METHOD OF PRODUCING TRANSPARENT, HAZE-FREE TIN OXIDE COATINGS

Abstract: A method of producing transparent, haze-free tin oxide coatings on glass by chemical vapor deposition from vaporized liquid monophenyltin trichloride. The produced glass is used to prepare double glassed window structures.

Description: METHOD OF PRODUCING TRANSPARENT, HAZE-FREE TIN OXIDE COATINGS This invention relates to tin oxide coatings, and, more particularly, to a chemical vapor deposition method of producing transparent, haze-free tin oxide coatings on glass. Tin oxide is widely used as a coating material in optical instruments. The tin oxide coating is required to be transparent and haze-free in order to avoid interference with the optical performance of the device. A tin oxide coating also is used to reduce or cancel iridescence in glass window structures. While such tin oxide coatings function effectively for the purposes intended, they intro¬ duce haze into the system unless formed under very restric¬ tive and disadvantageous deposition conditions. Thus, it is suggested to avoid tin tetrachloride, or any other similar compound containing a halide, which can produce an acid vapor at the hot glass surface. There is provided herein a method of producing trans- parent, haze-free tin oxide coatings on a substrate such as glass by chemical vapor deposition from vaporized liquid monophenyltin trichloride. As a feature of the invention, liquid monophenyltin trichloride is of low corrosivity and of low toxicity, and is rapidly decomposed in air at an elevated substrate temperature to provide transparent, haze-free tin oxide coatings. Typically, these tin oxide coatings have less than 11 haze and greater than 80% visible transmission, and are obtained in a thickness of up to 250 nm in a deposition time of less than 25 seconds at a glass temperature of about 450°-650°C. As another feature of the invention, the haze-free tin oxide coating can be used as an undercoat film. Thereby an overcoat film of tin oxide formed thereon will assume the haze-free characteristics of the undercoat film. Still another feature of the invention is the use of the haze-free layer to reduce iridescence in a reflecting glass structure which includes a transparent, conductive tin oxide coating. The FIGURE is a schematic diagram of an apparatus for carrying out the coating process of the invention. Referring now to the FIGURE, there is shown a diagram¬ matic representation of an apparatus suitable for carrying out the process of the present invention. Accordingly, a carrier gas 10, which includes oxygen is metered through a feed line 11 at a predetermined flow rate through an air dryer tower 12 to provide a stream 13 of dry air. A sepa¬ rate air stream may be directed through a humidifier 14 containing a suitable quantity of water 15 to provide a wet air stream 16 at a desired relative humidity. Thereby an air stream 17, either dry or wet, may be passed through an evaporator 18 containing vessel 19 for holding liquid monophenyltin trichloride. The liquid is supplied to evaporator 18 by syringe pump 20 and syringe 21. The air stream is heated from an oil bath (not shown) to a desired vaporization temperature. The vaporized liquid monophenyltin trichloride in the air stream 22 travels to a deposition chamber 23 having a coating nozzle 24 in which a glass substrate 25 is mounted on a plate 26 heated to a predetermined temperature. After deposition of the tin oxide coating on the glass substrate, the gaseous by-products of the deposition are exhausted. In accordance with the invention, transparent, haze- free tin oxide coatings may be prepared over a wide range of process conditions, as described hereinafter. Accordingly, the glass substrate suitably is held at a temperature of about 450° to 650°C, preferably 500° to 600°C. The vaporization temperature of liquid monophenyltin trichloride in the process suitably ranges from about 100° to 250°C, preferably about 120° to 175°C. The carrier gas is an oxygen-containing gas which suitably may be air, or a mixture of oxygen and an inert gas, and is preferably air. The carrier gas may be dry or wet; preferably the water vapor concentration is less than 10 moles of water per mole of monophenyltin trichloride. The carrier gas velocity suitably ranges from about 0.1 to about 10 m per