Note: Descriptions are shown in the official language in which they were submitted.
23~
13790:RDS -1-
ORGANOTIN POLYSILOXANE AND ACRYLIC
ANTIFOULING COATING
Field of the Invention
This invention relates to marine antifouling
coating cQmpositions including an acrylic resin
and a trisubstituted or~anotin substituted
polysiloxane in a paint ~ixture. Preferably, the
compositions also include copper or a copper salt
:l~or inhibiting marine ~ouling.
Back~round
When a ship moves through the water the drag
: resistance or watex frictional forces which must be
: overcome are responsible for as much as hal of the
power consumed in operation of the vessel. The
surface condition of ~he hull is a major factor
inducing drag~ It is therefore desirable to have
an extremely smooth surface on the hull and paint
formulations have been developed that are vçry smoo~h
when cured and/or are polished by moving water to
~: 30 pxo~ide an extremely smooth surface. It is desirable
to have a coating material that exhi~its this
polishing action to produce a microsmooth surlace to
minimize the drag penalty due to microroughness.
~ I
3~2~
--2--
1 Fouling of the hull by pestiferous marine
organisms is a major source o~ drag. The use
of antifouling protective coatings on a ship's hull
is a primary approach to controlling fouling and the
resulting drag. The antifouling coating inhibits
growth o~ marine organisms on the hull ~o keep it
smooth. Coatings can also be used on static
structures exposed to seawater to minimize growth of
organisms that could cause deterioration of such
structures.
A trul~ ef~ective an~ifouliny coating meets at
least three criteria: ~1) It will possess broad
spectrum antifouling effi~acy (i.e., inhibit yrowth
of a bxoad varie~y of organisms) for extended periods
of time, usually thxee years; ~2) it will possess a
smooth surface so as not to cause a microroughness
drag penalty; and (3) it will actively reduce drag
by reduciny the roughness profile of the sur~ace.
To meet the first criterion it is necessary to
deliver ~o the surface of the coating in a controlled
fashion~ minimum ef~ective amounts of ~oxin or fouling
control agents. The amount of toxin delivered at the
surface should no~ be substantially above the minimum
effective amoun~ for inhibiting fouling to avoid
premature depletion of the antifouling agent.
One technique for controlling release of toxin
involves khe use o~ latent toxicants which are activated
by an environmental or chemical trigger such as hydrolysis.
This is the principle behind the operation of organotin
polysiloxane materials as described in U. S. Pa ent
No. 4,080,190. In these materials a trisubstituted
organotin moiety is chemically bonded ~o a macromolecular
3~
1 polysiloxane backbone. Through hydrolysis the
organokin moiety is gradually liberated and diffuses
to the surface of the coating as the active fouling
control agent.
The organotin polysiloxane materials can act
as binders, co-resins, or toxic pigments or additives
depending on the tin to silicon ratio and related
physical form. A low tin to silicon ratio permits
the organotin polysiloxane to perform as a binder.
Such material is primarily inorgarlic in nature though
~he presence o~ the organotin groups do impart a
certain degree o~ organic character. This enhances
ccmpatability with organic materials and better
adhesion to me~al substrates, for example, than a
polysiloxane wi~hout organotin substitution.
As a binder the organotin polysiloxane can serve
as a matrix for essentially inorganic fillers and
pigments. The coating is microporous allowing
con~inual release o~ the toxic agent; that is, an
organotin radical is formed in situ through hydrolysis
~f the tin-oxygen-sili¢on bond. Such continual release
of t~xicant avoids surface passivation as frequently
occ~rs in conventional copper ~ased antifouling coatings.
Since this kype of formulation is microporous,
performance is essentially independent of turbulence;
that is, sufficient toxicant is l~ached to the surface
for preventing fouling under either static or dynamic
conditions.
With a higher tin to silicon ratio the organotin
polysiloxane can be an additive in a coating composition
using a vari~ty of binders. In such a composition the
release of toxicant is a function of the properties of
the binder plus hydrolysis characteristics of the
organo~in polysilo-xane.
