PAINT COMPOSITION

Abstract: A sea water-erodibel antifouling paint composition AFP for protecting marine surfaces, comprising a film-forming binder, >/= 10 percent (solids volume of the composition) of at least one sea water-soluble pigment ( >/= 1 mg/1), at least one antifouling agent which may be a pigment, the total pigment(s) constituting 10-60 percent (solids volume) and any sea water-insoluble pigments constituting </= 50 percent (solids volume); said binder comprising at least one water-insoluble polymer P1 of mw >/= 2 000 and which comprises segments (Ia), (Ib), (Ic), or (Id), wherein R1 and R2 each is hydrogen or C1-4 alkyl, A3, A4, A5, and A6 each is C1-4 alkylene or phenylene; a3, a4, a5, and a6 each is 0 or 1; and each group B<X> is a group D<X>, or a group -CO-O-D<X'> (B<1>), -CO-NH-D<X> (B<2>), -NH-CO-D<X> (B<3>), or -O-D<X> (B<4>), or the two groups B<X> in (Ic) or (Id) together constitute an imide group (B<5>), wherein D<X> is a group -(D1-O-)dD2, or a group -D3(D5)-O-D4, or a group D7; and D<X'> is a group -(D1-O-)dD2, or a group -D3(D5)-OH, wherein D1 is C1-4 alkylene, D2 is hydrogen or C1-4 alkyl; d is an integer from 2 to 300; D3 is C1-4 alkylene, optionally substituted phenylene or phenyl-C1-4alkyl; D4 is hydrogen or C1-4 alkyl; D5 is hydrogen, hydroxy or C1-4alkoxy, or, when D3 is C1-4 alkylene, -O-D4 and D5 together form C1-4 alkyleneoxy; and D7 is hydrogen or C1-4 alkyl; with the proviso that, in formula (Ia), when R1 is hydrogen, R2 is hydrogen or methyl, a3 is 0, B<X> is a group B<1>, and D3 is (CH2)1-4, then D4 is hydrogen, and that when D7 is hydrogen, then B<X> is a group B<4>; said binder and any other optional binders satisfying certain sea water erosion criteria, and the antifouling paint AFP having an erosion rate in sea water of 1-50 mu m per 10,000 nautical miles; with the proviso that AFP is free from compounds of tin, arsenic, lead, and mercury, and contains </= 8 percent (total solids volume) of hexachlorophene, tetrachloroisophthalonitrile, or 1,2,3-trichloro-4,6-dinitrobenzene in pigment form.

Description: PAINT COMPOSITION FIELD OF THE INVENTION The present invention relates to sea water-erodible an¬ tifouling paint compositions for protecting marine sur- faces, in particular for protecting water craft. BACKGROUND OF THE INVENTION For a number of years, intensive use has been made of sea water-erodible antifouling paint compositions in which the polymer of the binder is a trial yltin derivative of a polymer containing carboxylic acid groups in the monomer segments, the alkyltin groups being situated on the car¬ boxylic acid groups. The principle according to which such paints are erodible is that the carboxyl-alkyltin function slowly hydrolyzes in sea water, i.a. due to the slight alkalinity (pH ca. 8) of sea water. The result of the hydrolysis is partly that biocidal tin compounds are relea¬ sed, partly that the remaining polymer which now comprises free carboxylic acid groups becomes water erodible or soluble. Thus, the overall effect is that the outer layers of the paint coating on the ship's hull slowly dissolve or erode and thereby uncover deeper paint layers which are then eroded away in the same manner. However, the increasing problem of pollution with tin compounds in harbours as well as the emergence of antifoul- ing components not based on tin or other undesirable metals has lead to intensive research efforts to provide tin-free sea water-erodible antifouling paints. To a large extent, efforts have concentrated on finding other polymers that are capable of exploiting the same basic principle, namely that side groups on the polymer chain are hydrolyzed by the sea water which then causes the polymer to become water soluble and therefore to dissolve and to cause the paint coating to erode. Thus, WO 84/02915 describes marine paints of which it is claimed that they are erodible because the polymers in the paints hydrolyze in sea water although the only hydrolysis tests carried out are performed in a medium more alkaline than sea water, namely with a pH value of 9 and at a fairly high temperature, namely 35°C. Furthermore, the only other tests carried out on the paints were long-term tests of the antifouling properties on stationary fiberglass panels submerged at an ocean test site. Thus, no actual determina¬ tion of any erosion properties of the paint in sea water and when coated on to moving surfaces was carried out. It is the object of the present invention to provide a non-hydrolyzable sea water-erodible antifouling paint composition free of undesirable metals, in particular tin- free, for protecting surfaces of marine structures in order to reduce the fouling of such surfaces, in particular the outer surfaces of ships' hulls. A further object is to provide marine structures having an improved anti-fouling coating of a sea water-erodible, non- hydrolyzable free of undesirable metals, in particular tin- free, coating film. Still another object of the invention is to provide a method of operating a watercraft involving a first painting step in which a non-hydrolyzable, sea water-erodible an¬ tifouling paint composition free of undesirable metals, in particular tin-free, antifouling paint coating is applied to the part of the exterior of the craft which, during operation of the craft, is immersed in water, sailing the watercraft, and performing a second painting step with an erodible antifouling paint. SIJMARY OF * THE INVENTION It has been found that the above objects can be obtained by using coatings comprising film forming binders, which binders contain certain polymers which confer sea water erodibility to the binder where the sea water erodibility is not caused by hydrolysis of the polymers. Instead, it is believed that the erodibility is due to the polymers having a suitable hydrophilicity and conseguent water absorption properties in sea water which results in a poor mechanical strength of the outermost parts of a paint coating once sea water-soluble pigments therein have been leached out from those outermost parts, the mechanically weakened outer parts of the paint being removed by the action of sea water moving against the surface carrying the coating. Thus, the invention provides a sea water-erodible antifoul¬ ing paint composition AFP for protecting marine surfaces, comprising a film-forming binder, at least one pigment which is soluble in sea water in an amount of at least 1 mg/litre, at least one antifouling agent which may be the pigment or one of the pigments, the total pigment content of the composition being in the range of 10-60% of the solids volume of the paint composition, the sea water- soluble pigment or pigments constituting at least 10% of the solids volume of the paint composition, any sea water- insoluble pigments, when present, constituting at the most 50% of the solids volume of the paint composition, said binder comprising at least one polymer PI of a weight average molecular weight of at least 2000 which is water- insoluble and which comprises, as the sea water erodibili- ty-conferring segments, segments of the formula la, lb, Ic, or Id - (lb) - (Ic) (Id) )a3 wherein R- ^ and R2 each independently is hydrogen or ~_-4 alkyl, 3, A4, A5, and A 6 each independently is C-_-^ alkylene or phenylene, a3, a4, a5, and a6 each independently is 0 or 1 , and each group B x independently is a group D x , or a group B 1 , B 2 , B 3 , or B -CO-0-D x ' (B 1 ) -CO-NH-D x (B 2 ) -NH-CO-D x (B 3 ) -0-D x (B 4 ) or the two groups B x in (Ic) or (Id) together constitute an imide group B 5 0=C C=0 (B 5 ) \ / N D x wherein D x is a group - (D 1 -0-) f D 2 ; a group -D 3 -O-D 4 , or a group D 7 and D x ' is a group - (D 1 -0-) ζ -O 2 or a group 1 5 -D 3 -OH, wherein O- is C^^ alkylene, D 2 is hydrogen or C 1-4 alkyl, d is an integer from 2 to 300 D 3 is C;L_4 alkylene; phenylene optionally substituted with 1 or 2 C 1 _ 2 alkyl; or a phenyl-C 1 _ 4 alkyl moiety having the group D 5 attached to the phenyl ring, and having the free bond shown located on the phenyl ring and the group -0-D 4 attached to the alkyl part, or vice versa, the phenyl part option¬ ally being substituted with 1 or 2 substitu- ents selected independently from hydroxy and CL_4 alkoxy, D is hydrogen or alkyl, D5 is hydrogen, hydroxy or ^.-4 alkoxy, or, when D 3 is C - alkylene, -0-D 4 and D 5 together form C^_4 alkyleneoxy, and D 7 is hydrogen or C 1-4 alkyl, with the proviso that, when the polymer contains segments of the formula la, where R^ is hydrogen, R 2 is hydrogen or methyl, a3 is 0, B x is a group B 1 , and D 3 is (CH 2 ) 1 _ 4 , then D 4 is hydrogen, and that, when D is hydrogen, then B x is a group B 4 ; the kind and concentration of the segments la, lb, Ic, or Id in the polymer Pi being so selected that the polymer PI. when incorporated as the binder in a coating composition S_ of the following solids composition, stated as solids volume parts: 60 parts by volume of the polymer. 10 parts by volume of cuprous oxide with an average par¬ ticle size of 2-4 μ , 26 parts by volume of zinc oxide with an average particle size of approximately 0.2 μm, and 4 parts by volume of thixotropic bentonite results in an erosion rate of the coating in sea water with a salinity in the range of 37-38 parts per thousand of at least 1 μm per 10,000 nautical miles when the coating has been applied on and has been allowed to form a con- tinuous film on the convex surface of a cylinder of diame¬ ter 1 meter and the coated cylinder is rotated with a peripheral speed of 15 knots in sea water of a temperature between 10 and 30°C; whereby, when the film-forming binder comprises more than one polymer, each other polymer is either a polymer PI as defined above, a polymer P2 of a weight average molecular weight of at least 2000 which is water-insoluble and comprises segments of the formula la, lb, Ic, or Id as defined above, the kind and concentration of the segments la, lb, Ic, or Id and other segments in the polymer P2. being so selected that the polymer P2 . , when incorporated as the polymer in the coating composition S . as defined above, results in an erosion rate of the coating in sea water of less than 1 μm per 10,000 nautical miles when tested as defined above, or a film-forming polymer P3. of a weight average molecular weight of at least 2000 which does not comprise segments la, lb, Ic or Id, the polymer P3_, when incorporated as the binder in the coating composition S. as defined above, resulting in an erosion rate of the coating in sea water of less than 1 μm per 10,000 nautical miles when tested as defined above, or a polymer P4 . of a weight average molecular weight of at least 2000 which comprises sea water erodibility-conferring segments which are not segments la, lb, Ic or Id, the polymer P4 . , when incorporated as the polymer in the coating composition