Stock material or miscellaneous articles – Composite – Of silicon containing
Reexamination Certificate
1998-09-08
2001-01-30
Nakarani, D. S. (Department: 1773)
Stock material or miscellaneous articles
Composite
Of silicon containing
C106S287140, C106S287160, C427S387000, C524S265000, C524S267000, C524S268000, C524S493000, C524S731000, C524S837000, C524S858000, C524S859000, C524S863000, C528S014000, C528S017000, C528S018000, C528S901000
Reexamination Certificate
active
06180249
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to foul release coatings and articles coated therewith. More particularly, this invention relates to foul release coatings containing organic compatible oils that have enhanced foul release performance.
A perennial major aggravation to shippers and users of marine equipment in contact with water is the tendency of such equipment to become encrusted with varieties of wildlife, as illustrated by barnacles and zebra mussels. This tendency is often referred to as marine fouling.
U.S. Pat. No. 4,861,670 describes in considerable detail, the types of treatments that have been employed, starting as early as 1854, to minimize marine fouling. Treatment materials have included compounds of such metals as copper, tin, arsenic, mercury, zinc, lead, antimony, silver and iron, as well as toxic organic materials such as strychnine and atropine. Due to environmental concerns, the use of such materials has been discouraged.
More recently, polyorganosiloxanes (hereinafter sometimes designated “silicones” for brevity) have been found useful as anti-fouling coatings. They include condensation cured room temperature vulcanizable (hereinafter sometimes “RTV”) compositions comprising silica or calcium carbonate as a filler in combination with silanol- or dialkoxy-terminated silicones, catalysts and crosslinking agents. They may be made sprayable by dilution with solvents, typically volatile organic compounds such as hydrocarbons.
There is still a need, however, to improve various properties of RTV-based foul release coatings, particularly their release efficiency and their effective lifetime.
SUMMARY OF THE INVENTION
The present invention satisfies this need by the discovery that the addition of specifically defined organic compatible oils to a conventional RTV formulation improves foul release properties. It includes foul release coatings having said improved properties and articles coated with said improved foul release coatings.
In one of its aspects, the invention is directed to condensation curable coating compositions comprising the following and any reaction products thereof:
(A) a one- or two-part room temperature vulcanizable polyorganosiloxane composition, and
(B) a marine foul release-enhancing proportion of at least one organic compatible silicone fluid free from silanol groups and being capable of blooming to the surface of the cured product of component A.
Another aspect of the invention is articles comprising a marine structure coated with an anti-fouling coating, which is the condensation cured reaction product of the composition defined hereinabove.
DETAILED DESCRIPTION
The word “component” is frequently employed herein for brevity to designate the materials present in the compositions of the invention. Its use is independent of the possible interreaction of said materials to form other chemical constituents.
Component A of the compositions of the invention may be a conventional one-part or two-part RTV composition; it is most often a two-part composition. It typically comprises at least one reactive silicone, at least one condensation catalyst and at least one crosslinking agent.
The reactive silicone is most often a polydialkylsiloxane, typically of the formula
wherein each R
1
is a hydroxyl radical or
each R
2
is independently a hydrocarbon or fluorinated hydrocarbon radical, each R
3
and R
4
is a hydrocarbon radical, a is 0 or 1 and m has a value such that the viscosity of said reactive silicone under ambient temperature and pressure conditions is up to about 50,000 centipoise. Illustrative hydrocarbon radicals are C1-20 alkyl, C6-20 aryl and alkaryl, vinyl, isopropenyl, allyl, butenyl and hexenyl, with C1-4 alkyl and especially methyl being preferred. An illustrative fluorinated hydrocarbon radical is 3,3,3-trifluoropropyl. Most often, each R
2
, R
3
and R
4
is alkyl and preferably methyl.
It is within the scope of the invention to employ two or more reactive silicones, differing in average molecular weight. This may afford a bimodal composition having performance advantages over a simple monomodal composition.
