U.S. patent application number 09/964547 was filed with the patent office on 2003-06-19 for robust nontoxic antifouling elastomers.
Invention is credited to Brady, Robert F. JR..
Application Number | 20030113547 09/964547 |
Document ID | / |
Family ID | 25508679 |
Filed Date | 2003-06-19 |
United States Patent
Application |
20030113547 |
Kind Code |
A1 |
Brady, Robert F. JR. |
June 19, 2003 |
Robust nontoxic antifouling elastomers
Abstract
The invention herein pertains to a method for reducing adhesion
of marine organisms to a substrate and an article that is a
substrate having thereon a solid coating of a fluorinated
polyurethane elastomer. The elastomer is tough and has antifouling
and release properties in reference to marine organisms. The method
includes the steps of providing a liquid mixture of the fluorinated
polyurethane elastomer, applying the elastomer mixture to said
substrate, and curing the elastomer mixture to a solid coating of
the fluorinated polyurethane elastomer, the elastomer having
surface energy (which is a function of fluorine content) of 15-30
milli J/m.sup.2, Young's modulus of elasticity of 2-15 MPa, and
fluorine content of 3-25%.
Inventors: |
Brady, Robert F. JR.;
(Gaithersburg, MD) |
Correspondence
Address: |
NAVAL RESEARCH LABORATORY
ASSOCIATE COUNSEL (PATENTS)
CODE 1008.2
4555 OVERLOOK AVENUE, S.W.
WASHINGTON
DC
20375-5320
US
|
Family ID: |
25508679 |
Appl. No.: |
09/964547 |
Filed: |
September 28, 2001 |
Current U.S.
Class: |
428/423.1 |
Current CPC
Class: |
Y10T 428/31551 20150401;
C08G 18/10 20130101; C09D 5/1637 20130101; C09D 5/1662 20130101;
C08G 18/5015 20130101; C08G 18/10 20130101; C09D 175/04 20130101;
C08G 18/50 20130101 |
Class at
Publication: |
428/423.1 |
International
Class: |
B32B 027/00 |
Claims
What is claimed:
1. A method for reducing adhesion of marine organisms to a
substrate comprising the steps of: (a) providing a liquid mixture
of a fluorinated polyurethane elastomer, (b) applying the elastomer
mixture to said substrate, and (c) curing the elastomer mixture to
a solid coating of the fluorinated polyurethane elastomer, the
elastomer having surface energy of 15-30 milli J/m.sup.2, Young's
modulus of elasticity of 2-15 MPa, and fluorine content of
3-25%.
2. The method of claim 1 wherein surface energy of the elastomer is
20-29 mJ/m.sup.2, its Young's modulus of elasticity is 2-10 MPa and
its fluorine content is 6-18%.
3. The method of claim 1 wherein surface energy of the elastomer is
25-27 mJ/m.sup.2 and its Young's modulus of elasticity is 3-7 MPa,
and its fluorine content is 9-10%.
4. The method of claim 1 wherein the elastomer is a reaction
product of a base component comprising a polyol, or a mixture
thereof, with a curing agent containing a diisocyanate, or a
mixture thereof, the base component contains a mixture of at least
one diol and at least one triol.
5. The method of claim 4 wherein the ratio of the NCO/OH groups in
the curing agent and the base component is below 2.
6. The method of claim 4 wherein the NCO/OH ratio in the curing
agent and the base component is 1-1.8 and amount of trifunctional
OH is 18-32 mol percent.
7. The method of claim 4 wherein the NCO/OH ratio in the curing
agent and the base component is 1-1.5 and amount of trifunctional
OH is 23-27 mol percent.
8. The method of claim 6 wherein the elastomer is nontoxic to
marine organisms, contains no fugitive ingredients, is partially
cross-linked and is in the form of a pourable liquid, before
curing, that has a working life of 15 minutes to 8 hours.
9. The method of claim 8 wherein the substrate has a coating of a
primer thereon onto which the elastomer is applied.
10. The method of claim 9 wherein the base component includes a
metal salt catalyst.
