or alkyl-substituted cycloalkyl group having a three to six carbon atom ring and up to 12 carbon atoms, preferably cyclohexyl,

(6) an unsubstituted or a halo-, lower alkyl-, or lower alkoxy-substituted aralkyl group wherein the total number of carbon atoms in the aralkyl group does not exceed 10; preferably the aryl portion of the aralkyl group is phenyl and the halo-, alkyl-, or alkoxy- group, when present on the phenyl group, is chlorine, methyl, or methoxy, or

(7) an unsubstituted or a phenoxy-, hydroxy-, trihalomethyl, halo-, nitro-, lower alkyl-, or lower carbalkoxy-, substituted aryl group wherein the total number of carbon atoms in the aryl group does not exceed 10; preferably the substituent, if any, is carbalkoxy having 1-2 carbon atoms, halo, (C.-C₄) alkyl, trifluoromethyl, methoxy, methyl, hydroxyl, or phenoxy, and the aryl group is phenyl,

R is hydrogen, halogen, or a (C.-C₄) alkyl group, and is typically chlorine, and

R₁ is hydrogen, halogen, or a (C.-C^) alkyl group, and is typically chlorine, provided that at least one of R and R. is halogen, and the salts of the above compounds with a strong mineral acid.

In biocides of the above formula, the radical Y is preferably selected from those in which the solubility in water is between about 0.5 and 400 ppm, more preferably between about 0.5 and 300 ppm, and still more preferably between about 0.5 and 100 ppm.

Representative Y substituents include methyl, ethyl, propyl, isopropyl, butyl, hexyl, octyl, decyl, pentadecyl, octadecyl, cyclopropyl, cyclohexyl, benzyl, 3,4-dichlorobenzyl, 4-methoxybenzyl, 4-chlorobenzyl, 3 , 4-dichlorophenyl, hydroxymethyl, chloromethyl, chloropropyl, diethylaminoethyl, cyanoethyl, carbomethoxyethyl, ethoxyethyl, 2-methoxy-l- bromomethyl, 3,3,5-trimethylcyclohexyl, phenoxyethyl, p- chloroanilinomethyl, phenylcarbamoxymethyl, allylpropynyl, vinyl, carboxyethyl, 1-isothiazolonylethyl and 1,2,2-trichlorovinyl.

Representative R substitutes include hydrogen, bromo, chloro, iodo, methyl, ethyl, propyl, isopropyl, butyl and t- butyl, preferably hydrogen and chlorine.

Representative R, substituents are hydrogen, chloro, bromo, iodo, methyl, ethyl, propyl, isopropyl, butyl, t-butyl, chloromethyl, chloropropyl, bro o ethyl, bromoethyl and bromopropyl, preferably hydrogen and chloro. Typical 3-isothiazolones useful herein include: ,5-dichloro-2-cyclohexyl-3-isothiazόlone,

4,5-dichloro-2-n-hexyl-3-isothiazolone,

4,5-dichloro-2-n-octyl-3-isothiazolone,

4,5-dichloro-2-benzyl-3-isothiazolone, 4,5-dichloro-2-(4'-chlorobenzyl)-3-isothiazolone,

4-methyl-5-chloro-2-(4'-chlorophenyl)-3-isothiazolone,

5-chloro-2-(4'-chlorobenzyl)-3-isothiazolone,

5-chloro-2-(2'-phenylethyl)-3-isothiazolone,

4,5-dichloro-2-(2'-phenylethyl)-3-isothiazolone, 4-bromo-5-chloro-2-(4 -chlorobenzyl)-3-isothiozolone, and

The 3-isothiazolone suitable for purposes herein must not be highly soluble in water but it must be soluble in water up to about 500 ppm, preferably 0.1-400 ppm, and more preferably 0.5- 100 ppm, as measured by the UV method. Apparently, if the 3- isothiazolone is more soluble than stated above, it may be leached out of the coating in a short period of time and unable to exert its influence over the time required in normal usage. On the other hand, if the 3-isothiazolone is totally insoluble, it cannot leach at all to the surface of the coating to combat the development of the fouling organisms.

