Technical Field

This invention is concerned witn anπfou ^' nng coating comDosi ons used on surfaces likely to come into contact witn marine fouling organisms sucn as algae, seaweed and barnacles, for example on shiDS or boats or on the out¬ falls for cooling water from power stations. Sucn coating compositions generally comprise a biocide for marine organisms and a binder polymer. More particularly, it relates to compositions capable of forming a coating film having an improved binder polymer.

Background Art

The most successful antifculing paints in recent, years have been sel -pclishing antifouling paints using binders which are linear polymers containing pendent side groups (hereinafter called "leaving groups") which are liberated from the polymer by reaction with seawater, the residual polymer being sufficiently dispersible or soluble in seawater to be swept away from tne paint surface, exposing a fresh layer of the binder able to undergo a similar reaction with seawater. Such paints are described for examcle in British Patent 1457590. The gradual thinning of the paint film controls the release of a biocide active against fouling. The well-known benefits of such self- polishing paints are that the paint film tends to at least retain its initial smoothness and that the biociσe con¬ tained in the paint tends tc be delivered from the surface at a more uniform or constant rate.

The only commercially significant self-polishing paints employ binders which comprise triorganotin ester leaving groups. The triorganotin provides some of the biocidal action of the paints and the triorganotin ester readily undergoes the hydrolysis on which the self-polish¬ ing action is dependant. The biocidal activity can be augmented by other antifouling suDstances dispersed or

dissolved in the Daint film. There may be aαvantages in replacing some or al of the triorganotin ester leaving groups DV other leaving groups, which are not necessarily biocidal. botn fcr cost reasons and because the powerful biocidal effects of triorganotin may not be desired.

International Patent Application WO84/02915, for examDle, discloses an antifouling paint having a hyαroly- sable film-forming water-insoluble seawater-erooi le polymeric binder having recurring groups representec by the formula:

X I

( - CH - C -7 r B -J—

* ^• i

COOR

where X is hydrogen or methyl. R s a substituted alkyl, ary , aralkyl or triorganosi 1yl moiety and B is the residue of an ethylenical1y unsaturated comcno er. WOS^/02915 describes a wide range of groups R, but it has been found in practice that the less readily hydrolysable groups R such as benzyl, aminoalkyl and haloalkvl grouDS do not give a polymer which dissolves in seawater. OS4/02915 also describes hydrolysable groups R which are triorganosi lyl groups and these are further described in US Patent 4593055. The triorganosi1yl groups undergo rapid hydroly¬ sis, but this can give rise to gelation of the paint composition on storage and undesirably rapid dissolution of the paint from a ship's hull in use.

Japanese published unexaminec patent application 1-

146969 describes an antifouling coating containing a copolymer of 10-90 molar % triorganosilyl aerylate or methacrvlate units and 0.1-10 molar % tertiary aminoalkyl acrylate or methacrvlate units.

Disclosure of Invention

An antifouling coating composition according to the present invention containing a biocide for marine organisms

ano comprising as binder a polymer naving oenoent trior¬ ganosi lyl carboxylate groups, is cnaracteπ seo in that the coating composition contains a monoamine having at least 4 carbon atoms or a quaternary mcncammoni m compound.

5 The amine or cuaternary ammonium compound inhibits gelation of the coating composition curing storage. Paints containing a polymer having pendent triorganosi 1yl carboxy¬ late groups may be liable to gelation during storage, particularly when the paint contains a metal comoounc as 10 pigment, for example a copper or zinc compound such as cuprous oxide. The amine or quaternary ammonium compound also controls the rate of dissolution of the coating m use on a ship moving through seawater, prolonging the length of time for which the coating is effective.

15 The binder polymer is preferably a triorganosi lyl acrvlate or methacrvlate polymer containing reoeat units of the formula:

I

CH.

--U c = u

I

R

where X represents H or CH, and R represents a tπorgano- silyl moiety of the formula Si(R'),, where the groups R' . 25 which can be the same or different, represent straight- chain or branched alkyl groups having 1 to 10 carbon atoms or ohenvl qrouos.