11. The method of claim 9 wherein the base component is in a
solvent solution, contains a mixture of at least one diol and
trimethylol propane propoxylate, and a metal salt catalyst.
12. The method of claim 11 wherein the curing agent includes a
diisocyanate prepolymer and poly(propylene glycol) terminated with
toluene-2,4-diisocyanate.
13. An article comprising a substrate and a rubbery fluorinated
polyurethane elastomer in dry form adhering to said substrate, said
elastomer is a reaction product of a base component containing a
polyol, or a mixture thereof, and a curing agent containing a
diisocyanate, or a mixture thereof, said elastomer is nontoxic to
marine organisms and has surface energy of 15-30 milli J/m.sup.2,
Young's modulus of elasticity of less than about 2-15 Mpa, and
fluorine content of 3-25%, so that it has sufficient antifouling
and release properties with respect to marine organisms and
sufficient toughness to serve as a coating on the substrate.
14. The article of claim 13 wherein said elastomer is partially
cross-linked and its surface energy is 20-29 mJ/m.sup.2, its
Young's modulus of elasticity is 2-10 MPa, and its fluorine content
is 6-18%.
15. The article of claim 13 wherein surface energy of said
elastomer is 25-27 mJ/m.sup.2, its Young's modulus of elasticity is
3-7 Mpa, and its fluorine content is 9-10%.
16. The article of claim 14 wherein some OH groups in said
elastomer remain unreacted so the full cross-linking in said
elastomer is avoided.
17. The article of claim 16 wherein said elastomer has release
property that enables at least majority of accumulated marine
organisms on its surface to be removed by hosing or movement of
said elastomer through water at speed of a water craft.
18. The article of claim 17 wherein said substrate is metal having
a primer coating on which said elastomer is disposed.
19. The article of claim 18 wherein said primer coating is epoxy
polyamide and thickness of said elastomer is 500-6250 microns, said
elastomer is nontoxdicto marine organisms and contains no fugitive
ingredients.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to a fluorinated polyurethane
elastomer disposed on a substrate and to a process for its
preparation and application, which elastomer can be used as a tough
coating on a water craft with antifouling and release properties
relative to marine organisms.
[0003] 2. Background and Prior Art Description
[0004] All surfaces made by humans and immersed in water,
particularly seawater, become covered with marine organisms. The
diversity of these organisms and the environments in which they
live create complex problems that any useful antifouling coating
must overcome. The problem is most acute for ships because fouling
organisms add weight and hydrodynamic drag, increase fuel
consumption, speed up corrosion of the hull, and decrease speed,
range and maneuverability.
[0005] To prevent the formation of a fouling layer, antifouling
paints typically incorporate compounds which are toxic at low
concentrations to most forms of fouling. However, these compounds
persist in water and cause deformation in many kinds of sea life.
The International Maritime Organization, a unit of the United
Nations, approved in November of 1999 a resolution to phase out and
eventually prohibit the use of toxic organotin derivatives in
antifouling paints. The resolution includes a deadline of Jan. 1,
2003 for the new application of organotins acting as antifoulants
on ships, and a second deadline of Jan. 1, 2008 for the complete
prohibition and removal of antifouling paints containing
organotins. Several countries, including France and Japan, and some
states in the USA, have already banned organotins in antifouling
paint for most ships.
[0006] Nontoxic coatings intended to succeed toxic coatings have
been investigated for many years. However, every nontoxic coating
put into water fouls. Therefore, because one cannot as yet
completely stop settlement on nontoxic coatings, the coatings are
designed in a way that significantly limits the strength of the
bond to fouling, making the bond so weak that it can be broken by
the weight of the fouling or by the motion of a ship through water
of at least about 20 miles per hour.
[0007] Toxicity, as used herein, pertains to the ability of a
coating to kill marine organisms attached to it, or to repel the
organisms seeking to attach to it. Toxic coatings may have other
effects, such as illness, deformity, or reproductive failure on
marine organisms.
