GB2204046A - Self-polishing antifouling paints - Google Patents

Abstract

Marine self-polishing anti-fouling paint compositions, which may be free of organotin, comprise (i) one or more rosin-based component, preferably selected from rosin or its copper or zinc derivatives, (ii) a copolymer of monomers A which are cyclic tertiary amides or imides having an alkenyl group, acrylic comonomers B, and comonomers C selected from C1-C4 alkyl methacrylates and/or styrene, (iii) at least one sparingly soluble metalliferous pigment, (iv) at least one marine biocide which may be identical to the pigment, and optionally (c) one or more highly insoluble pigment.

Description

SELF-POLISHING ANTIFOULING PAINTS The invention relates to new antifouling (AF) marine paint compositions, which may be prepared totally free of organotin and which give coatings having self-polishing properties.

Self-polishing antifouling coatings are known to the art.

They gradually dissolve so that (i) a fresh anti-fouling paint surface is continuously revealed, and (ii) moving seawater smoothes the surface of the coating. British Patent 1,124,297 disclosed a film-forming copolymer containing a triorganotin comonomer which gives self-polishing antifouling coatings.

The known self-polishing antifouling paints use binders which are linear polymers containing side groups (also called leaving groups) which are liberated from the polymer by reaction with seawater, the residual polymer being sufficiently dispersible or soluble to be swept away from the paint surface, exposing a fresh layer of the binder able to undergo a similar reaction with seawater.

Coatings from such self-polishing paints retain their initial smoothness and may even become smoother from the action of relatively moving water.

The gradual thinning of the paint film controls the release of a biocide active against fouling, present as a pigment in the paint and/or released as a leaving group.

Thus, the biocide contained in the paint tends to be delivered from the surface at a relatively constant rate.

Most self-polishing paints employ binders which comprise triorganotin ester leaving groups. The triorganotin ester readily undergoes the hydrolysis on which the self-polishing action is dependent, and the triorganotin released provides a biocidal action. Examples of such paints may be found in British Patents 1,124,297 and 1,457,590, but also in European Patent Applications 51,930, 151,809 and 218,573, and Japanese Patent Application 231061/61 and 231062/61. British Patent Application 2,159,827 discloses similar paints with diorganotin leaving groups.

Many countries are introducing new stringent water quality programs, some of which call for a phased reduction in the organotin content of marine paints. There are also cost advantages in replacing the triorganotin comonomers. For exule, European Patent 69,559 discloses a copolymer prepared from quinolinyl esters of olefinincally unsaturated carboxylic acid with other olefinically unsaturated comonomers, and International Patent Application WO 84/02915 suggests a wide range of organic leaving groups for use in antifouling paint binders, but it has been said that these generally do not hydrolyse quickly enough in seawater. In European Patent Application 204,444, there is disclosed a binder which is an hydrolysable polymer prepared with a triaryl(methyl)methacrylate comonomer.However, it is known in the art that the esterification reactions are more difficult with all these comonomers than with triorganotin comonomers; therefore, the hydrolysis will be more difficult. This explains why a commercial development based on any of these copolymers is still awaited.

International Patent Application WO 86/02660 disclosed that certain polycarboxylic polymers, substantially non ionic, are changed by reaction with seawater into polycarboxylate polymers sufficiently dispersible or soluble, and may be used as binders for self-polishing AF paints. However, it is readily apparent that the resulting coatings swell when immersed. Also, these paints, which typically contain ZnO or cuprous oxide as the toxic agent, gel on storage.

There is therefore a need for organotin-free self-polishing antifouling marine paints which do not have these drawbacks.

The Applicant has found a new type of marine paint composition, which may be prepared without any organotin, giving self-polishing antifouling coatings.

The marine paint composition according to the invention comprises: (i) one or more rosin-based components; (ii) a polymer prepared by polymerisation of (a) from 5 to 40 wt % of at least one monomer A of general formula

wherein either R1 is an alkenyl group and R2 is selected from H and alkyl groups or R2 is an alkenyl group and R1 is selected from H and alkyl groups, R3 is selected from methylene and carhonyl, and n is an integer > / 1.