The polymer is preferably produced by addition polymerisation of a triorganosi 1yl acrvlate or methacrvlate 30 of the formula:

X -o

I H

CH. -- C - C - 0 - R (I

wnere R nas the above meaning. using a free radical catalyst such as an azo compound or a peroxide, preferably in solution in an organic solvent. Examples of monomers of the formula (I) are tributylsi lyl acrvlate, tπphenylsi lyl acrvlate, ohenyldimethylsi 1yl acrylate, oiphenylmetnylsi 1y1 acrvlate, tri-isopropylsi1yl acrylate and trimetny si lyl acrvlate, and the corresponding methacrylates. Examples of suitable solvents are an aromatic hydrocarbon such as xylene or toluene, optionally mixεo with an alionatic hydrocarbon such as white spirit, an ester such as butyl acetate, ethoxyethyl acetate or metnoxypropyl acetate, an alcohol such as butanol or butoxy-ethanol , or a ketone sucn as methyl isobutyl ketone or methyl lsoamyl ketone.

The triorganosi lyl acrylate or methacrvlate mcnomer is generally copolymerised with one or more ethylemcal 1y unsaturated comonomers which do not undergo hydrolysis in seawater, for example acrylic esters such as methyl acry¬ late, methyl methacrvlate, ethyl acrylate. butyl acrylate or 2-ethyl hexyl methacrvlate, styrene, acrylomtrile. vinyl acetate, vinyl butyrate. vinyl chloride or vinyl pyridine. Units of the triorganosi lyl acrylate or methacrvlate monomer can for example form 15 to 60 mole % of the resulting copolymer, preferably 20 to 45 mole % .

The polymer binder can alternatively be formec by reacting a carboxvlic-acid-functional polymer, for example a copolymer of acrylic or methacrylic acid witn an ethylenically unsaturated co onomer of the type described above, with a triorganosi lyl compound such as a hexa-alkyl disilazane or a bis(triorganosi1yl urea.

The polymer binder can alternatively be a clock copolymer of a triorganosilyl acrylate or methacrvlate polymer with oolyether or polymethane blocks or blocks of another addition polymer such as polymethyl methacrvlate as described in US Patent 4957989.

The monoamine used in tne coating composition is preferably a primary amine. although a secondary or ter¬ tiary amine can oe used. The amine or ouaternary ammonium compound preferably includes at least one organic group having at least 8 carbon atoms, more preferably 8 to 20 carbon atoms. Sucn amines ano quaternary ammonium com¬ pounds generally have the additional advantage that they are toxic to marine organisms. Primary amines having at least 8 carbon atoms are particularly preferred.

The monoamine can for example be a diterpene-oerived amine of the formula:

where R is a monovalent hydrocarbon group derived from a ditemene and R 2 and R3 are each independently hydrogen, an alkyl group having 1 to 18 carbon atoms or an aryl group having 6 to 12 carbon atoms. These amines are usually toxic. Such an amine is preferably derived from rosin. A primary amine derived from rosin is dehydroabietylamine sold commercially as "Rosin Amine D" . Its main constituent is

A corresponding secondary or tertiary amine, for example an N-methyl or N.N-di ethyl derivative of Rosin Amine D, can alternatively be used.

The monoamine can alternatively be an aliphatic amine containing an organic group of 12 to 20 caroon atoms, for example a straight-chain alkyl or alkenyl amine such as

cooecyl amine. hexadecyl amine, cctacecyl amine or oiey amine or mixtures of amines derived from aliphatic groups present in natural fats and oils such as tallow amine or nydrogenated tallow amine or coconut amine. These amines £ also are usually tcxic.

Alternative monoamines wnich can be used are aralkyl- a mes sucn as these sold commercially as "pneπalkamines ' . The quaternary monoammonium compound can for example be a halide salt, e.g. hexadecyl trimethyl ammonium chloride.

0 The proportion of triorganosi yl polymer binder to amine or quaternary ammonium compound in the coating composition is preferaply 98:2 tc 40:50 oy volume, most preferably 90:10 to 50:50. Amines naving no film-forming properties are preferably used at no more than 25 based en 5 the co binec volume of polymer and amine, wnereas film- forming amines such as the diterpene derivatives can be used at a higher proportion if desired.