srief Sun~ary of the Invention
In accordance with the present invention there is
provided a marine antifouling coating composition comprisi~g:
an acrylic resin selected ~rom the group
consisting of methyl methacrylate, ethyl methacrylate,
propyl methacrylate, isobutyl methacrylate, and
n-butyl methacrylate in the range of fxom 6 to 20
percent by weight;
an organotin polysiloxane having the
formula
rO X I
I
X-O- - si - o- -x
O - X m
where m is an average of up to about ten, each X is
independently selected from the gxoup consisting of
R and Y; where each R is selected fro~ the group
consi sting of hydrogen and alkyl and alkoxyalkyl
radicals containing less than six carbon atoms;
where each Y is a trisubstituted tin radical having
the formula
Rl _ f n R3
where Rl, R2, and R3 are independently selected from
the group co~lsisting of alkyl, cycloalkyl and aryl
radicals and Rl, R2, and R3 contain collectively up
to 18 carbon atoms; and the X's aLe selected so that
the ra~io of tin atoms to silicon atoms is in the
range of from 0.7:5 to 5:5~ the organotin polysiloxane
being in the range of from 7 to 25 percent by weight;
solvent for the acrylic resin and polysiloxane
in the range o~ from 18 to 52 percent by weight; and
3~
- 4a
a balance in the range of from 10 to 65
percent by weight of primarily marine paint and
toxicant agents selected from the group consisting
of pigment powders, fillers, thicken.ing agents,
antisettling agents, copper powder, cuprous salts,
zinc oxide, algicides, silica, clay, talc, metal
oxides, plasticizers and slightly water soluble
resins.
3~
1 Description
The marine antifouling coating composition
provided in practice of this invention comprises
a mixture of resins or binders, solvent and pigments
or fillers, along with associated marine paint and
antiouling ingredients in a consistency suitable
as a paint for brushing, spraying, or the like on
ship hulls or o~her s~ructures exposed to seawater.
~he binders in the composition comprise an acrylic
resin in the range of from about 6 to 20% by weight
and an.organotin substituted polysiloxane in the range
of from ahout 7 to 25% by weight. A volatile organic
solvent for the acrylic resin and polysiloxane is
preferably present in the range of from about 18 to
52% by wPight. The balance of the composition in ~he
range of from about 10 to 65% ~y weight comprises
conventional plasticizers, a small amount o~ water
soluble resin, pigment powders, fillers, thickening
agents, antisettling agents, copper powder, copper
salts, zinc oxide, algicides, clay, talc, metal
~xides and the like.
It is particularly desixable that the composition
include coppex powder or cuprous salts that are effective
for inhibiting growth of marine organisms. ~he
combination of organo~in polysiloxane, acrylic xesin and
copper supplying antifouling agent appears to avoid
passivation of the copper bearing antifouling agent which
of~en occurs in seawatex. Preferably the copper or
c-lprous salt is present in a proportion of up to
about 30% by w~ight.
-6
1 The acrylic resin is selected from the group
consisting oE methyl methacrylate, ethyl methacrylate,
propyl methacryla~e, isobutyl methacrylate, and
n-butyl methacrylate. Such materials can be used
separa~ely or as polymer blends. Preferably the
acrylic resin is pol~methyl methacrylate since
economical, readily commercially available, and
an excellent resin for marine coatings. The methyl
methacrylate forms a microsmooth coating and has
appropriate charac~eristics in moving seawater to
maintain a low drag profile on a vessel.
The acrylic resin is present in the composition
in the range of from about 6 to 20% by weight. If the
acrylic resin is present in a proportion less than
about 6% by weight, adhesion o~ the coating to metal
substrates can ~e excessively degraded. Further,
the microsmoothness and ablation characteristics of
the resultant coating may not be adequate for minimizing
drag when used on a ship or ~he like. If the proportion
of acrylic resin is more than about 20~ by weight, the
amount of polysiloxane in the composition may need to
~e re~uced to a level that the antifouling proper~ies
of the coating are degraded.
Prefera~ly the acrylic resin is present in the
range of ~rom about 8 to 12% by wei~ht. Such
proportions are found to give an excellent balance of
adhesion of the coating composition ~o a variety of
substrates, microsmoothness and ablation characteristics
suitable for reducing drag and lon~ life as an
antifouling coating. A particularly preferred
composition has fxom about 10 to 11% by weight of
aarylic resin.
3~
1 The organotin polysiloxane comprises a polymeric
pxecursor having the formula
O - X ~
X ~ ~ Si ~ 0- - X
O ~X
m
where m is in the xange up to an average of about 10
and preferably is an average of at least about 5. In
this formula each X is independently selected from
the group consis~ing of R and Y. Each R is selected
fr~m the group consisting of hydrogen, and alkyl and
alkoxyalkyl radicals containing less ~han six carbon
atoms~ Each ~ in the formula is a trisubstituted
organotin radical having the formula:
~2
Rl - Sn -
R3
In this organotin moiety Rl, R2 and R3 are independently
selected from the gro~p consisting of alkyl 9 ~ycloaklyl,
and aryl radicals and collectively contain up to about
18 carborl atoms. Preferably Rl, R~ and R3 are each
butyl for optimum toxicity of the composition to marine
organisms. Triphenyl tin polysiloxane can be
substituted or some of the tributyl tin siloxane in
some embodi~ents.