[0008] Two types of coatings are preeminent. Fluorinated coatings
are tough, have low surface energy and resist fouling, but
ultimately form a tight bond to fouling. The joint between fouling
and a fluorinated coating fails in shear, i.e., fouling is pushed
off and not peeled off, which is a relatively high-energy process,
without damage to the coating. Silicone coatings, on the other
hand, are soft, relatively weak, and are easily damaged or torn by
marine debris. Because their surface energy is higher than that of
fluoropolymers, they form a somewhat stronger bond with fouling.
Application of force to the joint deforms the rubbery silicone and
the resin peels away from the marine organism in a process which is
slower but requires less energy than shear. In the past, only
silicone elastomers have demonstrated foul resistance and foul
release; hydrocarbon and fluorocarbon elastomers have not.
[0009] U.S. Pat. No. 5,449,553 to Griffith discloses a nontoxic
antifouling coating on a substrate, such as a ship's hull, which
includes a two-component system of a release layer bonded to a
bonding layer, with the bonding layer bonded to the substrate. The
bonding layer is a silicone rubber that contains a toughening
ingredient and is a reaction product of an organopolysiloxane
containing terminal silicon-bonded hydroxyl groups and a
polymerizable vinyl aromatic ingredient. The release layer is a
silicone rubber that is a reaction product of an organopolysiloxane
containing terminal silicon-bonded hydroxyl groups. The bonding
layer is tougher than the release but its release property is
inferior to that of the release layer.
[0010] U.S. Pat. No. 4,157,358 to Field et al discloses random
fluorinated epoxy and urethane resins that are reaction products of
a bis(2-hydroxyhexafluoro-2-propyl)benzene, a linear unsaturated
fluorinated diol, and epichlorohydrin. The resins can be
crosslinked with a polyisocyanate to form highly fluorinated films,
coatings, adhesives, and structural materials having exceptional
heat, light and chemical resistance.
OBJECTS AND BRIEF SUMMARY OF THE INVENTION
[0011] It is an object of this invention to provide a one-component
coating on a substrate, which coating combines the best features of
fluorinated and silicone adhesion-resistant coatings for
antifouling and release of marine organisms.
[0012] Another object of this invention is a nontoxic coating that
does not incorporate any fugitive ingredient and thus does not
leach anything into the environment.
[0013] Another object of this invention is a coating that is tough
or robust and which is not damaged by impact, abrasion and
mechanical abuse nor is damaged by hydrolytic or chemical attack,
sunlight or heat.
[0014] Another object of this invention is a fluorinated
polyurethane elastomeric coating that can be applied in one
operation to any desired thickness in the range of 25-12,500
microns (0.001-0.5").
[0015] Another object of this invention is preparation of a
fluorinated polyunsaturated elastomer that has sufficient toughness
and antifouling and release properties with respect to marine
organisms for use as a coating on a substrate that is submerged in
water.
[0016] These and other objects of this invention can be attained by
a fluorinated polyurethane elastomer that is prepared by reacting
in a conventional way a polyol base component with a polyisocynate
curing agent and then applying the liquid mixture onto a substrate
to produce an elastomeric reaction product. The modulus, surface
energy, and fluorine content of the elastomer should be carefully
controlled.
DETAILED DESCRIPTION OF THE INVENTION
[0017] The tough and nontoxic elastomeric antifouling and release
coating described herein combines the best features of fluorinated
and silicone adhesion-resistant coatings. The coating is a tough
fluorinated elastomeric coating which tolerates no more than a weak
or imperfect joint between a fouling marine organism and itself, a
joint that is predisposed to early and easy failure in peel. The
elastomer coating has low surface energy and resists the attachment
of fouling; it has a low modulus of elasticity which, together with
low surface energy, correlate to provide sufficient toughness and
foul resistant and release of fouling properties; and it can be
applied in a thickness which favors failure of the fouling-coating
joint by peel. The elastic modulus of the coating also contributes
to the failure of the fouling-coating joint by peel.