(b) from 5 to 45 wt % of at least one acrylic comonomer B, the total of A + B amounting to from 15 to 75 wt % of the monomer composition, and (c) the balance being from 25 to 85 wt % of at least one C1 - C4 alkyl methacrylate and/or styrene comonomer C; the weight ratio of the rosin-based component to the polymer being from 10:90 to 70:30; (iii) at least one sparingly soluble metalliferous pigment; and (iv) at least one marine biocide which may or may not be identical to the pigment.

The invention is based on a totally new concept, based upon the combination of a non-reactive binder with a slowly dissolving rosin-based component. Although not wishing to be bound by theory, it is believed that this may be due to an interaction between rosin and the N-CO parts on the copolymer.

The compositions of the invention contain rosin. It is really surprising that such compositions give self-polishing coatings, because the prior art teaches that rosin cannot be used in self-polishing paints. Known rosin-based antifouling paints may be divided in two groups according to the solubility of the matrix. It is alleged that soluble-matrix rosin-based paints erode in service to form a brittle matrix of spent rosin which, although it may be gradually washed from the hull surface by seawater, increases in roughness with time and has a very limited lifetime. On the other hand, insoluble matrix rosin-based paints contain some vinyl resin and a lot of sparingly soluble pigments to open the surface; when the pigment is gradually washed by seawater, the surface becomes rougher because the binder is not washed away.Rosin is a loosely used term, denoting the result of a harvesting of the gum exudations from surface cuts made in certain species of trees. Rosin is usually defined as the product obtained from pines; similar products include congo, damar, kauri and manila gums. Other processes for obtaining rosin include dissolving wood rosin from pine stumps after forests have been felled, or refining a by-product of the Kr aft paper manufacturing process to produce tall oil rosin.

Pine-originating rosin is preferably chosen, although similar products may be contemplated providing they have a similar hydrophilic/lipophilic balance.

The principal component (about 80 wt %) of rosin is abietic acid, also called sylvic acid (Chemical Abstracts Service Registry Number: 514-10-3), which could be used instead of rosin. The preferred rosin-based components are rosin itself, its copper or zinc derivatives, hereinafter called copper resinate and zinc resinate, other resinic salts having a comparable solubility, or mixtures thereof. The salts are prepared by any known method, typically by metathesis with the metal carbonate, hydroxide or hydroxycarbonate. In some cases, the transformation of abietic acid into salts thereof may upgrade properties like the melting point, hardness, durability, water or solvent resistance.

It is known that reactions may occur within the paint, for example abietic acid can partially react with other components of the paint like ZnO, Cu2O or tributyltin oxide, or partial metathesis can occur between metal resinates and other metal derivatives contained in the paint. The non-reactive binder is a polymer prepared by polymerisation of (a) from 5 to 40 wt % of at least one monomer A of general formula

wherein either R1 is an alkenyl group and R2 is selected from H and alkyl groups or R2 is an alkenyl group and R1 is selected from H and alkyl groups, R3 is selected from methylene and carbonyl, and n is an integer > 1.

(b) from 5 to 45 wt % of at least one acrylic comonomer B, the total of A + B amounting to from 15 to 75 wt % of the monomer composition, and (c) the balance being from 25 to 85 wt % of at least one C1 - C4 alkyl methacrylate and/or styrene comonomer C.

As monomer A, there may be used any monomer, or combination of monomers, as hereinbefore described.

Preferred monomers A are the cyclic tertiary amides having a vinyl or alkenyl function, the most preferred being N-vinylpyrrolidone, N-vinylpiperidone and N-vinylcaprolactam.

The monomers A represent from 5 to 40 wt % of the monomers, preferably from 15 to 30 wt %. If amounts greater than 40 wt % were used, the resulting coating would swell in the seawater, and hence it would have low mechanical properties. On the other hand, if amounts lower than 5 wt % were used, the resulting copolymer would not have the desired properties.

Comonomers B are well known in the film-forming art.

Preferred examples of acrylic monomers include methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, amyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, the most preferred being butyl acrylate.

The comonomers B represent from 5 to 45 wt % of the monomers, preferably from 15 to 30 wt %. When using higher amounts, the resulting coating is excessively soft and sensitive to mechanical damage.

The preferred comonomer C is methyl methacrylate.

