GB2029831A - Triorganotin Salts and their use in Improved Ablative Antifouling Compositions - Google Patents

Abstract

The invention provides a monomeric or oligomeric triorganotin salt of a polyfunctional organic acid of the general formula: R(X)x(A)a where R represents an aliphatic, aromatic or aliphatic-aromatic hydrocarbon radical; X represents an acid radical; A represent an active hydrogen- containing radical capable of reaction with an isocyanate; and x and a which may be the same or different, are each an integer of at least 1. The triorganotin salt optionally being pre-reacted with a low molecular weight polyol. Such a triorganotin salt is combined with a functional isocyanate and optionally a biocidal agent to provide an antifouling composition which releases biocide and ablates.

Description

SPECIFICATION Improved Ablative Antifouling Compositione This invention relates to improved ablative antifouling compositions comprising new triorganotin salts of polyfunctional organic acids. The invention is more particularly concerned with the wetted area of ships' hulls and other immersed structures for which long term protection against marine fouling is desired.

The reason for seeking antifouling protection on powered vessels and on static structures are different; in the case of vessels, the important factor is the roughening of the surface caused by the adherent fouling organisms, and indeed the roughness of the surfaces itself, which, acting so as to increase the frictional component of drag on the vessel, results in either a slowing of the vessel or an increase in power required to maintain speed.In the case of static structures two factors are of important: (i) increased drag on the structure due to the waves and currents increases the stresses on the structure and adversely affects its stability, and (ii) the presence of biological fouling on the surface makes it difficult to inspect, and difficult to measure corrosion and to detect defects in the structure.

This is obviously of particular importance in offshore oil and gas installations. In both cases however, long service of the system is being increasingiy demanded. Antifouling processes in the past have been designed for a maximum lifetime of up to two years; at present it is proposed to increase the permitted period between surveys on a vessel (for the purposes of insurance) to five years; and in the near future vessels may be designed and built with the invention of never docking. Fixed offshore structures clearly cannot be docked for repair and maintenance, in the conventional sense at least, and they must be built with an envisaged service life of 25-30 years.Not only is the present generation of antifouling processes inadequate for such long term duty, but there are several limitations, both in theory and practice, which make it both pointless and uneconomic to pursue conventional techniques further.

Almost all antifouling compositions in the current art come into the category of "non-convertible coatings" (O.C.C.A. Paint Tech. F'ianuai Volume 1 defines this term), i.e. they are solutions of polymers or mixtures of polymers, plasticisers, pigments and fillers, which dry by solvent evaporation and contain biocides or mixtures of biocides. 'vA/hen films of these materials, and structures coated with them are immersed in sea-water, the biocidal materials are leached from the film at a rate sufficient to kill and/or repel the larvea and spores of fouling organisms. Compositions of this sort suffer from several handicaps: (i) Being based on high polymers (such as vinyl resins e.g.Vinyl VAGH (Trade Mark) manufactured by Union Carbide, or chlorinated rubber resins (e.g. Alloprene R10 (Trade Mark) manufactured by I.C.I.), they require large amounts of expensive and hazardous solvents to reduce their viscosity to a value suitable for application; (ii) Because of the amount of solvent required in these compositions, the limit on the volume solids (i.e. the volume fraction of the material applied which remains after volatilisation of the solvent) is low. For example, a vinyl antifouling composition would have a solids volume e of only 30 to 35%, requiring a wet film thickness of 285-333 microns for every 100 microns of dry film required.

Similarly, for a.chlorinated rubber-based antifouling composition it would be unusual to achieve a volume solids content in excess of 50%, requiring 200 microns of wet film thickness for every 100 microns of dry film required: (iii) Even the best of current "state of the art" antifouling compositions, however, have an intrinsic defect which iimits their potential as "long-life" compositions, and this is that water-insoluble resin and pigment components, such as vinyl and chlorinated rubber, persist on the surface of the antifouling composition of the biocides leach, and do in fact become the rate-determining step in the leaching.The process is thus self-limiting, and the application (beyond a certain point) of further coats of composition does not result in any increase in lifetime for the system.

