GB2214921A

GB2214921A - Self-polishing antifouling paints

Info

Publication number: GB2214921A
Application number: GB8803948A
Authority: GB
Inventors: Jozef Verborgt; Der Poel Hendrik Van; Peter Haak; Jozef Braeken; Jean-Paul Dekerk
Original assignee: Labofina SA
Current assignee: Labofina SA
Priority date: 1988-02-19
Filing date: 1988-02-19
Publication date: 1989-09-13
Anticipated expiration: 2008-02-19
Also published as: GB2214921B; RU2145618C1; GB8803948D0

Abstract

Marine paint compositions of a new type are disclosed, which may be prepared free of organotin, giving self-polishing and antifouling coatings. They comprise (i) one or more sparingly soluble metal salts of a saturated, branched-chain or alicyclic, fatty acid having from 6 to 12 carbon atoms, (ii) a copolymer of monomer A which is selected from cyclic tertiary amides or imides having an alkenyl group, acrylic ester comonomer B, and comonomer 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 (iii), and optionally (c) one or more highly insoluble pigments.

Description

SELF-POLISHING ANTI FOULING PAINTS The invention relates to new anti fouling (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 example, 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 sparingly-soluble metal salts of a saturated fatty acid having from 6 to 12 carbon atoms, selected from branched-chain acids, alicyclic acids, or mixtures thereof; (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 > (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 said metal salt of a fatty acid to the polymer being from 1:50 to 1:1; (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 very slowly dissolving metal salt. Although not wishing to be bound by theory, it is believed that this may be due to an interaction between salt and the N-CO parts on the copolymer.

The compositions of the invention contain one or more sparingly soluble metal salts of a saturated fatty acid having from 6 to 12 carbon atoms, preferably from 8 to 11 carbon atoms, selected from branched-chain acids, alicyclic acids, or mixtures thereof. The expression "sparingly soluble" is known in the art of marine paint (see e.g. U.S. Patent No. 4,407,997), where it characterizes some of the compounds usually defined as water-insoluble, as opposed to highly insoluble ones. As metal salt, there is generally used a transition metal salt, preferably selected from zinc, copper, cobalt or zirconium salts, or mixtures thereof, more preferably a zinc and/or a copper salt. These metal salts often contain a low percentage of the corresponding acids as one of the impurities.As examples of branched chain acids, there may be cited single-branched acids, among which 2-ethylhexanoic acid is preferred, or preferably tertiary acids. As examples of alicyclic acids, there may be cited the naphthenic acids, which are a mixture of acids of which the structure is predominantly a cyclopentane ring with the carbonyl group at the end of an alkyl side-chain.

It is known that reactions may occur within the paint, for example partial metathesis can occur between metal salts of fatty acids 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 40 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 and/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 70-140 0C.

The weight ratio of the metal salt of a fatty acid to the binder is from 1:50 to 1:1, preferably from 1:20 to 2:3.

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.

The 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 zinc 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 terolvmer A copolymer was produced by gradually adding over a period of about five hours 12.7 kg of methyl methacrylate (MMA), 0.7 kg of methacrylic acid (MA), 13.3 kg of butyl acrylate (BA) and 1 kg of tert-butyl peroxybenzoate (TBP) to a solution of 10.0 kg of vinylpyrrolidone (VP), 6.3 kg MMA, 6.7 kg BA and 0.3 kg MA in a mixture of 28.6 kg of xylene and 12.3 kg of n-butanol heated at 1050C while stirring.