The copolymer can contain up to 5 wt % of acrylic or methacrylic acid units, instead of the corresponding esters, although care must be taken to avoid gelation of the paint when using a copolymer containing free acid functions.

The binder can be prepared by addition polymerisation using a free radical catalyst, such as benzoyl peroxide, t-butyl peroxybenzoate, t-butyl peroxy 2-ethylhexanoate or azobis-isobutyronitrile, in an organic solvent such as xylene, toluene, butyl acetate, butanol, 2-ethoxy ethanol, cyclohexanone, 2-methoxy ethanol, 2-butoxy ethanol, methyl isobutyl ketone, methyl isoamyl ketone, (m)ethyl amyl ketone and/or 2-ethoxyethylacetate. The polymerisation may be carried out by heating all the ingredients in the solvent or preferably by gradually adding the monomers and catalyst to the heated solvent. A chain transfer agent such as a mercaptan can also be used to produce polymers of lower molecular weight. When xylene is used as the organic solvent, polymerisation is preferably carried out at a temperature in the range of 70-1400C.

The weight ratio of the rosin-based component to the binder is from 10:90 to 70:30, preferably from 20:80 to 60:40, most preferably from 25:75 to 50:50.

The paint composition according to the invention also comprises at least one sparingly soluble metalliferous pigment, and optionally one or more pigments which are highly insoluble in seawater and/or other biocides Xne metalliferous pigment sparingly soluble in seawater is exemplified by cuprous thiocyanate, cuprous oxide, zinc oxide, cupric acetate meta-arsenate, or zinc chromate.

The paint preferably includes at least one metalliferous pigment selected from zinc oxide, cuprous oxide and cuprous thiocyanate and pigments whose seawater solubility is similar to theirs. These pigments have a seawater solubility such that the pigment particles do not survive at the paint surface. The pigment has the effect of inducing the overall smoothing which the relatively-moving seawater exerts on the paint film, minimising localised erosion and preferentially removing excrescances formed during the application of the paint.Mixtures of sparingly soluble pigments can be used, the most preferred being a mixture of zinc oxide, which is most effective at inducing the gradual dissolution of the paint, with cuprous oxide and/or cuprous thiocyanate, which are more effective marine biocides, said mixture preferably comprising at least 25 wt % of cuprous oxide and/or thiocyanate, the balance being zinc oxide.

The paint composition can additionally contain a pigment which is highly insoluble in seawater, such as titanium dioxide or ferric oxide. Such highly insoluble pigments can be used at up to 40 percent by weight of the total pigment component of the paint. The highly insoluble pigment has the effect of retarding the dissolution of the paint.

The proportion of pigment to polymer is generally such as to give a pigment volume concentration of at least 25 percent, preferably at least 35 percent, in the dry paint film. The upper limit of pigment concentration is the critical pigment volume concentration. Paints having pigment volume concentrations of about 50 percent, for example, have been found very effective for smoothing in seawater and preventing fouling.

The paint can contain other biocides effective as antifouling agents. Examples of such biocides, are di-thiocarbamate derivatives such as zic dimethyl dithiocarbamate, zinc ethylene bis(dithiocarbamate), zinc diethyl dithiocarbamate, cuprous ethylene bis-di-thiocarbamate or 2-(N,N-dimethyl thiocarbamyl thio)-5- nitro thiazole, substituted isothiazolones particularly halogenated N-substituted isothiazolones, tetramethyl thiuram disulphide. Other known biocides include triorganotin derivatives such as tributyltin oxide, tributyltin fluoride or triphenyltin fluoride.

The invention is described further by the following examples which are intended to be illustrative and by no means limiting.

ExamPle 1 a. Preparation of the copper resinate 765 parts by weight (pbw) of rosin were dissolved in 275 pbw of white spirit, heated to about 130 0C, and 100 pbw of copper hydroxycarbonate were added while stirring. The temperature was increased under reflux to about 175 0C until the mixture clears the colour changes from green to light brown. After cooling, the mixture was diluted to about 70 wt % of dry matter by adding 75 pbw of isopropyl alcohol.

b. Preparation of the teroolymer A terpolymer was produced by gradually adding over a period of about five hours 16.7 kg of methyl methacrylate (MMA), 8.3 kg of butyl acrylate (BA) and 1 kg of tert-butyl peroxybanzoate (TBP) to a solution of 12.5 kg of vinyl pyrrolidone (VP), 8.3 kg MMA and 4.2 kg BA in 40.9 kg of xylene heated at 1150C while stirring.