S . as defined above, resulting in an erosion rate of the coating in sea water of at least 1 μm per 10,000 nautical miles when tested as defined above, and, when the film-forming binder consists of more than one polymer, the total binder polymer composition, when incorporated as the binder in a coating composition S_l of the following solids composition, stated as solids volume parts: 60 parts by volume of the binder, 10 parts by volume of cuprous oxide with an average par¬ ticle size of 2-4 μm, 26 parts by volume of zinc oxide with an average particle size of approximately 0.2 μ , and 4 parts by volume of thixotropic bentonite results in an erosion rate of the coating in sea water with a salinity in the range of 37-38 parts per thousand of at least 1 μ per 10,000 nautical miles when the coating has been applied on and has been allowed to form a con¬ tinuous film on the convex surface of a cylinder of diame- ter 1 meter and the cylinder is rotated with a peripheral speed of 15 knots in sea water of a temperature between 10 and 30°C; the antifouling paint AFP having an erosion rate in sea water, when tested under the conditions defined above, in the range between 1 μm and 50 μm per 10,000 nautical miles, with the proviso that A. the antifouling paint is free from compounds of tin, compounds of arsenic, compounds of lead, and compounds of mercury, and B. the paint composition contains less than 8% by volume, calculated on the total solids volume of the composi¬ tion, of any of the following compounds, or of any combination of the following compounds: hexachlorophene, - tetrachloroisophthalonitrile, - l,2,3-trichloro-4,6-dinitrobenzene in pigment form. US Patent 3,990,381 describes various hydrophilic polymer coatings for underwater surfaces, the purpose of such coatings being to provide a water-swollen coating on the surface of the underwater structure which apparently re¬ sults in reduced friction. The coatings of the reference may consist of linear polymers but preferably consist of cross-linked coatings in order to ensure more permanent adherence of the coating to the underwater structure. The antifouling components described specifically in US patent 3,990,381 are primarily compounds of lead, tin, mercury, and arsenic, but also include copper compounds and various organic compounds. However, the only coatings tested over short distances on watercraft with respect to any friction-reducing properties are either clear varnishes without any pigments at all or a coating comprising ex¬ clusively triphenyl lead acetate as the antifouling pig¬ ment. Other tests involve determining the antifouling properties of various coatings by applying a coating to metal or fiberglass-reinforced plastic panels which were then located stationary under water at a test site. Thus, it is not possible to determine from the reference whether any of the coatings consisting of linear, non-crosslinked polymer coatings erode, either because the tests carried out on moving watercraft are performed over far too short distances or because the coatings have been applied to stationary panels which means that any possible erosion properties will not be discernible. In the present context, the term "erodible" is intended to mean that the coating in question and under the test condi¬ tions described is subject to a reduction of the thickness of the coating of at least 1 μm per 10,000 nautical miles of relative movement between the coated surface and the surrounding aqueous medium due to removal of coating mate¬ rial from the surface of the coating. For each of the individual polymers Pi, P2., P3_, and P4 . it is preferred that the weight average molecular weight (Mw) of the polymer is in the range from 2,000 to 1,000,000, in particular in the range from 20,000 to 200,000. A preferred embodiment of the paint composition of the invention is that wherein A 3 , A4, A5, and A each indepen¬ dently is C^_ 4 -alkylene. In another preferred embodiment, each group B x independent¬ ly is a group B 1 , B 2 , B 4 or B 5 . A further preferred embodiment is a paint composition in which D 7 is hydrogen. Another preferred embodiment of the invention is a paint composition in which each group B x independently is a group B 1 or B 2 , and D x is different from D 7 . Within this embodi¬ ment, it is particularly preferred that the factors a3, a4, a5, and a6 each is 0. Among such compositions, it is particularly preferred that R-L and R 2 each independently is hydrogen, methyl or ethyl. When this is the case, it is especially preferred that D^ is C 1 _ 2 alkylene, and D 2 and D 4 each independently is hydrogen, methyl or ethyl. Within this preferred embodiment of the invention, it is particularly preferred that each group B x independently is a group B 1 , and in such cases it is especially preferred that R^ is hydrogen, and R 2 is hydrogen or methyl. With respect to the polymer PI, it is preferred that the sea water erodibility-conferring segments have the formula la over Ic, especially the formula la. In such polymers, it is preferred that D x is a group -D 3 D 5 )-0-D 4 in which D 4 and D 5 are both hydrogen, or that D χ is a group -0 3 (0 5 )- OH, especially where D x or D x ' is a group -0 3 (H)OH. A most preferred example of such compounds are those in which D x or D x ' is -CH 2 CH 2 OH. The term "C 1 _ 4 alkyl" is intended to mean a branched or unbranched saturated hydrocarbon group with 1-4 carbon atoms such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec.butyl, and tert.butyl. The term "cι- 4 alkoxy" is intended to mean an oxy function substituted with c^_ 4 alkyl as defined above. The term "C 1 »4 alkylene" is in¬ tended to mean a branched or unbranched bifunctional hydro¬ carbon group with 1-4 carbon atoms such as ethylene, dimethylene, trimethylene, tetramethylene, and 2-methyl- trimethylene. Examples of suitable or potentially suitable monomers which, upon polymerization, form segments of the formula la, lb, Ic, or Id are the following: Monomers containing PEG [poly(ethylene glycol)] and PPG [poly(propylene glycol)] sidechains PEG monomethacrylate PPG monomethacrylate PEG monoacrylates PPG monoacrylates methoxyPEG -monomethacrylates methoxyPPG monomethacrylates methoxyPEG monoacrylates methoxyPPG monoacrylates Monohydroxy functional acrylates and methacrylates 2-hydroxyethy1 ethacrylate diethylene glycol monomethacrylate 2-hydroxyethy1 aerylate butanediol monoacrylate butanediol monomethacrylate 2-hydroxypropyl methacrylate 2-hydroxypropyl aerylate 3-hydroxypropyl methacrylate 3-hydroxypropyl aerylate 3-methoxy-2-hydroxy propyl methacrylate 3-methoxy-2-hydroxy propyl aerylate 2-hydroxy-2-methyl ethyl aerylate 2-hydroxy-2-methyl ethyl methacrylate 2-hydroxybutyl aerylate 2-hydroxybutyl methacrylate Dihydroxy functional acrylates and methacrylates 2,3-dihydroxypropyl methacrylate 2,3-dihydroxypropyl aerylate 3,4-dihydroxybutyl acrylate 3,4-dihydroxybutyl methacrylate Methoxy and ethoxy functional acrylates and methacrylates methoxy ethoxy ethyl methacrylate methoxy ethoxy ethyl acrylate ethoxy ethoxy ethyl methacrylate Hydroxy functional acrylamides and methacrylamides N-(2-hydroxyethy1) methacrylamide N-(2-hydroxyethy1) aerylamide N-(2-hydroxypropyl) methacrylamide N-(2-hydroxypropy1) aerylamide N-methylol-methacrylamide N-methylol acrylamide N-(1-hydroxyethy1) acrylamide N-(1-hydroxyethy1) methacrylamide N-[1,1-bis(hydroxymethyl)ethyl] acrylamide N-[1,1-bis(hydroxymethyl)ethyl] methacrylamide N-(2,3-dihydroxypropyl) acrylamide N-(2,3 dihydroxypropyl) methacrylamide N-(l-ethyl-2-hydroxyethy1) methacrylamide Hydroxyfunctional vinyl ethers vinyl 2-methoxy ethyl ether vinyl hydroxybutyl ether vinyl 2-hydroxyethy1 ether Other vinyl ethers vinyl-2-(2-ethoxyethoxy) ethyl ether vinyl 2-methoxyethy1 vinyl ether vinyl methyl ether Hydroxyfunctional allyl ethers allyl 2-hydroxyethy1 ether 3-allyloxy-l,2-propanediol trimethylolpropane monoallyl ether 2-allyloxy ethoxy ethanol allyloxy propanol Other allyl ethers allyl methyl ether allyl glycidyl ether allyl ethyl ether Allyl alcohols allyl alcohol 1-methyl allyl alcohol 2-methyl allyl alcohol Hydroxyfunctional alkenes , l-butene-4-ol 2-methyl-l-buten-4-ol l-penten-4-ol l-penten-5-ol 2-methyl-l-penten-4-ol 3-methyl-l-penten-4-ol Particularly preferred monomers are following: PEG monomethacrylate PPG monomethacrylate PEG monoacrylates PPG monoacrylates methoxyPEG monomethacrylates methoxyPPG monomethacrylates methoxyPEG monoacrylates methoxyPPG monoacrylates 2-hydroxyethyl methacrylate diethylene glycol monomethacrylate 2-hydroxyethyl acrylate butanediol monoacrylate butanediol monomethacrylate 2-hydroxypropyl methacrylate 2-hydroxypropyl acrylate 3-hydroxypropy1 methacry1ate 3-hydroxypropy1 acrylate 3-methoxy-2-hydroxy propyl methacrylate 3-methoxy-2-hydroxy propyl acrylate 2-hydroxy-2-methyl ethyl acrylate 2-hydroxy-2-methyl ethyl methacrylate 2-hydroxybutyl acrylate 2-hydroxybutyl methacrylate 2,3-dihydroxypropyl methacrylate 2,3-dihydroxypropyl acrylate 3,4-dihydroxybutyl acrylate 3,4-dihydroxybutyl methacrylate Especially preferred monomers are: PEG monomethacrylate PPG monomethacrylate PEG monoacrylates PPG monoacrylates methoxyPEG monomethacrylates methoxyPPG monomethacrylates methoxyPEG monoacrylates methoxyPPG monoacrylates 2-hydroxyethyl methacrylate 2-hydroxyethy1 acrylate butanediol monoacrylate butanediol monomethacrylate 2-hydroxypropyl methacrylate 2-hydroxypropyl acrylate A most particularly preferred polymer PI is the homopolymer of 2-hydroxyethyl methacrylate (also known as HEMA) . The remaining segments in polymers PI and P2. not represen- ted by the formulas la, lb, Ic, and Id may be any segments arising from monomers that are capable of polymerizing with olefinic monomers to form polymers. It is preferred that such other segments are segments that originate from olefi¬ nic monomers different from those forming the segments of the formula la-d. Since the segment la-d confer seawater erodibility, the remaining other segments will be either hydrophilic (although usually not as hydrophilic as the segments la-d) or be hydrophobic. Typical types of hydro- phobic comonomers are esters of acrylic and methacrylic acid where the ester moiety does not contain any polar groups as well as other hydrophobic derivatives of acrylic or methacrylic acid, styrene or derivatives thereof or hydrophobic esters of vinyl alcohol. Typical specific examples of such comonomers are the fol¬ lowing: methyl methacrylate n-butyl methacrylate n-butyl acrylate tert-butyl methacrylate tert-butyl acrylate sec-butyl methacrylate sec-butyl acrylate ethylhexyl acrylate ethyl methacrylate octyl acrylate lauryl acrylate isopropyl acrylate isopropyl methacrylate styrene -methyl styrene vinyl acetate vinyl toluene acrylonitrile The polymer P3. may be any of the seawater non-erodible and