sec. The concentration of monophenyltin trichloride in the -5 -2 carrier gas suitably ranges from about 10 to 10 moles of monophenyltin trichloride per mole of carrier gas. In general, the process of the invention produces transparent, haze-free tin oxide coatings which have less than 1Z haze and greater than 80Z visible transmission, and are obtained in a thickness of up to 250 nm in a deposition time of less than 25 seconds. The haze content of the tin oxide coatings of the invention was determined from Gardner hazemeter measurements on glass slides, coated with tin oxide deposited from mono¬ phenyltin trichloride, according to ASTM D1003-61 (Reapproved 1977)-Method A. The visible transmittance was measured on a UV/vis spectrophotometer over the 400-800 ' n region, versus air, and the 1 T . was averaged over the wavelengths. The film thickness was measured by the beta-back- scatter method according to British Standards Institution method BS5411: Part 12, 1981, ISO 3543-1981. The advantages of the invention can be more readily appreciated by reference to the following specific examples in which the percent haze of tin oxide coatings on glass obtained from monophenyltin trichloride are compared to the percent haze of tin oxide coatings made from monobutyltin trichloride (Table I) ; and of the percent haze of coatings from monophenyltin trichloride over a range of process conditions (Table II) . TABLE I Haze-Content of Tin Oxide Coatings Obtained from Monophenyltin Trichloride (MPTC) and Monobutyltin Trichloride (MBTC) % Haze Concentration Substrate Uncoated Example (moles/ltr.) Temp. (°C.) MPTC MBTC Glass 1 0.079 600 0.90 5.5 2 " 550 0.75 2.7 3 " 500 0.75 1.1 0.75 TABLE II Haze-Content of Tin Oxide Coatings Obtained From Monophenyltin Trichloride Under Different Process Conditions % Haze Concentration Substrate Uncoated Exam le (moles/ltr.) Temp. (°C.) MPTC Glass 4 0.119 600 0.90 5 tl 550 0.75 6 11 500 0.75 7 0.159 600 0.75 8 II 500 0.75 0.75 Dew point, Exs. 1-3, 2.4; Exs. 4-8, 12.0; vaporization temp., Exs. 1-8, 157°C; thickness of coatings, Exs. 1-8, 1-90 nm; deposition times, Exs. 1-8, MPTC 6-22 seconds, Exs. 1-3, MBTC, 7-9 seconds; visible transmittance, Exs. 1-8, MPTC, 80Z; Exs. 1-3, MBTC, 75Z. The data in the tables show that tin oxide coatings obtained from monophenyltin trichloride exhibit a haze of less than IZ under a wide range of process * conditions, and at certain substrate temperatures show a value equal to that of uncoated glass. On the other hand, tin oxide coatings made from monobutyltin trichloride are hazy under all process conditions. Furthermore, coatings made using tin tetrachloride, ethyltin tribromide, dibutyltin dichloride, dimethyltin dichloride, methyltin trichloride, dibutyltin diacetate, tributyltin chloride and tetrabutyltin all show haze similar or more severe than monobutyltin trichloride. In addition, under a wide range of vapor deposition condi¬ tions, monophenyltin trichloride gave superior haze-free coatings. The reason that haze-free tin oxide coatings can be produced from monophenyltin trichloride, which is an organo- tin trihalide compound, is not well understood at present. However, this advantageous property may be related to the minimum of surface voids, or pitting, observed in tin oxide coatings made from this compound. As another feature of the invention, the haze-free tin oxide coating prepared from monophenyltin trichloride can be used as an undercoat film between glass and an overcoat tin oxide coating, whereupon the overcoat tin oxide coating assumes the haze-free characteristics of the undercoat film. The overcoat film them may be deposited from any tin com¬ pound which forms tin oxide coatings. If desired, a conduc¬ tive overcoat tin oxide coating may be formed by including a dopant with the tin compound. For example, such compounds as tin tetrachloride, monoalkyltin trichlorides, e.g. mono¬ butyltin trichloride, dibutyltin diacetate, dimethyltin dichloride, and the like, may be used. Monobutyltin tri¬ chloride is a preferred source compound. A dopant which imparts conductivity to the tin oxide overcoat may be included in the tin coating composition if desired. Such dopants include trifluoroacetic acid, tri- fluoroacetic anhydride, ethyl trifluoroacetate, pentafluoro- propionic acid, difluorodichloromethane, monochlorodifluoro- methane, 