Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From silicon reactant having at least one...
Patent
1992-12-17
1994-07-19
Marquis, Melvyn I.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From silicon reactant having at least one...
528 15, 528 18, 528 19, 528901, 528 33, 528 34, 528 38, 428907, 427387, 524267, 524731, C08G 7706
Patent
active
053310748
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to coatings which inhibit fouling on an underwater surface by aquatic organisms such as algae and barnacles. By an underwater surface we mean a surface which is intended to be underwater or in contact with water at least some of the time in use. The water may be sea water or fresh water. Examples of underwater surfaces are ships' hulls, the underwater and splash zone surfaces of oil production platforms and cooling water inlets and outlets for power stations.
BACKGROUND TO THE INVENTION
Silicone rubber fouling-resistant compositions are described for example in GB-A-1307001, 1470465, 1581727 and 2141436, EP-B-16195 and 32597, EP-A-89071 and 329375 and U.S. Pat. No. 3,702,778 and U.S. Pat. No. 4,525,565. They have significant advantages over conventional antifouling compositions containing marine biocides which are gradually leached from the paint. The silicone rubber coatings rely on their low surface energy, rather than on biocides, to inhibit settlement of marine organisms. Conventional anti-fouling paints eventually become ineffective as all their biocide is released. Silicone rubber coatings are potentially capable of retaining their low energy surface indefinitely.
The silicone rubber fouling-resistant coatings are generally based on a hydroxy-functional polydiorganosiloxane, usually an alpha, omega-dihydroxypolydiorganosiloxane, or a material which is hydrolysable to such a hydroxy-functional polydiorganosiloxane. These hydroxy-functional polydiorganosiloxanes, sometimes known as silicone gums, are curable through their hydroxy groups, and fouling-resistant coating compositions based on them include a crosslinking agent reactive with SiOH groups or hydrolysable to a substance reactive with SiOH groups. EP-B-32597 and EP-A-329375 describe two-pack compositions in which a crosslinking agent such as ethyl silicate is packaged separately from the hydroxy-functional polydiorganosiloxane. Single-pack compositions in which the crosslinking agent contains hydrolysable groups such as acyloxy or ketiminoxy groups are described for example in U.S. Pat. No. 4,525,565 and EP-B-32597.
Such single-pack compositions have the disadvantage that substantial excess of the crosslinking agent needs to be used to obtain a storage-stable composition as taught by U.S. Pat. No. 4,973,623. If the molar ratio of crosslinking agent to the silicon-bonded hydroxyl groups of the hydroxy-functional polydiorganosiloxane is low, the composition is liable to gelation on storage.
SUMMARY OF THE INVENTION
We have found that an increased level of silicon-bonded hydrolysable groups provided by the crosslinking agent in the coating after curing leads to a decrease in antifouling efficiency. In particular we have found that best antifouling performance is achieved if the amount of crosslinking agent is sufficient to cure the hydroxy-functional polydiorganosiloxane but below the levels which give long-term storage stability.
A coating composition resistant to fouling by aquatic organisms according to a first aspect of the invention comprises an organopolysiloxane composition which cures to an elastomer in the presence of moisture and which comprises a polydiorganosiloxane (A) having a viscosity of 500 to 1,000,000 mPa.s at 25.degree. C. and formed of recurring diorganosiloxy units of the formula --(R.sub.2)SiO--, where the radicals R, which can be the same or different within each unit and from unit to unit, represent hydrocarbon radicals having 1 to 10 carbon atoms, the polydiorganosiloxane (A) being terminated with silicon-bonded hydrolysable groups and/or being terminated with silicon-bonded hydroxyl groups and mixed with a crosslinking agent (B) for alpha, omega-dihydroxypolydiorganosiloxanes, said crosslinking agent (B) containing at least two silicon-bonded hydrolysable groups per molecule, is characterised in that the coating composition is packed an two separate packages to be mixed before application of the coating composition to an underwater surface, the first of the said package
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Brooks Rodney R.
Slater, deceased William W.
Slater, executrix Margaret
Winter Michael J.
Courtaulds Coatings (Holdings) Limited
Marquis Melvyn I.
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