Technical Field

This invention is concerned with antifouling coating compositions used on surfaces likely to come into contact with marine fouling organisms such as algae, seaweed and barnacles, for example on ships or boats or on the out¬ falls for cooling water from power stations. Such coating compositions generally comprise a biocide for marine organisms and a binder polymer.

Background Art

There have been many suggestions in recent years fcr self-polishing antifouling paints having binders which are linear polymers containing pendent side 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 the paint surface, exposing a fresh layer of the binder able to undergo a similar reaction with seawater. Such paints are described for example in GB-A-1457590. The gradual thinning of the paint film controls the release of a biocide active against fouling. The only commercially significant self-polishing paints employ binders which comprise triorganotin ester leaving groups.

EP-A-204456 describes a hydrolysable resin for use in antifouling coatings consisting of a resin having at least one side chain bearing at least one terminal group of the formul :

-X-(-O-M-R)

0 0 0 0 II li II II ^ wherein X represents : -C-, -S-. -P- or -P -. : h i ^ ^'

0 OH

M is a metal selected from zinc, copper and tellurium: x is an integer of 1 to 2: R represents an oroanic acid

residue selected from:

S O S 0

II il iι

-S—C-R ₁ , -0-C-R ₁ , -0-C-R. _j , -0-R ₁ , -S-R ₁ or -0-S-R ₁ : and

O R is a monovalent organic residue.

EP-A-342276 describes a process for preparing such a metal-containing resin composition comDrising reacting a mixture of: (A) an acid group-containing resin: (B) a metallic salt of a low-boiling organic acid, in which the metal is selected from those having 2 or more valences and a lesser iomzation tendency than those of alkali metals: and (C) a high-boiling organic monobasic acid: at an elevated temperature while removing the formed low- boiling organic basic acid out of the system.

US-A-2490925 discloses a pest-control composition comprising stabilised rosin amine or a co-ordinate covalent metal salt thereof dispersed in kerosine, gasoline, ben- zene, alcchol, acetone, water or pine oi . The composition is stated tc be particularly effective as a fungicide. The composition can be added to marine paint containing a dehydroabietylamine complex of copper acetate.

JP-A-54-64633 describes a marine antifouling biocide which is a long-chain (12 to 18 carbon atoms; linear aliphatic primary amine or salt thereof. JP-A-54-110322 describes certain long-chain (12 to 18 carbon atoms) linear aliphatic secondary and tertiary amines as marine antifoul¬ ing agents.

US-A-4675051 describes a marine antifouling paint which is gradually dissolved in seawater and which com¬ prises a binder which is a resin produced by the reaction of rosin and an aliphatic polvamine containing at least one

primary or secondary amine group.

Disclosure of the invention

An antifouling coating composition according to the present invention contains a biocide for marine organisms and comprises as binder a hydrolysable resin having at least one side-chain bearing at least one terminal group of the formula:

-X-(-O-M-R)

wherein X represents - . represents a. metal having a valency of at least 2, x represents i or 2, and represents a monobasic organic acid residue, and is characterised in that it contains a substantia ly non-volatile amine.

In the hydrolysable resin the metal M can for example be selected from the fcl lowing groups of the Periodic Table: Ibie.g. Cu ) , Ila (e.g. Ca, Ba), lib (e.g. ∑n, Cσ ; , Ilia (e.g. Sc, Y), Illb (e.g. A , In), IVa (e.g. Ti , Ξr). IVb (e.g. S.-, Pb, Si ), Va (e.g. V, Nb ) , Via (e.g. Cr, c . W), VIb (e.g. Se, Tel. Vila (e.g. Mn) anc VIII (e.g. Fe, Co, Ni ). The metal M is preferably divalent, for example ccpper, zinc, nickel, cobalt or manganese, in which case x is 1. Copper and zinc are particularly preferred metals.

0 II The linkage X is preferably a -C- linkage. The hydrolysable resin can for example be produced by the process of EP-A-342276 by reacting an acid group-containing base resin, preferably a carboxyl ic-acid-containing resin, with a metallic salt of a low-boiling organic acid and with a high-boiling organic monobasic acid.

