Organotin antifouling coatings with novolac and Bisphenol-A epoxy resins

An antifouling compound is formed of the esterification product of tributin oxide combined with the copolymer of styrene and maleic anhydride. An antifouling coating formulation is prepared by combining the esterification product with a selected blend of Bisphenol-A and novolac epoxies, fillers, pigment, solvent containing a ketone portion, and an amido amine based accelerator.

BACKGROUND OF THE INVENTION 
This invention generally relates to improvements in the formulation and 
production of marine antifouling compositions and more particularly, to 
organotin-based antifoulants for epoxy coatings. 
In the past, salts and oxides of metals such as copper, zinc, arsenic and 
mercury have been used in marine antifouling coatings. However, some of 
these compounds cause corrosion of the metal substrate and degradation of 
the paint coatings, as well as having a limited service life. Organotin 
based antifoulants such as tributyltin oxide and tributyltin fluoride have 
been developed to overcome some of the abovementioned drawbacks with the 
prior antifoulants. Although the organotin antifoulants are compatible 
with conventional antifouling coating systems, most coating systems 
contain various water soluble pigments, fillers and binders so that the 
antifoulant leaches into the water at an uncontrolled rate. In attempting 
to control the leaching rate of the antifoulants, various polymeric 
compounds have been developed as exemplified, for example, by U.S. Pat. 
Nos. 3,016,369; 3,382,264; 3,930,971; 3,979,354; 4,064,338; 4,075,319; and 
4,174,339. 
However, the reaction process of combining organotin oxides and hydroxides 
with various polymeric materials to control leaching, as discussed in the 
abovementioned patents, is more complex and costly than conventional 
preparation processes for other antifoulants. For example, the reaction 
process disclosed in U.S. Pat. Nos. 3,979,354 and 4,075,319 generally 
involves the esterification of an organotin compound with the acid group 
of a vinyl polymer. This reaction process not only produces water as a 
reaction by-product but also involves the sequential use of various 
solvents which must be removed along with the water to obtain a solids 
solution. The solids are then dissolved in another solvent to prepare the 
final coating composition. The process of making organometallic 
antifoulants envisioned by the present invention eliminates reaction steps 
disclosed by the prior art by eliminating the production of water 
by-product and by utilization of polymeric materials and solvents 
therefore which reduces the number of solvation-distillation steps. It was 
also found that the particular polymeric materials used to react with the 
organotin antifoulant exhibits controlled leaching characteristics not 
contemplated by the prior art. 
Epoxy coating formulations are generally exemplified by U.S. Pat. Nos. 
3,301,795; 3,417,045; 3,532,538; 3,676,388; and 4,172,177. Although 
antifoulant materials have been incorporated into the epoxy matrix such as 
disclosed, for example, in U.S. Pat. No. 3,676,388, problems have been 
experienced in providing uniform dispersion of antifoulant throughout the 
coating and controlling the leaching rate of antifoulant therefrom. Also, 
controlled physical properties are difficult to obtain when incorporating 
organotin polymers in the epoxy matrix. 
SUMMARY OF THE INVENTION 
The antifouling coating system of the present invention overcomes drawbacks 
experienced with the prior art by providing a durable antifouling coating 
which is simple to manufacture, easy to apply to ship surfaces, and which 
exhibits a controlled long-term leaching of antifoulant. This is 
accomplished by initially reacting a copolymer of styrene and maleic 
anhydride with tri-n-butyltin oxide to form an esterification product. 
Preferably, one mole of styrene-maleic anhydride is reacted with from 0.4 
to 0.8 mole of TBTO to esterify from about 40% to about 80% of the maleic 
anhydride groups, with the unreacted maleic anhydride groups being 
utilized to crosslink with compatible epoxy resin types, such as 
diglycidyl ether of bisphenol A blended with novolac resins. When blended 
with other compatible coating materials such as selected resins, binders, 
pigments and fillers, the crosslinked organotin polymer and epoxy blend 
coating system can be formulated to optimize coating longevity, provide 
coating strength and durability, and permit easy application. 
Accordingly an object of the present invention is to provide an inexpensive 
method for producing an efficient, long-lasting organometallic 
antifoulant. 
Another object of this invention is the provision of an antifouling 
composition for preventing biological growths on submerged surfaces for an 
extended period of time. 
A further object of the present invention is to provide an antifouling 
coating formulation which is durable, non-polluting, and effective in 
preventing fouling. 