[0018] The coating is prepared using conventional polyurethane
technology using particular ingredients and parameters. The
fluorinated polyurethane elastomer coating is formed from two
liquid components, namely, a polyol base component and a curing
agent, that are mixed immediately before use and which cure to form
a solid rubbery elastomer.
[0019] The fluorinated polyurethane elastomer coating can be
prepared by the reaction of a polyol in the base component with a
polyisocyanate in the curing agent. Fluorine can be present in
either or both polyol or polyisocyanate. A wide variety of
fluorinated and unfluorinated polyols, and fluorinated and
unfluorinated di-, tri- and polyisocyanates is available
commercially for this purpose. The proportion of starting materials
is chosen in order to control the crosslink density of the polymer,
which in turn controls both its degree of elasticity and its
resistance to physical abuse.
[0020] The base component, containing a polyol, or a mixture
thereof, and the curing agent, containing an isocyanate, or a
mixture thereof, are prepared separately. The base component and
the curing agent can be mixed and poured into a mold, mixed and
sprayed from a spray gun, sprayed with a plural-component spray gun
which mixes the components in the gun tip, or applied in any other
appropriate manner.
[0021] A reaction of an alcohol and an isocyanate to produce a
urethane is as follows, where reaction I is that of an alcohol and
an isocyanate to produce urethane; reaction II is between a diol
and a diisocyanate to produce a linear, uncrosslinked polyurethane;
and reaction Ill is that of a triol and a diisocyanate to produce a
partially crosslinked polyurethane: 1
[0022] (partially crosslinked polyurethane)
[0023] where R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5 and
R.sub.6 are organic radicals.
[0024] By controlling the cross-link density of the polyurethane,
as by varying the amount of the curing agent, a fluorinated
polyurethane elastomer can be obtained that will have sufficient
toughness and foul-release and antifouling properties for purposes
herein. In order to obtain the desired properties, the coating
should be prepared from a fluorinated and/or unfluorinated polyol,
which includes diols and triols, and a fluorinated and/or
unfluorinated polyisocyanates, which includes diisocyanates and/or
triisocyanates, so that the ratio of NCO/OH is about 1-2, and more
preferably 1-1.5. If the NCO/OH ratio is below about 1, then the
reaction proceeds according to reaction II, above, which produces a
linear polyurethane elastomer which is not crosslinked and does not
have the desired toughness to serve as a coating herein. The ratio
should be at least about 1 in order for the preparation reaction to
proceed by reaction III which can produce a partially cross-linked
fluorinated polyurethane with sufficient toughness to serve as a
coating herein.
[0025] The ratio of NCO/OH should be below about 2 so that the
resulting fluorinated polyurethane is not only tough enough but
also has sufficient antifouling and release properties to serve as
a coating herein. If too much of the curing agent is used, then the
polyurethane can become completely cross-linked and although its
toughness may be more than sufficient for purposes herein, its
antifouling and release properties may be insufficient. There is a
balance of properties herein which can be attained, inter alia, by
using a certain proportion of starting materials to control the
cross-linking density of the polyurethane, which in turn controls
its elasticity and resistance to physical abuse as well as allows
for its antifouling and release properties. By using a proportion
of a polyol and a polyisocyanate so that the ratio of NCO/OH is
below about 2, the preparation reaction proceeds according to
reaction III whereby a partially cross-linked fluorinated
polyurethane can be produced with desirable toughness and
antifouling and release properties. The preferred ratio of NCO/OH
is 1-1.5 and the optimum ratio appears to be about 1.2.
[0026] The NCO/OH ratio of 1.2 has the highest hardness and the
highest modulus of elasticity of any material tested. This
indicates that it will have the greatest resistance to physical
damage and the easiest fouling release. This combination of
properties in one material was merely additive but synergistic and
unexpected.
[0027] Another criterion for a desirable coating is its fluorine
content, particularly for the antifouling and release properties.