The base resin containing acid groups is preferably a

carboxylic-acic-functional polymer of eαuivalent weight 240 to 500. A preferred acid-functional polymer is an addition coDolymer of one or more olefinically unsaturated acids or anhydrides, for example acrylic acid, ethacrylic acid. malεic acic, maleic anhydride, fumaric acid, itacomc acid or uaconic anhydride, vinyl benzoic acid (for exa ole o- vinyl benzoic acid), 3-butenoic acid or beta-carboxy-ethy acrylate cr methacry ate, with at least one olefinically unsaturated comonomer. Copolymers of methacry ic acid or acrylic acid are preferred. (The σrεferred eαuivalent weight cf 240 to 600 corresponds tc an acrylic acid content of 14.3 to 35.8 by weight and a methacrylic acid content of 16.7 to 41.7% by weight). The acid monomer is prefer¬ ably copolymeπsed with one cr mere comonomers which are unreactive with acid groups, for example acrylic or meth¬ acrylic esters such as methyl acrylate, methyl methacry- late, ethyl acrylate, butyl acrylate or 2-ethylhexy methacrylate, styrene, acrylonitrile, vinyl acetate, vinyl butyrate. vinyl chloride, or vinyl yridine. Terpclymers may be preferred, for example methyl methacrylate or ethyl methacrylate, whicn tend tc form a hard film, can be used in conjunction with an acrylate such as ethyl acrylate or particularly an alky! acrylate of 3 to 8 carbon atoms in the alkyl moiety such as butyl acrylate, which helps tc form a more flexible film. Such an acid polymer preferably has a molecular weight of 1,000 to 100,000. The eαuivalent weight of the acid polymer (calculated as acid groucs) is most preferably 300 to 440, equivalent to an acrylic acid or methacrylic acid content of about 20 to 30% by weight.

Alternative carboxylic acid-functional polymers are alkyd resins.

Alternative acid-functional polymers are polymers containing sulphcnic acid, phosphonic acid or phosphoric acid (acid phosphate) groups. If alternative acid groups are used they are also preferably present in an addition polymer, for example an addition copolymer of an olefini-

cally unsaturated phosphonic, phosphoric or sulphonic acid. Examples of such unsaturated acids are vinyl phosphcnic acid, styrene phosphonic acid, 2-acrylamidopropane phos¬ phonic acid, ethyl idene-1 , 1-diphosphonic acid, hydroxy- ethyl acrylate monophosphate, vinyl sulphonic acid, 2- acrylamido-2-methylpropane sulphonic acid, methallyl sulphonic acid and styrene sulphonic acid. Polymers containing stronger acid groups such as sulphonic acid groups may have a higher equivalent weight, for example in the range 500 to 5000, preferably 1000 to 2000.

The monobasic organic acid residue R which is incor¬ porated in the hydrolysable resin is preferably selected from:

S 0 0 S iι -S-C ^,( -R1 ¹ -0- ¹ C ¹ -R1' -S-C-R -0-C "-R1 ^π -0-R ^■ S-R and

wherein R represents a monovalent organic residue linked through a carbon atom. The group R can alternatively represent an amino group.

When the process of EP-A-342276 is used, the metallic salt which is reacted with the base resin and the high- boiling acid is a salt of the metal M and a low-boiling organic acid such as acetic acid or propionic acid. The high-boiling acid RH , whose residue R is incorporated in the hydrolysable resin, preferably has a boiling point at least 20°C higher than that of the low-boiling organic acid. The high-boiling acid RH can be a carboxyl ic, sulphonic, thiocarboxyl ic, thionocarboxyl ic, carbamic, thiocarbamic, thionocarbamic, dithiocarboxyl ic or dithio- carbamic acid. The acid RH is preferably a carboxyl ic acid, most preferably an aliphatic carboxyl ic acid having

at least 8, for example 12 to 20. carbon atoms, for examDle lauπc, stearic, oleic, linoleic. ricinoleic or 12- hydroxystearic acid: alternative carboxylic acids include benzoic, salicylic, ni robenzoic. chloroacetic, dichloro- acetic or chlorobenzoic acic. The acid can be a mixture of carboxyl ic acids such as the mixed aliphatic carboxyl ic acids sold as naphthenic acic or versatic acid, or a mixture of acids derived from a natural fat or oil. Alternative acids include toluenesulphonic, beta-naoh- thalenesulohonic, o-chlorobenzenesulohonic, di ethyldithio- carbamic and diethyldi hiocarbaππc acid.

The base resin, metallic salt and high-boiling acid are generally reacted at a temperature above the boiling point of the low-boiling acid but below the boiling point of the high-boiling acic to fcr the hydrolysable resin. The reaction is preferably carried out in an organic solvent, for examole a hydrocarbon such as xylene or tri ethylbenzene, a ketone such as methyl isoamyl ketone or an ester such as butyl acetate. ethoxyethyl acetate or methoxypropyl acetate.

