Compositions: coating or plastic – Coating or plastic compositions – Contains fireproofing or biocidal agent
Patent
1995-09-20
1997-03-25
Green, Anthony
Compositions: coating or plastic
Coating or plastic compositions
Contains fireproofing or biocidal agent
424602, 424604, 4273855, 427386, 422 6, 523122, 523177, C09D 516
Patent
active
056140061
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to an anti-fouling composition. More particularly, it relates to a hardenable composition which contains particles of a water-soluble glass composition which particles dissolve slowly on contact with water or an aqueous solution thereby releasing a toxic chemical species therein.
Aquatic and marine organisms will grow on or attach themselves to any suitable surface which is exposed for an extended time to the aqueous environment in which they live. The bottoms of boats and ships are particularly prone to this problem since algae, seaweed and barnacles that grow there impede motion through the water by increased drag. Problems are also experienced at submerged water inlets to power stations where aquatic life forms, such as mussels, thrive and, thus, cause blockage of the inlets.
One method of preventing or reducing fouling of submerged surfaces is to provide a means of releasing copper II ions, which are toxic to the aquatic and marine life-forms that cause the problem, at a low level from a coating applied to the surface to be treated. This has conventionally been carried out by the incorporation of cuprous oxide into a paint formulation which is applied to the surface of the substrate to be treated. Such a means of providing copper ions into the aqueous environment relies on the intrinsic solubility of the cuprous oxide and the porosity of the paint to give some degree of controlled release. Unfortunately, this is not an efficient system since the release of copper is high initially and falls off with time. In order to overcome such a problem, the coating compositions are overloaded with cuprous oxide in order to ensure that sufficient copper is still being released at the end of the lifetime of the coating applied to the substrate. This practice not only is wasteful of the cuprous oxide but also risks causing damage to other forms of life in the aqueous environment.
GB 1,511,381 discloses an anti-fouling paint or coating which comprises a powdered glass composition dispersed in a resin vehicle. The glass composition used is slowly water-soluble and includes a glass forming oxide, such as phosphorus pentoxide or boric oxide, one or more oxides whose water-soluble ions are toxic to marine or aquatic life and one or more glass modifying oxides which affect the rate at which the glass is dissolved and the toxic ions are released. Although the use of the glass composition, according to GB 1,511,381, allows greater control over the rate of release our observations are that the active lifetime of the paint is far shorter than would have been predicted from the measured glass solubility. We have found that when a soluble phosphate glass dissolves in a limited amount of liquid such that the concentration of dissolution products of the glass builds up then the rate of dissolution of the glass varies as the concentration of the dissolution products changes. Depending on the composition of the glass it has been found that the rate of dissolution may increase or reduce as the concentration of dissolution products increases. There are also some glasses which, after an initial increase in rate, will reach a plateau after which the rate of dissolution changes either not at all or only slowly with increase in dissolution products.
The situation of a glass held in a paint/coating matrix is equivalent to the glass dissolving in a very small amount of liquid. Therefore, the preferred formulation of glass would be such as to produce products of dissolution which do not alter the rate of dissolution of the glass. If a constant rate of release of copper is to be achieved then the rate of dissolution of the glass must be substantially constant.
We have discovered that phosphate glasses within certain compositional limitations dissolve at substantially constant rates. When these are used in cast shapes or coatings on substrates exposed to an aqueous environment they are found to furnish toxic copper ions into the aqueous environment at a substantially uniform rate. The use of such glasses in anti-f
REFERENCES:
patent: 4042402 (1977-08-01), Drake et al.
Borden (UK) Limited
Green Anthony
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