Various proposals have been made for the amelioration of this state of affairs; the preferred current approaches can be conveniently summarised as follows: I. The "reactivating" approach. This method recognises the selflimiting nature of the superficial matrix layer, and proposes, by scrubbing a vessel or installation underwater, to remove it at regular intervals. The defects from which the method suffers, however, are: (i) that it is only the antifouling system, known in which it is proposed to scrub the vessel even when clean, and (ii) the low volume solids of the coating (approximately 33%) requires a multiplicity of coats to achieve a long service life.

II. The controlled diffusion approach. This method proposes to extend the lifetime of an antifouling system by superimposing a hydrophilic diffusion membrane over a high performance antifouling system, so that the leaching of the biocides approaches linearity more closely than in the conventional materials. The limitations of this system are as before: (i) a low volume solids, (ii) a multiplicity of coats, and (iii) the problems associated either with the removal of the hydrophilic varnish or its overcoating.

Ill. The self-pollshing approach. In this proposal, the trialEnyl tin salts of polymeric vinyl carbolic resins have been claimed to give long life antifouling systems. They are based on the observation that the tributyl tin copolymer resins hydrolyse in sea-water (pH 8-8.2) to give water-soluble components and that films variously pigmented with biocides, under the influence of turbulent flow, are ablated or polished at a steady rate.This overcomes the problem of matrix inhibition, but these compositions are also non-convertible coatings of low volume solids content (approximately 37.5%), requiring multiple coats to achieve adequate film thickness, with long drying periods, and are thus extremely expensive processes.

In this invention we have sought to provide anti-fouling compositions which can be applied at high volume solids and yet which have long service life.

The invention provides a monomeric oligomeric triorganotin salt of a polyfunctional organic acid of the general formula: R(X)X(A)e where R represents an aliphatic, aromatic or aliphatic-aromatic hydrocarbon radical; X represents an acid radical; A represents an active hydrogen-containing radical capable of reaction with an isocyanate; and x and a, which may be the same or different, are each an integer of at least 1, The triorganotin salt optionally being pre-reacted with a low molecular weight polyol.

The monomeric or oligomeric triorganotin salt is preferably derived from a polyfunctional organic acid of the general formula: R(X)x(Y)y(Z)z where R represents an aliphatic, aromatic or aliphatic-aromatic hydrocarbon radical; X represents a carboxylic, thiocarboxylic, dithiocarboxylic, sulphonic or phosphoric acid radical; Y represents a hydroxy (OH) or mercaptan (SH) radical; Z represents a primary amino (-NH2), secondary amino (-NHR' where R' is an alkyl or aryl grntlp) or amido (-CONH2) radical; x is an integer of at least 1; y and z are each 0 or an integer of at least 1, provided that y and z are not both 0.

The triorganotin salts according to the invention can be prepared, for example, by reacting a triorganotin compound (e.g. the oxide or hydroxide) with the organic acid, or by reacting a triorganotin halide with a metallic salt of the organic acid.

The invention also provides an antifouling composition comprising: (i) a functional isocyanate, and (ii) a triorganotin salt as defined above, the triorganotin salt optionally being pre-reacted with a low molecular weight polyol.

The isocyanate is preferably di-functional. This produces linear polymers, giving films which both leach biocide and ablate. Suitable di-functional isocyanates are, for example, isophorone di-isocyanate and diphenyl-methane-4,4'-di-isocyanate.

According to the invention, the antifouling composition is suitable for use in a finish coat for ships' hulls or submarine installations.

The antifouling composition preferably also comprises: (iii) at least one biocidal, substantially water-insoluble compound which may be inorganic, organo-metallic or organic; and/or (iv) at least one diluent resin, plasticiser, accelerator and/or suspending agent such as those normally used in the art to provide the necessary viscosity, stability and application properties.