Yet another object of this invention is to provide an antifoulant 
formulation characterized by a controlled, low leaching rate of the 
antifouling agent from the coating matrix. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention provides an improved organotin antifoulant coating 
possessing low leaching, nonpolluting, biological properties which 
exhibits controlled leaching characteristics when chemically bonded to 
selected blends of novolac and Bisphenol-A epoxy resins. The resulting 
organometallic polymers are surface hydrolyzed in sea water to initiate 
the antifouling action and the organometallic compounds are released at a 
rate that is dependent not only on the nature of the organometallic 
polymer but also on environmental conditions such as water temperature, 
oxygen content, and hydrogen ion concentration. Thus, hydrolysis of the 
organometallic compounds can be controlled to provide long-term 
antifouling protection while reducing pollution hazards. Preferably, the 
organotin compounds are incorporated into a polymeric material through an 
esterification reaction between the organotin compound and the anhydride 
functional groups of the polymeric material. 
The organotin compounds are of the general form (R.sub.3 Sn).sub.2 O where 
R represents butyl, propyl or phenyl groups with tributyltin oxide being 
preferred because of its higher toxicity levels towards marine life. 
Suitable polymeric resins with which organotin compounds may be chemically 
combined include thermoplastic polymers, such as vinyl polymers, and 
thermosetting polymers, such as polyester resins. Preferred polymeric 
materials comprise copolymers resulting from the copolymerization of 
.alpha.,.beta.-unsaturated carbonyl compounds, more particularly 
carboxylic acid anhydrides (ie. maleic anhydride), and alkenes, such as 
vinylbenzenes (ie. styrene). An example of a preferred compound is the 
copolymer of styrene and maleic anhydride, as shown below: 
##STR1## 
Preferably, m varies from 1 to 3 and n ranges from about 6 to about 8 so 
that the copolymer provides a means for controlling the uniform 
distribution of organotin oxide antifoulant throughout the polymer matrix. 
This particular range of variables was also found to provide good 
crosslinking between the unreacted maleic anhydride groups (ie. after 
esterification with tributyltin oxide) and permit controlled leaching of 
the antifoulant from the coating matrix. Accordingly, the average 
molecular weight of the styrene-maleic anhydride copolymer should range 
from about 1600 to about 2500. Commercial styrene-maleic anhydride 
copolymer is produced by ARCO Chemical Company, a division of 
Atlantic-Richfield Company under the trademark SMA Resins, characteristic 
examples of which are set forth below and in a copending U.S. patent 
application Ser. No. 266,236, filed May 22, 1981 by Albert R. Parks and 
Stephen D. Rodgers and entitled Organotin-Epoxy Antifouling Coating. 
__________________________________________________________________________ 
Solutions in Aqueous Ammonia 
15% NVM.sup.(1) 
20% NVM 
30% NVM 
SMA Molecular 
Melting 
Acid 
Viscosity 
Gardner 
Viscosity 
Viscosity 
Resin 
Weight.sup.(2) 
Range, .degree.C. 
No. 
(cps.) Color 
(cps.) 
(cps.) 
__________________________________________________________________________ 
1000 
1600 150-170 
480 
17 1-2 28 50 
2000 
1700 140-160 
350 
26 1-2 136 17000 
3000 
1900 115-130 
275 
52 1 gel gel 
1440 
2500 55-75 175 
27 2 88 3500 
17352 
1700 160-170 
270 
24 &lt;1 50 2400 
2625 
1900 135-150 
220 
30 &lt;1 350 gel 
3840 
2300 100-120 
105 
INSOLUBLE 
__________________________________________________________________________ 
.sup.(1) Nonvolatile material 
.sup.(2) Number average 
Other compounds having terminal vinyl groups such as vinylbenzene may be 
used instead of styrene, and examples of other compatible anhydrides 
include citraconic anhydride and methyltetrahydrophthalic anhydride. Thus, 
copolymers such as the maleic anhydride adduct of methylcyclopentadiene, 
and the copolymer of maleic anhydride and vinyl ether may be used in place 
of the styrene-maleic anhydride copolymer. The amount of organotin oxide 
that is combined with the styrene-maleic anhydride resins depends upon the 
desired degree of esterification of the maleic anhydride groups. 