Pre~era~ly the R radical on the polysiloxane is
ethyl. When the silox~ne is polymerized by hydrolysis
and condensation, the rea~tion by-product is ethyl alcohol
~.~Lg23~
1 which has a volatility similar to the organic solvents
in the composition, thereby making the composition
readily applicable as a paint. If desired, the
polysiloxane can be prehydrolyzed when making up
tne composition to speed polycondensation in which
cas~ at least a portion of R is hydrogen. Such
prehydrolysis can reduce the shelf li.fe of the
composition~
Such organotin polysiloxane and methods for
making them are described in U. S. Paten~ No. 4,080,190,
In the polysiloxane m represents the average
number of silicon atoms per molecule. Generally
there is a random distribution of molecules having
more or less than m silicon atoms. For example,
when m = 5, molecules containing 4, 5 and 6 silicon
atoms can be present. Preferably, m is less than
about 10 so that the siloxane can ~e properly
poly~erized by hydrolysis and polycondensation during
curing of the coating composition. Preferably m is
an average of about 5. Such a polysiloxane can
pol~merize, following transesterification to
in~roduce the organotin moiety, to produce linear
and/or crosslinked polymers. Such material has a
high silica content, hence a relatively high
proportion of solid binder following polycondensation
and removal of the preferred ethyl radical.
The X ' 5 in the formula are selected so that the
ratio of tin atoms to silicon atoms in the organotin
polysiloxane is in the range of from about 0.7:5 to 5:5.
'~
~3~3~1
1 If the ratio of tin atoms to silicon atoms in
the composition is less than about 0.7 tin atoms for
every 5 silicon atoms, the quantity of the
trisubstituted tin moiety can be so low that toxicity
of the coating to marin~ organisms is marginal. When
the tin ~o silicon ratio is low, extensive cross-linking
of the polysiloxane can be obtained so that the
polysiloxane forms a durable binder in the coating
composition. This permits a higher proportion of
polysiloxane and a lower proportion of acrylic resin
in the composition without degrading the desired
mechanical properties of the xesultant coating.
The proportion of tin atoms to silicon atoms
should be less than about 5:5 for polymerization of
the polysiloxane. The tris~bstituted tin moiety on
the polysiloxane introduces sufficient steric
hindrance that at high ~in to silicon ratios
cross-linking is inhibited. Thus, with high tin
to silicon ratios, the mechanical ~rope~ties of the
polymerized siloxane are redu~ed. In such an
embodimen the proportion of acrylic xesin to
polysiloxane is increased for maintaining the
mechanical properties of the coating. At high tin
to silicon ratios in the polysiloxane, conventional
plas~icizers may be omitted as the polysiloxane
~lend with the acrylic resin can provide sufficient
plasticizing.
Preferably, the tin to silicon ratio in the
polysiloxane is in the range of from about l.3:5
to 2.5:5. A particularly preferred composition
has a ratio of tin atoms to silicon atoms of about
2.5:5. A composition having a ratio of about 1.3
tin atoms or every 5 silicon atoms in the polysiloxane
--10--
1 fonms an excellent binder for the coating composition
with sufficient trisubs~ituted organotin moiety for
high toxicity of marine organisms. Such a composition
can ~e useful where a durable antifouling coating
is desired with low polishing action. In such an
embodiment a relatively higher proportion of
polysiloxane and relatively lower proportion of
acrylic resin ~ay be used in the composition~ A
particularly preferred composition has a ratio of
10 a~out 2.5 tin atoms per 5 silicon atoms. Such
matexial is not c~mpletely cross-linXed and serves
to modulate ~he properties of the acrylic resin in
the coating composition. ~ high proportion of tin
moiety is present in the composition providing
15 long life antifouling characteristics. Such a
material has about the optimum balance of mechanical
propexties and toxicity.
It will ~e recognized that the quantity of
organotin polysiloxane binder in the composition
20 following hydrolysis and condensation will be 12ss
than the proportion of oxganotin siloxane in the
uncured coating composition. For example, when
the organo~in siloxane comprises a tributyl tin
moiety on an ethoxy siloxane whereill each molecule
Z5 has an average of five silicon at~ms and the ratio
of tin atoms to silicon atoms is about 2.5:5, the
cured siloxane has about 73~ of the weigh~ of the
uncured pr~cursor. ~he weight loss comes about
from loss of the ethyl radical upon hydrolysis and
30 con~ensation,
~2~
--11--
l The acrylic resin and organotin polysiloxane in
the sompositlon act as co-resins forming a binder
for a paint coating. Evaporation of the solvent
from the composition and exposure of the composition
to en~ironmental water or water vapor results in
solidification of the binder blend through deposition
of the acrylic resin and concurrent hydrolytic
polycondensation of the siloxane. Depending on the
proportions of the materials, this binder system can
be in the orm of a resin blend or an intexpenetrating
pol~mer network.