The crosslinking of hydroxyl or amino groups of monomeric or oligomeric precursors by isocyanates of mono di- or polyfunctionality is a reaction well known in the art, and may be represented as follows:-

0 II R1OH + R2NCOo R1-O-N-C-R2 Hydroxy Isocyanate I H Urethane R,NH2 + R,NC6 R1--NN--CC-N-R, Amine Iso-cyanate I II I HOH Substituted Urea Where both components are polyfunctional, resinous or elastomeric products result, which are noted for their hardness, abrasion and chemical resistance.The tributyl tin salts of polycarboxylic polyhydroxyl acids can likewise be crosslinked with mono and polyfunctional isocyantes to produce tough, hard and adherent coatings; the general chemistry of the composition can be suitably exemplified by the reaction of, say, the tributyl tin salt of dl, or ditartaric acid,

and the commercial isocyanate Desmodur N (a Trade Mark of the Bayer Company), a trifunctional isocyanate with the formula:

Suitable functional acids for the production of the organotin salts are lactic acid, tartronic acid (hydroxy malonic acid), malic acid (hydroxysuccinic acid), tartaric acid (dihydroxy succinic acid) citric acid, salicylic acid (o-hydroxy-benzoic acid) and 5,5'-methylene disalicylic acid.

Suitable examples of amino acids are aspartic acid, (amino-succinic acid), glutamic acid and acids of mixed functionality such as hydroxyglutamic acid.

Suitable biocidal organotin compounds with which the polyfunctional acids can be reacted are organotin compounds of the general formula R1R2R3SnX, in which R1, R2 and R3 may be the same or different and represent aliphatic or aromatic hydrocarbon radicals (preferably C1-C6 alkyl or phenyl) and X represents an oxide or hydroxide radical, for example: tripropyl tin oxide, tributyl tin oxide, triphenyl tin hydroxide, tricyclohexyl tin hydroxide, and dibutyl cyclohexyl tin hydroxide.

An alternative method of forming the salts is to react together compounds of the general formula R1R2R3SnX in which R1, R2 and R3 are as defined above, and X is a halogen, normally chlorine, with a metallic salt of the polyfunctional acid, for example R.COOM/n where M is a mono- di- or trivalent metal (n=valency), and which may conveniently, be sodium yielding the required salt and an organicinsoluble metallic halide.

The salts used in this invention have been found to be either liquid or low melting solids, readily mixable with, or soluble in, a wide range of hydrocarbon, ketone or ester solvents or mixtures of these, to yield low viscosity liquids, and also to be compatible with a wide range of plasticisers such as phthalates, phosphates, chlorinated paraffins, chlorinated diphenyls, citrates and the like.

It is also envisaged as part of the invention that the triorganotin salts can be premixed or prereacted with diluting resins with hydroxy functionality such as hydroxypolyethers (e.g. Lankro Propylane D402, D702, D1002, D2002, D2122, or Desmophen 250U) or polyesters (e.g. Bayer Desmophen 650 or Desmophen 850).

These modifications can be made to alter the cross-link density, improve adhesion and flexibility, and to alter the hydrophilic/hydrophobic balance of the polymer so as to control the rate of ablation of the coating. The rate of ablation may also be modified by changing the curing ratio from the 1:1 stoichiometry of OH:-N=C=O required for ideal curing, or by the choice of, or the amount of plasticiser. The molar ratio of active hydrogen atoms to isocyanate groups is preferably from 1:3 to 3:1, more preferably from 1:2 to 2:1, and especially from 1:1.5 to 1.5:1.

It is well known in the art that the biocidal properties of the organotin compounds, taken singly, do not generally provide efficiently the necessary complete spectrum of antifouling activity. Provision is therefore made in a preferred embodiment of the invention for the inclusion of either additional "free" or unbound organotin compounds, or the addition of suitable amounts of the customary antifouling biocides, such as tributyl tin oxide, tripropyl tin oxide, triphenyl tin hydroxide, triphenyl tin fluoride, tricyclohexyl tin hydroxide, tributyl tin stearate, tributyl tin dibromosuccinate, tributyl tin tetrachlorophthalate, tributyl tin dimethyldithiocarbamate, tetramethyl thiurium disulphide, trichloromethylthiophthalimide (Captan), D.D.T., cuprous thiocyanate, cuprous oxide, cupric hydroxide, basic copper carbonate, copper acetoarsenite, copper metal, alloys of copper and zinc (brass), alloys of copper and other metals such as Cu:Ni 90:10), zinc metal, zinc oxide, organometallic biocides such as R.HgX where R is aliphatic, aromatic, alicyiic or substituted aliphatic, aromatic or alicylic, and X is a radical of an organic or inorganic acid; organic arsenical compounds such as 10.10' oxybis- phenoxarsine oxide, or phenarsazine oxide.

