Fouling inhibition

Details Fouling inhibition Fouling inhibition

2000-06-22

2004-04-20

Beck, Shrive P. (Department: 1762)

Coating processes

Restoring or repairing

Metal article

C427S140000, C427S301000, C427S302000, C427S407100, C427S409000, C427S419700

Reexamination Certificate

active

06723376

ABSTRACT:

FIELD OF INVENTION
This invention relates to a process for inhibiting fouling of a substrate in a fouling environment, more especially a marine or other aquatic environment.
BACKGROUND OF THE INVENTION
Man-made structures such as boat hulls, buoys, drilling platforms, oil production rigs and pipes which are immersed in water are prone to fouling by aquatic organisms such as green and brown algae, barnacles, mussels and the like. Marine structures are commonly of metal, but may also comprise other structural materials such as concrete. For smaller boats, the hulls may instead comprise, for example, wood or a fibre-reinforced resin. This fouling is a nuisance on boat hulls, because it increases the frictional resistance towards movement through the water, with the consequence of reduced speeds and increased fuel costs. It is a nuisance on static structures such as the legs of drilling platforms and oil production rigs, firstly because the resistance of thick layers of fouling co waves and currents can cause unpredictable and potentially dangerous stresses in the structure, and, secondly, because fouling makes it difficult to inspect the structure for defects such as stress cracking and corrosion. It is a nuisance in pipes such as cooling water intakes and outlets, because the effective cross-sectional area is reduced by fouling, with the consequence of reduced flow rates.
The commercially most successful methods of inhibiting fouling have involved the use of anti-fouling coatings containing substances toxic to aquatic life, for example tributyltin chloride or cuprous oxide. Such coatings, however, are being regarded with increasing disfavour because of the damaging effects such toxins can have if released into the aquatic environment. There is accordingly a need for non-fouling coatings which do not contain markedly toxic materials.
It has been known for many years, for example, as disclosed in GB 1 307 001 and U.S. Pat. No. 3,702,778 that silicone rubber coatings resist fouling by aquatic organisms. It is believed that such coatings present a surface to which the organisms cannot easily adhere, and they can accordingly be called non-fouling rather than anti-fouling coatings. Silicone rubbers and silicone compounds generally have very low toxic properties. Silicone rubber coatings have, however, gained little commercial acceptance. It is difficult to make them adhere well to the substrate surface that is to be protected, and they are mechanically rather weak and liable to damage.
EP 0 032 597. discloses that silicone polymers onto which organic polymeric segments are grafted may be is vulcanised to form non-fouling coatings. The vulcanisation procedure may utilise a crosslinking agent such as tetraethyl orthosilicate and a catalyst such as a tin salt.
GB 2 188 938 discloses that vinylic polymers containing polymeric silicone side chains may be used to form thermoplastic non-fouling coatings.
GB Patent Application 2 192 400 discloses anti-fouling paint compositions which comprise a vinylic copolymer obtained by copolymerisation of:
(a) 1-50% by weight of a polymerisable unsaturated polysiloxane compound;
(b) 0-30% by weight of a polymerisable unsaturated alkoxysilane compound; and
(c) 20-99% by weight of a polymerisable unsaturated vinyl monomer other than (a) or (b).
The disclosed anti-fouling paint compositions may also comprise a hydroxyalkyl-tipped poly(diorganosiloxane) to the extent of 1-50 parts by weight per 100 parts by weight of the vinylic copolymer. The vinylic copolymer and the poly(diorganosiloxane) are not curable one with the other, and the coatings disclosed in GB-A-2 192 400 are thermoplastic and not vulcanised.
Coatings which contain a chemically inert oil or grease, often called a slipping agent, have been reported to offer improved resistance to fouling. GB 1 470 465 discloses the use of silicone oils as slipping agents in a vulcanised silicone rubber formulation. GB 1 581 727 discloses the use of silicone-free organic compounds, for example polyolefins with a molecular weight up to about 5000, as slipping agents in a vulcanised silicone rubber formulation.
WO 93/13179 discloses a composition for fouling inhibition which comprises (A) a functional-group containing polymer having no more than a minor proportion of siloxane repeating units and (B) a polysiloxane which is curable with the polymer (A). After application of the composition to a substrate and curing, the innermost region of the resulting coating generally comprises no more than a minor proportion of siloxane material whereas the coating presents a siloxane-rich surface layer to the external environment. As a result, the coating provides fouling inhibition properties whilst at the same time the problems of mechanical weakness of previously proposed silicone rubber coatings are alleviated or avoided.
SUMMARY OF THE INVENTION
The present invention provides a process for inhibiting the fouling of a substrate in a fouling environment, which comprises forming on the substrate, before exposure to the environment, a coating comprising a film-forming polymer (A) carrying unreacted silicon-containing functional groups providing latent reactivity, and thereafter applying a layer comprising a curable polymeric fouling-inhibiting material (B) and bonding the applied layer to the coating by a condensation curing reaction involving the unreacted functional groups thereon.
The invention further provides a substrate bearing a coating which has been applied by the process, i.e., having an outer layer comprising cured component (B).
An especially important aspect of the present invention comprises inhibition of fouling of structures in aquatic and, in particular, marine environments, especially the hulls of boats and ships of all sizes.
The curable polymeric fouling-inhibiting material (B) carries functional groups capable of condensation curing with the unreacted silicon-containing functional groups on the initial coating comprising the film-forming polymer (A). The material (B) advantageously comprises a curable polysiloxane, but other curable polymeric materials, especially fluorine-containing polymers, for example, fluoro-acrylate polymers may be used.
DETAILED DESCRIPTION OF THE INVENTION
The invention is described hereinafter with particular reference to the preferred case in which the material (B) comprises a curable polysiloxane, but it will be appreciated that similar considerations apply in the case of other materials. Thus, in broad concept, the invention comprises the provision of an initial coating which, after application, carries unreacted silicon-containing functional groups which provide latent reactivity for subsequent curing with the curable polymeric fouling-inhibiting material (B).
The condensation curing reaction between the silicon-containing functional groups on the initial coating and a curable polysiloxane may proceed, for example, as follows:
(i) ≡Si—OH+HO—Si≡→≡Si—O—Si≡+H
2
O
(ii) ≡Si—OCH
3
+HO—Si≡→≡Si—O—Si≡+CH
3
OH
(iii) ≡Si—H+HO—SI≡→≡Si—O—SI≡+H
2
(iv) ≡Si—O—NR
a
—R
b
+HO—Si≡→≡Si—O—Si≡+R
a
—R
b
NOH
(v) ≡Si—NR
c
R
d
+HO—Si≡→≡Si—O—Si≡+R
c
R
d
NH
(vii) ≡Si—O—NCR′R
2
+HO—Si≡≡Si—O—Si≡+R′R
2
CNOH, which may hydrolyse to an aldehyde or ketone, R′R
2
CO and hydroxylamine, NH
2
OH, under the conditions of the condensation.
The film-forming polymer (A) may comprise pendant and/or terminal curable functional groups. Pendant curable functionality is preferred, for example, in the case where the polymer is derived from one or more ethylenically unsaturated monomers, and terminal curable functionality is preferred, for example, if the polymer (A) is polyurethane, epoxy or polyester based.
The silicon-containing curable groups may be mono-, di- or tri-functional. In the case of di- or tri-functional groups, it is in general not necessary to provide a separate

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