Preferably, the degree of esterification of the maleic anhydride groups 
ranges from about 40% to about 80% with an optimum value of about 60%, 
wherein the unreacted maleic anhydride groups are utilized to crosslink 
with the particular epoxy resins of the coating. Thus, the styrene-maleic 
anhydride copolymer serves as an intermediary for interlinking the 
organotin oxide antifoulant with the epoxy matrix of the coating. Suitable 
solvents for the esterification process between the styrene-maleic 
anhydride copolymer and the organotin oxide include aromatic hydrocarbons 
such as toluene and xylene and super high flash naptha such as 
manufactured by AMSCO Chemical Co. Since the solvent is not separated from 
the esterification product before the esterification products are further 
combined with the selected blends of epoxy resins, the solvent should be 
compatible therewith. The amount of solvent required for the 
esterification of tributyltin oxide and the styrene-maleic anhydride 
copolymer depends upon the viscosity and percent of solids in the final 
product that is desired, with the solvent ranging generally from about 10% 
to about 50%, by weight, of the reactants. The esterification process of 
the styrene-maleic anhydride copolymer and tributyltin oxide antifoulant 
is shown below:

EXAMPLE 
Preparation of TBTO and Styrene-Maleic Anhydride Copolymer 
404 grams of styrene-maleic anhydride resin (SMA Resin 1000A by ARCO 
Chemical Co.) was combined with 715 grams of tributyltin oxide (M & T 
Chemical Co.) and 200 ml. of toluene solvent for 2 to 4 hours with 
periodic sampling followed by infrared analysis to indicate the extent of 
esterification. Periodic mixing was performed to maintain the temperature 
of the mixture between about 60.degree. C. and 110.degree. C. during this 
period. The final analysis indicated a reaction product which contained 
the desired proportion of esterification product and unreacted maleic 
anhydride groups. The final esterification mixture was then combined 
directly with selected novolac and Bisphenol A type epoxy resins, pigment, 
and fillers to achieve the desired coating formulation. Prior to applying 
the epoxy based antifouling coating, an accelerator/initiator is mixed 
with the coating formulation to initiate the reaction of the epoxy 
molecules. 
One of the two preferred classes of epoxy resins found compatible for 
combination with the reaction product and byproduct of the esterification 
of tributyltin oxide and the styrene-maleic anhydride copolymer are epoxy 
compounds such as 2,2-bis(4,4'-hydroxy-phenyl) propane, often referred to 
as diglycidyl ether of Bisphenol A. Glycidyl ethers suitable for use in 
the present coating composition should exhibit viscosities of 16,00 to 
20,000 centipoises or less at ambient temperatures and have an epoxide 
equivalent weight in the range of about 170 to about 700, and preferably 
between about 175 and 250. The glycidyl ethers are derived from compounds 
containing one or more hydroxyl groups bonded to the carbon atoms of the 
aromatic ring structure. These compounds have the general structure 
##STR3## 
where Ar is representative of the aromatic groups and n varies, for 
example, from between 2 and 10. The Ar groups can be phenyl or naphthyl 
radicals which can be bonded directly to one another as in the biphenyl 
radical. Alternatively, the aromatic ring structures may be separated by 
alkylene or by other divalent radicals such as hydroxy-phenyl groups as 
occur in the Bisphenol-A epoxy. Other examples of suitable epoxy compounds 
include 2,2 bis(4-(2,3 epoxy propyl) cyclohexyl) propane, diglycidyl ether 
of resorcinol, bis(2-dihydroxynaphthyl) methane, hydroquinone, and 
bis(4-hydroxyphenyl)-1,1 isobutane. A number of commercially useful 
diglycidyl ethers of Bisphenol A epoxide resins and oligomers are listed 
in Chapter 4 of the publication entitled "Handbook of Epoxy Resins" by H. 
Lee and K. Nevill (McGraw Hill Book Company, New York, 1967). 
In accordance with the invention, the other class of epoxy resins are lower 
molecular weight novolac resins which are normally highly viscous at room 
temperatures. The blending of the novolac and Bisphenol-A type epoxies 
utilizes, for example, the structural or coating strength of the novolac 
resins and the uniform viscosity reduction provided by the Bisphenol-A 
resins. The epoxy novolac resins are represented by the general formula: 
##STR4## 
where R is selected from the group consisting of hydrogen and alkyl groups 
having up to 18 carbon atoms, and n is an integer of from 1 to about 10. 
Preferably, n should vary from 1 to about 5 and the alkyl group, if 
present, may be a straight or branched chain. Novolac resins are 
conventionally produced by condensing phenol with an aldehyde, such as 
acetaldehyde, chloral, and butyraldehyde, in the presence of an acid 
catalyst. Illustrative examples of alkylphenols from which the novolac 
resins may be derived include cresol, butylphenol, tertiary butylphenol, 
tertiary amylphenol, hexlphenol, 2-ethylhexylphenol, nonylphenol, 
decylphenol, and dodecylphenol. The epoxidized novolac resin is formed by 
combing the novolac resins with epichlorohydrin and then adding an alkali 
metal hydroxide to the mixture so as to effect the desired condensation 
reaction. Preferably, the viscosity of the novolac resins should range 
from about 4,000 cps to 70,000 cps with the epoxy equivalent weights 
ranging from about 172 to about 210. Examples of commercial novolac 
epoxies include DEN 438 by Dow Chemical Co. and EPN 1138 by Ciba Geigy Co. 