physically drying polymers that are normally used in coat- ing and paint compositions within the art. Typical examples are copolymers of vinyl acetate and vinyl isobutyl ether, copolymers of vinyl chloride and vinyl acetate, and copoly¬ mers of vinyl chloride and vinyl isobutyl ether; alkyd resins or modified alkyd resins such as styrenated alkyd resins; ketone resins; hydrocarbon resins such as petroleum fraction condensates; chlorinated rubbers; styrene copoly¬ mers such as styrene/butadiene copolymers, and styrene/- acrylate copolymers; acrylic resins such as isobutyl meth¬ acrylate copolymers, methyl methacrylate/n-butyl methacry- late copolymers; polyamide resins such as polyamide based on dimerized tall oil fatty acids; cyclized rubbers; and epoxy esters. The polymer P4 . may be for example one of the copper-con¬ taining acrylic polymers described in EP 342276 and EP 220965, both of which are hereby incorporated by reference. Alternatively, the polymer may be one of the polymers containing units of acrylic or methacrylic acid alkyl, aryl, or arylalkyl esters described in WO 84/02915 which is hereby incorporated by reference. Particularly preferred specific examples of polymers Pl which contain other segments than those of formula la-d are copolymers between on the one hand 2-hydroxyethyl methacry¬ late and on the other hand methyl methacrylate or butyl methacrylate, the content of methyl methacrylate or butyl methacrylate being in the range from 0-15 mole percent. Preparation of a polymer PI as well as a polymer P2, can in principle be carried out in two different ways. Either, a fully functionalized monomer corresponding to the formula la, lb, Ic, or Id, where the two carbon atoms bearing the free bonds are instead connected by a double bond, can be polymerized (either on its own to form a homopolymer or with one or more comonomers such as those indicated above in order to form a copolymer) or an already formed polymer which does not have all the functions comprised in the general formulas la-d in its structure can be reacted with one or more reagents which inserts the necessary functional group to obtain the functional polymer. It is normally preferred to polymerize the functional monomer due to the problems with unreacted reagents, side-chains and difficul- ties in purification of the polymer which may occur when functionalizing a polymer. Homopolymerization of acrylates, methacrylates, acryalmides and methacryla ides as well as copolymerization of these with each other and with other monomers such as the hydro- phobic monomers mentioned above and copolymerization of vinyl ethers, allyl alcohols and allyl ethers (such as those mentioned above) with other monomers (such as meth¬ acrylates, acrylates, vinyl acetate, styrene etc.) is normally carried out in an organic solvent which is a solvent for the resulting polymer. The solvent may be an alcohol such as n-butanol, ethanol, n-propanol, methoxypro- panol, isopropanol, sec-butanol, or another solvent such as xylene, toluene, hexane or diethyl ether, the concentration of the monomer in the solution normally being in the range of 10-60% by weight depending on the monomer, the desired polymer and the molecular weight thereof, and the desired viscosity. The polymerization is carried out by means of a fee-radical initiator such as benzoyl peroxide, N,N-azobis- (isobutyronitrile) , and tert-butyl peroxide at a tempera¬ ture that is optimal for the initiator. About 25% of the initiator is dissolved in the solvent, and the purified monomer or monomer mixture and about 50% of the initiator dissolved in some of the solvent is added to the mechanically stirred solvent over a period of about two to six hours and the reaction temperature is maintained for additional several hours (usually between two and ten) to ensure completion of the reaction. The remaining 25% of the initiator, dissolved in some of the solvent, is added in small portions distributed evenly over the remaining reac¬ tion time. Nitrogen is bubbled through the reaction mixture for at least ten minutes before and during the polymeriza¬ tion. The polymer solution is then cooled down to room temperature. Instead of dissolving some of the initiator in the solvent before adding the monomers, all the initiator can be added dropwise during the polymerization, and in¬ stead of adding the initiator and the monomer separately, the initiator can be dissolved in the monomer and added together. Alternatively, all the ingredients can be mixed together and heated to the reaction temperature, which is maintained for several hours (normally two to six hours) . Homopolymerizatibn of vinyl ethers is carried out in dry and pure inerts solvents (such as lower alkanes, ether, xylene, toluene) bubbled through with nitrogen and follow¬ ing addition of an initiator for cationic polymerization (such as boron triflouride, aluminium trichloride, tin chloride, boron triflouride etherate) at temperatures below 0°C. The monomer must be purified just before polymeriza¬ tion. The initiator is dissolved in the solvent and the mixture is cooled down. The monomer is cooled down and added dropwise to the solution over a period of time, the length of which depends on the system. In the event it is desired to prepare functional polymers by functionalizing an already prepared polymer, examples of monomers that are to form the basis of segments of the formula la-d may be monoacids such as crotonic acid, vinyl acetic acid, acrylic acid, and methacrylic acid; diacids such as fumaric acid, maleic acid, itaconic acid, citraco- nic acid, and mesaconic acid; triacids such as aconitic acid; and amides such as acrylamide, methacrylamide, and crotonamide. The further functionalization of the polymer containing the above mentioned acid and amide monomers may be performed in a manner known per se such as esterification of the acid functions with the desired group or substitution of the nitrogen atom in amide with the relevant group. It is preferred that the total pigment content of the composition is in the range of 25-50% of the solids volume of the paint composition. With respect to the sea water- soluble pigment or pigments, it is preferred that they constitute at least 20% of the solids volume of the paint composition. It is also preferred that any sea water-in¬ soluble pigments, when present, constitute at the most 40% of the solids volume of the paint composition. An antifouling agent present in the paint composition of the invention may either be one of several different types of biocides such as algicides, fungicides or bactericides, or it may be one of several types of fouling release a- gents, i.e. agents which prevent the marine organisms from achieving significant adhesion on the painted surface. Typical examples of biocides are copper compounds, such as cuprous oxide, cuprous thiocyanate, copper powder, copper alloy powder, copper naphthenate, copper octoate or copper rosinate; metal dithiocarbamates, such as zinc ethylene bis(dithiocarbamate) , zinc methylene bis(dithiocarbamate) , copper ethylene bis(dithiocarbamate) , zinc dimethyl dithio- carbamate; zinc oxide; zinc pyridinethione; tetramethyl thiuram disulfide; methylene bis(thiourea) ; n-butyl cate- chol; captan; substituted isothiazolones, such as 4,5- dichloro-2-n-octyl-n-isothiazolin-3-one; 2-(N,N-dimethyl- thiocarbamoylthio)-5-nitrothiazole; tetrachloroisophthalo¬ nitrile; 2-methylthio-4-(tert.butylamino)-6-(cyclopropyl- amino)-s-triazine; N,N-dimethyl-N'-phenyl-N'-(fluorodi- chloromethylthio)-sulfamide; N'-(3,4-dichlorophenyl)-N,N- dimethylurea; and mixtures thereof. Typical examples of fouling release agents are silicone compounds, such as a dimethylsiloxane-containing liquid or resin, or a liquid methyl phenyl silicone; or hydrocarbons, such as petrolatum, white oil, paraffin oil, or paraffin wax; or mixtures thereof. Apart from the polymer PI and optionally the polymers P2. P3, and P4 . and the antifouling agent or agents and pigment or pigments, the antifouling paint composition AFP accord- ing to the invention may contain any of the other commonly used formulating materials within the paint technology. Such component may include fillers, colouring materials, auxiliary agents and, optionally, carriers depending on whether the paint composition is to be formulated as a liquid paint or is to be formulated as a paint in powder form. Sea water-insoluble pigments may for example be selected from grades of titanium dioxide, red iron oxide, carbon black, graphite, yellow iron oxide, phthalocyanine blue, and phthalocyanine green. Such materials are characterized in that they render the final paint coating non-transparent and non-translucent. However, the paint composition accord¬ ing to the invention may also comprise pigment-like in- gredients such as fillers selected from calcium carbonate, dolomite, talc, mica, barium sulphate, kaolin, and quartz flour. Such materials are characterized in that they do not render the paint non-translucent and therefore do not contribute significantly to hide any material below the coating of the paint composition of the invention. Auxiliary agents may be any of those that are commonly used within paint technology. Examples of such auxiliary agents include natural gum rosin or gum rosin derivatives such as zinc calcium rosinate, limed rosin, dimerized rosin and rosin ester, or vegetable oils such as linseed oil. Auxiliary agents may also comprise plasticizers such as chlorinated paraffin; low molecular weight polybutene; phthalates such as dibutyl phthalate, benzyl butyl phtha- late, dioctyl phthalate, and diisodecyl phthalate; phos- phate esters such as tricresyl phosphate, and 2-ethylhexyl diphenyl phosphate; sulfonamides such as alkyl-p-toluene sulfonamide; and polymeric acrylic plasticizers such as liquid polyacrylic acid n-butyl ester. Other auxiliary agents include surfactants such as deriv- ates of propylene oxide or ethylene oxide such as alkyl- phenol-ethylene oxide condensates; and soya lecithin. Further auxiliary agents include defoaming agents such as silicone oils. Further examples of auxiliary agents include, if necessary, catalysts such as dryers, e.g. metal octoates and metal naphthenates. Yet further auxiliary agents include stabilizers such as stabilizers against light and heat, e.g. 2(2'-hydroxy-3'-Z- butyl-S , -methylphenyl)5-chlorobenzotriazole; stabilizers against moisture such as molecular sieves; and stabilizers against oxidation such as 2,5-ditert.butyl-hydroquinone. Other auxiliary agents include inhibitors such as polymeri- zation inhibitors, e.g. para-benzoquinone, hydroquinone, and ethyl-hydroquinone. Still further auxiliary agents include coalescing agents such as glycols; and thickeners and anti-settling agents such as colloidal silica, aluminium stearate, hydrogenated castor