Stock material or miscellaneous articles – Composite – Of silicon containing
Reexamination Certificate
2000-05-22
2001-02-13
Nakarani, D. S. (Department: 1773)
Stock material or miscellaneous articles
Composite
Of silicon containing
C428S450000, C428S452000, C114S361000, C106S018120
Reexamination Certificate
active
06187447
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to foul release coatings and articles coated therewith.
As poetically stated in U.S. Pat. No. 4,861,670, “Marine fouling due to pernicious and pestiferous sessile organisms is a problem which reaches from ancient times to the present.” In more simple terms, 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.
Said patent goes on to describe 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. With increasing interest in the state of the environment, the use of such materials has been strongly 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 as a filler in combination with silanol- or trialkoxy-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 is based on the discovery that addition of specifically defined water-insoluble silicones to a conventional RTV formulation improves foul release properties. It includes foul release coatings having said improved properties and articles coated therewith.
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 polyorganosiloxane free from silanol groups and comprising about 10-60% by weight of at least one hydroxy- or alkoxy-terminated polyoxyalkylenealkyl radical,
component B 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; PREFERRED EMBODIMENTS
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 hydroxyl 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 C
1-20
alkyl, C
6-20
aryl and alkaryl, vinyl, isopropenyl, allyl, butenyl and hexenyl, with C
1-4
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. Typical reinforcing fillers are commercially available in the form of relatively large aggregated particles, typically having an average size significantly greater than 300 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 80-150 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 hexamethyldisilazane, 1,3-divinyl-1,1,3,3-tetramethyldisilazane, 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 a water-insoluble polyorganosiloxane free from silanol groups and containing at least one hydroxy- or alkoxy-terminated polyoxyalkylenealkyl radical. Said radical or radicals comprise about 10-60% by weight of component B; that is, the molecular weight attributable to said radicals is about 10-60% by weight of the total molecular weight attributable to component B.
In general, component B comprises compounds of the formula
wherein each R
5
is a hydrocarbon radical and each R
6
is a hydrocarbon or fluorinated hydrocarbon radical, with the proviso that at least one of the R
5-6
radicals has the formula
—R
7
—(OR
8
)
z
—OR
9
, (IV)
wherein R
7
and each R
8
is independently C
2-6
alkylene and R
9
is hydrogen or C
1-4
primary or secondary alkyl; n has a value such that the weight average molecular weight of the compound of formula III is in the range of about 500-40,000; and z and the number of radicals of formula IV are such that said radicals of formula IV comprise about 10-60% by weight of component B. The illustrative and preferred hydrocarbon radicals for R
5-6
are the s
Burnell Timothy Brydon
Cella James Anthony
Stein Judith
Bennett Bernadette M.
General Electric Company
Ingraham Donald S.
Nakarani D. S.
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