Preparation of the antifouling coating is accomplished by mixing together 
two components "A" and "B" prior to application of the antifouling coating 
material to the substrate. A stand-in time is allowed prior to application 
of the antifouling formulation to allow sufficient chemical reaction 
between the materials in components "A" and "B". Component "A" normally 
contains the epoxy resin blend (Bisphenol-A and novolac) and the 
organometallic antifoulant (ie. tributyltin oxide ester of the copolymer 
of styrene-maleic anhydride in the preparation solvent) and component "B" 
contains the amido amine based accelerator in a solvent which is 
compatible with the materials in component "A". A ketone based solvent for 
component "B" is preferred to produce a partial ketamide complex that 
blocks or otherwise reduces the reaction rate of the accelerator with the 
epoxide group. Upon application of the antifouling formulation to a ship 
surface, the ketone solvent evaporates and the amido amine accelerator 
reacts with the epoxy groups. Selected fillers, pigments and other 
materials can be added to component "A" or "B" or the mixture thereof 
prior to application of the coating. 
EXAMPLE 1 
______________________________________ 
Preferred 
Range 
Parts (percent 
(by weight) 
by weight) 
______________________________________ 
Organotin copolymer 180 25-50 
(tributyltin oxide ester of styrene-maleic 
anhydride copolymer) 
solvent 
methyl ethyl ketone 50 7-30 
ethyl Cellosolve 15 3-12 
Novolac epoxy(EEW about 178) 
25 6-10 
Bisphenol A epoxy(EEW about 180) 
75 18-30 
Accelerator 40 10-20 
(Epi-Cure 855 or 
Epi-Cure 856) 
Filler 6 2-8 
(ie. Quso WR by 
Philadelphia Quartz) 
Pigment 6 2-8 
(black pigment, 
ie. Ravin 8000) 
______________________________________ 
(1) EEW is epoxy equivalent weight 
In the above formulation, ethyl Cellosolve, which is a glycol ether, 
provides viscosity reduction of the coating system and extends the pot 
life of the epoxy resin misture. One example of a lower equivalent weight 
Bisphenol-A type epoxy is EPON Resin 828, a trademarked product of Shell 
Chemical Co. having an average molecular weight of about 380 and an 
average equivalent weight of about 180. Examples of commercial novolac 
resins include DEN 438, a trademarked product of Dow Chemical Company 
having an average equivalent weight of 178. The accelerators used in the 
above formulation are aliphatic amido amines manufactured by Celanese 
Resin Company under the trademark EPI-CURE. Another compatible filler is 
fumed silica, such as Cab-O-Sil, a trademarked product of the Cabot 
Corporation. 
EXAMPLE 2 
______________________________________ 
Preferred 
Range 
Parts (percent 
(by weight) 
by weight) 
______________________________________ 
Organotin copolymer 180 30-55 
(tributyltin oxide ester of styrene-maleic 
anhydride copolymer) 
Solvent 
methyl ethyl ketone 50 8-30 
ethyl Cellosolve 15 3-12 
Novolac epoxy(EEW about 210) 
50 8-20 
Bisphenol-A epoxy(EEW about 180) 
50 12-20 
Accelerator 40 10-20 
(Epi-Cure 855 or 
Epi-Cure 856) 
Filler 6 2-8 
(ie. Quso WR by 
Philadelphia Quartz) 
Pigment 6 2-8 
(black pigment 
ie. Ravin 8000) 
______________________________________ 
Preferred curing agents for the antifouling formulations include aliphatic 
amido amines, such as EPI-CURE 855 and 856 by Celanese Resins; aromatic 
amines such as EPI-CURE 8494; and tertiary amines such as 
trisdismethylaminomethylphenol. Aliphatic polyamines include polyalkylene 
amines such as diethylene/triamine, triethylene/tetraamine, and 
tetraethylene. Other useful amines include ethylene diamine, 
tetramethylene diamine, hexamethylene diamine, xylylene diamine, and the 
like. 
Obviously many modifications and variations of the present invention are 
possible in light of the above teachings. It is therefore to be understood 
that within the scope of the appended claims the invention may be 
practiced otherwise than as specifically described.