oil, polyethylene fibers, and organo-modified clays. When preparing a liquid paint composition, a carrier may be any suitable medium in which the components of the antifou¬ ling paint AFP are dissolved or dispersed. Such media are usually organic-based. The role of the medium is to permit easy application of the antifouling paint AFP, to evaporate after application and leave a dry film. Thus, it may be media in which the various polymers in the paint composi¬ tion may be dissolved, but it may also be a medium in which the polymer is dispersed such as when forming a dispersion or latex paint. Examples of liquid carries include water; alcohols, such as methanol, ethanol, propanol, isopropanol, butanol, isobuta- nol, or benzyl alcohol; alcohol/water mixtures such as ethanol/water mixtures; aliphatic and aromatic hydrocar- bonε, such as white spirit, toluene, xylene, or naphtha solvent; ketones, such as methyl ethyl ketone, acetone, methyl isobutyl ketone, methyl isoamyl ketone, diacetone alcohol, or cyclόhexanone; ether alcohols, such as 2-but- oxyethanol, propylene glycol monomethyl ether, or butyl diglycol; esters, such as methoxypropyl acetate, n-butyl acetate, or 2-ethoxyethy1 acetate; chlorinated hydrocar- bons, such as methylene chloride or trichloroethylene; and mixtures thereof, as well as any other carriers usually employed within the coating industry. The antifouling paint composition AFP may be prepared by any suitable technique that is commonly used within the field of paint production. Thus, the various components may be mixed together using a high speed disperser, a ball mill, a pearl mill, a three-roll mill etc. The antifouling paint composition according to the inven¬ tion may be applied to the marine structure to be protected by means of any of the usual techniques used within the paint field such as by means of a brush, a roller, a pad, by dipping, by spraying etc. The exact technique chosen depends upon the object to be protected and also upon the particular composition (such as its viscosity etc.) and upon the particular situation such as whether the object is in the water or is out of the water. Preferred applications techniques are spraying and by means of a brush or a rol¬ ler. The paint composition according to the invention may be applied to a variety of solid objects that come into con¬ tact with sea water, for example vessels (including but not limited to boats, yachts, motorboats, motor launches, ocean liners, tugboats, tankers, container ships and other cargo ships, submarines (both nuclear and conventional) , and naval vessels of all types) ; pipes; shore and off-shore machinery, constructions and objects of all types such as piers, pilings, bridge substructures, underwater oil well structures etc; nets and other mariculture installations; and buoys; and is especially applicable to the hulls of ships and boats and to pipes. Prior to the application of a paint composition of the invention to a marine structure, the marine structure may first be coated with a primer which may or may not contain antifouling agents, but otherwise contain the ingredients as described for the antifouling paint AFP. In a preferred embodyment, the primer is a sea water non-erodible paint having a composition as that of the antifouling paint AFP but which erodes at a rate of less than lμm per 10,000 nautical miles. Such a primer may i.a. be obtained by using only a polymer P2 as a polymer containing the segments Ia- d. Thus, the present invention also concerns a marine struc¬ ture having an adherent continuous exposed sea water-ero¬ dible coating film of an antifouling paint, the coating comprising a film-forming binder as defined in claim 1, at least one pigment which is soluble in sea water in an amount of at least 1 mg/litre, at least one antifouling agent which may be the pigment or one of the pigments, the total pigment content of the coating being in the range of 10-60% of the solids volume of the coating, the sea water- soluble pigment or pigments constituting at least 10% of the solids volume of the coating, any sea water-insoluble pigments, when present, constituting at the most 50% of the solids volume of the coating, the average dry film thick- ness of the coating being at least 40 μm, in particular 40- 1,000 μ , especially 50-600 μm. A useful average total dry film thickness of a paint com¬ position AFP on a marine structure may also be expressed in terms of the expected service life combined with the erosion rate. Thus, the dry film thickness will preferably be between 1 and 50 μm per month of expected service life, which will usually be between 40 μm and 600 μ average dry film thickness for a service life of between 1 and 5 years. The desired film " thickness may be obtained either by ap¬ plication of a single coat or by application of several coats to achieve the desired average total dry film thick¬ ness. In view of the relationship between film thickness and erosion rate, the present invention also concerns a method for operating a watercraft, involving a first painting step in which an erodible antifouling paint coating is applied to the part of the exterior of the craft which, during operation of the craft, is immersed in water, sailing the watercraft, and performing a second painting step with an erodible antifouling paint, the method comprising establishing the distance M which the watercraft is to cover between the first and the second painting steps, selecting an antifouling paint composition comprising a film-forming binder, at least one pigment which is soluble in sea water in an amount of at least 1 mg/- litre, at least one antifouling agent which may be the pigment or one of the pigments, the total pigment content of the composition being in the range of 10- 60% of the solids volume of the paint composition, the sea water-soluble pigment or pigments constituting at least 10% of the solids volume of the paint composi- tion, any sea water-insoluble pigments, when present, constituting at the most 50% of the solids volume of the paint composition, said binder comprising at least one polymer PI of a weight average molecular weight of at least 2000 which is water-insoluble and which comprises, as the sea water erodibility-conferring segments, segments of the formula la, lb, Ic, or Id B x - )a4 - (Id) ) a6 wherein R^ and R 2 each independently is hydrogen or C!_ 4 alkyl, A 3 , A 4 , A 5 , and A 6 each independently is C- L _ 4 alkylene or phenylene, a3, a4, a5, and a6 each independently is 0 or 1, and each group B x independently is a group D x , or a group B 1 , B 2 , B 3 , or B 4 -C0-0-D x ' (B 1 ) -C0-NH-D x (B 2 ) -NH-C0-D x (B 3 ) -0-D x (B 4 ) or the two groups B x in (Ic) or (Id) together constitute an i ide group B^ 0=C C=0 (B ) \ / N A* wherein D x is a group - (D 1 -0-) ( jD 2 , a group -D 3 -O-D 4 , or a group D 7 and D x ' is a group -(D 1 -0-) (j D or a group 1 5 -D 3 -0H, wherein O-_ is C^_ 4 alkylene, D 2 is hydrogen or C^_ 4 alkyl, d is an integer from 2 to 300 D 3 is C^_ 4 alkylene; phenylene optionally substituted with 1 or 2 C^_ 2 alkyl; or a phenyl-C 1 _ 4 alkyl moiety having the group D5 attached to the phenyl ring, and having the free bond shown located on the phenyl ring and the group -0-D 4 attached to the alkyl part, or vice versa, the phenyl part option¬ ally being substituted with 1 or 2 substitu- ents selected independently from hydroxy and c l -4 alkoxy, D 4 is hydrogen or C ] __4 alkyl, D5 is hydrogen, hydroxy or C^_ 4 alkoxy, or, when D 3 is C- j ^ alkylene, -0-D 4 and D 5 together form C^_4 alkyleneoxy, and D 7 is hydrogen or C^_4 alkyl, with the proviso that, when the polymer contains segments of the formula la, where R- ^ is hydrogen, R 2 is hydrogen or methyl, a3 is 0, B x is a group B 1 , and D 3 is (CH 2 )ι_4, then D 4 is hydrogen, and that, when D 7 is hydrogen, then B x is a group B 4 ; the kind and concentration of the segments la, lb, Ic, or Id in the polymer PI being so selected that the polymer PI, when incorporated as the binder in a coating composition S of the following solids composi¬ tion, stated as solids volume parts: 60 parts by volume of the polymer, 10 parts by Volume of cuprous oxide with an average particle size of 2-4 μ , 26 parts by volume of zinc oxide with an average particle size of appoximately 0.2 μm, and 4 parts by volume of thixotropic bentonite results in an erosion rate of the coating in sea water with a salinity in the range of 37-38 parts per thou¬ sand of at least 1 μm per 10,000 nautical miles when the coating has been applied on and has been allowed to form a continuous film on the convex surface of a cylinder of diameter 1 meter and the coated cylinder is rotated with a peripheral speed of 15 knots in sea water of a temperature between 10 and 30°C; whereby, when the film-forming binder comprises more than one polymer, each other polymer is either a polymer P_l as defined above, a polymer P2 . of a weight average molecular weight of at least 2000 which is water-insoluble and comprises segments of the formula la, lb, Ic, or Id as defined above, the kind and concentration of the segments la, lb, Ic, or Id and other segments in the polymer P2 . being so selected that the polymer P2 . , when incor¬ porated as the polymer in the coating composition S_ as defined above, results in an erosion rate of the coating in sea water of at less than 1 μm per 10,000 nautical miles when tested as defined above, or a film-forming polymer P3 of a weight average molecu¬ lar weight of at least 2000 which does not comprise segments la, lb, Ic or Id, the polymer P3_, when incor- porated as the binder in the coating composition S. as defined above, resulting in an erosion rate of the coating in sea water of less than 1 μm per 10,000 nautical miles when tested as defined above, or a polymer P4_ of a weight average molecular weight of at least 2000 which comprises sea water erodibility- conferring segments which are not segments la, lb, Ic or Id, the polymer P4_, when incorporated as the poly- mer in the coating composition S. as defined above, resulting in an erosion rate of the coating in sea water of at least 1 μm per 10,000 nautical miles when tested as defined above, and, when the film-forming binder consists of more than one polymer, the total binder polymer composi¬ tion, when incorporated as the binder in a coating composition £>i of the following solids composition, stated as solids volume parts: 60 parts by volume of the binder, 10 parts by volume of cuprous oxide with an average particle size of 2-4 μm, 26 parts by volume of zinc oxide with an average particle size of appoximately 0.2 μm, and 4 parts by volume of.thixotropic bentonite results in an erosion rate of the coating in sea water with a salinity in the range of 37-38 parts per thou¬ sand of at least 1 μm per 10,000 nautical miles when