If an amine or quaternary ammonium compound wnich is biocidal to marine organisms is usec the resulting coating C Gcmocsition can be a clear antifouling varnish or can ce oigmentec. If a non-biocidal amine or quaternary ammonium compound is used the coating compcs tion should contain a marine biocide. The coating preferably contains a pigment, and the same material may function simultaneously bctn as a 5 marine biocide and as a pigment if a biocidal pigment is used. The coating composition preferably contains an organic solvent for the triorganosi lyl polymer binder; if tne polymer is prepared in solution the polymer solution produced can be used in preparing tne paint.

0 The amine or quaternary ammonium compound can oe premixed with the triorganosilyl polymer binder before addition" of other components of the coating composition, or the binder polymer can simultaneously be mixed with the amine or duaternary ammonium compound and a pigment. For

example, the triorganosi lyl polymer binoer and tne amine cr quaternary ammonium compound can ce mixed with pigment using conventional paint-b enoing procedures to provide a composition having a pigment volume concentration of, for example, 25 to 55*-. The pigment is preferably a sparingly soluble pigment having a solubility in seawater of from 0.5 to 10 parts per million oy weicnt and is preferably a metalliferous pigment. The pigment is most preferaoly a ccpper or zinc ccmpouno, for example cuprous oxide, cuprous thiocyanate, zinc oxide, zinc etnylene bisCdithiocaroa- mate), zinc dimethyl dithiocarbamate, zinc diethyl dithio¬ carbamate or cuprous ethylene bis(di hiocarbamate) . These sparingly soluble pigments whicn are copper anc zinc compounds are generally also marine biocides. The spaπng- ly soluble metalliferous pigments produce water-scluole metal compounds on reaction with seawater so that the pigment particles do not survive at the paint surface. Mixtures of sparingly soluble pigments can be used, for example cuprous oxide, cuprous thiocyanate or zinc ethylene bisCdithiocarbamate) , which are highly effective biocical pigments, can be mixed with zinc oxice, which is less effective as a biocide but dissolves slightly more rapidly in seawater.

The paint composition can additionally or alternative- ly contain a pigment which is not reactive with seawater and may be highly insoluble in seawater (solubility below 0.5 part per million oy weight) such as titanium dioxide or ferric oxide or an organic pigment such as a phthalocyanine pigment. Such highly insoluble pigments are preferably used at less than 0% by weight of the total pigment component of the paint, most preferably less than 20%.

The antifouling paint can also contain a non-metal¬ liferous biocide for marine organisms, for example tetra- methyl thiuram disulphide, methylene bisithiocyanate ) , captan, a substituted isothi ∑olone or 2-methylthιo-4-t-

3 cutylarmno-6-cyclocrocylamino-s-tπazine.

The antifouling coating composition of the invention is generally applied from a solution in an organic solvent: for example when the triorganosi 1yl polymer is prepared in 5 an organic solvent the polymer solution can be used direct¬ ly in the paint. It can optionally be di uted by further solvent, preferaply selected from the solvents listed above.

The invention is illustrated by the following Example.

10 Example

15 molar % phenyldimethylsi 1yl acrylate, 15 molar % tπmethylsilyl methacrvlate and 70 molar % butyl methacry- late were copolvmerised as a 40% by weight solution in xylene at 70°C using azobisisooutvronitri le as initiator. 15 The resulting triorganosi lyl copolymer solution was mixed with pigments, structuring agents. Rosin Amine D and additional solvent in a high-speed disperser and ground to a particle size of 25 microns to produce an antifouling paint having the following formulation:

ϋ'

Triorganosi lyl copolymer

Xylene

Methyl isoamyl ketone

Cuprous oxide 25 Titanium dioxide

Structuring Agents (bentonite clay. zeo ite and silica)

Rosin Amine D

A sample of the paint produced was stored in a can at 30 45°C for ^" 22 days. A slight skin formed at the surface of the paint but the paint was still sprayable. By compari¬ son, a paint IA) based on the same copolymer ano having

the same pigment volume concentration but containing no Rosin Amine C hac gel lee on storage anc was not sorayable.

Furtner samples of tne paints croouceo were acclieo as twe stripes 90 microns tmck on a disc. The disc was rotated in seawater for 30 days as a test designed tc measure the rate of dissolution of tne caints when used as a self-polisning antifouling paint. The th cκness of tne oaint strioes was measured pefore and after tne trial anc the rate of polishing away of oamt was calculated. The rate of dissolution of the oaint cf tne invention was only 44% cf that of the ccmoarison oaint lA).