Preferably the organotin polysiloxane is present
in thP composition in the range of from about 7 to 25~
by weigh~. If the proportion is less ~han about 7~ by
weight, the quantity ~f the organotin moiety can
become so low that the antifouling characteristics
of the co~position can be ~oo low fox practical use.
The rate of release of toxicant at the coating suxface
can be less than the minimum required for inhibiting
growth of organisms.
If the proportio~ of organotin polysiloxane in
the composition is more than about 25% by weight,
the mechanical properties of the organotin polysiloxane
can predominate over those o the acrylic resin,
~5 thereby reducing the desirable properties of the
acrylic. Further, high proportions of organotin
polysiloxane can reduce the content of other toxicants
such as copper bearing antiouling agents, thereby
narrowing the spectrum of organisms agains~ which the
antifouling coating is e~ective.
~3~3~
-12-
1 Preferably the oryanotin polysiloxane is
present in the cQmposition in the range of from
about 12 to 16~ by weight. This gives a good
halance of the antifouling proper~ies of the
siloxane and the mechanical properties of the acrylic.
Such a coating has a long useful lifetime in bo~h
static and dyn~nic fouling control situations.
Preferably the quantity o~ organotin
polysiloxane is somewhat larger than the proportion
of acrylic resin in the composition. Preferably
the weight ratio of acrylic resin to organotin
polysiloxane is in the range of from about 0.5 to
1.0 and most particularly in ~he range of ~rom about
0.6 to 0.8. These provide optimum balance of
an~ifouling characteristics in the combination of
controlled release of toxicant and mechanical
properties in ~he resultant coating.
As co-resins in the binder system the organotin
polysiloxane moderates the physical properties of the
acrylic resin. Ordinarily, a polysiloxane is
incompatible with an acrylic resin, however, it is
found that th p~esence of the trisubstituted organotin
moiety on the polysiloxane makes the two types of
~inder compatible so ~hat a coating composition with
Z5 reasonable shelf life can he formulated.
In the cured composition, the acrylic in the binder
provides a microsmooth surface that minimizes
microroughness drag penalty, and a slow controlled
poiishing action can be obtained for providing
m~ximum reduction of drag. In the preferred embodiment
of this invention, the surface profile roughness
envelope is in the 15 to 25 micron range throughout
the ser~ice life of the coating and its ablation
rate is less ~ha~ 3 microns o coa ing loss per month
at a speed of 15 kno~s. T~e organotin moiety in the
-13-
1 binder is released at a controlled rate since it is
chemically bonded to a polymeric content of the
coa~ing and is not free to migrate or diffuse before
hydrolysis frees the tin moiety from the.polysi.loxane.
S In other compositions in which an acrylic resin
is used as binder and antifouling agen~s are included
as addLtives, such as cuprous salts or tributyltin
oxide, the toxicant is released at a rate controlled
only by matrix properties. Since diffusion rate depends
on concentration, release of toxicant at the surface
is relatively high when ~he coating is fresn and
diminishes steadily thereafter. To maintain an
effective release rate at the surface after a long
time, an excessive release rate is needed in the
beginning.
.... _ . . , . _ . .. . _ _ .. . . .. . .. .... . .. . . . .. _ .. _ .. _ . . . .. . _ _ . .. . . _ .
In a composition with organotin polysiloxane and
acryllc resin, release of toxicant occurs upon
hydrolysis of the tin-oxygen-silicon bond. The rate
~o~ release is thus~control~ed by the rate of hydrolysis
which r~mains steady throughout the life of the
çoating. Since the xate of release is nearly constant~
the amount of toxicant ~an be selected to provide
slightly more than an efestive amount at the projected
end of the useful li~e of the coating. Little excess
toxi~ant is released during the early lifP of the
coating and longer life can ~e ob~ained fQr a selec~ed
total amount of toxicant.
An or~anic solvent for the acxylic resin and
organotin polysiloxane is preerably present in the
range of from about 18 to 52% by wei~ht. Xylene is
an excellent solvent for both the acrylic resin and
~23%~
-14-
l polysiloxane. In an exemplary embodiment acrylic
resin is included in the composition by way of a
commercially available solution of acrylic resin
and -toluene. In such an embodiment the solvent in
the composition compri.ses a blend of toluene and
xylene. Other nonpolar solvents for acxylic resin
and polysiloxane can also be used, along with limited
amounts of alcohols. Exemplary solvents are xylene,
toluene, various Cellosolves,* naphtha and mineral
spirits. The organic solvents should be selected
to provide 2 volatility that permits drying of the
coating composition in a reasonable time when
applied to the hull of a vessel or other substrate.
