Method of depositing tin oxide coatings on flat glass and the resulting coated glass

STATE OF THE ART FOR THE INVENTION

1. Field of the invention

The invention relates to a method for applying titanium oxide coatings on a flat glass substrate and the resulting coated glass. It is particularly directed to a vapor deposition process for producing titanium oxide coatings on flat glass using a coating precursor gas mixture comprising titanium tetrachloride and an organic oxidizer.

Second Summary of the prior art

Titanium oxide coatings have been proposed for use on glass containers, such as bottles, to increase the mechanical strength of these containers. Furthermore, the use of titanium oxide coatings on flat glass has been proposed to modify the properties of the glass for architectural purposes wherein titanium oxide coatings deposited under vacuum (by reactive sputtering) are used as components of sputtered multilayer infrared reflective coatings.

GB patent specification 1,115,342 discloses a process for producing glass containers having good internal strength and good abrasion resistance by spraying the containers, which are still hot from the manufacturing process, with a solution or dispersion of tin chloride (ie tin tetrachloride ) in an organic liquid, with isopropyl alcohol being preferred. In this case, a small amount of titanium chloride can be incorporated as a modifier. The liquid solution is supplied to atomizers capable of working with a pressure jet and placed on each side of a tunnel above a conveyor belt for the hot glass bottles to produce a "liquid reagent mist" such that a liquid layer is formed on the entire outer surface of the bottles is formed where it reacts to form a tin oxide layer.

In GB patent specification 1 187 784 there is described an improvement of the previously described method of GB patent specification 1,115,342 which obviously is more suitable for incorporation into a process for the automatic manufacture of glassware without interfering with the normal operation of such a process and without requiring additional monitoring. The patent proposes to treat glass containers at high temperature with a liquid solution of an organic tin compound. The compound has such properties that it decomposes into two materials upon heat application, one of which is an organic tin compound having a high decomposition temperature with the glass surface reacts, forming a diffusion layer of tin oxide in the glass surface, while the other is a volatile tin compound such that a substantial proportion of vapor is formed from this compound, and the containers are subjected to such a heat treatment as to cause a reaction between the glass of at least the surfaces of the tin compound containers. " The material used to treat the glass containers can be provided by reacting tin tetrachloride with organic substances containing moderate activity carbonyl groups, for example, organic esters of ethyl, n-propyl, isopropyl, n-butyl and isobutyl alcohol with acetic acid. Propionic and butyric acid. The resulting solution can be sprayed in the presence of the surrounding atmosphere on the hot containers, for example in the form of a fine mist, after they have left the molding machine and before they enter the cooling furnace. GB patent specification 1 187 783 describes a method analogous to that described in 1 187 784, wherein, instead of the organic tin compound, an organic titanium compound is sprayed onto the hot glass containers. The organic titanium compound can be prepared in an analogous manner as the organic tin compound by reacting titanium tetrachloride with an organic ester, for example, n-butyl acetate. Again, the resulting solution is sprayed onto the glass in ambient atmosphere on the container in the production line.

Processes involving the use of gaseous reactants (also called CVD or vapor deposition) have certain advantages over spray techniques for coating flat glass, especially when the reactants can be premixed prior to application to the glass. Unfortunately, tin tetrachloride readily reacts with water, so that previous proposals for the use of tin tetrachloride and water vapor in gaseous form usually involve the separate supply of the gases to the glass surface and their mixing while in contact with the glass.

GB patent specification 2 044 137 A relates to such a process in which discrete laminar streams are formed from the respective reactant and passed onto a hot glass substrate by bringing the streams above the glass into reverse tangential contact. Instead of tin tetrachloride, titanium tetrachloride may be used as one of the gaseous reactants to form a titanium oxide coating. The patent also suggests adding hydrogen to one of the gas streams to mitigate the violent reaction between tin tetrachloride and water vapor. This can be done either by the direct addition of gaseous hydrogen or by the addition of methanol which reacts in situ to form the desired gaseous hydrogen.

European patents 0 365 239 B1 and 0 376 240 B1 describe a method and apparatus for applying a tin oxide coating to a hot glass ribbon. A first gas stream of tin tetrachloride is allowed to flow in preheated dry air along the surface of the hot glass ribbon which advances under a coating chamber while a turbulent second stream of hydrofluoric acid and water vapor flow into the coating chambers perpendicular to the glass plane and flow direction of the first gas stream becomes, wherein the combined first and second gas streams are drawn across the glass under turbulent flow conditions through the coating chamber. The method and apparatus may also be used to apply a titanium oxide coating using titanium tetrachloride instead of tin tetrachloride.

