Coating apparatus – Gas or vapor deposition – With treating means
Reexamination Certificate
1998-03-03
2001-04-10
Jones, Deborah (Department: 1775)
Coating apparatus
Gas or vapor deposition
With treating means
C118S7230DC, C219S121470, C219S121500, C219S076160
Reexamination Certificate
active
06213049
ABSTRACT:
This invention relates to arc plasma deposition of protective coatings on various substrates such as glass, quartz, metal or metallized materials, and plastics; and more particularly to a combined nozzle-injector for directing plasma flow and injecting reactive reagents into the plasma for high rate deposition of transparent coatings which are abrasion resistant, UV absorbing, or IR reflective.
BACKGROUND OF THE INVENTION
The technological importance of thin films has led to the development of a variety of deposition methods.
Chemical vapor deposition (CVD) produces a solid film on a substrate surface by thermal activation and surface reaction of gaseous reagents which contain the desired constituents of the film. Energy required to pyrolyze the reactants is supplied by heating the substrate. For reasonable reaction rates the substrate is heated to relatively high temperatures in the range of about 5000 to 2000° F. degrees. These temperatures preclude application of the process to heat sensitive substrate materials.
Plasma enhanced chemical vapor deposition (PECVD) supplies energy to the reactants by an electrical discharge in a gas which forms a plasma in the deposition chamber. Generally the substrate is immersed in the plasma. The deposition rate is usually low.
Polycarbonate is often the engineering material of choice for glazing and optical applications because of its high impact strength, low density, optical clarity, and good processibility. However, the polycarbonate material is soft, lacks glass-like abrasion resistance, and is sensitive to temperatures above about 300° F. Prior work had shown that a silicon oxide coating by plasma-enhanced chemical vapor deposition (PECVD) can improve the abrasion resistance of polycarbonate, qualifying it for glazing applications. However, the prior PECVD technology using silane and nitrous oxide as the precursors was slow and therefore uneconomical, having a typical deposition rates of only about 0.05 microns per minute. Organosilicon precursors were later used in PECVD for a plasma-generated abrasion-resistant polymer coating, but the deposition rate was not significantly improved.
The process of this invention provides coatings and layers which impart improved adhesion, thermal expansion compatibility, radiation protection, or abrasion resistance to articles or products made by the deposition process of the invention. The deposition of such protective coatings by plasma on high and low temperature materials in the form of sheets, films, and shaped substrates can be achieved by the apparatus and methods disclosed herein.
SUMMARY OF THE INVENTION
A nozzle-injector was designed and fabricated for plasma deposition of thin-film coatings using a wall-stabilized arc torch as the plasma generator. The design of the nozzle-injector controls the injection, ionization, and reaction of the reagents, and these functions, in turn, determine the coating deposition rate, coating area, coating composition, and coating quality. Using the nozzle-injector of this invention with oxygen and a siloxane as the reagents, clear coatings at a deposition rate of about 30 microns per minute, at the center, were demonstrated on polycarbonate and glass substrates. The siloxane-derived coating greatly improved the abrasion resistance of a polycarbonate substrate. By substituting appropriate organometallic reagents for the siloxane, other oxide coatings, such as zinc oxide or titanium oxide, were also deposited on a plastic substrate. Such coatings are useful as infrared or ultraviolet protective coatings. The nozzle-injector of this invention combines in a single device the direction control function of a nozzle with the reactant introduction function of one or more injectors.
Organosilicon compounds useful as monomers in the arc plasma deposition process using the nozzle-injector of this invention include silane and other silicon compounds in which at least one silicon atom is bonded to at least one carbon or one hydrogen atom such as siloxanes, silazanes and organosilicones.
DESCRIPTION OF THE INVENTION
The disclosed nozzle-injector is suitable for use with a variety of plasma generating apparatus such a wall stabilized arc plasma torch having at least one water cooled electrically isolated plate located between the cathode and the anode. Multi plate wall-stabilized arc devices are described in U.S. Pat. Nos. 4,948,485 and 4,957,062.
The cascaded arc with multiple plates has been used as a plasma source for making diamond-like carbon and plasma-polymerized coatings from hydrocarbon and organosilicon reagents, respectively. Deposition rates of a few micrometers per minute were reported. However, the coating area was small, a few centimeters in diameter, and the degree of material utilization was low, less than about 20%. Depending on the conditions, powder or powdery coatings could also be formed outside of the central deposition zone. To make the coating technique practical and economical, it is critical to enlarge the coating area, to increase the deposition rate, and to minimize powder formation. The nozzle injector of this invention accomplishes those improvements.
The nozzle-injector was designed to improve coating performance of wall stabilized arc plasma generators for use in low temperature plasma deposition and polymerization methods. Shower-ring or slit-ring injectors were built into the nozzle for the delivery of gas or vapor reagents. The locations of the injectors affect the degree of gas ionization, which affects the extent of reaction, and hence the chemical stoichiometry and structure of the coating, and ultimately its performance. The shape and the size of the nozzle-injector also affect the extent of reaction, the coating area, and the thermal load on the substrate. With this nozzle-injector, optically clear coatings 30 cm×30 cm in area were deposited at a rate of about 30 microns per minute at the center. Without such a nozzle-injector powdery coatings formed.
The nozzle-injector, configuration and structure included both cylindrical and conical plasma channels and a 2-stage conical channel with a cylindrical section in between. The divergent angle of the conical channel of the nozzle-injector ranged from about 0 to 60°. The opening of the plasma channel at the base of the nozzle ranged from about 4 to 7 mm in diameter. Smaller diameter channels can be used for coating small objects. The length of the nozzle-injector ranged from 1.5 to 25 cm thereby controlling the volume of the zone in which reaction can take place. The nozzle-injector can be a single integral construction or can be assembled from parts such as a stainless steel main body with injectors for introducing reagents into the plasma, a copper adapter for mounting the nozzle-injector to the plasma generator, and a extension attached to the downstream end of the main body to provide a suitable volume for the reaction zone which exists within the nozzle-injector. An injector can be built into the copper adapter for oxygen injection, and the copper adapter was gold-plated to resist oxidation. The modular design of the nozzle-injector allows the effect of nozzle size and gas injection position eliminates the need for separate direction control and reagent injection units.
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General Electric Company
Johnson Noreen C.
Jones Deborah
McNeil Jennifer
Santandrea Robert P.
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