Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2000-03-29
2002-08-20
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S261000, C524S264000, C524S265000, C524S266000, C524S493000
Reexamination Certificate
active
06437039
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a one-part room temperature vulcanizable organopolysiloxane rubber composition that does not contain volatile organic compounds (VOC) and which crosslinks in the presence of moisture to form a coating for use to protect a surface from environmental effects such as a corrosion protection, waterproofing, anti-fouling or weathering protection of surfaces, or for secondary containment of liquid spills, or high voltage insulator coating.
BACKGROUND OF THE INVENTION
The protection of surfaces against environmental effects is important in many different applications. For example, metal and other surfaces such as concrete exposed to moisture such as rain or fog in combination with contaminated atmospheres as are found in industrial locations may be subject to extensive corrosion unless protected in some way from exposure to the corrosive atmosphere. Other potentially corrosive environments include along sea coasts where salt spray is found and in areas where agricultural chemicals are widely distributed. In addition, metal and concrete surfaces directly exposed to water such as marine structures and vessels are also subject to the potential for extensive corrosion. Currently, such surfaces are most commonly protected by being painted with alkyd based paints. Such paints form a relatively rigid coating on the surface which can become brittle and when subjected to stress, can flake or chip off, thereby exposing the underlying surface to the corrosive elements. In addition, such paints generally are susceptible to UV damage thereby further reducing their effective life.
Two-part organopolysiloxane rubber compositions for use as a corrosion protection coating on metals have been developed. For example, Lampe describes in U.S. Pat. No. 4,341,842 a two-part room temperature vulcanizable composition for coating the underside of vehicles to protect the metal from rusting or being corroded by road salts or other similar compounds. However, such two-part compositions have a major disadvantage in that they require the use of complex dual mixing and spray nozzle apparatus or require pre-mixing and immediate use on site when used with conventional spray equipment. If conventional spray equipment is used, the amount of material pre-mixed must also be exact to prevent wastage as the composition has a finite pot life.
One part compositions for coating of surfaces have also been described. Such compositions generally utilize a volatile organic solvent such as petroleum naphtha, toluene, petroleum ether and chlorinated hydrocarbons as a diluent to improve the working efficiency and ease of application of the coating composition. If no solvent is utilized, the coating compositions are difficult to apply due to high viscosity. The use of solvent creates environmental pollution and potential danger to the health of workers as it evaporates.
Yaginurua et al in U.S. Pat. No. 5,445,873 describe a solventless coating that cures at room temperature through a condensation reaction. The coating is designed for packaging circuit boards and does not require high physical strength. The composition utilizes a low molecular weight organopolysiloxane with a viscosity in the range of 20 to 500 centipoise.
Another solventless coating composed of silicone resin and polydiorgano-silicone fluid has been described in
U.S. Pat. No. 4,780,338. The coating requires elevated temperatures for curing which requires the heating of the substrate or oven drying after the coating is applied.
U.S. Pat. No. 4,929,703 also describes a solventless coating composed of A) silicone resin reaction product prepared by hydrolyzing, then neutralizing an equilibrated mixture of a silane and a diorganopolysiloxane, B) a silane and C) diorganopolysiloxane fluid. The coating cures when exposed to moisture as a result of condensation reaction of siloxane to form a matrix.
Many other applications where silicone coatings are used include waterproofing, anti fouling, protection of underground pipes and high voltage insulating coatings among others. Such applications generally use either a one part or two part composition as described above, which are subject to the same problems. There still remains a need for a one part room temperature vulcanizable silicone coating composition which is easily applied to surfaces as a protective coating and which does not contain volatile organic compounds (VOC).
The term VOC mainly refers to the hydrocarbons but may also include other compounds. The VOC's that are of most concern and the use of which has been regulated worldwide are those which participate in photochemical reactions and result in toxic oxidates.
SUMMARY OF THE INVENTION
The present invention provides a VOC free, one part room temperature vulcanizable coating for easy and convenient application by conventional methods such as dipping, flow or spraying. The coating provides a guard against environmental effects along with high physical strength and adhesion achieved with a suitable blend of reinforcing and extending fillers.
In one aspect, the present invention provides for a one-part room temperature vulcanizing organopolysiloxane rubber composition for use as a protection coating on surfaces. The composition comprises the product which is obtained by mixing the following:
a) from about 20 to about 98 weight percent of one or more polydiorganosiloxane fluids of the formula
R″[(R)
2
SiO]
n
R″
in which R is a monovalent alkyl or alkylene radical having 1 to 8 carbon atoms or a phenyl radical, R′ is a monovalent alkyl or alkylene radical having 1 to 8 carbon atoms or a phenyl radical, R″ is OH or a monovalent alkyl or alkylene radical having 1 to 8 carbon atoms or a phenyl radical and n has an average value such that the viscosity is from about 1 to about 100,000 centipoise at 25° C., wherein at least one of the polyorganosiloxane fluid has R″ equal to OH and n has an average value such that the viscosity is in the range from 1,000 to 100,000 centipoise at 25° C., preferably from 3,000 to 40,000 centipoise at 25° C.;
b) from 0 to about 40 weight percent of a cyclo-organosiloxane of the formula
[(R)
2
SiO]
n
in which R is a monovalent alkyl or alkylene radical having 1 to 8 carbon atoms or a phenyl radical which may optionally be substituted with an alkyl radical having 1 to 8 carbon atoms and n has an average value of 3 to 10
c) from 0 to about 40 weight percent of an inorganic extending or non-reinforcing filler
d) from about 0.5 to about 10 weight percent of an amorphous SiO
2
reinforcing filler having a surface area of between about 100 to 250 m
2
/g and a particle size range between about 0.01 and 0.03 microns;
e) from about 1 to about 7 weight percent of an oximinosilane cross-linking agent of the formula;
RSi (ON═CR′
2
)
3
in which R and R′ are independently selected from monovalent alkyl or alkylene radicals having 1 to 8 carbon atoms or a phenyl radical which may optionally be substituted with an alkyl radical having 1 to 8 carbon atoms;
f). from about 0.2 to about 3 weight percent of an adhesion promoter of the formula
in which R
2
and R
3
are independently selected from monovalent alkyl or alkylene radicals having 1 to 8 carbon atoms or a phenyl radical which may optionally be substituted with an alkyl radical having 1 to 8 carbon atoms, b is an integer between 0 and 3, and R
1
is a saturated, unsaturated or aromatic hydrocarbon radical having 1 to 10 carbon atoms which may optionally contain a functional group; and
g) from about 0.02 to about 3 weight percent of an organotin salt as a condensation catalyst.
In an aspect of the invention, the composition is for coating high voltage electrical insulators and further includes about 36 to about 48 weight percent of alumina trihydrate, the alumina trihydrate having a median particle size of 13 &mgr;m, containing 65.1 percent Al
2
O
3
, 34.5 percent combined H
2
O, 0.3 percent Na
2
O, 0.02 percent CaO, 0.01 percent SiO
2
and having a specific gravity of 2.42, the aluminum tr
Ahmed Farooq
Barr John
Huda Faisal
Huda Seraj ul
Cain Edward J.
CSL Silicones Inc.
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