The amount of the biocide in the coating system should be enough to dissuade the marine organisms from attaching themselves to the surface on which the coating system is provided. The amount of biocide can be in the range of 0.5-25%, typically about 1-15%, based on the weight of the dry coating system.

In a preferred embodiment, the coating system comprises 70- 99% of an organopolysiloxane, described above; 0.1-5% of an alkyl silicate; 0.1-5% of a curing agent; and 0.5-25%, typically 1-15% of a biocide, defined above; based on the weight of the dry coating system.

The alkyl silicates suitable herein include those defined by the following general formulas:

where the R groups are individually selected from alkyl and halogenated alkyl groups of 1-15 carbon atoms such as methyl, ethyl, propyl, isopropyl, butyl, amyl, isoamyl, octyl, isooctyl, decyl, dodecyl, and beta-chloroethyl. The R* groups can be the same as R, although R^* may also be -OZ where Z is selected from the alkyl groups defined above and aryl, aralkyl, alkaryl, as well as derivatives thereof attached to the silicon atoms through the oxygen atoms.

Partially hydrolyzed alkyl silicates are also useful herein. Partial hydrolysis in water can be attained in presence of a small amount of an acid or an acid-forming acid salt to a point where the alkyl silicate is still water-insoluble and it is still possible to isolate a liquid, partially hydrolyzed alkyl silicate.

A typical alkyl silicate for purposes herein is ethyl silicate, (C₂H₅0)₄Si.

RECTIFIED SHES (RULE 91} The silicone coating systems containing organopolysiloxanes can generally be cured by polyalkoxysilane, polyalkoxysiloxane, metal salt or peroxide curing agents. Certain metallic salts of organic carboxylic acids can be employed to give satisfactory cures. Curing salts soluble in the organopolysiloxane are preferred, especially lead and tin salts, because of their marked catalytic activity in combination with an alkyl silicate.

In a preferred embodiment, a duplex coating system can be used on a substrate for controlling fouling by marine organisms. The duplex system consists of a bonding layer and a release layer, both based on same or different organopolysiloxane. The bonding layer is bonded on one side to a substrate and on the opposite side to a release layer. The release layer of the duplex system corresponds to the silicone coating system described above, with or without the biocide. The biocide in the duplex system can be provided in either the bonding layer or in the release layer, or in both layers. The release layer in the duplex coating system is characterized by a quasi mechanical toughness that is imparted to it by the bonding layer which it does not have in absence of the bonding layer. Synergistic or unexpected toughness of the release layer in the duplex coating system is manifested by increase in scratch resistance by 50-300% compared with a typical silicone release layer bonded to the bonding layer. Another advantage of the duplex coating system is the strong bonding of the bonding layer to both the release layer and the substrate, which is generally an epoxy polyamide corrosion barrier. The bond at the interface between the bonding layer and the release layer is such that when an attempt is made to seperate the two layers, cohesive failure occurs in the release layer.

Typically, the bonding layer has a stronger bond to a substrate than the release layer and the bonding layer is tougher than the release layer. However, the release layer has better release properties than the bonding layer or polytetrafluoroethylene. The reason for the difference between the bonding and the release layers is due to the fact that they

REQFTO SHEET (RULE 91} 8/1

contain different ingredients and are made differently.

9

On dry weight basis, the release layer of the duplex coating system comprises about 10-80%, preferably 25-60% hydroxy-terminated organopolysiloxane, defined above; 30-80%, preferably 40-70% monofunctional monomer; less than 5%, preferably 0.1-2% of a free radical initiator; less than 2%, preferably 0.001-1% of a polyfunctional monomer; and when present, 0.5-25%, preferably 5-20% of a biocide selected from the 3-isothiazolones, defined above.

