Antifoulant composition and method

The durability of coatings formed from antifouling compositions containing a biologically active organotin-containing polymer as the film-forming component is improved by the presence of at least one biologically inactive organotin-containing polymer in an amount of from 0.01 to 10% based on the weight of the initial coating composition.

This invention relates to novel biologically active polymeric materials. 
More specifically, it relates to novel marine antifoulant compositions 
containing mixtures of organotin polymers as the film-forming component, 
wherein at least one of the said organotin polymers is biologically 
active. 
Organotin polymers, such as those described in U.S. Pat. Nos. 3,167,473, 
4,064,338, and 4,121,034 are known to be effective film-forming 
antifoulant agents which can serve as the binder component of a marine 
antifoulant paint. Such paints are typically comprised of binder; pigments 
such as red iron oxide, titanium dioxide, and zinc oxide; thickeners such 
as bentonite and fumed silica; extenders such as talc; and inert diluents 
typified by mineral spirits, naphtha, xylene, methyl isobutylketone, etc. 
Typical film-forming organotin-containing polymers useful as biologically 
active binders in marine antifoulant compositions are disclosed in U.S. 
Pat. Nos. 3,167,473, 4,064,338, and 4,121,034. Coatings resulting from the 
drying of such compositions exhibit weak structural integrity, 
particularly under dynamic flow conditions such as exposure to moving sea 
water, due to the inability of the relatively soft organotin polymer to 
bind the solid additives into a tightly cohesive matrix. Consequently, the 
useful life of such coatings when exposed to dynamic flow conditions in 
relatively short due to weakness of the binder-pigment interaction that 
results in excessive erosion of the coating. 
It is the object of this invention to provide a novel method for improving 
the dynamic cohesive strength of marine antifoulant coatings based on 
biologically active, film-forming organotin polymers through the addition 
of another film-forming organotin polymer which is not necessarily 
biologically active. 
It has now been found that the dynamic cohesive strength of a marine 
antifoulant coating is improved or modified resulting in a predictable and 
extended performance lifetime under dynamic conditions by utilizing a 
film-forming system based on a combination of organotin-containing 
polymers whereby at least one of said organotin polymers contains less 
than 15 mole % of triorganotin compound and the other contains more than 
25 mole % of the triorganotin compound. 
SUMMARY OF THE INVENTION 
This invention provides an improved composition for protecting marine 
surfaces against the growth of fouling organisms, said composition 
consisting essentially of: 
(a) 1 to 30% by weight of the total composition of a biologically active 
film-forming polymer derived in part from a first triorganotin compound 
exhibiting the formula R.sub.3 SnOOCR' 
wherein 
R is selected from the group consisting of alkyl, cycloalkyl, and aryl 
radicals, and 
R' is a polymerizable group selected from the group consisting of vinyl, 
.alpha.-methylvinyl, and phenylvinyl radicals, 
wherein 
repeating units derived from said compound constitute from 25-80 mole % of 
the total repeating units present in said polymer, the remaining 20-75 
mole % of said repeating units being derived from at least one 
ethylenically unsaturated compound that is copolymerizable with said first 
triorganotin compound, 
(b) 1 to 50% by weight of the total composition of at least one 
metalliferous pigment, and 
(c) 30 to 80% by weight of the total composition of an inert diluent, 
the improvement which consists of the presence in said composition of from 
0.01 to 10% by weight of the total composition of a biologically inactive 
film-forming polymer derived in part from a second triorganotin compound 
exhibiting the formula R.sub.3.sup.2 SnOOCR.sup.3, 
wherein 
R.sup.2 is selected from the same group as R and 
R.sup.3 is selected from the same group as R' and the repeating units 
derived from said triorganotin compound constitute from 1 to 15 mole % of 
the total repeating units present, the remaining 85-99 mole % of said 
repeating units being derived from at least one ethylenically unsaturated 
compound that is copolymerizable with said second triorganotin compound. 
Through the selection of the ratios of the polymers comprising the 
film-forming component of the paint system, predictable and extended 
performance lifetimes relative to prior art compositions under dynamic 
conditions can be achieved. 
The novel feature of the composition of this invention resides in the 
presence in said composition of a polymer derived from a monomer mixture 
containing a relatively small amount of biologically active triorganotin 
compound, the remaining monomers being those which are known to yield 
tough, durable films when in polymer form. The concentration of 
triorganotin species in the final polymer is insufficient to yield 
significant biological activity as specified in U.S. Pat. No. 4,064,338 
and 4,121,034. 
