News Column

Patent Issued for Room Temperature Cured Vinyl Silazane Compositions

September 3, 2014



By a News Reporter-Staff News Editor at Journal of Engineering -- From Alexandria, Virginia, VerticalNews journalists report that a patent by the inventor Bulluck, John W. (Spicewood, TX), filed on June 22, 2012, was published online on August 19, 2014.

The patent's assignee for patent number 8809445 is Texas Research International, Inc. (Austin, TX).

News editors obtained the following quote from the background information supplied by the inventors: "This invention pertains to coatings containing polysilazane, including camouflage coatings for aircraft.

"In certain types of aircraft, especially certain military aircraft such as a C-17, the leading edge of titanium (or other metal) slats move perpendicular to the wing's front spar; hence, the gap between the slat and the pylon widens on extension. The flaps are externally blown by the engine efflux for extra lift. It is believed that many of the coating problems on the C-17 are due to the hot blasts of the reverse engine thrusts that thermally damage the current polyurethane camouflage coating on the titanium slats. For the C-17 and other platforms a coating composition that cures at room temperature would be useful for OEM and depot repair.

"The inventors herein have determined that a need exists for thermally resistant, low gloss, camouflage coating, especially for the leading edge of aircraft slats and in areas proximal to the engine. The inventors have also determined that a need exists for a coating for aluminum heat shields on the C-130 aircraft or other coated aircraft areas subject to engine efflux."

As a supplement to the background information on this patent, VerticalNews correspondents also obtained the inventor's summary information for this patent: "This invention provides a solution to one or more of the problems and disadvantages discussed above.

"The inventor herein has recognized that commercial ethoxy capped polysilazane is available that cures at room temperature. The problem with the traditional moisture curing ethoxy capped polysilazanes is shelf life stability and pressure build-up in the can over time. The commercial vinyl functional polysilazanes offer good shelf stability but require elevated temperature cure temperatures; the lowest temperature peroxide curing system we were able to previously achieve was 90.degree. C. A vinyl polysilazane that cures below 90.degree. C. would be desirable.

"The inventor has discovered that an organometallic catalyst in conjunction with certain peroxides permits curing of vinyl polysilazanes at room temperature within a day. Typical moisture cured elevated temperature cured Taber testing non-catalyzed results from the prior art were similar to those obtained for one day using the catalyzed room temperature cured compositions disclosed herein. In some cases, the ambient cured catalyzed system had slightly better Taber results.

"There are commercial off the shelf polysilazanes that cure at room temperature but these polysilazanes are very sensitive to any moisture in head space, fillers, or additives. Even with meticulous drying of coating components the reaction of these ambient cure polysilazanes generates copious amounts of ammonia gas; the pressure can actually distend a sealed thick steel one gallon container within weeks. However, the inventor has determined a way method for free radical curing at room temperature of vinyl functional polysilazanes in a reasonable time or temperature. The inventor has found a viable method for curing these vinyl functional polysilazanes at room temperature (20 to 25 degrees Centigrade). In general, there is an A and B component for the coating. The B component contains a peroxide in, for example, t-butyl acetate/butyl propionate solvent and the peroxide at approximately 4% to provide good shelf life. The A component has the remainder of the ingredients including, by way of example, resin, fillers, dispersant, Teflon, pigments, organometallic accelerator, and/or t-butyl acetate/butyl propionate solvent at approximately 35%. The new accelerated coating cures tack free to 50% of completion after a period two hours at 30.degree. C. It cures 70% to completion at a temperature of 30.degree. C. for 180 minutes. The coating cures to 95% of completion at 30.degree. C. after 5.6 hours or at room temperature within 24 hours. These cure projections are based upon differential scanning calorimetry data (DSC), cure exotherm information.

"In one broad respect, this invention is a cured composition, comprising: a cured polysilazane formulated using an organometallic catalyst. In one embodiment, the cured composition is formed using an organometallic catalyst especially a copper (II) catalyst. Examples of such copper (II) catalysts include copper (II) alkylcarboxylates.

"In another broad respect, this invention is a process for making a camouflage composition, comprising: providing a formulation containing polysilazane resin, at least one pigment, at least one matting agent, and at least one diluent; allowing at least one diluent to evaporate; and curing the resin to form the polysilazane camouflage composition. In one embodiment, the curing is accomplished using moisture from air. In another embodiment, the curing is accomplished under a nitrogen atmosphere.

"In another broad respect, this invention is a camouflaged aircraft component, comprising: an aircraft component having a coating thereon, wherein the coating comprises: cured polysilazane, at least one pigment, and at least one matting agent. In one embodiment, the component is a wing slat made of titanium.

"In another broad respect, this invention is a process for manufacturing a camouflaged aircraft component, comprising: providing an aircraft component; applying an uncured coating onto the aircraft component wherein the uncured coating comprises polysilazane resin, at least one pigment, at least one matting agent, and at least one diluent; allowing the diluent to evaporate; curing the coating to provide a cured coating that comprises cured polysilazane, at least one pigment, and at least one matting agent. In one embodiment, the component is a wing slat made of titanium.

"This invention provides a number of advantages. The coating is formed from a two component vinyl silazane system that does not suffer from the poor shelf life and moisture sensitivity associated with moisture cured, ethoxy capped silazanes. Advantageously, the two component coating system is easily applied, dries quickly, and cures at room temperature. In service, the jet blasts during reverse thrusting may have a postcure effect and result in property enhancement by further conversion of the polysilazane to silicon nitride or carbide ceramic. The coating to be sprayed is HAP free. In thermogravimetric analysis, some coating exhibited low weight losses such as 1.4% at 800 degrees Centigrade, thus demonstrating excellent high-temperature stability. When thermal cycling at 650 degrees Centigrade was conducted, very little color and gloss changes were noted and the resistance to diluents was excellent."

For additional information on this patent, see: Bulluck, John W.. Room Temperature Cured Vinyl Silazane Compositions. U.S. Patent Number 8809445, filed June 22, 2012, and published online on August 19, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=8809445.PN.&OS=PN/8809445RS=PN/8809445

Keywords for this news article include: Titanium, Light Metals, Nanotechnology, Emerging Technologies, Organometallic Organosol, Texas Research International Inc..

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Source: Journal of Engineering


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