Erodible ship-bottom paints for control of marine fouling

Details Erodible ship-bottom paints for control of marine fouling Erodible ship-bottom paints for control of marine fouling

1984-01-17

1986-06-10

Kight, John

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Processes of preparing a desired or intentional composition...

523177, 106 16, 106 1505, 524555, 524558, 524547, 524544, 524551, C08L 3100, C08L 3102, C09D 514

Patent

active

045943656

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

This invention relates to marine antifouling paints which erode at a predetermined rate, and more particularly to a polymeric binder for an antifouling paint where the polymer includes moieties which hydrolyze at a predetermined rate in the presence of sea water.


BRIEF DESCRIPTION OF THE PRIOR ART

The superiority of antifouling paints based on organotin acrylate polymers over the old, conventional leaching type systems has been established by the major ship owners and marine paint companies. Such paint systems offer superior antifouling performance over extended periods because of a constant release of toxicant from the surface of the paint film by hydrolysis of the organotin acrylate copolymer in seawater, normally slightly alkaline.
In paint systems of this kind, the organotin acrylate copolymer serves as the film-forming component (binder).
The organotin portion of the copolymer provides a site for hydrolysis of the polymer by seawater (app. pH=8.0 to 8.3), by which process the polymer surface is slowly converted to a water-soluble or water-swellable form which is able to be eroded away by moving seawater and expose a fresh paint surface.
In addition, the hydrolysis of the organotin polymer releases bis-tributyltin oxide, an effective antifouling toxicant.
In practice, additional toxicants are usually physically incorporated into the antifouling paint. These cotoxicants are released during the gradual hydrolysis and erosion of the organotin copolymer vehicle and serve to provide additional protection against fouling. An additional advantage claimed for such systems is fuel savings which results from a reduction in surface roughness as a consequence of water-planing or erosion of the paint film. Such systems can be designed to hydrolyze and erode at high or low rates by incorporating a retarder characterized by having a low seawater solubility as described in Milne and Hails, U.S. Pat. No. 4,021,392. Milne and Hails also claim that a commercial plant cannot be formulated solely by adjusting the organotin monomer content in the organotin copolymer.
The mechanism by which organotin copolymer anti-fouling paints function is described in Journal of Coatings Technology, Vol. 53, Number 678, pages 46-52. Such paints, however, are relatively expensive and possess undesirable irritative properties due to the necessary presence of the hydrolyzable tributyltin moiety.
These paints represent a major improvement over the conventional, leaching-type paints wherein the cuprous oxide toxicant is dispersed in a binder consisting of a mixture of a film-forming insoluble resin and a water sensitive or slowly water-soluble component such as gum rosin. An example of such a "soluble matrix" paint formulation is given in Table A.


TABLE A ______________________________________ Soluble Matrix Copper Oxide Antifouling Paint U.S. Navy 121/63 Formula Ingredient Pounds Gallons ______________________________________ Cuprous oxide 1440 50.0 Rosin 215 24.1 Vinyl resin (VYHH).sup.(a) 55 4.7 Tricresyl phosphate 50 11.7 Xylene 115 16.1 MIBK 165 24.7 Antisettling agent 7 1.0 1:4 Resin:Rosin Ratio ______________________________________ .sup.(a) Union Carbide?
Such paint systems, however, fail to provide a constant toxicant release, and moreover, do not erode in service. This is due to the selective extraction of the water-soluble component and consequent leaching of toxicant (cuprous oxide) from the interior of the paint film. A matrix of the insoluble vinyl resin component remains behind after the water-soluble component of the film (gum rosin) is leached away. Moreover, the spent paint film no longer controls fouling even though it might contain up to 30-40% of the initial level of cuprous oxide because water penetration required for leaching the copper to the surface is limited through the matrix of residual vinyl resin. Spent antifouling systems of this type do not provide a suitable base for repainting since they possess poor mechanical properties due to t

REFERENCES:
patent: 4052354 (1977-10-01), Beiter et al.

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