US Pat. No. 4,590,096 describes a process in which a coating solution comprising a substantially solvent-free mixture of an organotin chloride and a reactive organic fluorine compound which is soluble or miscible in the organotin chloride is passed into a preheated carrier gas stream. which contains sufficient water vapor for the relative humidity of the gas stream at 18 ° C to be from about 6% to about 100%. The resulting gas stream is passed over a hot glass surface to deposit a fluorine-doped tin oxide coating on the hot glass. A wide range of organotin compounds can be used, with the possibility of using tin tetrachloride being mentioned. Similarly, a wide range of organic fluorine compounds, including oxygen-containing compounds, such as trifluoroacetic acid and ethyl trifluoroacetate, may be used. Some of the fluorine-containing dopants have limited solubility in the organotin compounds employed, optionally employing a solubilizer to increase the solubility of the fluorine-containing dopant in the organotin compound, with acetic anhydride, ethyl acetate, hexane, methyl isobutyl ketone and butyraldehyde exemplifying solubility promoters to be used are called. In the US patent, as in the other patents, in which vapor deposition processes are used to apply a metal oxide of gaseous metal tetrachloride, however, water vapor is used as the oxygen source.

U.S. Patent 4,751,149 to Vijaykumar et al. relates to the deposition of zinc oxide coatings by vapor deposition at low temperatures (60 to 350 ° C and preferably 100 to 200 ° C) on heat-sensitive photoconductive substrates, wherein the application of the zinc oxide coatings may be from an organozinc compound and an oxidizing agent which may be an oxygen-containing organic compound, for example an ester , and an inert carrier gas is proposed. Although that patent is not entirely clear, it is obviously suggested to direct separate streams of the organozinc compound and the oxidant into the deposition chamber, and certainly no suggestion is made to premix these components prior to delivery to the coating chamber.

EP 0 186 481 relates to tin oxide coatings, US 5 401 305 relates to coatings on substrates, US 4 731 256 relates to fluorine doped tin oxide coatings and US 5 124 180 relates to fluorine-containing metal oxide coatings on substrates.

It would be advantageous to have a method of depositing titanium oxide coatings by a CVD method applied to hot flat glass using a premix of titanium tetrachloride as a low cost reactant and an oxygen source, wherein between the metal tetrachloride and the source of oxygen (which was previously water) does not undergo premature reaction, which results in the formation of metal oxide in the coating equipment with the consequent problems and consequent inefficiency. It would be particularly advantageous if the method allowed the coating to be applied at a high speed, thus enabling a required layer thickness to be applied to a moving glass ribbon during the glass manufacturing process.

SUMMARY OF THE INVENTION

According to the present invention, there is provided a vapor deposition method for depositing a titanium oxide coating on a hot glass substrate using a precursor gas mixture containing titanium tetrachloride and an organic oxygen source without requiring the incorporation of water vapor with the consequent risk of premature reaction.

According to the invention, a method is provided for applying a titanium oxide coating on a hot flat glass, which comprises the steps

(a) preparing a precursor gas mixture comprising titanium tetrachloride and an oxygen-containing organic compound as an oxygen source for the formation of the metal oxide,

(b) maintaining the precursor gas mixture at a temperature below the temperature at which the titanium tetrachloride reacts to form metal oxide while passing the mixture into a coating chamber open to the hot glass, and

(c) passing the precursor gas mixture into the coating chamber, thereby heating the mixture, whereby titanium oxide containing oxygen from the organic compound is deposited on the hot glass surface,

includes.

Surprisingly, a wide range of oxygen-containing organic compounds can be used as the source of oxygen without the need for the presence of water vapor or gaseous oxygen, including compounds normally considered to be reducing agents rather than oxidants, for example, alcohols. However, the preferred organic compounds are carbonyl compounds, especially esters, with particularly good results having been obtained with the use of esters having an alkyl group with a β-hydrogen. The alkyl group with a β-hydrogen usually contains two to ten carbon atoms.

It is preferred to use organic compounds, especially esters, containing from two to ten carbon atoms, as larger molecules tend to be less volatile and thus less suitable for use in the CVD process of the present invention.

