Coating processes – With post-treatment of coating or coating material – Heating or drying
Reexamination Certificate
2003-03-26
2004-05-11
Cameron, Erma (Department: 1762)
Coating processes
With post-treatment of coating or coating material
Heating or drying
Reexamination Certificate
active
06733838
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
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.
2. Background and Prior Art Description
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.
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.
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.
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.
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.
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.
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
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.
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.
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.
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″).
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.
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
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.
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.
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.
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
Cameron Erma
Kap George A.
Karasek John J.
The United States of America as represented by the Secretary of
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