The organopolysiloxane used in the bonding layer of a duplex coating system can be same or similar to the one in the release layer, described earlier.

The monofunctional monomer may be any polymerizable mono- olefinic monomer. Examples of suitable olefinic monomers are low-molecular-weight, straight-chain hydrocarbons such as ethylene, propylene, butylene, halogenated straight-chain hydrocarbons, for example, vinyl halides such as vinyl fluoride and vinyl chlorides; vinyl esters such as vinyl acetate; vinyl containing aromatics such as styrene, ring-substituted styrene; and other aromatics; unsaturated acids; unsaturated nitriles; and vinylsilicon compounds. Disbustituted ethylenes may also be used as monofunctional monomers.

The monofunctional monomer may also be a conjugated diolefin, such as 1, 3-butadiene, isoprene, or chloroprene, inasmuch as the second double bond in these monomers is not readily available for cross-linking.

The free radical initiators suitable herein are typically selected from organic peroxides although other free radical initiators, such as azo compounds,or other well-known initiators can be used. The polyfunctional monomers must have a functionality of at least two. The term "polyfunctional" is intended to include difuncional and trifunctional monomers; that is, monomers having at least two nonconjugated olefinic linkages. Preferably, the olefinic groups should have nearly equal reactivity.

Suitable polyfunctional monomers herein include the polyol esters of acrylic and methacrylic acid such as ethylene dimethacrylate, tetramethylene diacrylate, 1,3-butylene 10 dimethacrylate, trimethylolpropane trimethacrylate, and pentaerythritol tetramethacrylate.

Various fillers, pigments and other additives may be included in the mixture of ingredients in the usual amounts when preparing a silicone coating system. In a duplex coating system, the additives can be added to either or both the bonding and the release layers.

In one embodiment of preparing the hydroxy-terminated silicone polymers of this invention, an organosiloxane or a mixture of such organosiloxanes heated at about 125-170°C with a small amount of a siloxane rearrangement catalyst and the polymerization is carried out until a high molecular weight product of about 100,000-2,000,000 cps viscosity, measured at 25°C, is obtained. The high molecular weight product thus obtained is then treated, typically by blowing steam over it, to reduce its viscosity to about 1,000-50,000 cps at 25°C and to provide the terminal hydroxy groups. The preparation of the organopolysiloxane may occur in the presence or absence of an inert organic solvent. When reactive olefinic monomers are grafted to the organopolysiloxane, a volatile organic solvent may be used to control the temperature by evaporation and reflux. Any organic solvent boiling within range of 50°- 150°C and having a relatively low chain transfer constant may be used in the grafting step. When a solvent is used, it should be 2-50%, preferably 10- 40% by weight of the solvent and the reactants.

Grafting and cross-linking normally occur simultaneously, particularly when all of the polyfunctional monomer is present during the initial grafting step. The polyfunctional monomer may be added to the grafted composition after the initial grafting has occurred, in which case the cross-linking occurs as a separate step. Whether cross-linking takes place separately or together with the grafting reaction, only the dispersed particular matter is cross-linked and the bulk of the material remains fluid. The products, where desirable, may be separated from the unreacted monomers by any conventional technique known in the art. 11

The organopolysiloxane may be endblocked with groups which are hydrolyzable in ambient moisture. Silanes of the general formula X^SiY,. wherein X is a relatively unreactive group such as alkyl or aryl; Y is an acryloxy, oximo, alkoxy, aryloxy, halogen, aminoxy, amido or phosphate group; and is an integer of from 3 to 4; are added as endblocking agents to hydroxyl- terminated modified organopolysiloxane thereby replacing the hydroxyl groups with functional groups of the type OSiX^.Y,,.,. Examples of these silanes are methyltriacetoxysilane, i s o p r o p y l t r i a c e t o x y s i l a n e a n d methyltris (diethylphosphato) silane.

