Stock material or miscellaneous articles – Composite – Of silicon containing
Reexamination Certificate
2002-02-14
2003-11-25
Robertson, Jeffrey B. (Department: 1712)
Stock material or miscellaneous articles
Composite
Of silicon containing
C428S446000, C428S447000, C427S387000, C524S588000, C528S033000, C528S034000, C528S038000, C528S901000, C556S412000, C106S287110
Reexamination Certificate
active
06652978
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to silicon containing polymers and methods of making, and more particularly, to coating compositions comprising selected substituted polysilazanes and substituted polysiloxazanes which moisture cure at room temperature without requiring a catalyst. The coatings are thermally stable, and in the case of metal substrates, are corrosion-resistant as well. In some cases, the coatings may also be nonwetting. The invention additionally encompasses methods of preparing coated substrates having the aforementioned properties.
BACKGROUND OF THE INVENTION
A variety of resin systems undergoing moisture cure at ambient temperature conditions have been prepared heretofore. Other than polysilazanes and polysiloxazanes, many employed the hydrolytic sensitivity of isocyanate groups and alkoxy silyl groups to induce room temperature moisture cure. Resin systems utilizing alkoxy silyl groups have been particularly successful. The vast majority of these systems employ tetra-alkoxysilanes (orthosilicates) or oligomers of tetra-alkoxysilanes as moisture curable alkoxy silanes.
One representative example is U.S. Pat. No. 5,413,628 to Savin, which teaches a moisture curable composition comprising an alkyl silicate as a film forming substance, zinc powder, zinc flakes, amorphous silica, and ferrophosphate, wherein the alkyl silicate comprises from about 5% to 20% of tetraethyl orthosilicate.
U.S. Pat. No. 4,810,293 to Sano discloses an anti-corrosive paint composition containing a hydrolyzed condensate of tetraalkoxy silicate, zinc dust, and titanium oxide which undergoes a moisture cure.
U.S. Pat. No. 4,277,284 to Ginsberg et al. discloses a single-package, moisture curable zinc-rich coating composition utilizing zinc, a partially-hydrolyzed organic silicate and an aminosilane.
U.S. Pat. No. 4,571,268 to Frain et al., discloses a single package, moisture curable zinc-filled coating comprising a mixture of partially hydrolyzed ethyl silicate with large amounts of metal particles, such as zinc dust in an organic solvent with an alkali metal nitrate as the catalyst.
U.S. Pat. No. 5,508,360 to Cifuentes et al., discloses a silicon pressure-sensitive adhesive composition curable upon exposure to ambient moisture comprising an organopolysiloxane resin which is appended by alkoxy or oximino radicals.
U.S. Pat. No. 4,525,566 to Homan et al., discloses a moisture-curable silicone composition for adhesive-release coatings comprising an alkoxysilylorganosiloxane, a titanium ester and an aminoorganosiloxane.
U.S. Pat. No. 5,840,794 to Palmer, discloses an RTV sealant composition of a polymer with silicon-containing end groups with at least two silicon-bonded alkoxy groups and a titanium catalyst.
U.S. Pat. No. 5,208,300 to Krahnke et al., discloses silicone pressure sensitive adhesive compositions which are stable in the absence of moisture, but which cure in the presence of moisture comprising an adhesive component bearing alkoxy curing radicals and, optionally, a catalyst to accelerate the reaction of moisture with the alkoxy radicals to form siloxane bonds.
U.S. Pat. No. 5,895,713 to Miyazaki et al., discloses a method for treating an outdoor article, wherein a surface treating agent comprising a medium containing a tetraalkoxysilane or a silane compound having a silanol group obtained by hydrolyzing an oligomer of such a tetraalkoxy silane is used in a moisture curable coating composition.
While polysilazane and polysiloxazane resins have been used to provide coatings with good thermal stability and nonwetting properties, including oxidation and corrosion resistance to metal substrates, most were not moisture curable. Other polysilazanes and polysiloxazane resins provided adherent, protective coatings, but required added catalyst or activator in order to become moisture curable at ambient temperatures.