1,1-difluoroethanol, and the like. A preferred conductive tin oxide overcoating composi¬ tion is monobutyltin trichloride and trifluoroacetic acid, suitably in a composition range of about 70-99 wt. Z of the organotin compound and 1-30 wt.Z of the dopant. The undercoat tin oxide film suitably has a thickness of at least 10 nm, preferably 30 nm. The tin oxide over¬ coating can have any desired thickness; usually for conduc¬ tive coatings on glass it is about 150-250 nm. The tin oxide coatings obtained using monophenyltin trichloride as an undercoat are haze free under a wide range of process conditions, and at certain substrate temperatures show a value substantially equal to that of uncoated glass. On the other hand, tin oxide coatings made from monobutyltin trichloride directly on glass are hazy under all process conditions. There are provided herein also non-iridescent, haze- free, infrared reflecting glass structures including a transparent, conductive tin oxide coating which reflects infrared radiation, and a transparent, haze-free tin oxide coating made from monophenyltin trichloride, which is present to reduce iridescence in said structure. Such tin oxide coatings are also referred to herein as interference masking films." * In an embodiment, the coatings are applied on opposed surfaces of a glass sheet and the thickness of the haze-free tin oxide coating made from monophenyltin trichloride is predetermined in relation to the thickness of the conductive tin oxide coating, to provide a substantially non-iri¬ descent, haze-free structure. As described above, the haze-free tin oxide coating made from monophenyltin trichloride can be applied as a single layer or it can form an undercoat for subsequent layers thereon which assume the haze-free characteristics of the undercoat. The conductive tin oxide coating is formed by conventional methods, e.g. pyrolysis, chemical vapor deposition, powder coating, and cathode sputtering, and from conventional sources of doped tin oxide, e.g. dibutyltin difluoride, dibutyltin diacetate, monobutyltin trichloride, etc. and, where necessary a dopant such as a fluorine dopant. A double-glazed glass window article which is transpar¬ ent and haze-free also is provided herein. The interference masking (iridescence reducing) films are tin oxide films made from monophenyltin trichloride. Such interference masking films are colorless tin oxide films with a visible reflectance high enough to mask the visible interference effect of the tin oxide infrared reflecting film. The thickness of the tin oxide masking film is selected in accordance with known criterion estab¬ lished to provide the desired iridescence reduction effect. In one embodiment of these structures, an infrared reflecting coating is applied to one surface of a glass sheet and a more visible reflective masking film is depos¬ ited on the opposite surface of the glass sheet. This coated product may be used monolithically or preferably may be mounted in a multiple glazed unit. in another embodiment, an infrared reflecting film is applied to surface of a glass sheet, while a more visibly reflective masking film applied to one surface of a second glass sheet. The two coated glass sheets are assembled into a multiple glazed window unit, preferably with both coatings facing the interior space in the unit. The preferred orientation for the multiple glazed unit in a building is with the infrared reflective film on the interior glass sheet. In still another embodiment, both sheets of a double glazed unit are coated on both sides, with tin oxide infra¬ red reflecting films on the interior surfaces and colorless tin oxide masking films on the exterior surfaces. The two coatings may be applied simultaneously. In another embodiment of a double-glazed window struc- ture, the interior surface of one glazing is infrared- reflecting, and the interior surface of the other glazing, facing each other, is iridescent-reducing made from mono¬ phenyltin trichloride. Such articles are effective for passive solar heating applications because the high transmittance allows solar energy (light and heat) into a structure, while the high infrared reflectance and low emissivity keep heat inside the structure from being lost. In one embodiment of the glass structures, a glass sheet, typically