Generally, the endblocking agent is added to the organopolysiloxane immediately after formation of the organopolysiloxane while the same is still hot or at least warm. Under these conditions, the terminal hydroxy groups carried by the organopolysiloxane are converted to hydrolyzable functional groups.

In order to prepare the silicone coating system herein described, it is only necessary to mix the ingredients, including the biocide, preferably adding curing agent and the crosslinking agent last, since shortly after incorporation of these last ingredients in the organopolysiloxane, setting up of the mixture of ingredients will begin to take place. In a matter of a few minutes, a tight cure will begin to be noticed and within one to two hours, the ultimate cure at room temperature will be attained whereby the silicone coating system is cured to a solid, elastomeric coating.

Crosslinking of the organopolysiloxanes can be facilitated by the use of an aminoacetoxyi e and an alkoxysilane. The silicone coating systems described herein can be cured to a solid state at room temperature of about 20^*C or at an elevated temperature of about 50-100*C. The cures obtained at elevated temperatures are generally quicker.

In a preferred embodiment, the biocide is dissolved in an aliphatic hydrocarbon, such as mineral spirits, to form a solution which is then dissolved in a liquid silicone material.

RErøEDSHEET(RULE91) li/l

Upon combining with the silicone material, the biocide may precipitate in the form of fine needles, which does not detract

12

from the performance of the coating system. A silicone curing agent catalyst is added with mixing to the solution of the silicone material and the biocide before application in a liquid state to a substrate with curing to a solid state taking place almost spontaneously.

The adhesion between the silicone coating composition and a substrate can be improved by known means such as by cleaning the surface of the substrate, by the use of a suitable primer or by the use of another substance to improve adhesion between the coating composition and the substrate. An anti-corrosion system can be provided on a substrate before the coating system is applied.

The substrate may be any surface. For example, the substrate may be metal, wood, rubber, plastic, caramic (such as concrete) and mixtures thereof. Plastic substrates include plastic substrates reinforced with fibers. The substrate can be a ship bottom, a buoy, a fishing net and other structures submerged in water, preferably sea water. Examples of other structures include cooling water towers, piers, and water intake and water discharge pipes. Fouling marine organisms typically include barnacles, tube worms and algae.

The silicone coating system is typically in a liquid or paint-like state. It can be applied to a substrate by brushing, spraying, rolling, wiping, dipping, or by any similar means as in the case of a typical paint, and then allowed to dry.

Some embodiments of the release layer of the duplex coating system, without the biocide, are sold under trademarks Dow Corning RTV 3140 and 236 and General Electric RTV 11 and Exsil 2220. USP 2,843,555 discloses preparation of a typical release layer, and is incorporated herein by reference. One embodiment of the bonding layer of the duplex coating system, without the biocide, is sold under trademark Silgan J-501. USP 3,776,875 discloses preparation of a typical bonding layer , and is incorporated herein by reference. The release and the bonding layers of the duplex coating composition can be prepared by admixing the biocide therewith before applying the layer in

RECTIFIED SHEET (RULE 91} 12/ |

liquid state to a substrate. In a one component

13 coating composition, the silicone material is mixed with the biocide before application to a substrate.

The fluid one component and the duplex coating systems can be applied to any substrate in any manner that a paint can. In connection with the duplex coating system, the procedure involves application, for example by spray or brush painting, of the paint-like, fluid bonding layer to a substrate and semi- curing the bonding layer thereon to a tacky surface. The semi- cure time at ambient temperature under typical conditions will be about 0.5-2 hours, which can be accelerated by curing at an elevated temperature. When the applied bonding layer is tacky but not dry, the release layer is applied, for example by spraying or brushing, directly over the bonding layer after being mixed with a curing agent. The release layer dries in 1- 12 hours at which time, a duplex coating system is obtained which is elaεtomeric and is in a solid state. The one component coating system is applied to a substrate but it is allowed to fully dry before it is placed into use.