the coating has been applied on and has been allowed to form a continuous film on the convex surface of a cylinder of diameter 1 meter and the cylinder is rotated with a peripheral speed of 15 knots in sea water of a temperature between 10 and 30°C; the antifouling paint having an erosion rate in sea water, when tested under the conditions defined above, in the range between 1 μm and 50 μm per 10,000 nauti¬ cal miles, determining the value ER of the erosion rate expressed in μm per 10,000 nautical miles, applying the paint composition in an amount resulting in an average dry film thickness T of at least 40 μm and equal to a thickness which, in view of the conditions under which the ship is to be sailed, will be sufficient to provide a coating of the paint on at least part of the coated area after the ship has covered the distance M; sailing the watercraft and thereby eroding the coating, and performing the second painting step by applying a new coating of the antifouling paint before or when the first layer has been partially or completely eroded. In an extremely idealized and simplified model, a very rough guide to the average dry film thickness T expressed in μm may be provided by the formula ER x M T = 10,000 However, as it will be well known to the person skilled in the art, the above formula is not able to take into account the many other factors, apart from covered distance, that determine the erosion rate of a particular paint coating on a ship. Such factors include, but are not limited to, average sailing speed, since higher speed will tend to erode a coating faster for a given distance; salinity and temperature of the sea regions through which the ship passes since these parameters may affect the water absorp¬ tion of the polymer as well as the rate at which water- soluble pigments are leached from the coating; the opera- tional pattern of the ship, i.e. primarily the ratio bet¬ ween time at sea and time in port since erosion of the coating also takes place, albeit at a significantly lower rate, when the the ship is stationary; as well as the fact that erosion of a paint coating on the hull of a ship does not proceed at the same rate on different areas of the hull in that the coating will probably be eroded faster for example at the bow or the rudder than for example at the keel or at the waterline. As a result of such influences, the optimum dry film thick¬ ness of a paint coating on a ship operated according to the method of the invention will vary considerably compared to the average dry film thickness calculated from the simple formula above and may in practice vary between 0.1 and 10 times this calculated thickness. However, it will be well within the capabilities of the person skilled in the art to determine the average dry film thickness as well as the dry film thickness distribution on a ship given the distance M and the erosion rate ER when taking into consideration i.a. the various factors discussed above. The discussion above is initially directed to the situation where a coat of a single erodible paint composition is used. However, the method of the invention may also be applied to a situation where the part of the exterior of the craft which, during operation of the craft, is immersed in water is coated with several superimposed layers of several paints, especially where such coats have different erosion rates. Thus, it would in some circumstances be advantageous for the craft to be provided with for example 3 erodible coats, where the first or innermost coat has a relatively slow erosion rate such as between 1 and 5 μ per 10,000 nautical miles when tested as described above, the second coat has a higher erosion rate such as between 5 and 10 μm per 10,000 nautical miles, and the third and outer¬ most coat has a still higher erosion rate of for example between 10 and 20 μm per 10,000 nautical miles or even higher. Such coating patterns would have the advantage that it would reduce the chance of the craft suddenly being without any erodible coating at all on part of or all of the exterior of the craft which is immersed in water during operation of the craft, since the erosion rate becomes progressively slower as the coating layers are eroded away. It is to be understood that the application of such multi¬ layer coatings is also encompassed by the method of the invention. The invention is further illustrated by means of the fol¬ lowing non-limiting examples. EXAMPLE 1 A polymer was synthesized by solution polymerization in the following manner: 331.2 g of methoxypropanol (MePr) , 129.6 g of 2-hydroxy- ethyl methacrylate (HEMA) and 1.2 g of dilaurylperoxide (DLP) was placed in a closed 1 liter Erlenmeyer flask and placed in an oven at 80°C for 21 hours. The density Dm in gram per millilitre of the resulting solution was measured at 25°C (ASTM D 1475-90) to be 1.00. The content in percent by weight of non-volatile (NV) was measured (ASTM D 1644-88, test method A) to be 29.0. The absorption (SWA) of sea water in percent by weight of a a polymer film was measured as follows. The polymer solu¬ tion was applied by means of a Doctor Blade applicator with a clearance of 200 μm on to a pre-weighed (weight A) glass panel. The film was then dried for 24 hours at 45°C in an oven after which the glass panel was weighed again (weight B) . The panel was then immersed in aerated artifi¬ cial sea water (ASTM 0 1141-75) for 72 hours. The panel was then dried gently on its surface with filter paper and weighed again (weight C) . SWA was calculated from the formula SWA = (C - B) x 100/(B - A) which gave the result of 8. EXAMPLE 2 • The polymerization in example 1 was repeated with the following ingredients: 331.2 g MePr, 55.1 g HEMA, 62.1 g methyl methacrylate (MMA) and 1.2 g DLP. The following characterizing data were obtained in the same manner as in example 1: Dm = 0.98 NV = 24.7 SWA = 4 EXAMPLE 3 A polymer was synthesized by solution polymerization in the following manner: 690 g MePr, 360 g n-butanol (n-BU) , and 4,5 g N,N-azobis- (isobutyronitrile) (AIBN) was mixed in a 3-necked, 2 liter polymerization flask equipped with thermometer, condenser and separation funnel for addition of monomer. The solution was heated to 80°C. 450 g HEMA was added dropwise over a period of 1 hour from the separation funnel to the mechani¬ cally stirred solution. The temperature was maintained at 80°C during the addition. After conclusion of the addition, the heating was switched off and stirring was continued for 1 hour. The following characterizing data were obtained in the same manner as in example 1: Dm = 0.98 NV = 29.8 SWA = 11 The viscosity (GH) expressed as Gardner-Holdt Letter (ASTM D 1545-89) of the polymer solution was measured to be V. EXAMPLE 4 The polymerization in example 3 was repeated with the following ingredients: 690 g MePr 360 g n-BU 4.5 g AIBN 425.5 g HEMA 24.5 g n-butyl methacrylate (BMA) The following characterizing data were obtained in the same manner as in example 1 and 3: Dm = 0.97 NV = 30.3 SWA = 15 GH = P EXAMPLE 5 The polymerization in example 3 was repeated with the following ingredients: 690 g MePr 360 g n-BU 4.5 g AIBN 401.0 g HEMA 51.2 g n-butyl methacrylate (BMA) The following characterizing data were obtained in the same manner as in example 1 and 3: Dm = 0.97 NV = 30.4 SWA = 12 GH = S EXAMPLE 6 Tests were made on a commercially available solution of an erodible tin-containing reference polymer. The polymer used was "BioMet 300" from M&T Chemicals Inc. (a tributyltin methacrylate/methyl methacrylate copolymer dissolved in naphtha solvent) . The following characterizing data were obtained in the same manner as in example 1: Dm = 1.02 NV = 50 SWA = 0 EXAMPLE 7 A coating was prepared using the polymer solution prepared in example 1 and having the following composition (cor- responding to coating composition S : Polymer solution from example 1: 60 parts by volume (pbv) cuprous oxide with an average particle size of 2-4 μm: 10 pbv zinc oxide with an average particle size of 0.2 μm : 26 pbv Bentone 38: 4 pbv. (Bentone 38 is an organic modified bentonite product from NL Chemicals) MePr was added as an additional carrier to the ingredients in such an amount that the calculated solids volume con¬ centration (SVC) in percent of the coating was 19.8. 200 ml of the thoroughly mixed coating composition was introduced into a tight metallic container of 0.5 liter capacity together with 100 ml (bulk volume) of glass pearls with a diameter of 2-3 mm. The container was then shaked for 45 minutes on a mechanical shaker. The coating composi¬ tion was separated from the glass pearls by filtration and the fineness of dispersion was determined (ASTM D 1210-79) to be lower than 30μm. An acrylic test panel (13.5 x 7 cm) with a curvature cor¬ responding to that of a cylinder with a diameter of 1 meter was first coated on its convex surface with 80 μm (dry film thickness, DFT) of a commercial vinylic primer (Hempanyl Tar 1628, from Hempel's Marine Paints) applied by air spray. The primed panel was then coated with the above experimental coating composition in a DFT of 200 μm using a Doctor Blade. After drying, bands of 1 cm width of a co - mercial, non-erodible vinylic antifouling coating (Classic 7655, from Hempel's Marine Paints) were applied along each longitudinal edge by dipping. As a result of this, the central part with a width of 5 cm remained uncovered by the non-erodible coating. The panel was fixed onto the convex surface of a cylindri¬ cal drum of 1 meter in diameter and was rotated in sea water with a salinity in the range of 37-38 parts per thousand at an average temperature of 26°C at a test site in the harbour of Villanueva y Geltrύ in northeastern Spain (se also Morales E. & Arias E. , Rev. Iber. Corros. y Prot. , vol XIX(2) , 1988, pp 91-96). The rotor was rotated at a peripheral speed of 15 knots for a relative distance of 10,900 nautical miles. Paint chips were collected from the test panel in such a way that their surface comprised both a part coated with the experimental coating only as well as a part coated with both the experimental coating and the non-erodible coating. The chips were embedded in paraffin wax and cut with a microtome. Cross sections of the experimental coating were examined under a microscope. Compared to the part coated with the non-erodible coating, the experimental coating showed a decrease of DFT of the outer layer of 38 μm cor¬ responding to an erosion rate (ER) of 35 μm per 10,000 nautical miles. The above experimental coating was also tested for antifou¬ ling properties by applying it onto an acrylic test panel (10 x 20 cm) in a DFT of lOO±lO μm using a Doctor Blade. From a raft, the test panel was immersed into the sea at a depth of 35 cm below the surface at the test site at Vil- lanueva y Geltrύ described above. An uncoated