Particularly preferred esters for use in the practice of the invention include ethyl formate, ethyl acetate, ethyl propionate, isopropyl formate, isopropyl acetate, n-butyl acetate and tert-butyl acetate.

The method according to the invention is generally used in connection with the formation of an endless substrate in the form of a glass ribbon, for example in float glass production. However, the method according to the invention can also be used in the coating of other flat glass substrates either in a production line or separately therefrom.

The invention comprises the preparation of a precursor gas mixture comprising titanium tetrachloride and an organic compound containing oxygen, wherein a carrier gas or diluent gas, for example nitrogen, air or helium, is normally also contained in the gas mixture. Since the thermal decomposition of the oxygen-containing organic compound can initiate the metal oxide precipitation reaction at a high rate, it is desirable that the precursor mixture be maintained at a temperature below the thermal decomposition temperature of the oxygen-containing organic compound to pre-react the gas mixture to form the metal oxide to prevent.

The gas mixture is maintained at a temperature lower than that at which it would react to form metal oxide and delivered to a location proximate to the flat glass substrate to be coated, the substrate being at a temperature above the reaction temperature (FIG. and above the decomposition temperature of the oxygen-containing organic compound in the precursor gas mixture).

The precursor gas mixture is then passed into the vapor space directly above the substrate. The heat of the substrate increases the temperature of the precursor gas above the thermal decomposition temperature of the oxygen-containing organic compound. Then, the oxygen-containing organic compound decomposes, reacting with the metal tetrachloride, and forms a metal dioxide coating on the substrate.

The invention permits the preparation of titanium oxide coatings deposited on a hot glass at a high deposition rate, for example greater than 130 Å / second, and in preferred embodiments greater than 250 Å / second.

The deposition rate is dependent on the particular oxygen-containing organic compound used and both the concentration of the oxygen-containing organic compound and that of the metal chloride and the glass transition temperature. For any particular combination of compounds, the optimum concentrations (and particularly the optimum ratio of oxygen-containing organic compound to metal tetrachloride) and the rates of rapid application of the coating can be determined by a simple experiment. It will be appreciated, however, that higher concentrations of reactants and high gas flows are likely to result in less efficient overall conversion of the reactants to a coating, so that the optimal condition for a commercial process may differ from the conditions which give the highest deposition rates.

Preferably, the oxygen-containing organic compound has a volume concentration which is about 0.5 and more preferably 1 to 5 times higher than the volume concentration of the metal chloride. It is usually used in an amount of at least 30% by weight of the weight of the metal chloride.

The process of the present invention allows the formation of titanium oxide coatings on hot flat glass substrates in the production line during the high speed glass making process. The titanium oxide coatings can be made with a high refractive index (of at least 2.4), allowing the achievement of desired optical effects, especially when used with other coatings.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other advantages of the invention will become apparent from the following detailed description of preferred embodiments with reference to the attached drawings, wherein

1 shows a schematic longitudinal section through an apparatus for carrying out a flat glass process, which contains gas distributors, which are arranged in a suitable manner in order to enable the implementation of the method according to the invention,

FIG. 2 shows a cross-section of a detail of a product coated according to the invention, FIG.

3 is an enlarged schematic cross section through the end of a gas distribution nozzle, which is suitable for use for carrying out the method according to the invention, and

Figure 4 is an enlarged schematic cross-section through the end of an alternative gas distribution nozzle which may be used to practice the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings, there is illustrated generally in Figure 1 a float glass plant 10 which is used to carry out the process of the present invention. In particular, the float glass plant comprises a channel section 12 in which molten glass 14 is supplied from a melting furnace (not shown) to a float bath section 16 wherein an endless glass ribbon 18 is formed according to the known float process. The glass ribbon 18 moves from the bath portion 16 through a subsequent cooling furnace 20 and a cooling section 22. The endless glass ribbon 18 serves as a substrate to which the metal oxide coating is applied according to the invention.

The float portion 16 includes a sole portion 24 in which a molten tin bath 26 is contained, a top 28, opposed side walls 30 and end walls 32. The top 28, side walls 30 and end walls 32 together form a container 34 in which a non-oxidizing atmosphere is maintained to prevent the oxidation of the molten tin.