If the coating system is in a sheet form, it can be secured to a substrate by wrapping it around or by clamping it onto the substrate. This mode of securing allows relatively easy removal of the sheet for inspection of the substrate. The substrate or the back side of the sheet can be coated with an adhesive before applying the coating system to the substrate to facilitate attachment with the substrate. The sheet can also be spirally wound around the substrate, assuming the substrate is of a proper shape. Applying the sheet around or onto the substrate can be carried out under water, unlike painting.

The thickness of a one component coating system in a cured state, disposed on a substrate, is at least about 20 microns, preferably 100-1000 microns. When the duplex system is in a solid state disposed on a substrate, the thickness of the bonding layer is at least about 20 microns, preferably 100-1000 microns, and the thickness of the release layer is at least about 20 microns, preferably 100-1000 microns.

The coating system of this invention comprises, in a cured state, a solid silicone rubber layer containing a biodegradable 3-isothiozolone biocide embedded in the silicone rubber that 14 slowly diffuses to the silicone rubber layer surface in contact with water to prevent fouling by marine organisms.

The coating system is both antifouling and foul-releasing. The antifouling property means that the marine organisms do not attach themselves to a surface. The foul-releasing property means that although some marine organisms can attach themselves to a surface, they can be easily removed therefrom. The antifouling property is imparted mostly by the active or the biocide component of the coating system, whereas the foul- releasing characteristic is imparted by the passive or the silicone material component of the coating system.

After the biocide has leached out from or through a silicone rubber layer to the point where it is ineffective against marine organisms, the silicone rubber layer can be re- painted with a coating system to provide additional biocide. The duration of effectiveness of the coating system against marine organisms is much longer than can be determined from leach rates. This enhanced duration is due to the interaction of the silicone material with the biocide. The invention having been generally described, the following example is given as a particular embodiment of the invention to demonstrate the practice and advantages thereof. It is understood that the example is given by way of illustration and is not intended to limit the specification or the claims that follow, in any manner.

Example This example describes application of a duplex system to an aluminum plate coated with a conventional anti-corrosion coating. The duplex system consisted of a bonding layer and a release layer. The bonding layer was Wacker Chemie Silgan J-501 silicone coating containing Rohm & Haas C-9211 tin-free powder biocide and the release layer was General Electric RTV 11 silicone coating.

The biocide was ,5-dichloro-2-n-octyl-3-isothiazolinone which was admixed with the bonding layer to the extent of 15% loading. After admixing the biocide, the bonding layer was brushed onto an aluminum substrate test panel measuring 7"x 12" x 1/4" coated with a conventional anticorrosion coating. 15

The Wacker Chemie technical product brochure on the Silgan

J-501 bonding layer states that this material is a silicone dispersion which cures at room temperature on contact with atmospheric moisture, liberating s-butylamine and naphtha. On curing at room temperature, a coating is formed, which makes it possible to handle gently in 2 to 3 hours, with full cure achieved in about 24 hours at 50% relative humidity. The product brochure also discloses that on cure, this material becomes tough, remains flexible to -80°C, has Durometer Shore A hardness of 75, has tensile strength of 500lbs/in. , elongation of 60%, tear strength of 351bs/in. , and a service temperature of 125°C. This brochure also discloses that for most applications, adhesion of this material to clean, dry surfaces is good and primers can be used for increased adhesion.

The thickness of the bonding layer disposed on the aluminum plate was about 300 microns and it semi-cured at room temperature in about one hour to a tacky elastomeric state.

A release layer was then brushed over the bonding layer. The release layer was General Electric RTV 11 product, two- component commercial silicone rubber. Before application to the bonding layer, the release layer was mixed with 1/2% by weight of dibutyltin dilaurate curing agent, which was provided. The release layer cured to a solid, elastomeric material overnight and was about 300 microns in thickness.

Strong interlayer forces between the release and bonding layers increased the toughness of the release layer.

Leach rates for the biocide from the bonding layer can be calculated from the equation F « 36/t°^" where F is flux or leach rate in ug/cm -day and t is time in days.