The proportion of solvent in the composition is
subject to rather wide variation and is determined
largely by the desired viscosity in the composition
to permit application to substrates by spraying,
brushing, or the like. If the ~roportion of solvent
is less than about 18% by weight, the viscosity of
the composition may be so high that application to
substrates in coatings of reasonable thickness is
rather di.fficult. Levelling to obtain a smooth
coating may also be inhibite~. If the composition
has more than about 52% by weight of solvent,
application of coatings of reasonable thickness can
be limited by sagging or running. Preferably, the
solvent is present in the range of from abou-t 24 to
36% by weight. It is found that such a proportion
of solvent with the preferred resin compositions and
other marine paint additives hereinafter described
provides a viscosity range quite suitable for
application to substrates by brushing and/or spraying.
* Cellosolve is a trademark of Union Carbide Corporation.
329
1 A variety of other ingredients can form the
balance of the composition in the range of ~rom
ahout 10 to 65~ by weight. Such additional
ingredients are conven~ional additions ~o marine paints
and are employed ~or modifyiny the properties of the
coating composition or providing antifouling toxicity~
In addition to the organo~in su~stituted
polysiloxane, oth~r marine antifouling ingredients
can ~e included in the composition, in particular it
is found desirable to include up to about 30% by weight
of copper powder and/or cuprous salts, such as Cu20,
CuSCN, Cu2S, CuO~, or the like in the composition.
Cuprous oxide is a preferred copper base antifouling
a~ent. Such copper based materials are widely
recognized ~s agents for inhibiting growth of marine
organisms and are desirable additives in the marine
coating cQmposition. Pre~erahly such copper base
antifouling agents are present in the composition
in the range of frorn about 10 to 20% by weight.
~en the copper bearing antifouling agent is
present at less than about 10 weight percent, the
minimum e~ective release rate may not be achieved
o~er a lons lifetime of the coating. If the proportion
is much above about 20%, passiva~ion of the copper
agent may occur under some conditions.
It is desirable to include copper bearing
antifouling agents in the composition for enlarging
the spectrum of marine organisms combated by the
antifouling coating. Copper and cuprous salts tend
to be somewhat more e~fective for inhibiting growth
3Z~
-16-
of algae and more primitive soft organisms, where~s
the organotin moiety is somewhat more effective
against higher organisms, barnacles or the like,
which are often referred to as "hard" fouling.
When the proportion of copper base antifouliny agent
i5 ~n the order o~ about 15% by weight, good
long-life antifouling characteristics are obtained
without decreasing the other desirable properties
of the coating.
When a copper ba ed antifouling agent is 1ncluded
in the composition, it is also desirable to include
zinc oxide in a proportion of about one-hal~ the
proportion of copper base antifouling agent. The
zinc oxide is desirable since it pot~ntiates ~he
antifouling activi~y of the copper by enhancing the
transport of copper ion across the biological
membranes of marine organisms. Zi~c oxide can also
promote gal~anic release o copper from the
antifouling coating. An exc~ss amount of zinc oxide
can suppress the antifouling activity of the copper,
hence, it is desirable that the maxim~m ~inc oxide be
i~ a proportion o a~out 50% of the copper base
antifoulant. If zinc is included in the composition,
the propor~ion of zinc oxide should be reduced.
It is believed that no single toxicant is
available for compositions that can be applied to
surfaces in practical situations and khat will
universally protect marine surfaces against fouling.
While organotin compounds are very e~fec~ive as
3~ antifouling toxicants, practical compositions that
232~
1 provide controlled relea~e of toxicant over long
periods of time do not have sufficiently broad
antifouling properties ~or the full spectrum of
organisms. I~ is ~ound, however, that hy combining
the organotin polysiloxane with other toxicants,
such as copper or cuprous salts or organic algicides,
the an~ifouling perormance of the coating can be
effecti~e in a wide variety of fouling en~ironments
for periods of ~ime far in excess of cvnventional
lo coatings. This effectiveness is present under both
static and turbulen~ conditionsO This diff~rs from
prior compositions for con~rolled xelease of toxicants
which are optimized for either static or dynamic
c~nditions, rather than both.
It is particularly advantageous to employ copper
bearing an~ifouling agents such as copper powder or
cuprous salts as an additional toxicant in a coating
composition having trisubstituted organotin
polysiloxane and acrylic resin as binders. Ordi~arily
in a seawater environment at least a portion of the
¢opper is converted to inactive salts, such a~ copper
oxychloxides, which are rela~ively ineffective in
inhibiting growth of marine fouling organisms. The
reason that the acrylic and organotin polysiloxane
2S binders tend to s~abilize the copper or copper salts
in seawater is not yet un~lers~ood. It is believed that
with organo~in polysiloxane in the composition ~he
amount o~ copper bearing antifouling agent can be
reduced, as compared with pxior compositions, withou~
reducing antifouling activity. Lower copper
concentration may avoid passivation.