As already noted, the fluorine can be either on the polyol or the
polyisocyanate, or both. The fluorinated polyurethane elastomer of
this invention should have fluorine content, on molar basis, of
3-25%, and preferably 6-18%, and more preferably 9-10%. If the
minimum fluorine amount is exceeded in that the amount of fluorine
is below about 3%, then antifouling and release properties of the
fluorinated polyurethane elastomer will be insufficient for
purposes herein. The upper amount of fluorine is governed by
economics, and an elastomer with more than about 25% fluorine will
be impractical because it would be too expensive.
[0028] The ratio of diol to trio is important in the context of
preparing coatings with desirable toughness and antifouling and
release properties. Based on data observed, the percent of
trifunctional OH groups in the base component should be about
10-40%, preferably 18-32%, and more preferably 23-27%. Presence of
trifunctional OH enables preparation by reaction III, above, which
makes possible the partial cross-linking to take place and imparts
the desirable toughness to the elastomer. If content of
trifunctional OH is below about 10%, the coating is too weak,
whereas if it is above about 40%, the coating is too rigid and
inelastic.
[0029] To discourage fouling of the coating, i.e., the fluorinated
polyurethane elastomer, in dry or wet form, the coating should have
a surface energy of 15-30 milli J/m.sup.2, preferably 20-29 m
J/m.sup.2, and more preferably 25-27 m J/m.sup.2 ; and Young's
elastic modulus of 2-15 MPa, preferably 2-10 MPa, and more
preferably 3-7 MPa. Both surface energy and the modulus of
elasticity correlate with the performance of the coating as
foul-resistant and release of fouling with toughness. Typically,
when the amount of the polyol is reduced, the modulus of elasticity
also declines.
[0030] It was not expected that the combination of low surface
energy and low modulus of elasticity would give sufficient
anti-fouling and foul release properties. There is synergy here
between fluorine content, surface energy and elastic modulus,
provided that each is kept within a narrow range. Low surface
energy minimizes fouling and low modulus of elasticity makes it
easier to get it off.
[0031] With respect to the reaction of a polyol and a
polyisocyanate to produce the polyurethane elastomer, as generally
depicted by the reaction III, above, a suitable polyol, which can
be fluorinated or unfluorinated, has molecular weight of about
400-1000 and OH functionality of 2 or more, such as 2 or 3. A
suitable fluorinated polyol is the unsaturated fluorinated polyol
disclosed in U.S. Pat. No. 4,157,358. This polyol contains a
backbone comprised of carbon-carbon and carbon-oxygen bonds to
impart chemical stability, sufficient hydroxyl groups to form an
elastomer, and trifluoromethyl groups evenly spaced along the
backbone to reduce surface energy and shield the backbone from
chemical attack. This material is made by 21.sup.st Century
Coatings under the trade name WC-10, is supplied as a 70%
weight/weight solution in n-butyl acetate/xylene, and the solution
has an equivalent weight of 535.
[0032] Other suitable fluorinated polyols include Fluorobase C from
Ausimont Chemical, supplied as a 50% w/w solution in n-butyl
acetate with equivalent weight of 906 and fluorine content of 27%.
Fluorobase C is a difunctional OH-terminated perfluoropolyether of
the general structure
HOCH.sub.2[CF.sub.2O(CF.sub.2CF.sub.2O).sub.a(CF.sub.2O).sub.bCF.sub.2]CH.-
sub.2OH
[0033] Another suitable polyol is polypropylene glycol. It has a
viscosity of 80 cP at 25.degree. C., a number average molecular
weight of 425, and an equivalent weight of 212. It contains no
fluorine.
[0034] The polyol may be typically dissolved in a solvent or a
mixture thereof to give desirable viscosity or workability. A
suitable solvent is volatile and non-reactive with the NCO groups
of the curing agent. Suitable solvent for the polyols include
xylene, butyl acetate and other esters, aromatic hydrocarbons,
toluene, ethers, and the like. Alcohols and amines are not
considered to be suitable solvents since OH and NH groups react
with the NCO groups of the curing agent. DMSO is also not
considered to be a suitable solvent for purposes herein since it is
not volatile and would not evaporate from the coating.