The auxiliary organotin polymeric binder, when incorporated at useful 
concentrations, must be compatible with the biologically active organotin 
polymer and the solvent system utilized in the coating composition. It 
must provide sufficient cohesiveness to the coating (without adversely 
affecting the antifoulant properties of the coating), to extend the 
performance lifetime of said coatings. 
The auxiliary organotin polymeric binders are film-formers in their own 
right, yielding tough, glassy coatings. When used as the auxiliary binder, 
as the minor component of the binder system, the dynamic cohesive strength 
of the coating formed from the antifoulant paint is improved, allowing 
extended performance lifetime without sacrificing antifoulant properties. 
The concentration of the organotin polymer auxiliary binder to be 
incorporated into the biologically active organotin polymer containing 
antifoulant paint will depend on the upper concentration limit of 
compatibility and on the effective concentration for optimizing dynamic 
cohesive strength while maintaining antifouling performance. The effective 
concentration will vary depending on the pigment type(s) utilized in the 
coating compositions. 
In the foregoing formulae, R and R.sup.2 represent those hydrocarbon 
radicals normally associated with biologically active triorganotin 
compounds. For example, R and R.sup.2 may be an alkyl radical containing 
from 1 to 8 carbon atoms, a cycloaliphatic radical such as cyclopentyl or 
cyclohexyl, or a phenyl radical. It is understood that R and R.sup.2 may 
be inertly substituted, e.g. may bear a nonreactive substituent such as 
alkyl, cycloalkyl, aryl, arakyl, alkaryl, alkenyl, ether, halogen, ester, 
etc. 
The composition of the biologically active organotin polymer consists of at 
least one of the R.sub.3 SnOOCR' compounds and at least one 
copolymerizable compound selected from the groups which are described in 
the pertinent sections of U.S. Pat. Nos. 3,167,473, 4,064,338, and 
4,121,034 which are hereby incorporated by reference. The concentration of 
the R.sub.3 SnOOCR' compound is from 25 to 80 mole % of the total monomers 
present in said polymer. The polymer can be prepared by either 
polymerization of the desired monomer mixture or by reacting a preformed 
organic polymer containing a reactive carboxylic acid with a suitable 
triorganotin compound. 
The composition of the auxiliary organotin polymeric binder consists of at 
least one of the R.sub.3.sup.2 SnOOCR.sup.3 compounds and at least one 
copolymerizable compound selected from the groups which are described in 
the pertinent sections of U.S. Pat. Nos. 3,167,473, 4,064,338, and 
4,121,034. The concentration of the R.sub.3.sup.2 SnOOCR.sup.3 compound is 
.ltoreq.15 mole % of the total monomers present in said polymer. The 
polymer can be prepared by either polymerization of the desired monomer 
mixture or by reacting a preformed organic polymer containing a reactive 
carboxylic acid with a suitable triorganotin compound. 
Among the metalliferous pigments that can be included are inert compounds 
such as iron oxide, zinc oxide, titanium dioxide and talc, and 
biologically active compounds such as cuprous oxide, copper thiocyanate, 
tributyltin fluoride, tricyclopentyltin fluoride, tricyclohexyltin 
hydroxide, triphenyltin fluoride, and triphenyltin hydroxide.

The following examples illustrate the present method and the improved 
coating compositions obtained thereby. 
EXAMPLE 1 
Preparation of the auxiliary binder. 
A 2-liter capacity polymerization reactor equipped with a N.sub.2 inlet, 
H.sub.2 O cooled condenser, thermometer, and stirrer is charged with 37.5 
g tributyltin methacrylate, 137.8 g butyl methacrylate, 500 ml "Hi-Flash 
Naphtha.RTM.", and 0.036 g benzoyl peroxide. The contents of the flask are 
heated at 80.degree. C. for 8 hours to obtain greater than 95% conversion 
of monomers to polymer. 
EXAMPLE 2 
The polymer solution prepared in Example 1 was added at 5, 10, and 25% 
solids volume concentration to a 50% by weight solution of a biologically 
active organotin polymer prepared as described in Example 1 of U.S. Pat. 
No. 4,064,338. All solutions were miscible and none exhibited phase 
separation after 6 months at room temperature (77.degree. F.). 
EXAMPLE 3 
Dry films prepared from the mixtures of the two polymer solutions as 
described in Example 2 were clear and transparent and remained so when 
examined 6 months after preparation. These results demonstrate excellent 
compatibility between the biologically active organotin polymer and the 
auxiliary organotin film-forming polymer. 