After about 12 hours heating, no further polymerisation was observed by monitoring residual monomers by gas chromatography. The solution was then heated to 1300C for about one hour to destroy any residual activity of the catalyst. The product was cooled and diluted with 9.1 kg of xylene to obtain an approximately 50 wt % solution of polymer in xylene.

c. PreParation of the paint composition 4.37 pbw of the copper resinate solution were mixed with 8.53 pbw of the polymer solution, then blended with 30.96 pbw of cuprous oxide, 29.38 pbw of zinc oxide, 0.79 pbw of bentonite (as anti-settling agent), 2.18 pbw of isobutyl alcohol, and a further 23.79 of xylene.

d. Evaluation of the self-polishinq ProPerties The anti fouling paint thus obtained was tested for its self-polishing properties according to the following procedure. A steel disc of 20 cm diameter was first coated with a 220 Wm dry film thickness layer of a co-. m-rcially available anti-corrosive paint based on coal tar and epoxy resin. The antifouling paint was applied as a layer having a dry film thickness of about 120 wm within 48 hours from the time the anti-corrosive paint layer became dry to the touch. After drying, the disc was rotated in a tank filled with continuously renewed natural seawater at a temperature of 200C. The c rcum,ferential speed of the disc was about 19 knots (35 km/h).

Thickness measurements were made after seven days conditioning, then 294 days thereafter, on 10 different places at 9 cm from the disc's centre. The average erosion rate was 3.0 Wm/month.

For comparative purposes, a second steel disc was coated according to the same procedure as above, and conditioned during a period of seven days ending 294 days after the conitioning of the first plate. The eroded coating was slightly smoother than the reference coating.

e. Evaluation of the antifouling properties The paint thus obtained was also tested for antifouling activity by applying it to a plaque over a vinyl resins/ tar anti-corrosive paint, mounting the plaque on a panel and immersing the panel from a raft in an estuary off Southern Netherlands for 12 months. Each panel also included plaques coated with a non-toxic control (which became heavily fouled with seaweed and some animal life within 4 weeks).

No weed or animal fouling was observed on the panels coated with the paint of the invention, and the algal slime was practically non-existent.

ExamPle 2 Zinc resinate was prepared as an approximately 70 wt % so'-t o^. according to the prodcedure disclosed nn l(a), using the following proportions: - rosin 200 pbw - white spirit 72 pbw - zinc carbonate 27 pbw - isopropanol 19 pbw The terpolymer was prepared as described in Example l(b).

The paint composition was: - zinc resinate 4.38 pbw of the 70 wt % solution - terpolymer 8.56 pbw of the 50 wt % solution in xylene - cuprous oxide 31.07 pbw - zinc oxide 29.49 pbw - bentonite 0.79 pbw - additional xylene 21.72 pbw - isobutanol 2.19 pbw - isopropanol 0.38 pbw - additional white 1.42 pbw spirit All properties were evaluated as described in Example 1.

The average erosion rate was of 2.1 m/month. The eroded coating was slightly smoother than the reference coating.

The anti fouling properties were as good as those of the copper resinate-based coating.

Example 3 A paint was prepared with the following ingredients: - rosin (undissolved) 3.65 pbw - terpolymer (Example l(b)) 8.04 pbw of the 50 wt % solution in xylene - cuprous oxide 31.92 pbw - zinc oxide 30.30 pbw - bentonite 0.81 pbw - additional xylene 19.91 pbw - isobutanol 4.06 pbw The average erosion rate was of 3.8 m/month, and the smoothness of the eroded coating was unmodified.

Comparative Examples 1 and 2 A copolymer was prepared by gradually adding over a period of about four hours 460 g of MMA, 220 g of ethyl acrylate (EA) and 20 g of TBP to a solution of 220 g of MMA and 100 g of Era in 1 1 of xylene heated at 115 C while stirring.