3~
-18-
l Preferably the weight ratio of trisubstituted
organotin polysiloxane to copper powder or cuprous
saLt in the composition is in the range of from
about 0.5 to 1.5. When the ratio is either above or
below this range there is a decrease in the spectrum
of organisms combated by the anti~ouling composi~ion.
A proportion near the middle of this range appears
to give the best broad spectrum antifouling activity.
It is also desirable that the weight ratio of binders
to copper powder or cuprous salt be in the range of
fr~m about 0.~ to 2 to provide an appropriate range
of strength and controlled release of toxicant for
good long life antiouling activity. When ~he ratio
of ~inder to copper bearing antifouling agent is
less tha`n about 0.8 the erosion resistance of the
coa~ing and the life of the copper constituent can
~e significantly reduced. If the proportion of
~inder relative to the copper bearing constituent is
more ~han-about 2, there is a reduction in the
a~ailability of copper at the surface an~ a decrease
in the antifouling activity, particularly for algae
and soft organîsms against which copper is
particularly effective.
Pre~erably, the composition includes a
conven~ional plasticizer for the binders in the
range of ~rom about 0.5 to 5% by weight, and most
preferably about 0~5 to 2~ by weight. The
plasticizer imparts flexibili~y and resilience
to the ~ured composition. External plasticizers
that maintain theix molecular identity are preferred,
3~
--19--
1 rather than plasticizers that chemically bond in
the polymer system. A variety of conventional
plasticizers that are compatible with the acrylic
resin and organotin polysiloxane are suitable,
such as alkyl benzyl, phthalates, dialkyl phthalates,
phosphate esters, sulfonamides, butyl phthalyl
butyl glycolate, diphenyl phthalate, dicyclohexyl
phthala~e, tricresyl phosphate, and the like~ The
amount of plasticizer employed in the compositio~
is somewhat proportioned to the tin to silicon
ratio in the polysiloxane. A smaller amount of
plasticizer can be used when the tin to silicon
ratio is high since the polysiloxane can also act
as a plasticizer. Conversely, when the tin to
silicon ratio is low so that the polysiloxane is
extensively cross-linked and xigid, a somewhat
higher proportion of other plasticizer can be
i~cluded in the co~position.
It is desirable to include a slightly water
soluble resin in the composition for enhancing
~radual dissolution and ablation of the coating.
Addition of such resins ~hat are slightly soluble
in seawater enhances the microporosity of the coating
and can help control the hydrolysis of the organotin
moiety for maintaining antifouling characteris~ics
over a long li~etime. Pre~erably, the water soluble
resin is water white rosin, since it is economical,
easily blended into the composi~ion, and quite
suitable in stability and water solubility. Other
sli~htly soluble resins can be substituted such as
hydroxy et~yl methacrylate, polyvinyl acPtate,
polyvinyl alcohol, or the like.
3~
(
-20-
1 The proportion of water soluble resin in the
composition depends on the degree of solubility of
the resin and desired xate of ablation and penetration
of water into the coating. For example, when rosin is
the seawater soluble portion of the composition, it is
preferably present in the range of from about 1 to 10
by weight, and most preferably in the rangé of from
about 3 to 6~ by weight. If the rosin is present at
less than about 1~ by weight, the coating may become
passivated, and a~tifouling characteristics degraded,
particularly when copper or copper salts are included
in the composition. Rosin content o more than about
10~ by weight leads to excessive ablation and short
lifetime of such a coating. Preferably, rosin is
present in the range of from about 3 to 6~ by weight,
to provide a good balance of coating lifetime and
water penetration to provide long antifouling activity.
It is highly desirable to include a thixotropic
agent such as alcohol swellable clay, talc, or colloidal
silica. Such conventional thickeners are widely used
in paint compositions for modifying viscosity and
obtaining paints that can be sprayed or brushed to
provide a coating of reasonable thickness without
sagging or running. An exemplary thickening agent
particularly useful is dimethyl dioctodecyl ammonium
bentonite avallable from the Baroid Division of
National Lead Company, Houston, Texas, as Bentone*34.
Preferably the thickener is present in the composition
in the range of from about 0.5 to 4% by weight and
most preferably in the range of from about 0.5 to 2.0
by weight, as is conventional in paint compositions.
*Bentone is a trade mark of National Lead ~ompany.
2~
-21-
1 It is desirable to include antisettling agents
for the copper base materials and other fillers and
pigments employed in the composition. A variety of
antisettling agents used in paint compositions are
suitable for preventing settling and minimizing
mixing that might be nee~ed before a composition is
used after a prolonged shelf life. Antisettling
agents are employed in marine paint compositions up
to a~out 3% by weight.