acrylic panel was also immersed in the same manner as a blank. The panels were inspected every 4 weeks during a total immersion period of 20 weeks. At each inspection, the panels were rated on a scale from 0 (no fouling) to 5 (100% fouling) with respect to each of the three categories of fouling, namely slime, algae, and animals. At the end of the immersion period, all ratings from each inspection were cumulated to provide a sum of fouling ratings (SFR) with which relative comparisons could be made within groups of samples tested during the same period of time. The panel coated with the experimental coating had a SFR of 6, whereas the blank had a SFR of 50. EXAMPLE 8 An experimental coating was prepared as in example 7 using the polymer solution from example 2. The coating composi¬ tion had the following characteristics: SVC = 25.3 ER = 0 SFR = 17 Thus, the polymer from example 2 is an example of polymer P2. EXAMPLE 9 An experimental coating was prepared as in example 7 using the polymer solution from example 3. The coating composi¬ tion had a SVC of 24.4. A special primer was prepared in the same manner as the experimental coating of this example and with the following composition: Polymer solution from example 3: 40 ppv Vinylic resin: 15 ppv Cuprous oxide: 26 ppv Zinc oxide: 10 ppv Titanium oxide (with an oil absorption of 17-23 (ASTM D 281)): 4 ppv Wetting agent (alkyd with amino fatty acids) : 1 ppv Bentone 38: 4 ppv (The vinylic resin was Laroflex MP 25 (a copolymer of vinyl chloride and vinyl isobutyl ether) from BASF, and the wetting agent was Nuosperse 657 from Tenneco.) The special primer was applied as an intermediate coat on the curved test panel between the vinyl primer and the experimental coating in a DFT of 40 μm by air spraying. The erosion rate (ER) was 38 μm per 10,000 nautical miles. EXAMPLE 10 The procedure of example 9 was repeated using the polymer solution from example 4. SVC of the experimental coating was 29.4, and the erosion rate ER was 6 μ . EXAMPLE 11 The procedure of example 9 was repeated using the polymer solution from example 5. SVC of the experimental coating was 26.9, and the erosion rate ER was 3 μm. EXAMPLE 12 Using the reference polymer tested initially in example 6, the procedure of example 7 was repeated with the modifica¬ tion that MePr was replaced with xylene as additional carrier. The coating composition had the following charac- teristics: SVC = 38.9 ER = 32 SFR = 9 Solutions of other polymers PI may be prepared as follows: EXAMPLE 13 Poly(2-hydroxypropyl methacrylate) To a 500 ml 4-necked roundbottomed flask is added 125 g of methoxypropanol and 0.25 g benzoyl peroxide. The solution is heated to 80°C, and nitrogen is bubbled through. There- after, 100 g 2-hydroxypropyl methacrylate and 0.75 g ben¬ zoyl peroxide dissolved in 25 g methoxypropanol is added dropwise to the stirred solution over 2 hours after which the temperature is maintained at 80°C for further 4 hours. The reaction mixture is then allowed to cool to room tempe- rature. EXAMPLE 14 Poly(2-hydroxyethy1 vinyl ether-co-2-hydroxyethy1 methacry¬ late) To a 500 ml 4-necked roundbottomed flask is added 140 g of methoxypropanol and 0.15 g N,N-azobis(isobutyronitrile) . The solution is heated to 80°C, and nitrogen is bubbled through. Thereafter, 0.45 g N,N-azobis(isobutyronitrile) dissolved in a mixture of 24.2 g 2-hydroxyethy1 vinyl ether and 35.8 g 2-hydroxyethyl methacrylate is added dropwise to the stirred solution over 4 hours after which the tempera¬ ture is maintained at 80°C for further 4 hours. The reac¬ tion mixture is then allowed to cool to room temperature. EXAMPLE 15 Poly[poly(ethylene glycol) monomethacrylate] To a 500 ml 4-necked roundbottomed flask is added 120 g n- butanol and 0.3 g N,N-azobis(isobutyronitrile) . The solu¬ tion is heated to 80°C, and nitrogen is bubbled through. Thereafter, 60 g poly(ethylene glycol) 440 monomethacrylate [poly(ethylene glycol) having an average molecular weight of 440 monoesterified with methacrylic acid] and 0.9 g N,N- azobis(isobutyronitrile) dissolved in 20 g ethanol is added dropwise to the stirred solution over 2 hours after which the temperature is maintained at 80°C for further 4 hours. The reaction mixture is then allowed to cool to room te pe- rature. EXAMPLE 16 Poly(butyl methacrylate-co-2-hydroxyethyl methacrylate) To a 2000 ml 4-necked roundbottomed flask is added 360 g of n-butanol and 690 g methoxypropanol. The solution is heated to 80°C under stirring, and nitrogen is bubbled through. Thereafter; a mixture of 50 g butyl methacrylate and 400 g 2-hydroxyethy1 methacrylate, and a solution of 4.5 g N,N- azobis(isobutyronitrile) in 20 g methoxypropanol are sepa¬ rately added dropwise to the stirred solution over 1.5 hours after which the temperature is maintained at 80°C for further 2 hours. The reaction mixture is then allowed to cool to room temperature. EXAMPLE 17. A polymer was synthesized by solution polymerization in the following manner: a solution I was prepared as 50 g MePr, 6.5 g formaldehyd and 0.1 g triethylamine were mixed in a 3-necked, 0.5 liter polymerization flask equipped with thermometer, condenser and separating funnel for addition of monomers. The solution was heated to reflux and kept refluxing during the entire synthesis. A solution II of 55 g MePr, 90 g butylmethacrylate (BMA) and 7 g acrylamid were mixed and dissolved in an erlenmeyer flask. 3 g tert-butyl- peroxybenzoate was added to solution II. The solution was transferred to separating funnel. 10 w/w % of the solution II was added from the separating funnel to the mechanically stirred solution I. The mixture was refluxed for 15 minu¬ tes. The rest of solution II was added dropwise for a period of 2 hours. After conclusion of the addition, the mixture was refluxed for 2 hours and the heating and stirr- ing were switched off and the polymer left to cool off. The following characterizing data were obtained: Dm = 0.99 NV = 47.4 Molecular weight Mw = 32.500 EXAMPLE 18 : The polymerization of example 1 was repeated with the following ingredients: 50.0 g MePr 8.4 g formaldehyd 0.1 g triethylamine 55 g MePr 80 g butylmethacrylate 10 g acrylamide 3 g tert-butyl peroxybenzoate The following characterizing data were obtained in the same manner as in example 1: Dm = 0.99 NV = 47.1 Molecular weight Mw = 30.500 EXAMPLE 19: The polymerization of example 1 was repeated with the following ingredients: 50.0 g MePr 16.8 g formaldehyd 0.1 g triethylamine 55 g MePr 59.7 g butylmethacrylate 20 g acrylamide 3 g tert-butyl peroxybenzoate The following characterizing data were obtained in the same manner as in example 1: Dm = 1.04 NV = 45.9 Molecular weight Mw = 128.500 EXAMPLE 20. A polymer was synthesized by solution polymerization in the following manner: 1.0 g AIBN, 50 g n-butanol and 50 g toluen were mixed and dissolved in a 250 ml erlenmeyer flask equipped with thermometer, condenser and separating funnel for addition of monomers. The solution was heated to 80°C. 100 g isobutoxymethyl acrylamide (IBMA) was added dropwise over a period of 2 hours from the separating funnel to the mechanically stirred solution. The tempara- ture was maintained at 80°C during the addition. After conclusion of the addition, the heating was continued for two hours. After this period the stirring and heating were switched off and the polymer left to cool off. The following characterizing data were obtained: Dm = 0.94 NV = 45.6 Molecular weight Mw = 236.000 EXAMPLE 21. A polymer was synthesized by solution polymerization in the following manner: 50 g n-butanol, 50 g toluen and 1 g AIBN were mixed and dissolved in a 250 ml erlenmeyer flask equipped with thermometer, condenser and separating funnel for addition of monomers. The solution was heated to 80°C. 25 g isobutoxymethyl acrylamide (IBMA) and 75 g MMA (me- thylmethacrylate)' were mixed and added dropwise over a period of 2 hours from the separating funnel to the mecha¬ nically stirred solution. The temparature was maintained at 80°C during the addition. After conclusion of the addition, the heating was continued for two hours. After this period the stirring and heating were switched off and the polymer left to cool off. The following characterizing data were obtained: Dm = 1.08 NV = 45.0 Molecular weight Mw = coming soon EXAMPLE 22. A polymer was synthesized by solution polymerization in the following manner: 46.8 g n-butanol, 46.8 g toluen and 0.94 g AIBN were mixed and dissolved in a 250 ml erlenmeyer flask equipped with thermometer, condenser and separating funnel for addition of monomers. The solution was heated to 80°C. 25.2 g isobutoxymethyl acrylamide (IBMA) and 68.4 g BMA (butylmethacrylate) were mixed and added dropwise over a period of 2 hours from the separating funnel to the mechanically stirred solution. The temparature was main¬ tained at 80°C during the addition. After conclusion of the addition, the heating was continued for two hours. After this period the stirring and heating were switched off and the polymer left to cool off. The following characterizing data were obtained: Dm = 0, .93 NV = 46.3 Molecular weight Mw = coming soon EXAMPLE 23 * . A polymer was synthesized by solution polymerization in the following manner: 420 g MePr was weighed off in a 4-necked, 1 liter polymerization flask equipped with thermometer, condenser and 2 separating funnels for addition of monomers and initiator. The solution was heated to 90°C. 231 g HEMA and 36 g 4-Acetoxystyrene were mixed and added dropwise for a period of 2 hours from the separating funnel to the mechanically stirred solution. 80 g MePr and 0.8 g benzoyl- peroxid were dissolved and simultaniously added dropwise over a period of 2 hours and 15 minutes from the separating funnel to the mechanically stirred solution. The tempera¬ ture was maintained at 90°C during the addition. After conclusion of the addition, the temperaturand stirring was continued for 4 hours. After this period the heating and stirring were switched off and the polymer left to cool off. The following characterizing data were obtained: Dm = 1.03 NV = 35.7 Molecular weight Mw = 220.000 EXAMPLE 24. The polymerization in example 7 was repeated with the following ingredients: 320 g MePr 234 g HEMA 32 g 4-acetoxystyrene 0.8 g benzoylperoxid 80 g MePr The following characterizing data were obtained: Dm = 1.03 NV = 37.6 Molecular weight Mw = 275.000 EXAMPLE 25. The polymerization in example 7 was repeated with the following ingredients: 408 g MePr 247 g HEMA 16 g 4-acetoxystyrene 0.8 g benzoylperoxid 80 g MePr The following characterizing data were obtained: Dm = 1.03 NV = 35.8 Molecular weight Mw = 185.000 EXAMPLE 26. A polymer was synthesized by solution polymerization in the following manner: 80 g isopropylalcohol, 27 g 96% ethanol and 20 g n-butanol were mixed in a 3-necked, 500 ml polyme¬ rization flask equipped with thermometer, condenser and 2 separating funnels for addition of monomers and initiator. The solution was heated to 80°C. 49 g HEMA and 14 g HPMA (hydroxypropyl methacrylate) were mixed and added dropwise for a period of 1 hour. 0.4 g benzoylperoxid (BP) , 0.1 g AIBN, 20 g isopropylal¬ cohol, 3 g MePr and 3 g 96% ethanol were mixed and dis¬ solved. " of this solution were added at once simultaneous- ly with the start of addition of monomers from the separat¬ ing funnel to the mechanically stirred solution. The tempe¬ rature was maintained at 80°C during the addition. After conclusion of the addition, the temperature and stirring was maintained for 1 hour. After this period the rest of the initiator solution was added dropwise over a period of 1 hour. heating and stirring were switched off and the polymer left to cool off. The following characterizing data were obtained: Dm = 0.90 NV = 27.8 Molecular weight Mw = 108.000