After about 12 hours heating, no further polymerisation was observed by monitoring residual monomers by gas 0 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 2.7 kg of n-butanol and 6.4 kg of xylene to obtain an approximately 50 wt % solution of polymer in xylene/n-butanol.

b. Preparation of the saint comcosition 88 parts by weight (pbw) of the polymer solution were mixed with 11 pbw of zinc Siccatol (Trade Mark of AKZO Chemie for a zinc salt of saturated branched-chain synthetic fatty acids, having a zinc content of 10%), then blended with 177 pbw of cuprous oxide, 58 pbw of zinc oxide, 3 pbw of bentonite (as anti-settling agent), 30 pbw of chalk, 40 pbw of isobutylalcohol, and a further 80 pbw of xylene.

c. Evaluation of the self-polishina properties The antifouling 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 m dry film thickness layer of a commercially 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 rum 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 20 C. The circumferential speed of the disc was about 19 knots (35 km/h).

Thickness measurements were made after seven days conditioning, then 91 days thereafter, on 10 different places at 9 cm from the disc's centre. The average erosion rate was 6 m/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 91 days after the conditioning of the first plate. The eroded coating was slightly smoother than the reference coating.

d. 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 6 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 68 pbw of a polymer solution prepared as in Example l(a) were mixed with 37 pbw of copper naphtenate, then blended with 177 pbw of cuprous oxide, 17 pbw of zinc ethylene dithiocarbamate, 3 pbw of bentonite, 30 pbw of chalk, 40 pbw of isobutylalcohol, and a further 80 pbw of xylene.

All properties were evaluated as described in Example 1.

The average erosion rate was of 5/4m/month; the eroded coating was slightly smoother than the reference coating.

The antifouling properties were as good as those observed in Example 1.

Claims

CLAIMS:

1. Marine paint composition comprising: (i) one or more sparingly-soluble metal salts of a saturated fatty acid having from 6 to 12 carbon atoms, selected from branched-chain acids, alicyclic acids, or mixtures thereof; (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 said metal salt of a fatty acid to the polymer being from 1:50 to 1:1; (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 metal salt is a salt of a transition metal, preferably selected from zinc, copper, cobalt or zirconium.

4. Paint according to any one of Claims 1 to 3, wherein the metal salt is a zinc and/or a copper salt.

5. Paint according to any one of Claims 1 to 4, wherein the saturated fatty acid has from 8 to 11 carbon atoms.

6. Paint according to any one of Claims 1 to 5, wherein the saturated fatty acid is selected from branched-chain acids.

7. Paint according to any one of Claims 1 to 5, wherein the saturated fatty acid is selected from alicyclic acids.

8. Paint according to Claim 7, wherein naphthenic acids are used as saturated fatty acids.

9. Paint according to any one of Claims 1 to 8, wherein monomer A is selected from cyclic tertiary amides having a vinyl or alkenyl function or mixtures thereof.

10. Paint according to any one of Claims 1 to 8, wherein monomer A is selected from N-vinyl pyrrolidone, N-vinyl piperidone, N-vinyl caprolactam, or mixtures thereof.

11. Paint according to any one of Claims 1 to 10, wherein monomer A represents 15 to 30 wt % of the monomer composition.

12. Paint according to any one of Claims 1 to 11, wherein monomer B is butyl acrylate.

13. Paint according to any one of Claims 1 to 12, wherein monomer B represents from 15 to 40 wt % of the monomer composition.

14. Paint according to any one of Claims 1 to 13, wherein comonomer C is selected from C1 - C4 alkyl methacrylates or mixtures thereof.

15. Paint according to any one of Claims 1 to 14, wherein comonomer C is methyl methacrylate.

16. Paint according to any one of Claims 1 to 15, wherein the weight ratio of (i) : (ii) is of from 1:20 to 2:3.

17. Paint according to any one of Claims 1 to 16, wherein the copolymer contains up to 5 wt % of acrylic and/or methacrylic acid instead of the corresponding ester.

18. Paint according to any one of Claims 1 to 17, wherein the sparingly soluble metalliferous pigment is selected from zinc oxide, cuprous oxide, cuprous thiocyanate or mixtures thereof.

19. Paint according to any one of Claims 1 to 18, 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.

20. A marine paint composition substantially as described in any one of the foregoing Examples 1 or 2.