If desired, organic algicides can ~e included
in the composition, such as dichlorisothiazalone or
diiodomethyl p-tolyl sulfone. Preferably, such
algicides are present in a proportion up to about
16% ~y weightr and most preferably up to about 5%
by weight. 5uch algicides can promote gelling of
the composition and the proportions are preferably
kept low e~ough to inhibit such gelling and maintain
a long shel li~e.
A variety of conventional fillers and pigments
can also be included in the coating composition.
Such materials can modify the properties of the
paint as it is applied, such as body to promote
good spreading and leveling without runs or sags.
Such materials can also modify properties o the
~ured coating such as strength, toughness, opa~ity and
color. Pigments and fillers can also help protect
the substrate on which the coating composition is
placed. Exemplary pigments and illers include red
iron oxide, talc, silica, titanium ~ioxide, chromium
oxi~e, and the like.
3~
3~
-22-
1 Such pigments and fillers can be included in
the composition up to about 20% by weight. If
present in a proportion more than about 20~ by
weight,it hecomes necessary to reduce the
propo~tions o~ algicides and other ingredients in
the composition that are active in inhibiting growth
of marine organisms. Preferably the pigments and
fillers are present in the order o~ about 7% by
weight which provides good protection for
substrates, opacity and strength.
The proportions of liquid and solid ingredients
are selected so that the composition can be sprayed
or brushed onto a variety of substrates as a marine
paint.
Miscellaneous other ingredients can also be
included in the composition. Zinc powder can be
included for inhibiting corrosion. A small amount
of phosphoric acid ~e.g., 0.5%) can be included
for inhibiting premature gelling. The composition
is preera~1y packaged in a single container for
ready use as a paint. I~ desired it can be prepared
in two packages ~or longer shelf life and mixed
shortly ~efore use. Many other modifications and
variations will be apparent.
When th~ coating composition is applied to a
surface, concurrent effects are occurring in the
acrylic and polysiloxane binders. The acrylic resin
foxms a solid binder network as the volatile solvents
evaporate. The organotin polysiloxane hydrolyzes
and condenses. If desired, the polysiloxane can be
Z32
-23-
l at least partially hydrolyzed before application of
the coating. Such prehydrolysis can be desirable
for rapid cure of the coatiny but the shelf life of
the mi~ure may be decreased. Hydrolysis of the
polysiioxane can occur from ambient water vapor of
exposure to water. ~ variety of bases or acids can
be present in small quantities ~o promote hydrolysis
as descrIbed in U. S. Paten~ No. 4,080,190. Algicides,
zinc oxide and other ingredients in the composition
can ~e sufficient to promote hydrolysis. I~ might be
note~ that use of some basic promoters of hydrolysis
may not be totally compatible with copper bearing
antifouling agents. Such promoters may be omitted or
the composition used within a reasonable time after
mixing, or ~he copper ~earing materials can be added
shortly before applying the coating.
EXAPPLES
Table I sets forth the compositions o six
antifoulihg coating compositions prepared in practice
of this invention. The compositions were mixed much
as one would mix other paint compositions. The
composi~ions were applied to standaxd test panels by
spraying and the tes~ panels were immersed in seawater
at Daytona Beach, Florida, for detenmining antifouling
activity.
~92~
-24-
1 TABLE I
EXAMPLES
INGREDIENT A B C D E F
Acryloid B-48N ~26.8 26.8 17.818.0 26.8 22.5
OTPS 15~3 15.2 12.212.4 15.2 14~7
Cuprous oxide - 22.2 19.018.7 17.0 15.5
Zinc oxide 8.0 8.8 8.8 8.9 9.0 7.5
Ethyl aminoethanol 0.8 0.8 - - 1.1 0.8
Di-isodecylphthalate 1.0 2.0 1.3 1.2 2.0 1.2
W. W. Rosin 4.2 4.8 5.8 5.9 4.8 4.0
Red iron oxide11.4 - 2~8 7.3 ~ 2.4
Nytal 300 C~ ~ )7.0 2.5 ~.5 ~ 3.0 2.1
MP~-1078X ~f.~ l.g 1.9 - 1.6
Bentone 34 (~ ~ ~ 1.5 1.3 0.9 0.9 0.7 1.1
~eosol ~-r ~.~ 0.4 0.4 0.3 0.2 0.2 0.3
Amical 48 (~. n ) _ - 6.0
C-9211 C~ ~ ) 6.0 6.0 - 6.1 6.0 6.6
Xylene _ 17.6 9.2 20.718.5 1~.2 19.7
TOTAL100~0 100.0 100.0 100.0 100.0 100.0
~
The proportions of ingredients listed in Table I are set
forth in percentayes by weight for each of the six coating
compositions. The materials set forth in Table I are
identified as follows:
Acryloid*B~48N comprises a solution of methyl
methacrylate in toluene available from Rohm and Haas,
Philadelphia, Pennsylvania. The solution has 45~ by
weight polymethyl methacrylate and 55% by weight toluene.