[0035] A suitable isocyanate is one that contains 2 or more NCO
groups, such as 2. A suitable fluorinated isocyanate is Fluorobase
Z from Ausimont Chemical which is supplied as a 60% solution in
n-butyl acetate and has equivalent weight of 1200 and viscosity of
200 cP at 25.degree. C. Fluorobase Z is a difunctional
NCO-terminated perfluoropolyether made by reacting Fluorobase C
with the triisocyanurate of hexamethylene diisocyanate. Another
suitable fluorinated diisocyanate can be made by reacting
Fluorobase C with isophorone diisocyanate. Suitable non-florinated
polyisocyanates are made from hexane-1,6-diisocyanate or isophorone
diisocyanate. Polyisocyanates made from hexane-1,6-diisocyanate
include Desmophen N-3000, Desmophen N-3100, and Desmophen N-3200,
made by the Bayer Corporation. Polyisocyanates made from isophorone
diisocyanate include Vestanat, made by Degussa-Huels
Corporation.
[0036] In a preferred embodiment, the base polyol component
contains a diol, a triol and a catalyst and is prepared by
thoroughly mixing the following materials in the indicated
proportions:
[0037] 1) 6.42 grams of fluorinated polyol WC-10 as a 70% w/w
solution in n-butyl acetate xylene;
[0038] 2) 0.41 g of trimethylol propane propoxylate having
molecular weight of 308 and an equivalent weight of 103 (CA
Registry No. 25723-16-4); and
[0039] 3) 0.04 g dibutyltin dilaurate (DBTDL) catalyst having
molecular weight of 631 (CA Registry No. 77-58-7).
[0040] The DBTDL catalyst is used to speed up the reaction between
polyol and curing agent so that the reaction can be completed in 5
minutes to 8 hours. In absence of a catalyst, the reaction may take
several days. Sufficient amount of a suitable metal salt catalyst
is used to carry out the reaction in 5 minutes to 8 hours,
preferably 2-4 hours.
[0041] The base polyol component comprised of ingredients 1, 2 and
3, identified above, was prepared by mixing the ingredients to
produce a pourable liquid having viscosity of 2000-12,500 cP
at40.degree. C.
[0042] In a preferred embodiment, the curing agent contains a
diisocyanate oligomer which is prepared by using the following
product in the indicated proportion:
[0043] 1) 9.60 g diisocyanate prepolymer, a poly(propylene glycol)
terminated with toluene-2,4-diisocyanate having weight average
molecular weight of about 1000, viscosity of 12,500 cP at
40.degree. C., and an average isocyanate content of 8.4% by weight
(CA Registry No. 9057-91-4).
[0044] The base polyol component and the curing agent are mixed for
about 20 minutes to produce a liquid polyurethane elastomer and
then applied to a substrate by spraying. Sufficient time is
provided for mixing and reacting the base polyol component and the
curing agent, which typically takes less than about 1/2 hour and
generally about 10 minutes, although it can be accomplished in 5-30
minutes, depending on sample size. The liquid polyurethane
elastomer should have sufficient working time to be applied to a
substrate, allowing air bubbles and solvent, if any is used, to
escape before cure takes place to form a rubbery solid coating. The
working time, after mixing the base polyol and the curing agent, is
typically 1/4-2 hours, and more typically 1/2-1 hour. Curing time
is typically overnight or until tack-free.
[0045] Cured thickness of the coating applied to a substrate is
typically 500-6250 microns, more typically 1250-5000 microns. The
coating should be thick enough to permit the foulant to be removed
from a substrate by peel. If thickness of the coating is too small,
the amount of elastomer between foulant and substrate is
insufficient to impart a rubbery nature to the surface and disguise
the rigidity of the substrate. The foulant, in effect, experiences
a rigid surface and the bond between foulant and surface must fail
in shear. For this reason, thickness of the coating should be such
as to allow separation between the substrate and the foulant to
take place by peel, which typically requires less force than shear.
