Organic compounds -- part of the class 532-570 series – Organic compounds – Silicon containing
Reexamination Certificate
1997-11-25
2001-11-06
Shaver, Paul F. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Silicon containing
C528S026000, C528S028000, C524S588000, C524S589000, C524S838000, C525S440030, C525S448000, C428S391000, C428S543000, C428S544000
Reexamination Certificate
active
06313335
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to novel dispersions comprising silane terminated urethanes containing fluorine and/or silicone moieties useful as surface adhesion preventers or release promoters for fouling agents on surfaces that need protection. The invention also relates to novel waterborne, low surface energy and room temperature curing coating compositions prepared therefrom.
BACKGROUND OF THE INVENTION
Fouling refers to the accumulation of airborne or waterborne biological materials on surfaces. Marine surfaces are especially prone to fouling, due to the affinity of marine organisms for areas at or below the waterline. In marine environments, fouling a involves surfaces on ship hulls, buoys, drilling platforms, pipes, and the like. Fouling build up on these surfaces can lead to a number of problems, such as increased weight or drag in the water, which, in the case of ships, can result in increased fuel consumption and operating costs.
The most common approach to prevention of marine fouling is through use of toxic antifouling coatings. The most commonly used antifouling coatings contain metallic toxicants, such as organo-tin or copper, which prevent marine organisms from attaching to the surface through release of the toxicant into the surrounding water. Such coatings may also contain an organic toxicant. A common form of these coatings, known as ablative antifouling coatings, wear away as the ship's hull passes through the water. This ablative action constantly brings fresh toxicant to the surface, until the toxicant concentration falls below a critical level, at which point the coating becomes ineffective. In order to restore the coating, the ship must be dry-docked and go through a recoating process.
A major concern of the use of antifouling coatings is the impact the leaching metallic toxicant poses to the environment. The use of organotin-based coatings has been found to kill, or at least severely restrict, the growth of marine life. This is especially true in areas of high ship traffic, such as harbors, bays, and estuaries. The use of copper based antifouling coatings is also being scrutinized for environmental hazards. It has been estimated that a ship having 3250 square meter hull area releases approximately 0.91 kg of copper per day, which is sufficient to bring approximately 18.9 million liters of sea water to toxic copper concentrations. (“Fluorinated Ship-Hull Coatings for Non-Polluting Fouling Control”; http://inel.gov
ew/funding/serdp/p2prj005. html; May 30, 1996). Restrictions as to release of toxins into the environment are in place in certain areas. In addition to these problems, hulls coated with copper based coatings may experience the need for more frequent recoating than or anotin-based coatings.
Organic toxicants are considered to be less of a problem in this regard, since they tend to decompose to non-hazardous materials over time in water. Health hazards to dock workers exposed to organotin compounds and disposal of large quantities of toxic waste generated from removal of coatings during dry docking provide additional constraints to the use of or canotin-based antifouling coatings.
An alternative to the toxicant release approach is providing a coating or surface to which fouling organisms have difficulty adhering. Ideally, the turbulence created by the motion of the ship through water or simple cleaning methods would remove fouling organisms.
Pioneering work conducted by J. Griffith, “Nontoxic Alternatives to Antifouling Paints,”
Journal of Coatings Technology
, vol 59 (755), 1987, pp 113-119, demonstrated that low surface energy coatings derived from fluoropolymers can function as fouling release coatings. Although these coatings demonstrated the principle of fouling release, certain marine organisms such as barnacles adhered strongly to the surface, requiring a cleaning step to remove them.
A. Beca and G. Loeb (“Ease of Removal of Barnacles from Various Polymeric Materials,”
Biotechnical and Bioengineering
, v. 26, p. 1245-1251, 1984) studied the attachment of barnacles to a variety of polymeric surfaces and concluded that barnacles attached to a low surface energy surface were easier to remove than those attached to surfaces with higher surface energy. Researchers have also demonstrated through testing that marine organisms, in particular barnacles, attach more strongly to hard plastics than they do to soft elastomers.
A low surface energy approach was also demonstrated by Lindner, (“Low Surface Free Energy Approach In The Control of Marine Biofouling,”
Biofouling
, 1992, Hardwood Academic Polyurethane Publishers, Vol. 99, pp. 193-205) who calculated coating surface energies based on contact angles with water and other liquids, and correlated them with contact angles critical to prevention of fouling by marine organisms. The higher the contact angle with water, the lower the surface energy of the coating surface. These materials were exemplified with oriented monolayers of perfluorinated surfactants fixed by polymers on the surface and by comb-like polymers with perfluorinated side chains. The preparation of a durable, water-borne polymer was not exemplified by this disclosure.
These studies confirm the need for a low surface energy surface, but also indicate that other factors, such as low glass transition temperature (<−20° C.) and elastomeric nature of the coating also play an important role in governing adhesion of marine organisms to polymeric surfaces.
Many commercially available silicones also contain leachable additives or residuals, which slowly move to the surface to form a weak boundary layer, resulting in easier removal of fouling organisms. Often, this additive is a silicone fluid.
While silicone coatings meet the requirements of low surface energy, low glass transition temperature, and elastomeric nature, there are major drawbacks to their use. These include poor abrasion resistance, tensile strength, and tear strength. These drawbacks result in susceptibility to mechanical damage. Also, silicone coatings do not exhibit good resistance to marine grasses and algae. Other potential problems with commercially available silicone fouling release coatings may include high solvent content and high material cost. Application cost may be high due to the necessity of multiple coats of dissimilar layers in order to achieve acceptable adhesion. Many of the silicone products are multi-component, requiring on-site mixing and pot life concerns.
Teflon™ filled materials, such as epoxies and vinylesters, are available, but they have a high glass transition temperature, are non-elastomeric, and are not low enough in surface energy to prevent strong adhesion of marine fouling organisms.
Polyurethanes have achieved commercial acceptance in surface finishing systems because of their overall balance of properties such as abrasion resistance, flexibility, toughness, high gloss, as well as mar and organic solvent resistance. Early commercial systems were either solvent based one-component reactive high solids prepolymers reacted with a second component, organic solvent-based moisture curing compositions or fully reacted urethane lacquers generally dissolved in alcohols and/or aromatic solvents.
In an effort to eliminate organic solvents and their associated emission and handling problems, waterborne urethane coatings were developed. Aqueous poly(urethane/urea) dispersions are binary colloidal systems in which a discontinuous polyurethane phase is dispersed in a continuous aqueous phase. Aqueous poly(urethane/urea) dispersions have been known for a long time. They are becoming increasingly important in coating and adhesive applications due to environmental and safety regulations of organic solvent based systems. Aqueous poly(urethane/urea) dispersions can be formulated using little or no co-solvent to produce high performance coatings and adhesives at ambient temperatures. They not only replace organic solutions but find applications in new areas as well. For instance, they are not aggressive towards plastic surfaces and
Guerra Miguel A.
Hansen Richard G.
Holland Lowell W.
Moore George G. I.
Roberts Gary P.
3M Innovative Properties
Pribnow Scott R.
Shaver Paul F.
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