Claims: CLAIMS 1. A sea water-erodible antifouling paint composition AFP for protecting marine surfaces, comprising a film-forming binder, at least one pigment which is soluble in sea water in an amount of at least 1 mg/litre, at least one antifoul¬ ing agent which may be the pigment or one of the pigments, the total pigment content of the composition being in the range of 10-60% of the solids volume of the paint composi¬ tion, the sea water-soluble pigment or pigments constitut- ing at least 10% of the solids volume of the paint composi¬ tion, any sea water-insoluble pigments, when present, constituting at the most 50% of the solids volume of the paint composition, said binder comprising at least one polymer PI of a weight average molecular weight of at least 2000 which is water- insoluble and which comprises, as the sea water erodabili- ty-conferring segments, segments of the formula la, lb, Ic, or Id B x I (lb) (Id) wherein R^ and R each independently is hydrogen or C 1-4 alkyl , A 3 , A 4 ' , A 5 , and Ag each independently is C-j^ alkylene or phenylene, a3, a4, a5, and a6 each independently is 0 or 1, and each group B x independently is a group D x , or a group B 1 , B 2 , B 3 , or B 4 -CO-0-D x ' (B 1 ) -C0-NH-D x (B 2 ) -NH-C0-D x (B 3 ) -0-D x (B 4 ) or the two groups B x in (Ic) or (Id) together constitute an imide group B 5 0=C C=0 (B 5 ) \ / N O~ wherein D x is a group -(D 1 -0-) f D 2 , a group -D ι 5 3 -O-D 4 , or a group D 7 and D x ' is a group -(Dι-0-) (j D 2 or a group D 5 -D 3 -OH, wherein D-^ is C-_- alkylene, D 2 is hydrogen or C 1-4 alkyl, d is an integer from 2 to 300 D 3 is Cη ^ .4 alkylene; phenylene optionally substituted with 1 or 2 C 1 _ 2 alkyl; or a phenyl-C 1 _ 4 alkyl moiety having the group D 5 attached to the phenyl ring, and having the free bond shown located on the phenyl ring and the group -0-D 4 attached to the alkyl part, or vice versa, the phenyl part option¬ ally being substituted with 1 or 2 substitu- ehts selected independently from hydroxy and Cι_4 alkoxy, D 4 is hydrogen or C 1-4 alkyl, D 5 is hydrogen, hydroxy or C- -^ alkoxy, or, when D 3 is C-L_4 alkylene, -0-D4 and D 5 together form C^_ 4 alkyleneoxy, and D 7 is hydrogen or C-_- 4 alkyl, with the proviso that, when the polymer contains segments of the formula la, where R-^ is hydrogen, R 2 is hydrogen or methyl, a3 is 0, B x is a group B 1 , and D 3 is (CH 2 ) 1 _ 4 , then D 4 is hydrogen, and that, when D 7 is hydrogen, then B x is a group B 4 ; the kind and concentration of the segments la, lb, Ic, or Id in the polymer PL being so selected that the polymer PI. when incorporated as the binder in a coating composition S_ of the following solids composition, stated as solids volume parts: 60 parts by volume of the polymer, 10 parts by volume of cuprous oxide with an average par- ticle size of 2-4 μ , 26 parts by volume of zinc oxide with an average particle size of appoximately 0.2 μm, and 4 parts by volume of thixotropic bentonite results in an erosion rate of the coating in sea water with a salinity in the range of 37-38 parts per thousand of at least 1 μm per 10,000 nautical miles when the coating has been applied on and has been allowed to form a con¬ tinuous film on the convex surface of a cylinder of dia¬ meter 1 meter and the coated cylinder is rotated with a peripheral speed of 15 knots in sea water of a temperature between 10 and 30°C; whereby, when the film-forming binder comprises more than one polymer, each other polymer is either a polymer PI as defined above, a polymer P2 of a weight average molecular weight of at least 2000 which is water-insoluble and comprises segments of the formula la, lb, Ic, or Id as defined above, the kind and concentration of the segments la, lb, Ic, or Id and other segments in the polymer P2 . being so selected that the polymer P2_, when incorporated as the polymer in the coating composition S as defined above, results in an erosion rate of the coating in sea water of less than 1 μm per 10,000 nautical miles when tested as defined above, or a film-forming polymer P3 of a weight average molecular weight of at least 2000 which does not comprise segments la, lb, Ic or Id, the polymer P3_, when incorporated as the binder in the coating composition S as defined above, resulting in an erosion rate of the coating in sea water of less than 1 μm per 10,000 nautical miles when tested as defined above, or a polymer F4 of a weight average molecular weight of at least 2000 which comprises sea water erodability-conferring segments which are not segments la, lb, Ic or Id, the polymer P_4, when incorporated as the polymer in the coating composition S_ as defined above, resulting in an erosion rate of the coating in sea water of at least 1 μm per 10,000 nautical miles when tested as defined above, and, when the film-forming binder consists of more than one polymer, the total binder polymer composition, when incorporated as the binder in a coating composition S_l of the following solids composition, stated as solids volume parts: 60 parts by volume of the binder, 10 parts by volume of cuprous oxide with an average par¬ ticle size of 2-4 μm, 26 parts by volume of zinc oxide with an average particle size of appoximately 0.2 μm, and 4 parts by volume of thixotropic bentonite results in an erosion rate of the coating in sea water with a salinity in the range of 37-38 parts per thousand of at least 1 μm per 10,000 nautical miles when the coating has been applied on and has been allowed to form a con¬ tinuous film on the convex surface of a cylinder of diame¬ ter 1 meter and the cylinder is rotated with a peripheral speed of 15 knots in sea water of a temperature between 10 and 30°C; the antifouling paint AFP having an erosion rate in sea water, when tested under the conditions defined above, in the range between 1 μm and 50 μm per 10,000 nautical miles, with the proviso that A. the antifouling paint is free from compounds of tin, compounds of arsenic, compounds of lead, and compounds of mercury, and B. the paint composition contains less than 8% by volume, calculated on the total solids volume of the composi¬ tion, of any of the following compounds, or of any combination of the following compounds: hexachlorophene, tetrachloroisophthalonitrile, 1,2,3-trichloro-4,6-dinitrobenzene in pigment form. 2. A paint composition according to claim 1 , wherein the weight average molecular weight (Mw) of the polymer PI is in the range from 2000 to 1,000,000. 3. A paint composition according to claim 2, wherein the weight average molecular weight (Mw) of the polymer PL is in the range from 20,000 to 200,000. 4. A paint composition according to claim 1, wherein the weight average molecular weight (Mw) of the polymer P2 . is in the range from 2000 to 1,000,000. 5. A paint composition according to claim 4, wherein the weight average molecular weight (Mw) of the polymer P2 . is in the range from 20,000 to 200,000. 6. A paint composition according to claim 1, wherein the weight average molecular weight (Mw) of the polymer P3_ is in the range from 2000 to 1,000,000. 7. A paint composition according to claim 6, wherein the weight average molecular weight (Mw) of the polymer P3_ is in the range from 20,000 to 200,000. 8. A paint composition according to claim 1, wherein the weight average molecular weight (Mw) of the polymer P4. is in the range from 2000 to 1,000,000. 9. A paint composition according to claim 8, wherein the weight average molecular weight (Mw) of the polymer P4. is in the range from 20,000 to 200,000. 10. A paint composition according to any of the previous claims, wherein the total pigment content of the composi¬ tion is in the range of 25-50% of the solids volume of the paint composition. 11. A paint composition according to any of the previous claims, wherein the sea water-soluble pigment or pigments constitutes at least 20% of the solids volume of the paint composition. 12. A paint composition according to any of the previous claims, wherein any sea water-insoluble pigments, when present, constitute at the most 40% of the solids volume of the paint composition. 13. A paint composition according to any of the preceding claims, wherein A 3 , A 4 , A 5 , and A~ each independently is Cη . -4-alkylene. 14. A paint composition according to any of the preceding claims, wherein each group B x independently is a group B 1 , B 2 , B 4 or B 5 . 15. A paint composition according to any of the preceding claims, wherein D 7 is hydrogen. 16. A paint composition according to any of claims 1-14, wherein each group B x independently is a group B 1 or B 2 , and D x is different from D 7 . 17. A paint composition according to claim 16, wherein a3, a4, a5, and a6 each is 0. 18. A paint composition according to claim 17, wherein R± and R 2 each independently is hydrogen, methyl or ethyl. 19. A paint composition according to claim 18, wherein O-_ is C~_-2 alkylene, and D 2 and D each independently is hydrogen, methyl or ethyl. 20. A paint composition according to claim 19, wherein each group B x independently is a group B 1 . 21. A paint composition according to claim 20, wherein R^ is hydrogen, and R 2 is hydrogen or methyl. 22. A paint composition according to claim 21, wherein the sea water erodability-conferring segments in the polymer PI have the formula la or Ic. 23. A paint composition according to claim 22, wherein the sea water erodability-conferring segments in the polymer PI have the formula la. 24. A paint composition according to claim 23, wherein D 4 and D 5 are both hydrogen. 25. A paint composition according to claim 24, wherein D x is a group -D 3 (H)0H. 26. A paint composition according to claim 25, wherein D x is -CH 2 CH 2 OH. 27. A paint composition according to any of the preceding claims, wherein the antifouling agent is a biocide or a fouling release agent. 