EXAMPLE 4 
The antifouling properties of the auxiliary binder prepared as described in 
Example 1 was compared to that of the biologically active organotin 
polymer. Fiberglass discs with a 2.5 inch radius were coated with clear 
films of the two polymers. The test discs together with untreated discs 
were immersed below tide level in the ocean at Biscayne Bay, Fla. 
After 5 weeks of immersion, the untreated discs and the disc coated with 
the auxiliary binder coating were completely fouled whereas the disc 
coated with the biologically active organotin polymer was completely free 
of fouling organisms showing that the organotin polymeric auxiliary binder 
is not an effective antifoulant agent. 
EXAMPLE 5 
Fiberglass panels (8 inches by 12 inches) were coated with the polymer 
mixtures from Example 2 which contain the auxiliary binder at 5 and 10% 
solids volume concentration. The test panels together with untreated 
panels were immersed below tide level in the ocean at Biscayne Bay, Fla. 
After 12 months of immersion, the coated panels were free of fouling 
organisms whereas the untreated panels were completely fouled, 
demonstrating that the auxiliary binder does not adversely affect 
antifouling performance of the biologically active organotin polymer. 
EXAMPLE 6 
Antifouling paints suitable for test purposes were prepared according to 
known commercial practices. Table I shows the coating compositions of test 
panels treated with antifouling paints containing the biologically active 
organotin film-forming polymer but without the auxiliary organotin 
polymeric binder. Constituent concentrations are in volume percent, as 
100% solid. 
TABLE I 
______________________________________ 
A B C D E F G H I 
______________________________________ 
Biologically Active Organotin Polymer 
75 75 75 60 60 60 45 45 45 
Iron 
Oxide 25 12.5 0 40 20 0 55 27.5 
0 
ZnO 0 12.5 25 0 20 40 0 27.5 
50 
100 100 100 100 100 100 100 100 100 
Pigment Volume Concentration (PVC) 
25 25 25 40 40 40 55 55 55 
______________________________________ 
Paint E was modified so as to contain varying amounts of the auxiliary 
organotin polymeric binder as shown in Table II. 
TABLE II 
______________________________________ 
E-1 E-2 E-3 E-4 
______________________________________ 
Biologically Active Organotin Polymer 
60 57 54 51 
Auxiliary Organotin Polymeric Binder 
(Ex. 1, as 100% solid) 
0 3 6 9 
______________________________________ 
The paints were adjusted to a solids content of 25% by weight, by the 
addition of xylene. Test panels were treated with the test paints to give 
dry coating thickness of 300.mu.. 
EXAMPLE 7 
The resistance to erosion in moving sea water of the test coatings 
described in Example 6 were tested using apparatus specifically designed 
to measure the rate of erosion of coatings under dynamic conditions as 
described by de la Court et al in J. Oil Col. Chem. Assoc., 56, 388 
(1973). The results are summarized in FIGS. 1 and 2. 
FIG. 1 shows the rate of erosion in moving sea water of coatings A-I 
described in Example 6 (without auxiliary binder). Increasing pigment 
volume concentration and zinc oxide cause an increase in erosion rate. The 
minimum erosion rate obtainable, 0.7 .mu./day, demonstrates that a 300.mu. 
coating will completely wear off in 430 days. 
FIG. 2 shows the influence on erosion of the auxiliary binder in coatings 
E-1-E-4, described in Example 6, when added as an auxiliary binder to 
coating composition E of Example 6. At a concentration of 5% by volume of 
the binder system, erosion rate in moving sea water is reduced to 0.2 
.mu./day, giving a 300.mu. coating a lifetime of 1500 days, a 300% 
increase over the coating of Example 2 which erodes at 0.7 .mu./day. 
EXAMPLE 8 
Test panels treated with coating compositions E-1 and E-2, described in 
Example 6, were immersed below tide level in the ocean at Biscayne Bay, 
Fla. 
After 6 months immersion, both panels were free of fouling organisms. 
Coating E-1 easily released pigment when finger-rubbed after the immersion 
period, as evidenced by the red stain from the iron oxide, demonstrating 
that there is a weak pigment binder interaction in the coating. 
Coating E-2 did not release pigment when finger-rubbed after the period of 
immersion, demonstrating the strengthening effect of the organotin 
polymeric auxiliary binder.