OTPS refers to organotin polysiloxane. In each of the
coating compositions set forth in Table I, the organotin
* Acryloid is a trade mark of Rohm and Haas~
- ~s -
1 polysiloxane had the formula:
O - X 1
x - o - - Si - t X
o - X ~
m
where m was an average of about 5 and X was either an
ethyl radical o~ a tributyl tin radica~ and the X ' s
were selected so that the ratio of tin atoms to silicon
10 a~oms was about 2. 5: S.
Cuprous oxide is present as a ~inely divided powder
which, as pointed out above, inhibits gxowth of marine
org2nisms. 2inc oxide is also present as a finely
divided powder and serves as a pigment plus potentiat~:~g
the activity of the copper salt.
Ethyl aminoethanol is present in the composition to
promote hydrolysis and condensation of ~he siloxane.
Di~isodecylphthalate is present as an external plasti~izer
for the acrylic and siloxane binders. W. W. rosin (water
20 white rosin) is present as a slightly wa~er soluble resin
to modiy the binder matrix and help control gradual
release of toxicants when he GOating is immersed in
seawatex.
Red iron oxide is present in the ~orm of a powder
serving as a pigment. The pigment improves the strength
and opa~ity of the composition. Nytal 300 is a finely
divided talc available from Ro T. Vanderbilt Company,
Wo~walk, Connecticut. The talc is present as a filler
that improves ~iscosity of the coa~ing composi~ion and
~0 inhi~its sagging.
, .
-26-
1 MPA-1078X available from Baker Castor Oil Company,
Bayonne, New Jersey, is a colloidal thixotropic agent
used to prevent settling of solid powders. It is added
as a paste of solids dispersed in a solvent o~ xylene
or toluene.
Bentone 34, a-railable from National Lead Company,
Baroid Division, ~ouston, Texas, is finely divided
dLmethyl dioctodecyl ammonium bentonite for thickening
the composition and aiding in suspension of solids~
Neosol, available from Shell Chemical Company,
~ouston, Texas, is ethyl alcohol denatured with small
amounts of me~hyl isobutyl ke~one, ethyl acetate and
a~ia~ion gasol.ineO As a preliminary step in formulating
the coating eomposi~ion the Neosol i~ mixed with the
Bentone 34 to form a pas~a and cause swelling of the
Bentone 34.
kmical-48 available from Abbott Laboratories, North
Chicago~ Illinois, comprises di~-iodometh~ tolyl sulfone
and serves as an additional algicide.
C-9211 is a 4,5~dichloro-2-n-octyl-4-isothiazalin-~-one
algicide available ~rom Rohm and Haas Company, Philadelphia,
Pennsylvania. The algicide can also provide a source o
protons to promote hydrolysis of the sil~xane. It ~s
aesirable in preparin~ a composition to add ~he algicide
after all o~ the other ingredients have been mixed to
minimi~e the possibility o premature gelation.
The composition is made by first diluting the
acrylic resi~ solution with additional sol~en~. Some
of the xylene can ~e reserved .for making a paste of the
solid ingredients to speed mixing~ The organotin
3~
~z~æ~
l polysiloxane is added and mixed, followed by the
plasticizer. After all of the liquid and soluble
~aterials have been mixed, the solid material~ are
added with as much mixing shear as required to obtain
a smooth paint composition. The order of adding
in~.redients to the composition is not c.ritical,
although it is desirable to add the algicide or any
catalyzing amine last in order to minimize premature
gelation.
The coating compositions set forth in Table I
were applied to standard blan~ panels of primer coated
steel or plastic for measuring resistance to marine
fouling. These panels wexe then exposed to sewater at
Daytona Beach, ~lori~a. The foulinq resistance of the
composition as a function o months of exposure is set
forth in Table II.
TABLE II
H~D FOULING _ ALGAL FOULING _ _
EXAMPLE 612 18 24 Mos. 6 12 18 24 Mos.
~
A 10 1~10 10 9 5 5
B 10 1010 10 10 9 9 9
C 10 109 - 1010 10
D 10 109 - 1010 10
E 10 1010 - 1010 10
10~0 - 1010 10 -
Control 0 0 00 0 0
Control panel refers to a blank panel with no antifouling
~oating. Hard fouling refers to the growth o barnacles
and similar organisms with hard body parts. Algal fouling
~5
3%~
-28-
1 refers to algae and other soft organisms. The
ratings of the test panels or fouling resistance is
on a scale of 0 to 10, where 10 represents no fouling
whatsoever, 9 represents a very minor or trace amount
of fouling, 5 represents approximately 50% of the
test panel fouled and 0 represents complete ailure
or fouling over the entire surface.