The amine used in the coating composition is substan¬ tially non-volatile at ambient temperature (20°C) and standard pressure. Preferably, it has a boiling point of at least 200°C, most preferably at least 250°C. The amine is preferably a monoamine and is preferably a primary amine, although a secondary or tertiary amine can be used. The amine preferably includes at least one organic group containing at least 10 carbon atoms, more preferably 12 to 20 carbon atoms. Such amines generally have the advantage that they are toxic to marine organisms. The amine can for examole be a diteroene-derived amine of the formula:

where R is a onovalent hydrocarbon group derived from a diterpene and R 2 and R3 are each independently hydrogen, an alky! group having 1 to 18 caroon atoms or an aryl group

naving 6 to 12 carbon atoms. 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 examole an N-methyl or N,N-cimethyl derivative cf Rosin Amine D, can al ernatively be used. The diterpene amines are effective marine biocides. The amine can alternatively be an ali¬ phatic amine containing an organic group of 12 to 20 carbon atoms, for example a straight-chain alkyl cr alkenyl primary amine such as dodecyl amine. hexadecyl amine, octadecyl amine or oleyl amine or mixtures of amines derived from aliphatic groups present in natural fats and oils such as tallow amine or hydrogenated tallow amine or coconut amine (coco-ami ne) or a corresponding secondary amine or tertiary amine such as N-methyl dodecyl amine or N,N-dimethyl coco-amine. The long chain aliphatic amines having 12 to 16 carbon atoms are very effective marine biocides. Alternative amines which can be used are aral kylami nes such as those sold commercially as "phen- alkamines", or hvdroxv-substituted amines such ethanolamine or diethanolamine,

The antifouling coating composition is preferably applied as a solution in an organic solvent, for example a hydrocarbon such as xylene or white spirit, a ketone such as methyl isobutyl ketone or methyl isoamyl ketone, an alcohol such as n-butanol , ethoxyethanol or methoxypropanol or an ester such as butyl acetate, ethoxy- ethvl acetate or methoxyorooyl acetate. When the hvdro-

lysable resin binder is prepared in an organic solvent the resin solution can be used directly in preparing the paint. It can optionally be diluted by further solvent, preferably selected from the solvents listed above.

The non-volatile amine has the advantage that it reduces the viscosity of solutions of the hydrolysable resin in organic solvents such as those listed above. The amine is believed tc react at least in part to form a co¬ ordination complex with the metal M in the hydrolysable resin. In the co-ordination complex the metal M may be co¬ ordinate!y bonded both to the amine as ligand and to an anion, for example a carboxylate anion, acting as organic acid residue R. For those metals which form coloured hydrolysable resin solutions complex formation can be seen by a colour change. Solutions of hydrolysable resin in which the metal M is copper, for example, are generally green in the absence of amine but change colour to blue when the amine is added. The amine can reduce the vis¬ cosity of the hydrolysable resin solution by a factor of up to 4. The amine can thus be used with hydrolysable resin solutions which without amine are too viscous to form the basis of a sprayable paint, that is hydrolysable resin solutions which have an increased resin content. For example, the amine can be added to hydrolysable resin solutions having a resin content of 30 to 35 per cent by volume to produce solutions whose viscosity is equal to that of hydrolysable resin solutions without amine having a resin content of 25 to 30 per cent by volume. Moreover, since the amine is non-volatile it also directly increases the non-volatile content of the coating composition. There has been recent pressure for the use of a reduced content of volatile organic solvent in various types of coating compositions.

The proportion of hydrolysable resin to amine in the coating composition is preferably from 98:2 to 10:90 by volume, most preferably from 90:10 to 30:70. Amines having

no film-forming properties are preferably used at no more than 40% based on the combined weight of polymer and amine, whereas film-forming amines such as the diterpene deriva¬ tives can be used at a higher proportion if desired. More than one amine can be used: for example a diterpene amine can be used with a long-chain aliphatic amine.

If an amine which is biocidal to marine organisms is used, the resulting coating composition comprising hydro¬ lysable resin and amine can be used as a clear antifouling varnish or can be pigmented. If the metal M in the hydro¬ lysable resin is a metal which is toxic to marine organ¬ isms, for example copper, it can augment the marine bio¬ cidal properties of the coating, although since the metal content of the hydrolysable resin is only for example 10 to 15% by weight its effect may not be large.

If a non-biocidal amine is used the coating composi¬ tion should contain a marine biocide. The coating prefer¬ ably contains a pigment, and the same material may function simultaneousl as a marine biocide and as a pigment if a biocidal pigment is used.