Test panels with the duplex system containing the biocide in the bonding layer were continuously kept in the Chesapeake Bay sea water over a period of 10 months from July 1, 1993, to May 1, 1994, and remained clear whereas control panels with the duplex system but without the biocide were covered by various fouling marine organisms.

Many modifications and variations of the present invention are possible in light of the above teachings. It is, 16 therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

Claims

17

What ia claimed is:

1. A silicone coating system comprising an organopolysiloxane and an organic and a biodegradable biocide, said biocide being present in an effective amount against marine organisms and being selected from the group consisting of 3-isothiazolones.

2. The coating system of claim 1 wherein said organopolysiloxane is represented by the following structural formula:

where n is an integer corresponding to the degree of polymerization and R and R substituents are individually selected from the group consisting of lower alkyl radicals, aryl radicals, alkaryl radicals, haloaryl radicals, and alkenyl radicals; and said biocide is represented by the following structural formula:

wherein Y is

(1) an unsubstituted alkyl group of 1-18 carbons, (2) a substituted alkyl group having at least one hydrogen atom replaced by hydroxy, halo, cyano, alkyla ino, dialkylamino, phenylamino, halophenylamino, carboxy, carbalkoxy, alkoxy, 18 aryloxy, morpholino, piperidino, pyrrolidonyl, carbamoxy, or isothiazolonyl, wherein the total number of carbon atoms in the substituted alkyl group does not exceed 18, (3) an unsubstituted or halo-substituted alkenyl group of 2-18 carbon atoms,

(4) unsubstituted or halo-substituted alkynyl group of 2-18 carbon atoms,

(5) an unsaturated or alkyl-substituted cycloalkyl group having a three to six carbon atom ring and up to 12 carbon atoms,

(6) an unsubstituted or a halo-, lower alkyl-, or lower alkoxy-substituted aralkyl group wherein the total number of carbon atoms in the aralkyl group does not exceed 10, or

(7) an unsubstituted or a phenoxy-, hydroxy-, trihalo-, methyl, halo-, nitro, lower alkyl-, or lower carbalkoxy-, substituted aryl group wherein the total number of carbon atoms in the aryl group does not exceed 10,

R is hydrogen, halogen, or a C,-C₄ alkyl group, and R₁ is hydrogen, halogen, or a C.-C₄ alkyl group, provided that at least one of R and R. is halogen, and the salts of a biocide of the above formula with a strong acid, and the solubility of the biocide in water, as determined by the UV method, is between about 0.5 and 500 ppm.

3. The coating system of claim 2 wherein said organopolysiloxane has molecular weight in the range of about 40,000-100,000 and viscosity in the range of about 10-1,000 stokes, at 25 C; and wherein the concentration of said biocide is 0.5-25%, based on the weight of said coating system, and said biocide is selected form the group consisting of: 4,5-dichloro-2-cyclohexyl-3-isothiazolone, 4,5-dichloro-2-n-hexyl-3-isothiazolone, 4,5-dichloro-2-n-octyl-3-isothiazolone, 4,5-dichloro-2-n-vinyl-3-isothiazolone. 4,5-dichloro-2-(4 '-chlorobenzyl) -3-isothiazolone, 4-methyl-5-chloro-2-(4 '-chlorophenyl) -3-isothiazolone, 19

5-chloro-2-(4 •-chlorobenzyl) -3-isothiazolone, 5-chloro-2-(2 '-phenybethyl) -3-isothiazolone, 4,5-dichloro-2-(2 '-phenylethyl)-3-isothiazolone, 4-bromo-5-chloro-2-(4'-chlorobenzyl) -3-isothiozolone, and 4-methyl-5-chloro-2-(3',4 -diethylbenzyl)-3-isothiozolone.

4. The coating system of claim 3 comprising 70-99% organopolysiloxane, 0.1-5% alkyl silicate, 0.1-5% curing agent, and 0.5-25% of said biocide, based on the weight of said coating system, said coating system is a reaction product of said organopolysiloxane, said alkyl silicate and said curing agent, with said biocide being distributed in said coating system.