a glass window pane, is coated on one major surface thereof with an interference masking tin oxide coating formed by chemical vapor deposition of monophenyltin trichloride. This coating is non-conductive, since its function in the structure is only to mask or reduce irides¬ cence without introducing haze over a wide range of desir¬ able process conditions and within a rapid deposition rate. This coating is substantially haze-free, that is, has a percent haze of less than IZ, and, in fact, is about equal to the percent haze for uncoated glass. * A conductive infrared-reflecting tin oxide coating is provided on the opposite surface of the sheet. This coating may be made from any conventional doped tin oxide source, e.g. dibutyltin trichloride, dibutyltin diacetate, mono¬ butyltin trichloride, and a suitable dopant, e.g. fluorine, from such sources as trifluoroacetic acid and ethyl tri- fluoroacetate acid. The haze-free interference masking tin oxide layer also may be used in a double-glazed window structure enclosing an insulating air space between an inner transparent sheet and an outer transparent sheet. These sheets are formed of glass and the conductive tin oxide coatings are present on the inner surfaces of the glass, facing each other. In a typical embodiment, there is a difference of about 1/4 wavelength between the conductive and masking coatings, e.g. the conductive coating is about 0.2 microns while the masking coating is about 0.27 microns, the difference being 0.07 microns.

Claims: CLAIMS 1. A method for producing a transparent, haze-free tin oxide coating characterized by: vaporizing monophenyltin trichloride and contacting said vapor in an oxygen-contain¬ ing atmosphere with a substrate at an elevated substrate temperature. 2. A method according to claim 1 further characterized in that said substrate temperature is about 450° to 600°C. 3. A method according to claim 1 still further charac¬ terized in that said substrate is glass. 4. A method according to claim 1 still further charac¬ terized by forming a haze-free tin oxide undercoat film on said substrate, and thereafter depositing said desired tin oxide coating thereon, whereby the tin oxide overcoat assumes the haze-free characteristics of said undercoat. 5. A method according to claim 4 further characterized in that said tin oxide overcoat is a conductive tin oxide coating. 6. A method according to claim 5 further characterized in that said conductive tin oxide overcoat is formed from a monoalkyltin trichloride and a fluorine dopant therewith. 7. A method according to claim 6 wherein said conduc¬ tive tin oxide coating is deposited from monobutyltin trichloride and trifluoroacetic acid- 8. A method according to claim 4 wherein said under¬ coat has a thickness of at least 10 nm. 9. A method according to claim 1 characterized by being used for making a transparent, non-iridescent, infra¬ red-reflecting glass window structure which includes a glass sheet, an infrared-reflecting tin oxide coating on one major surface of the sheet, and an iridescence-reducing tin oxide coating on the opposed surface of the sheet, said irides¬ cence-reducing tin oxide coating being haze-free and made by contacting said sheet with monophenyltin trichloride in an oxygen-containing atmosphere. 10. A method according to claim 9 further characterized in that said infrared-reflecting layer includes an under¬ coat, haze-free tin oxide layer made from monophenyltin trichloride, and an overcoat infrared-reflecting tin oxide layer, said overcoat layer assuming the haze-free character¬ istic of the undercoat layer. 11. A method according to claim 9 for making a double- glazed glass window structure including at least two transparent, non-iridescent, infrared-reflecting glass window structures further characterized by being assembled with the surfaces of the infrared-reflecting tin oxide layers facing each other. 12. A method according to claim 11 further character¬ ized by including a glazing having a transparent, infrared- reflecting layer on the interior surface thereof, and an iridescent-reducing layer on the interior surface of the other glazing.

Inventors: LINDNER GEORG HEINRICH, LINDNER, GEORG, HEINRICH
Applicants: M & T CHEMICALS INC, M&T CHEMICALS INC.
Application year: 1986
Main classification: B05D3
IPC codes: C03C17, C23C16