In the bath section 16 gas distribution nozzles 64, 66 and 68 are additionally arranged. The gas distribution nozzles 64 and 66 in the bath section may be used to apply additional coatings to the substrate prior to depositing the titanium oxide coating by the method of the present invention. The additional coatings may include silicon and silica.

In operation, the molten glass 14 flows in controlled amounts along the channel 36 under a control passage 38 and down to the surface of the tin bath 26. The molten glass spreads laterally on the tin bath under the influence of gravity and surface tension and under certain mechanical influences and moves through the bathroom to the front, with the glass band 18 forms. The glass ribbon is withdrawn via withdrawal rollers 40 and then transported through the cooling furnace 20 and the cooling section 22 on aligned rollers 42. The application of the coating according to the invention can take place in the float bath section 16 or thereafter along the production line, for example in the intermediate space between the float bath and the cooling furnace or else in the cooling furnace itself.

In the bath tank 34 is maintained a suitable non-oxidizing atmosphere, generally of nitrogen or a mixture of nitrogen and hydrogen in which nitrogen predominates, to prevent the oxidation of the tin bath. The atmosphere gas is supplied through lines 44 which are connected to a gas distributor 46. The non-oxidizing gas is introduced at a rate sufficient to compensate for normal losses and to maintain a slight overpressure of from about 0.001 to about 0.01 atmospheres above atmospheric pressure so as to prevent intrusion of the external atmosphere. The heating for the maintenance of the desired temperature regime in the tin bath 26 and in the container 34 is ensured by radiant heater 48 in the container. The atmosphere in the annealing furnace 20 is typically atmospheric air while the cooling section 22 is unconverted and the glass ribbon is open to the surrounding atmosphere. The ambient air can be directed by blower 50 in the cooling section on the glass ribbon. Heaters (not shown) may also be provided in the cooling furnace to gradually lower the temperature of the glass ribbon in accordance with a specified regime as it is transported therethrough.

Figure 1 illustrates the use of gas distribution nozzles 64, 66 and 68 disposed in the float bath 16 to apply the various coatings to the glass ribbon substrate. The gas distribution nozzle is a form of a reactor which can be used to carry out the process according to the invention.

A suitable design for the gas distribution nozzles suitable for feeding the precursor materials of the present invention is shown generally schematically in FIG. A housing 70 having the shape of a generally U-shaped channel and formed by inner walls 74 and outer walls 72 surrounds cavities 76 and 78. The enclosed cavities 76 and 78 allow a suitable heat exchange medium to flow to maintain the distribution nozzles at the desired temperature.

The precursor gas mixture is supplied through a supply conduit 80 cooled by a fluid. The supply line 80 runs along the distribution nozzle and supplies the gas through drop lines 82, which are spaced along the supply line. The supply line 80 leads into a supply chamber 84 with a mouthpiece 86, which is supported by the housing. The precursor gases passing through the downcomers 82 are discharged from the supply chamber 84 through an orifice 88 into a coating chamber forming a vapor space opening on the glass in which they travel along the surface of the glass 18 in the direction of the arrows in FIG stream.

Deflectors 90 may be provided in the supply chamber 84 to equalize the flow of precursor materials through the distribution nozzle to ensure that the materials are dispensed onto the glass 18 along the entire distribution nozzle in a smooth, laminar uniform flow. Other precursor materials are collected and removed through suction chambers 92 on the sides of the distribution nozzle.

Various forms of distribution nozzles used for the vapor deposition are suitable for the process according to the invention and are known from the prior art.

Such an alternative construction of a distribution nozzle is schematically illustrated in Fig. 4 of the drawings. Using this distribution nozzle, generally numbered 100 (and more fully described in European Patent EP 0 305 102 B), the precursor gas mixture is introduced through a gas supply line 101 where it is cooled by a cooling fluid flowing through the conduits 102 and 103 flows. The gas supply line 101 opens through an elongated opening 104 in a gas throttle 105th

Gas choke 105 is of the type described in more detail in U.K. Patent GB 1 507 996 and includes a plurality of metal strips bent longitudinally in the form of a sine wave and extending vertically in abutting relationship with each other along the length of the distribution nozzle. are attached. Adjacent bent metal strips are arranged "out of phase" to form a plurality of vertical channels between them. These vertical channels have a small cross section with respect to the cross section of the gas supply line 101, so that the gas is discharged from the gas restrictor 105 at a substantially constant pressure along the length of the distribution nozzle.