U.S. Pat. Nos. 5,405,655 and 5,919,572 to Blum et al. disclose certain polysilazane, polysiloxane and polysiloxazane coatings which can be made to undergo cure in the presence of an oxygen donor, such as water with the addition of a ruthenium catalyst. The mechanism of cure does not utilize alkoxy silyl groups as reactive moieties to effect the moisture cure, but rather relies on the activation of Si—H, N—H, and OH bonds by the metal catalyst to promote crosslinking reactions.
Accordingly, there is a need for silicon-containing polymers which are useful in preparing improved coatings which meet the foregoing criteria, i.e., moisture curable at ambient temperature conditions without requiring added catalyst or activator for rapid curing; wherein the coatings possess desirable properties, namely adherent, protective and heat-stable, while displaying excellent hardness, remain intact even when the substrate is deformed, all with good corrosion resistance over time. Additionally, the silicon polymer-containing coating compositions could be nonwetting.
SUMMARY OF THE INVENTION
It has been discovered that novel silazane and siloxazane polymers with selectively substituted alkoxy silyl groups or mixtures of such groups can be employed as resins in coating compositions, wherein the polymers are capable of undergoing rapid moisture cure at room temperature conditions without requiring added catalyst. These moisture curable substituted silazane and siloxazane polymeric coatings not only have protective properties, e.g., corrosion resistance, but provide hard, durable coatings with excellent thermal stability while displaying good adhesion properties to a wide range of substrates.
The silicon-containing polymers are alkoxy silyl substituted silazanes and siloxazanes of the formula:
Z—A
wherein Z is any silazane or siloxazane polymer and A is an alkoxy silyl group of the formula:
wherein
X is bonded to a silicon atom of Z and is either O or ═NR
4
wherein R
4
is a member selected from the group consisting of hydrogen, lower alkyl, lower alkenyl, aryl, lower alkoxy, silyl, siloxyl and silazanyl;
R
1
is alkylene or alkylene substituted with a heteroatom;
R
2
is a member selected from the group consisting of
(i) hydrogen,
(ii) hydroxyl,
(iii) C1 to C10 alkyl, either unsubstituted or substituted with hydroxyl, lower alkoxy, lower alkenyl, silyl and —N(R
5
)
2
where R
5
is independently selected from the group consisting of hydrogen, lower alkyl and lower alkenyl,
(iv) C1 to C10 alkenyl, either unsubstituted or substituted with hydroxyl, lower alkoxy, silyl and —N(R
5
)
2
, and
(v) aryl of 1 or 2 rings, unsubstituted or substituted with hydroxyl, lower alkyl, lower alkenyl, lower alkoxy, silyl and —N(R
5
)
2
,
R
3
is the same as (iii), (iv) or (v);
n=0, 1 or 2, and the ratio of the total number of OR
3
groups of A to Si—N bonds in Z is generally from about 0.05 to about 2.5, preferably from about 0.1 to about 1.0, and most preferably from about 0.1 to about 0.50.
Generally, the novel substituted silazane and siloxazane polymers, Z—A, as disclosed hereinabove, are prepared by the reaction of preformed silazane or siloxazane polymers with certain reagents having reactive amine, ester or hydroxyl functionalities. The novel alkoxy silyl substituted polysilazanes and polysiloxazanes are prepared by heating a mixture of an alkoxy silyl reagent with the chosen polysilazanes or polysiloxazanes in the desired ratio, with the proviso that the ratio of the total number of OR
3
groups of A to Si—N bonds in Z, i.e., silazane or siloxazane polymer, prepared by the reaction is from about 0.05 to about 2.5, and preferably from about 0.1 to about 1.0, and most preferably from about 0.1 to about 0.50
The resulting substituted polysilazane or polysiloxazane can then be coated onto a substrate from solution or without the use of a solvent, depending on the physical form of the coating resin. For solid resins and liquid resins which have high viscosity, solvent coating is preferred; for liquid resins having low viscosity, a solventless coating method is preferred.
Coatings prepared by this method are cured in an atmosphere which promotes crosslinking of the polymer by its reacti
Knasiak Gary J.
Lukacs III Alexander
Ellis Howard M.
Kion Corporation
Robertson Jeffrey B.
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