The condensation catalyst may be any of those known to be useful for promoting condensation curing of an RTV material. Suitable catalysts include tin, zirconium and titanium compounds as illustrated by dibutyltin dilaurate, dibutyltin diacetate, dibutyltin methoxide, dibutyltin bis(acetylacetonate), 1,3 -dioxypropanetitanium bis(acetylacetonate), titanium naphthenate, tetrabutyl titanate and zirconium octanoate. Various salts of organic acids with such metals as lead, iron, cobalt, manganese, zinc, antimony and bismuth may also be employed, as may non-metallic catalysts such as hexylammonium acetate and benzyltrimethylammonium acetate. For most purposes, the tin and titanium compounds are preferred.
As crosslinking agents, trifunctional (T) and tetrafunctional (Q) silanes are useful, the term “functional” in this context denoting the presence of a silicon-oxygen bond. They include such compounds as methyltrimethoxysilane, methyltriethoxysilane, 2-cyanoethyltrimethoxysilane, methyltriacetoxysilane, tetraethyl silicate and tetra-n-propyl silicate. The Q-functional compounds, i.e., tetraalkyl silicates, are often preferred.
Component A may contain other constituents, including reinforcing and extending (non-reinforcing) fillers. Suitable reinforcing fillers have a primary particle size of about 10 nm and are available in the form of aggregated particles of about 100 to about 250 nm. The preferred fillers are the silica fillers, including fumed silica and precipitated silica. These two forms of silica have surface areas in the ranges of 90-325 and 8-150 m
2
/g, respectively.
The reinforcing filler is most often pretreated with a treating agent to render it hydrophobic. Typical treating agents include cyclic silicones such as cyclooctamethyltetrasiloxane and acyclic and cyclic organosilazanes such as hexamethyidisilazane, 1,3-divinyl-1,1,3, 3-tetramethyld isilazane, hexamethylcyclotrisilazane, octamethylcyclotetrasilazane and mixtures of these. Hexamethyldisilazane is often preferred.
Non-reinforcing fillers include titanium dioxide, lithopone, zinc oxide, zirconium silicate, iron oxides, diatomaceous earth, calcium carbonate, glass fibers or spheres, magnesium oxide, chromic oxide, zirconium oxide, aluminum oxide, crushed quartz, calcined clay, talc, kaolin, asbestos, carbon, graphite, cork, cotton and synthetic fibers.
The proportions of the constituents of component A may be varied widely. The amount of filler is generally about 5-200 parts and preferably about 10-150 parts by weight per 100 parts of reactive silicone. Catalysts and crosslinkers are generally present in the amounts of about 0.001-2.5% and about 0.25-5.0% by weight respectively, based on the combination of reactive silicone and filler.
Component B is an organic compatible silicone fluid. An organic compatible silicone fluid is an organosiloxane fluid that has imparted organic character from incorporated alkyl groups or aromatic substituted alkyl (aryl-alkyl and aryloxy-alkyl) groups. Preferably, the organic compatible silicone fluid comprises about 2 to 100 mole % higher alkyl (C6-C20) or substituted aryl-alkyl radicals. More preferably, the organic compatible silicone fluid comprises about 10 to 70 mole % higher alkyl (C6-C20) or substituted aryl-alkyl radicals. The organic compatible silicone fluids suitable in the present invention are free from silanol groups and are characterized by pour points in the range from about −60° C. to about 80° C., preferably from about −50° C. to about 30° C. and most preferably from about −50° C. to about 0° C. These fluids exhibit an extended range of organic compatibility and lubricity.
Examples of organic compatible silicone fluids include alkylmethylsiloxane homopolymers such as polyoctylmethylsiloxane, polytetradecylmethylsiloxane and polyoctyidecylmethylsiloxane; alkylmethylsiloxane/arylmethylsiloxane copolymers such as ethylmethylsiloxane/2-phenylpropylmethylsiloxane copolymer, hexylmethylsi
General Electric Company
Johnson Noreen C.
Nakarani D. S.
Stoner Douglas E.
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