The coating thickness ranges given above, will allow separation of
a foulant, particularly a marine foulant, from a substrate to take
place in peel rather in shear. Very thick coating s would be ideal,
for they would completely mask the properties of the substrate and
ensure failure of the foulant-substrate joint by peel. However,
thicknesses beyond the upper ranges given above are economically
impractical. Since a typical coat of paint is about 75 microns
thick, it should be apparent that even the thinnest effective layer
of the coating herein is relatively thick, compared to a paint
coating.
[0046] The coating is applied onto a substrate, which is generally
steel, which is typically coated with a 2-component epoxy polyamide
primer layer. The primer thickness is typically on the order of
25-125 microns. The coating can be applied onto a substrate, as by
spraying, or it can be in the form of a film secured to a
substrate.
[0047] Lifetime of the coating of this invention is on the order of
10 years.
EXAMPLE 1
[0048] Pursuant to the invention, a series of fluorinated
polyurethane elastomers were made to evaluate versatility of the
synthesis and performance of the coatings.
[0049] The curing agent (Part A) and the base component (Part B)
were as follows:
[0050] Part A (curing agent)
[0051] 9.60 g diisocyanate prepolymer, a poly(propylene glycol)
[0052] terminated with toluene-2,4-diisocyanate having weight
[0053] average molecular weight of about 1000, viscosity of 12,500
cP
[0054] at 40.degree. C., and an average isocyanate content of 8.4%
by weight 7.2-12.0 g
[0055] Part B (base component)
[0056] 1) 6.42 grams of fluorinated polyol WC-10 as a 70% w/w
solution in n-butyl acetate xylene;
[0057] 2) 0.41 g of trimethylol propane propoxylate having
molecular weight of 308 and an equivalent weight of 103; and
[0058] 3) 0.04 g dibutyltin dilaurate (DBTDL) catalyst having
molecular weight of 631. 6.42 g
[0059] Proportion of triol in the above base component was kept
constant at 25% and the NCO/OH ratio in the above reactions was
either 1.1, 1.2 or 1.3. The above base component and the above
curing agent were made separately, blended thoroughly, poured into
a mold and allowed to cure at room temperature for 72 hours,
producing tough, translucent elastomers light yellow in color. The
Durometer hardness was measured with a Shore A Hardness tester, and
is shown in Table 1, below.
[0060] Contact angle measurements were made with an AST 2500 Video
Contact Angle System. Drops of triply-distilled water, methylene
iodide, and formamide were applied separately to the elastomer, and
the contact angle between each drop and the surface was measured
immediately. The measured contact angles and the surface tensions
of the test liquids were used to calculate the surface energy by
the geometric mean method. The dispersive component .gamma..sub.d,
polar component .gamma..sub.p, and total surface energy
.gamma..sub.T of the elastomers are shown in Table 1, below. These
values for the fluorinated polyurethane elastomers are well below
corresponding values of .gamma..sub.T for commodity polymers such
as polystyrene (.gamma..sub.T=40 dynes/cm) and polyethylene
(.gamma..sub.T=33 dynes/cm), indicating that the trifluoromethyl
groups are aggregated at the surface.
[0061] Hardness and Young's elastic modulus were measured with a
Fisherscope H-100 Microindenter which senses both load and
displacement. The applied load on a Vickers four-sided pyramid
indenter was increased incrementally in 30 1-second steps to three
maximum load levels of: 10, 30 and 100 mN. WinUMIS 2 software was
used for analysis of the data. The values for universal hardness
Hu, Young's elastic modulus E, and recovery are shown in Table
1,
1TABLE 1 Physical Properties of the Fluorinated Polyurethane
Elastomers NCO/ Recov- OH .gamma..sub.d .gamma..sub.p .gamma..sub.T
Hu E ery Shore A ratio dy/cm dy/cm dy/cm dy/cm Mpa % Hardness 1.1
21.8 3.4 25.2 0.36 4.8 72 62 1.2 24.9 3.2 27.1 0.49 6.2 75 62 1.3
24.9 3.2 27.1 0.31 3.9 76 65
[0062] Seawater immersion tests were conducted in the Chesapeake
Bay at Deale, Md. beginning in May of 2000. The elastomers were
attached to polymethyl methacrylate (PMMA) panels with epoxy cement
and immersed in still water to a depth of 1-4 feet, depending on
tides. Fouling was assessed at about two-month intervals. At each
evaluation, the extent of fouling, ease of cleaning, residual
fouling, and integrity of the coating were judged and rated on a
scale of 0 (best) to 5 (worst). Data is given in Table 2,
below.