5. The coating system of claim 4 wherein said organopolysiloxane is hydroxy-terminated polydimethylsiloxane and said biocide is 4, 5-dichloro-2-n-octyl-3-isothiazolinone.

6. An article comprising a substrate and a silicone coating system disposed on said substrate, said silicone coating system including an effective amount of a biocide for reducing fouling of said substrate by marine organisms, and said biocide being selected from the group consisting of 3-isothiazolones and mixtures thereof.

7. The article of claim 6 wherein said biocide is selected from the group consisting of:

4,5-dichloro-2-cyclohexyl-3-isothiazolone, 4,5-dichloro-2-n-hexyl-3-isothiazolone, 4,5-dichloro-2-n-octyl-3-isothiazolone, 4,5-dichloro-2-n-vinyl-3-isothiazolone. 4,5-dichloro-2-(4 *-chlorobenzyl) -3-isothiazolone, 4-methyl-5-chloro-2-(4 '-chlorophenyl) -3-isothiazolone, 5-chloro-2-(4 '-chlorobenzyl) -3-isothiazolone, 5-chloro-2-(2 '-phenybethyl) -3-isothiazolone, 4,5-dichloro-2-(2 '-phenylethyl) -3-isothiazolone, 4-bromo-5-chloro-2-(4 -chlorobenzyl) -3-isothiozolone, and 4-methyl-5-chloro-2-(3 ,4 -diethylbenzyl)-3-isothiozolone. 8. The article of claim 6 wherein said biocide is 4, 5-dichloro- 2-n-octyl-3-isothiazolone.

9. The article of claim 7 wherein amount of said biocide is about 0.5-25%, based on the weight of said coating system. 20

10. The article of claim 7 wherein said amount of said biocide is about 5-20%, based on the weight of said coating system, and said substrate is selected from the group consisting of metal, wood, rubber, plastic, ceramic and mixtures thereof. 11. The article of claim 9 wherein said silicone coating system comprises a reaction product of 70-99% of said organopolysiloxane, 0.1-5% alkyl silicate and 0.1-5% curing agent, based on the weight of said silicone coating system, and is at least about 20 microns in thickness in cured state. 12. The article of claim 11 wherein said organopolysiloxane is hydroxy-terminated polydimethylsiloxane and said biocide is 4,5-dichloro-2-n-octyl-3-isothiazolinone.

13. An article comprising a substrate and a duplex silicone coating system disposed on said substrate, said duplex coating system containing an effective amount of a biocide for reducing fouling of said substrate by marine organisms, said biocide being selected from the group consisting of 3-isothiazolones and mixtures thereof, and said duplex coating system consisting essentially of a bonding layer bonded, at one surface, to said substrate and a release layer bonded, at a surface, to said bonding layer opposite said one surface.

14. The article of claim 13 wherein said bonding layer is at least about 20 micrometers in thickness in cured state and is a reaction product comprising, on the weight thereof, 10-80% organopolysiloxane, 30-80% monofunctional monomer, less than 5% free radical initiator, less than 2% polyfunctional monomer, and 0.5-25% of said biocide dispersed therethrough, when present; said release layer being at least 20 microns in thickness and being a reaction product comprising, on weight basis, 70-99% organopolysiloxane, 0.1-5% alkyl silicate, 0.1-5% curing agent, and 0.5-25% of said biocide dispersed therethrough, when present.