After about 12 hours heating, no further polymerization was observed by monitoring residual monomers by gas chromatography. The solution was then heated to 130 C for about one hour to destroy any residual activity of the catalyst. The product was cooled and diluted with 130 g of xylene to obtain an approximately 50 wt gd solution of polymer in xylene.

Two paint compositions were prepared: - comparative example 1 : with copper resinate, as described in Example 1 (c), - comparative example 2 : with rosin as described i Example 3.

When evaluating the self-polishing properties according to the procedure of Example l(d), no erosion was observed.

This example shows that when the polymer does not satisfy the requirements of the present invention, the paint has no self-polishing properties (even though BA was replaced as comonomer by the more hydrophilic EA).

ComParative ExamPle 3 An anti fouling paint was prepared from - rosin 19.8 pbw - phenolic varnish, neutralized with CaO in a ball mill, used as plasticiser 6.6 pbw - calcium carbonate 19.0 pbw - cuprous oxide 27.0 pbw - solvents 23.6 pbw (toluene/white spirit 1:1) - additives 4.0 pbw The paint was prepared by first incorporating the calcium carbonate in the vehicle and ball milling during 24 hours. Cuprous oxide was then added and dispersed during three hours.

When evaluating the properties as described in Example 1, it was found that the surface had become rougher.

Further, after 11 months exposure to fouling, an important amount of algal slime was observed although macrofouling (barnacles, etc.) was rare.

Claims (15)

CLAIMS:

1. Marine paint composition comprising: (i) one or more rosin-based components; (ii) a polymer prepared by polymerisation of (a) from 5 to 40 wt % of at least one monomer A of general formula

wherein either R1 is an alkenyl group and R2 is selected from H and alkyl groups or R2 is an alkenyl group and R1 is selected from H and alkyl groups, R3 is selected from methylene and carbonyl, and n is an integer > 1.

(b) from 5 to 45 wt % of at least one acrylic comonomer B, the total of A + B amounting to from 15 to 75 wt % of the monomer composition, and (c) the balance being from 25 to 85 wt % of at least one C1 - C4 alkyl methacrylate and/or styrene comonomer C; the weight ratio of the rosin-based component to the polymer being from 10:90 to 70:30; (iii) at least one sparingly soluble metalliferous pigment; and (iv) at least one marine biocide which may or may not be identical to the pigment.

2. Paint according to Claim 1, additionally comprising, for up to 40 wt % of the total weight of the pigments, one or more pigments which is/are highly insoluble in seawater.

3. Paint according to Claim 1 or 2, wherein the rosin-based component is selected from rosin, copper resinate, zinc resinate, or mixtures thereof.

4. Paint according to any one of Claims 1 to 3, wherein monomer A is selected from cyclic tertiary amides having a vinyl or alkenyl function or mixtures thereof.

5. Paint according to any one of Claims 1 to 3, wherein monomer A is selected from N-vinyl pyrrolidone, N-vinyl piperidone, N-vinyl caprolactam, or mixtures thereof.

6. Paint according to any one of Claims 1 to 5, wherein monomer A represents 15 to 30 wt % of the monomer composition.

7. Paint according to any one of Claims 1 to 6, wherein monomer B is butyl acrylate.

8. Paint according to any one of Claims 1 to 7, wherein monomer B represents from 15 to 30 wt % of the monomer composition.

9. Paint according to any one of Claims 1 to 8, wherein comonomer C is selected from C1 - C4 alkyl methacrylates or mixtures thereof.

10. Paint according to any one of Claims 1 to 9, wherein comonomer C is methyl methacrylate.

11. Paint according to any one of Claims 1 to 10, wherein the weight ratio of a:b is from 20:80 to 60:40.

12. Paint according to any one of Claims 1 to 11, wherein the weight ratio of a:b is from 25:75 to 50:50.

13. Paint according to any one of Claims 1 to 12, wherein the sparingly soluble metalliferous pigment is selected from zinc oxide, cuprous oxide, cuprous thiocyanate or mixtures thereof.

14. Paint according to any one of Claims 1 to 13, wherein the sparingly soluble metalliferous pigment is a mixture comprising at least 25 wt % of cuprous oxide and/or thiocyanate, the balance being zinc oxide.

15. A marine paint composition substantially as described in any one of the foregoing Examples 1 to 3.