2TABLE 2 Immersion Testing of the Fluorinated Polyurethane
Elastomers NCO/OH ratio Fouling Ease of Cleaning Residual Fouling
Jun. 26, 2000 1.1 2 1 0 1.2 3 0 0 1.3 3 0 0 Aug. 15, 2000 1.1 3 1 0
1.2 3 1 0 1.3 3 1 0 Oct. 3, 2000 1.1 0 0 0 1.2 2 0 0 1.3 2 0 0
[0063] The above Table 2 shows that, at each inspection, all
elastomers had accumulated fouling on their surfaces. Fouling
included shell fouling and soft fouling. Shell fouling is fouling
by barnacles, mussels and clams whereas soft fouling is fouling by
grasses and weeds. The amoung of fouling on the elastomers was
significantly less than that on the PMMA panels to which they were
attached. The elastomers were placed flat on the pier and washed
with a garden hose at 15 psi water pressure. The force of water
issuing from the hose was sufficient to remove all fouling from
panels rated 0. Finger pressure was needed to remove fouling from
all panels rated 1. In this way all of the panels were restored to
the condition characteristic of new panels before testing.
EXAMPLE 2
[0064] This is an example that did not work because both its
modulus and fluorine content were too high.
3 Part A Fluorobase Z, 60% w/w solution in nBuOAc 23 g (viscosity
of 200 cP at 20.degree. C.) Part B Fluorobase C, 50% w/w solution
in nBuOAc 10.9 g (viscosity of 80 cP at 25.degree. C.) Trimethylol
propane propoxylate, MW.sub.wt 308 0.4 g DBTDL catalyst 0.1 g
[0065] This had a NCO/OH ratio of 1.2, surface energy of 11.1
mJ/m.sup.2, an elastic modulus of 1420, and a fluorine content of
38%. Cleaning required scraping with a metal or plastic tool, and
some fouling could not be removed.
EXAMPLE 3
[0066] This is an example that did not work simply because it's
fluorine content was too high.
4 Part A Fluorobase Z, 60% w/w solution in nBuOAc 23 g viscosity of
200 cP at 20.degree. C. Part B Propylene glycol, 80 cP at
25.degree. C., MW of 425 2.5 g Trimethylol propane propoxylate, MW
308 0.4 g DBTDL catalyst 0.06 g
[0067] This had a NCO/OH ratio of 1.2, surface energy of 9.1
mJ/m.sup.2, an elastic modulus of 2.9 Mpa, and a fluorine content
of 36%. Cleaning required moderate effort with a sponge or cloth,
and a small amount of fouling could not be removed.
EXAMPLE 4
[0068] This is an example that did not work simply because it's
modulus was too high.
5 Part A Polypropylene oxide , toluene diisocyanate terminated, 9.6
g MW of about 1000, viscosity of 12,500 cP at 40.degree. C., and
containing 8.4 weight % isocyanate Part B Fluorobase C., 50% w/w
solution in nBuOAc 10.9 g Trimethylol propane propoxylate, MW 308
0.4 g
[0069] DBTDL catalyst 0.05 g
[0070] This had a NCO/OH ratio of 1.2, surface energy of 29.5
mJ/m.sup.2, an elastic modulus of 18 MPa, and a fluorine content of
9%. Cleaning required scraping with a metal or plastic tool, and
all fouling could be removed.
[0071] While presently preferred embodiments have been shown of the
novel fluorinated polyurethane elastomers disposed on a substrate
and a process for preparing the elastomers, and of the several
modifications discussed, persons skilled in this art will readily
appreciate that various additional changes and modifications may be
made without departing from the spirit of the invention as defined
and differentiated by the following claims.
* * * * *