15. Article of claim 14 wherein the solubility of the biocide in water is 0.5-300 ppm. 16. The article of claim 14 wherein the amount of said biocide is 5-20%, based on the weight of either said bonding or said release layers and wherein said biocide is selected form the group consisting of: 21

4,5-dichloro-2-cyclohexyl-3-isothiazolone, 4,5-dichloro-2-n-hexyl-3-isothiazolone, 4,5-dichloro-2-n-octyl-3-isothiazolone. 4,5-dichloro-2-n-vinyl-3-isothiazolone, 4,5-dichloro-2-(4 '-chlorobenzyl) -3-isothiazolone,

4-methyl-5-chloro-2-(4 '-chlorophenyl) -3-isothiazolone, 5-chloro-2-(4 '-chlorobenzyl) -3-isothiazolone, 5-chloro-2-(2 '-phenybethyl) -3-isothiazolone, 4,5-dichloro-2-(2 '-phenylethyl) -3-isothiazolone, 4-bromo-5-chloro-2-(4 -chlorobenzyl)-3-isothiozolone, and 4-methyl-5-chloro-2-(3 ,4 -diethylbenzyl) -3-isothiozolone.

17. The article of claim 16 wherein said bonding layer is a reaction product comprising 25-60% of said organopolysiloxane, 40-70% of said monofunctional monomer, 0.1-2% of said free radical initiator, 0.001-1% of said polyfunctional monomer, and 5-20% of said biocide dispersed therethrough, when present.

18. The article of claim 17 wherein said biocide is 4,5- dichloro-2-n-octy1-3-isothiazolone.

19. The article of claim 18 wherein said bonding layer without said biocide is Silgan J-501 silicone material and said release layer is selected from the group consisting of RTV 11, RTV 3140, RTV 236, and Exsil 2220 silicone materials.

20. A method for controlling fouling by marine organisms of an underwater substrate in water, comprising the steps of: applying a silicone coating system to said surface and exposing said surface to fouling conditions in water, said silicone coating composition containing an effective amount of a 3- isothiazolone biocide.

21. The method of claim 20 wherein said coating system is a duplex coating system comprising said biocide, said duplex coating system consists essentially of a silicone bonding layer bonded, at one surface, to said substrate and a silicone release layer bonded, to a surface of said bonding layer, said bonding layer being a reaction product of 70-99% of an organopolysiloxane, 0.1-5% of an alkyl silicate, and 0.1-5% of a curing agent, based on the weight of said bonding layer, said bonding layer including 0.5-25% of said biocide, if present; and said release layer being a reaction product of 25-60% of 22 an organopolysiloxane, 40-70% of a monofunctional monomer, 0.1- 2% of a free radical initiator and 0.001-1% of a polyfunctional monomer, said release layer including 0.5-25% of said biocide, if present. 22. The method of claim 21 wherein said substrate is selected from the group consisting of metal, wood, rubber, plastic, ceramic, and mixtures thereof; said method further including the step of mixing a curing agent with said release layer before applying said release layer to said solidified but tacky bonding layer.

23. The method of claim 21 wherein said biocide is selected form the group consisting of:

4,5-dichloro-2-cyclohexyl-3-isothiazolone, 4,5-dichloro-2-n-hexyl-3-isothiazolone, 4,5-dichloro-2-n-octyl-3-isothiazolone. 4,5-dichloro-2-n-vinyl-3-isothiazolone, 4,5-dichloro-2-(4 '-chlorobenzyl) -3-isothiazolone, 4-methyl-5-chloro-2-(4 '-chlorophenyl) -3-isothiazolone, 5-chloro-2-(4 '-chlorobenzyl) -3-isothiazolone, 5-chloro-2-(2 '-phenybethyl)-3-isothiazolone,

4,5-dichloro-2-(2 '-phenylethyl)-3-isothiazolone, 4-bromo-5-chloro-2-(4 -chlorobenzyl) -3-isothiozolone, and 4-methyl-5-chloro-2-(3 ,4 -diethylbenzyl)-3-isothiozolone.

24. The method of claim 22 wherein said biocide is 4,5- dichloro-2-n-octyl-3-isothiazolone, said bonding layer is

Silgan J-501 silicone material, and said release layer is selected from the group consisting of RTV 11, RTV 3140, RTV 236, Exsil 2220 silicone materials and mixtures thereof.