28. A paint composition according to claim 27, wherein the biocide is an algicide, a fungicide, or a bacteriocide. 29. A paint composition according to claim 27 or 28, where¬ in the biocide is selected from copper compounds, such as cuprous oxide, cuprous thiocyanate, copper powder, copper alloy powder, copper naphthenate, copper octoate or copper rosinate; metal dithiocarbamates, such as zinc ethylene bis(dithiocarbamate) , zinc methylene bis(dithiocarbamate) , copper ethylene bis(dithiocarbamate) , zinc dimethyl dithio- carbamate; zinc oxide; zinc pyridinethione; tetramethyl thiuram disulfide; methylene bis(thiourea) ; n-butyl cate- chol; captan; substituted isothiazolones, such as 4,5- dichloro-2-n-octyl-n-isothiazolin-3-one; 2-(N,N-dimethyl- thiocarbamoylthio)-5-nitrothiazole; tetrachloroisophthalo- nitrile; 2-methylthio-4-(tert.butylamino)-6-(cyclopropyl- amino)-s-triazine; N,N-dimethyl-N'-phenyl-N'-(fluorodi- chloromethylthio)-sulfamide; N'-(3,4-dichlorophenyl)-N,N- dimethylurea; and mixtures thereof. 30. A paint composition according to claim 27, wherein the fouling release agent is a silicone compound, such as a dimethylsiloxane-containing liquid or resin, or a liquid methyl phenyl silicone; or a hydrocarbon, such as petrola¬ tum, white oil, paraffin oil, or paraffin wax; or mixtures thereof. 31. A paint composition according to any of the previous claims, wherein the sea-water insoluble pigments are selec¬ ted from grades of titanium dioxide, red iron oxide, carbon black, graphite, yellow iron oxide, phthalocyanine blue, and phthalocyanine green, as well as pigment-like ingredi- ents selected from calcium carbonate, dolomite, talc, mica, barium sulphate, kaolin, and quartz flour. 32. A paint according to any of the preceding claims which comprises a liquid carrier selected from water; alcohols, such as methanol, ethanol, propanol, isopropanol, butanol, isobutanol, benzyl alcohol, 1,2-propanediol; alcohol/water mixtures such as ethanol/water mixtures; aliphatic and aromatic hydrocarbons, such as white spirit, toluene, xylene, or naphtha solvent; ketones, such as methyl ethyl ketone, acetone, methyl isobutyl ketone, methyl isoamyl ketone, diacetone alcohol, or cyclohexanone; ether alco¬ hols, such as 2-butoxyethanol, propylene glycol monomethyl ether, or butyl diglycol; esters, such as methoxypropyl acetate, n-butyl acetate, or 2-ethoxyethyl acetate; chlori¬ nated hydrocarbons, such as methylene chloride or trichlo- roethylene; and mixtures thereof. 33. A marine structure having an adherent continuous ex¬ posed sea water-erodible coating film of an antifouling paint, the coating comprising a film-forming binder as defined in claim 1, at least one pigment which is soluble in sea water in an amount of at least 1 mg/litre, at least one antifouling agent which may be the pigment or one of the pigments, the total pigment content of the coating being in the range of 10-60% of the solids volume of the coating, the sea water-soluble pigment or pigments con¬ stituting at least 10% of the solids volume of the coating, any sea water-insoluble pigments, when present, constitut¬ ing at the most 50% of the solids volume of the coating, the average dry film thickness of the coating being at least 40 μm. 34. A marine structure according to claim 33, in which the average dry film thickness of the coating is in the range of 40-1000 μm. 35. A marine structure according to claim 34, in which the average dry film thickness of the coating is in the range of 50-600 μm. 36. A marine structure according to any of claims 33-35 in which the coating further exhibits any of the features disclosed in any of claims 2-31. 37. A method for operating a watercraft, involving a first painting step in which an erodable antifouling paint coat¬ ing is applied to the part of the exterior of the craft which, during operation of the craft, is immersed in water, sailing the watercraft, and performing a second painting step with an erodable antifouling paint, the method comprising establishing the distance M which the watercraft is to cover between the first and the second painting steps, selecting an antifouling paint composition comprising a film-forming binder, at least one pigment which is soluble in sea water in an amount of at least 1 mg/- litre, at least one antifouling agent which may be the pigment'or one of the pigments, the total pigment content of the composition being in the range of 10- 60% of the solids volume of the paint composition, the sea water-soluble pigment or pigments constituting at least 10% of the solids volume of the paint composi¬ tion, any sea water-insoluble pigments, when present, constituting at the most 50% of the solids volume of the paint composition, said binder comprising at least one polymer PI of a weight average molecular weight of at least 2000 which is water-insoluble and which comprises, as the sea water erodibility-conferring segments, segments of the formula la, lb, Ic, or Id B x I (lb) wherein R-^ and R 2 each independently is hydrogen or C 1 »4 alkyl, A 3 , A 4 , A 5 , and Ag each independently is ^-4 alkylene or phenylene, a3, a4, a5, and a6 each independently is 0 or 1, and each group B x independently is a group D x , or a group B 1 , B 2 , B 3 , or B 4 -COrO-D x ' - (B 1 ) -CO-NH-D x (B 2 ) -NH-CO-D x (B 3 ) -0-D x (B 4 ) or the two groups B x in (Ic) or (Id) together constitute an imide group B 5 0=c C=0 (B ) \ / N D X wherein D x is a group -(D 1 -0-) d D , a group -D I 5 3 -O-D 4 , or a group D 7 and D x ' is a group -(D 1 -0-) f D2 or a group 1 5 -D 3 -OH, wherein O± is C-^- 4 alkylene, D 2 is hydrogen or C^.4 alkyl, d is an integer from 2 to 300 D 3 is C^_4 alkylene; phenylene optionally substituted with 1 or 2 C 1 _ 2 alkyl; or a phenyl-C 1 _ alkyl moiety having the group D5 attached to the phenyl ring, and having the free bond shown located on the phenyl ring and the group -0-D 4 attached to the alkyl part, or vice versa, the phenyl part option¬ ally being substituted with 1 or 2 substitu- ents selected independently from hydroxy and C-L_4 alkoxy, D 4 is hydrogen or ^- 4 alkyl, D 5 is hydrogen, hydroxy or C 1 _ 4 alkoxy, or, when D 3 is ^. 4 alkylene, -0-D4 and D 5 together form C^-4 alkyleneoxy, and D 7 is hydrogen or C- -4 alkyl, with the proviso that, when,the polymer contains segments of the formula la, where R^ is hydrogen, R 2 is hydrogen or methyl, a3 is 0, B x is a group B 1 , and D 3 is (CH 2 )ι_ 4 , then D4 is hydrogen, and that, when D 7 is hydrogen, then B x is a group B 4 ; the kind and concentration of the segments la, lb, Ic, or Id in the polymer P_l being so selected that the polymer PI, when incorporated as the binder in a coating composition S of the following solids composi- tion, stated as solids volume parts: 60 parts by volume of the polymer, 10 parts by volume of cuprous oxide with an average particle size of 2-4 μm, 26 parts by volume of zinc oxide with an average particle size of appoximately 0.2 μ , and 4 parts by volume of thixotropic bentonite results in an erosion rate of the coating in sea water with a salinity in the range of 37-38 parts per thou¬ sand of at least 1 μm per 10,000 nautical miles when the coating has been applied on and has been allowed to form a continuous film on the convex surface of a cylinder of diameter 1 meter and the coated cylinder is rotated with a peripheral speed of 15 knots in sea water of a temperature between 10 and 30°C; whereby, when the film-forming binder comprises more than one polymer, each other polymer is either a polymer PI as defined above, a polymer £2 of a weight average molecular weight of at least 2000 which is water-insoluble and comprises segments of the formula la, lb, Ic, or Id as defined above, the kind and concentration of the segments la, lb, Ic, or Id and other segments in the polymer P2 being so selected that the polymer P2., when incor¬ porated as the polymer in the coating composition S . as defined above, results in an erosion rate of the coating in sea water of at less than 1 μ per 10,000 nautical miles when tested as defined above, or a film-forming polymer P3_ of a weight average molecu¬ lar weight of at least 2000 which does not comprise segments la, lb, Ic or Id, the polymer P , when incor¬ porated as the binder in the coating composition S_ as defined above, resulting in an erosion rate of the coating in sea water of less than 1 μm per 10,000 nautical miles when tested as defined above, or a polymer P4_ of a weight average molecular weight of at least 2000 which comprises sea water erodibility- conferring segments which are not segments la, lb, Ic or Id, the polymer P , when incorporated as the poly¬ mer in the coating composition S. as defined above, resulting in an erosion rate of the coating in sea water of at least 1 μm per 10,000 nautical miles when tested as defined above, and, when the film-forming binder consists of more than one polymer, the total binder polymer composi¬ tion, when incorporated as the binder in a coating composition SI of the following solids composition, stated as solids volume parts: 60 parts by volume of the binder, 10 parts by volume of cuprous oxide with an average particle size of 2-4 μm, 26 parts by volume of zinc oxide with an average particle size of appoximately 0.2 μm, and 4 parts by volume of thixotropic bentonite results in an erosion rate of the coating in sea water with a salinity in the range of 37-38 parts per thou- sand of at least 1 μm per 10,000 nautical miles when the coating has been applied on and has been allowed to form a continuous film on the convex surface of a cylinder of diameter 1 meter and the cylinder is rotated with a peripheral speed of 15 knots in sea water of a temperature between 10 and 30°C; the antifouling paint having an erosion rate in sea water, when tested under the conditions defined above, in the range between 1 μm and 50 μm per 10,000 nauti- cal miles, determining the value ER of the erosion rate expressed in μm per 10,000 nautical miles, applying the paint composition in an amount resulting in an average dry film thickness T of at least 40 μm and equal to a thickness which, in view of the conditions under which the ship is to be sailed, will be sufficient to provide a coating of the paint on at least part of the coated area after the ship has covered the distance M; sailing the watercraft and thereby eroding the coating, and performing the second painting step by applying a new coating of the antifouling paint before or when the first layer has been partially or completely eroded.

Inventors: CHRISTENSEN THOMAS, CODOLAR SANTIAGO ARIAS, GARMIN HENRIETTE, WARNEZ MICHEL YVES, CHRISTENSEN, THOMAS, CODOLAR, SANTIAGO, ARIAS, GARMIN, HENRIETTE, WARNEZ, MICHEL, YVES
Applicants: HEMPELS SKIBSFARVE FAB J C, J.C. HEMPEL'S SKIBSFARVE-FABRIK A/S
Application year: 1992
Main classification: C09D5
IPC codes: C09D5, C09D7, C09D129, C09D133, C09D137, C09D139