Patent Application
20080014466
The above and other objects, features and advantages of the invention will become apparent from a consideration of the subsequent detailed description presented in connection with accompanying drawings, in which:
The invention coats glass panels, which may or may not be soda glass panels (i.e. including NaO), having an air side and an opposite side having a layer of tin oxide or chemically similar oxide, hereinafter the tin-oxide side. Such glass is usually called float glass, and sometimes soda lime glass. The thickness of the tin oxide layer is estimated to be at least 20 nm, and is typically from 20 nm to 50 nm. In some embodiments, the glass is chemically strengthened.
Referring now to
Referring to
In a next step 33 the chamber is evacuated to a base pressure of approximately 10−5 Torr, and then acetylene (or a similar hydrocarbon gas) is injected (bleeded) into the chamber. The pressure in the chamber after the acetylene is again typically 15 millitorr. In a next step 34, a pulsed high voltage (2000-6000 Volts) is applied to the metal base plates supporting the panels to be coated, so as to impart to the base plates a pulsating negative voltage. The pulsed high voltage produces a so-called glow discharge plasma from the air and acetylene gas. The plasma is a mixture of electrons and positively-charged hydrocarbon ions, as well as excited neutral atoms and molecules in various energy states (electronic, vibrational, and rotational). The negative voltage on the base plates pulls the positive hydrocarbon ions out of the plasma. In a next step 35, the voltage is turned off after waiting a predetermined duration of time, depending on the DLC thickness wanted.
As shown in
By selective adjustment of key parameters such as gas composition, voltage, pulse frequency, and deposition time, the coating thickness (and darkness), hardness, and uniformity can be tailored to be most suitable for a given application.
In arriving at the invention, in addition to pure acetylene (C2H2) as the feed gas, a number of feed gas mixtures with acetylene were tested (including C2H2:SiH4, C2H2:H2) and also with methane (CH4) (including CH4:H2:Ar). Also, as mentioned, the efficacy of the tin-oxide layer was tested. Although other recipes tested satisfactorily, a recipe using pure acetylene as the feed gas at a pulsed high voltage of 4.1 kV and a pulse frequency of 500 Hz tested as particularly satisfactory. A typical flow rate for the acetylene is 60 sccm (standard cubic centimeters per minute). A duration of approximately 10-20 minutes yields a DLC coating of 50-100 nm, and in the testing performed, up to twenty square feet of glass surface was coated in 20 minutes. Also, as mentioned, when the air-side of the glass was coated, the DLC coating proved less environmentally stable, i.e. it came off.
Other recipes that appear satisfactory from the testing by the inventors include using pulsed voltages in the range of from 1500 volts to 6500 volts, pulse rates in the range of from 250 Hz to 2250 Hz, and feed rates of the hydrocarbon gas in the range of from 10 to 200 standard cubic centimeters per minute.
Although the use of glow discharge as described above is advantageous, the invention encompasses any method used for providing glass coated by DLC but having an intermediate layer of tin-oxide or other chemically similar metal oxide. Prior to the invention it was not appreciated that a tin-oxide layer provides advantageous environmental stability for at least some methods of application, and in particular those allowing high rates of production of DLC coatings.
As mentioned, in some embodiments of the invention the glass is chemically strengthened. Again, glass having an air side and a tin-oxide side is used. First it is annealed. Next it is preheated to 800° F. and then dipped into a molten bath of potassium salt at approximately 1050° F. (from 900° F. to 1100° F.). While in the salt the small alkali sodium ions in the glass near the surface are replaced with larger potassium ions. The depth of the ion exchange is believed to be only 64 microns as an average (and typically 20-100 microns) into the glass. This causes surface compression because of a wedging effect from the larger potassium ions. After 15-20 minutes, the glass is removed from the salt and allowed to cool.
Both sides of the glass are strengthened, the air side and the tin oxide side. The tin oxide layer is still present after the chemical strengthening, from direct testing for its presence. (Whether the potassium ions from the potassium salt bath simply migrate through the relatively thick tin oxide layer and into the glass, or whether some other phenomenon occurs is unknown to the inventors.)
The end result of the chemical strengthening is glass that is two to five times stronger than only annealed glass, and with much better optics than heat processed strengthened glass due to the temperatures used being 200° F. or more lower than what is used in heat processed strengthening.
The glass that is DLC coated can be either low-iron glass (ultra-clear glass) or so-called green glass. In case of glass used as transparent armor—i.e. so-called ballistic glass, the thickness is several multiples of the thickness of glass typically used in a non-armoring application. Ordinary (green) glass has a green tint when provided at such thickness. Low-iron glass does not. Both were found to receive a satisfactory DLC coating according to the invention, i.e. a coating that is environmentally stable.
It is to be understood that the above-described arrangements are only illustrative of the application of the principles of the present invention. Numerous modifications and alternative arrangements may be devised by those skilled in the art without departing from the scope of the present invention, and the appended claims are intended to cover such modifications and arrangements.