The amine is preferably pre-mixed with the hydrolys¬ able resin binder before addition of other components of the coating. The hydrolysable resin binder solution can alternatively be mixed simultaneously with the amine and with the pigment. For example, the hydrolysable resin solution and the amine can be mixed with pigment using conventional paint blending procedures to provide a com¬ position 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 100, most preferably 1 to 10, parts per million by weight, and is preferably a metalliferous pigment. The pigment is most preferably a copper or zinc compound, for example cuprous oxide, cuprous thiocyanate, zinc oxide, zinc dimethyl dithiocarbamate, zinc diethyl dithiocar-

bamate, cuprous ethylene bis( dithiocarbamate ) and zinc ethylene bis(dithiocarbamate) . These sparingly soluble pigments which are copper and zinc compounds are generally also marine biocides. The sparingly soluble metalliferous pigments produce water-soluble metal compounds or. reaction witn 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 bis(dithiocarbamate5 , which are highly effective biocidal pigments, can be mixed with zinc oxide, which is less effective as a biccide 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 by weight) such as titanium dioxide or ferric oxide or an organic pigment such as a ohthalccyanine pigment. Such highly insoluble pigments are preferably used at less than 40% by weight of the total pigment

The anti-fouling paint can also contain a ncn-rnetal- liferous biocide fcr marine organisms, for example tetra- methyl thiura disulphide, methylene bis(thiocyanate) , captan, a substituted isothiazolone, fcr example as des- cribed in GB-A-1575226, or 2-methylthιo-4-t-tuty!ammo-6- cyclopropy1amino-s-triazine.

The invention is illustrated by the following Examples:

Examples 1 to 4

A 28.9% by volume solution A in a 4:1 xyleπe:butanol mixture of a hydrolysable resin based on a methacrylic acid copolymer with acrylate and methacrylate esters, in which the pendent carboxylic groups derived from the methacrylic

acid had been converted to

groups, wherein R is derived from a high boiling ali- phatic carboxyl ic acid (naphthenic acid or similar), was mixed with Rosin Amine D in the proportions shown in Table 1 below. The ratio of mixing is quoted as a volume ratio of hydrolysable resin to Rosin Amine D on a dry weight basis. The green resin solution and colourless amine formed a blue solution, the blue colour being most intense at a mixing ratio of 40:60 (Example 3).

Table 1

Example No. Mixing Ratio Solids Content Viscosity % by volume in mPa s

(A) 100:0 28.9 240 1 80:20 33.7 90 2 60:40 40.4 90

3 40:60 50.4 190 4 20:80 67.0 190

As shown in Table 1, the addition of Rosin Amine D decreased the viscosity of the hydrolysable resin solution (Rosin Amine D is itself a viscous liquid resin of vis¬ cosity well above 1000 mPa s). The products of Examples 1 to 4 can be used as clear antifouling varnishes. Alterna- tively, they can be mixed with pigments, for example biocidal pigments known for use in antifouling paints such as cuprous oxide, cuprous thiocyanate or zinc ethylene bis(dithiocarbamate) .

Examples 5 to 12

The process of Examples 1 to 4 was repeated using two

different hydrolysable resin solutions, each being acrylic resins containing pendent groups of the form:

0 0 II H ι -C-0-Cu-O-C-R '

The viscosities after mixing are shown in Table 2. The hydrolysable resin solution B of Examples 5 to 8 had a solids content of 27.6% by volume and the solution C of Examples 9 to 12 a sol ds content of 29.5% by volume.

Examples 13 to 21

Hydrolysable resin solution (A, B or C above), pigment and Rosin Amine D were mixed by conventional paint mixing technology in a high-speed disperser to form paints of the compositions shown in Table 3 (amounts of ingredients in % by weight) .

The paints of Examples 13 to 21 were applied to primed steel panels and were immersed in seawater in an area rich n marine fouling. After 12 months' immersion they

resisted fouling by algae and animal fouling, whereas a non-toxic comparison panel showed heavy fouling.

The paints of Examples 19, 20 and 21 were applied as test patches below the waterline on the side of the hull of an oil tanker. After 11 months in service, mainly in tropical latitudes, the test patches were substantial y free from algal and animal fouling, whereas a neighbouring patch not coated with antifouling paint was heavily fouled.

Table 3

Example No. 13 1 15 16 17 18 19 20 21

Hydrolysable Resin Solution 21.52(A) 22.47(B) 22.99(C) 26.38(A) 24.23(B) 24.64(C) . 33.13(A) 34.12(B) 32.83(C)

Rosin Amine D 6.64 6.54 6.67

Chlorinated paraffin plasticiser

Cuprous Oxide 54.05 53.25 54.29

Titanium Dioxide

Red Iron Oxide 4.16 4.10 4.18

Structuring Agents (bentonite, 1.74 2.04 2.04 1.98 2.01 2.01 2.02 2.00 2.03 clay and silica)

Methyl isobutyl ketone

Xylene

Volume ratio of hydrolysable resin to amine

% solids content by volume

Paint viscosity (poise)