The invention also allows for the inclusion of such fillers, suspending agents, thixotropss or colouring pigments as are recuired to give the necessary application properties of the finished material.

The methods of application are those normal to the trade. Although it is recognised that application by brush and roller is unlikely, this is possible on small areas. The preferred method of application is by airless spray: 2-component airless spray in which the components are mixed immediately before atomisation, and hot airless spray, in which the two components are pre-hested to reduce application viscosity before atomisation. In this way the potential of the invention for providing a means for rapid curing of high-build antifouling coatings can be most readily exploited.

The following Examples illustrate the invention.

Example 1 A. hydroxy-functional triorganotin carboxylate is formed by heating together Tributyl Tin Oxide 1 Mole 595 grams 5,5'-Methylene disalicyclic Acid 1 Mole 288 grams under reflux as a 75% solide in xylene, collecting the evolved water (1 mole, 18 grams), and drying the product ova calcium sulphate. The resulting solution has a viscosity of 1.00 poidse (determined on an I.C.I. cons and plats viscometer at 25 C).

Example 2 r'n antifouling paint was made by grinding the following ingredients in a ball mill:- Component A Medium as in Example 1 10b grams Cuprous Oxide 285 grams Zinc Oxide 25 grams Thixatrol (Trade Mark, Baker Castor Oil) 2.5 grams Sylodex A24 (Trade Mark, Grace) 2.5 grams Tributyl Tin Oxide 2.5 grams Methyl isobutyl Ketone 20.5 grams followed by reacting with Component B Isophorone Di-isocyanate 19.5 grams The above paint, when mixed in the above proportions, has a volume solids of 70% and a viscosity of 2 poise (determined on an l.C.I. cone and plate viscometer at 250C.

The above paint was mixed in the above proportions to give a product which was applied to a rotor disc and cured for 36 hours. After immersion in running sea water for 1 month it gave a film which both leached biocide and in which ablation of the film took place.

Claims (10)

Claime

1. A monomeric or oligomeric triorganotin salt of a polyfunctional organic acid of the general formula: R(X)g(A)a where R represents an aiiphatic, aromatic or aliphatic-aromatic hydrocarbon radical; X represents an acid radical; A represents an active hydrogen-containing radical capable of reaction with an isocyanate: and ;:'and a, which may be the same or different, are each an integer of ar least 1, The triorganotin salt optionally being pre-reacked with a low molecular weight polyol.

2. A triorganotin salt as claimed in Claim 1, wherein the polyfunctional organic acid has the general formula: R(X)x(Y)y(Z)z where R represents an aliphatic, aromatic or aliphatic-aromatic hydrocarbon radical: X represents a carboxylic, thiocarboxylic, dithio-carboxylic, sulphonic or phosphoric acid radical; V represents a hydroxy (OH) or mercaptan (SH) radical; Z represents a primary amino (-NH2), secondary amino (-NHR' where R' is an alkyl or aryl group) or amido (-CONH2) radical; xis an integer of at least 1; and y and z are each 0 or an integer of at least 1, provided that y and z are not both 0.

3. A triorganotin salt as claimed in Claim 1 or 2, wherein the triorganotin radical has the formula R1R2R3Sn, in which each of R1, R2 and R3 independently is a C1-C6 alkyl or a phenyl radical.

4. A triorganotin salt as claimed in Claim 1, substantially as hereinbefore described with reference to any of the Examples.

5. A process for preparing a triorganotin salt as claimed in Claim 1, which comprises reacting a triorganotin compound with the organic acid, or reacting a triorganotin halide with a metallic salt of the organic acid.

6. A process as claimed in Claim 5, substantially as hereinbefore described with reference to any of the Examples.

7. A triorganotin salt when prepared by a process as claimed in Claim 5 or 6.

8. An antifouling composition, comprising: (i) a functional isocyanate, and (ii) a triorganotin salt as claimed in any one of Claims 1 to 4 and 7, the triorganotin salt optionally being pre-reacted with a low molecular weight polyol.

9. An antifouling composition as claimed in Claim 8, also comprising: (iii) at least one biocidal, substantially water-insoluble, inorganic, organo-metallic or organic compound; and/or (iv) at least one diluent resin, plasticiser, accelerator and/or suspending agent.

10. An antifouling composition substantially as hereinbefore described with reference to any of the Examples.