The coating gas is delivered from the gas restrictor to the inlet side 107 of a generally U-shaped guide channel, generally numbered 106, which includes the inlet leg 107, the coating chamber 108 opening to the hot glass substrate 110 to be coated, and the suction leg 109 , whereby spent coating gas is withdrawn from the glass. The rounded corners of the blocks forming the coating channel promote uniform laminar flow of the coating gas parallel to the glass surface along the glass surface to be coated.

The following examples (in which gas volumes are given under standard conditions, that is, one atmosphere of pressure and ambient temperature, unless otherwise stated) illustrate the invention.

Examples 1 to 5

In this series of experiments, a bidirectional coating reactor of the type shown in Fig. 3 was used in the laboratory to apply a titanium oxide coating.

In Examples 1, 2 and 3, the glass was heated in a production furnace to simulate the conditions of the coating reaction of a float glass process and to test the process of the present invention. For the furnace, successively arranged rolls were used to transport a glass substrate through a heating zone before the process of the invention was carried out. In Example 1, the glass substrate was float glass, which was first provided with a silica coating. The silica coating was applied to the float glass by a known vapor deposition method employing a monosilane precursor in an oxygen-rich atmosphere. The deposition of the silica is not part of the invention.

According to the invention, a titanium oxide coating was applied to the silicon dioxide-coated substrate. The substrate had a temperature of 1 170 ° F / 630 ° C and the transport speed of the substrate was 300 inches / 8 meters per minute.

For depositing the titanium oxide, a precursor gas mixture comprising titanium tetrachloride, ethyl acetate, oxygen and helium was developed. Helium was included in the precursor mixture as a carrier gas for the reactants. The precursor mixture was prepared by simultaneously passing all four gas streams through a distribution system. A static mixer placed in the gas line was used to ensure a homogeneous precursor mixture. The volumetric composition of the precursor mixture was 0.7% titanium tetrachloride, 17.2% ethyl acetate, 7.2% oxygen and 74.9% helium, with the component gas distributor flow rates being those given in Table 1.

The temperature of the precursor mixture was maintained above 300 ° F / 150 ° C to prevent the addition reaction of titanium tetrachloride with ethyl acetate. The precursor temperature was also maintained below the thermal decomposition temperature range of 950 ° F to 1130 ° F (510 ° C to 610 ° C) of the ethyl acetate to prevent the mixture from pre-reacting.

The precursor mixture was passed into the reactor immediately above the advancing substrate. The temperature in the precursor tower was 250 ° F / 120 ° C. The temperature at the reactor bottom was 350 ° F / 175 ° C. The higher substrate temperature triggered the thermal decomposition of the ethyl acetate, which resulted in the deposition of the titanium oxide.

The resulting coated glass was allowed to cool in air and the coating was analyzed. Titanium oxide having a carbon content of 2.5 to 3.5 atomic percent was found. The thickness of the titanium oxide coating was measured to be 490 Å, and the thickness and growth rate (150 Å per second) are shown in Table 1. The optical properties of the obtained product included a light transmittance under standard illuminant C (10 ° to the observer) of 62.3% and an observed light reflectance under standard illuminant C of 35.6%. The extinction coefficient was 0.008 at 550 nm and the refractive index of the titania coating was 2.44.

In Examples 2 and 3, the coating procedure described in Example 1 was repeated, except that in Example 2, ethyl formate as the organic oxygen source and in Example 3, isopropanol as the organic oxygen source and uncoated glass (in place of the silica coated glass of Examples 1 and 2) as the substrate has been used. The gas flows and in Example 2 thickness and growth rate of the prepared titanium oxide layer are listed in Table 1. In Example 3, the isopropanol burned in the reactor left only particulate titanium oxide on the glass, the corresponding deposition rate was therefore given as 0 Å / second.

The procedure in Examples 4 and 5 was the same as that in the previous examples (reactor temperature and substrate were identical to Example 1) except that the substrate was static and not dynamic. The static sample was placed under the reactor for 10 seconds. Under static conditions, the residence time of the substrate under the reactor was increased by a factor of 5 over the dynamic conditions.

In Example 4, methyl acetate was used as the organic oxygen source and Example 5 tert-butyl acetate, wherein in each case a titanium oxide coating was prepared. Gas flows, the resulting thickness of the titanium oxide coating and coating growth rates are listed in Table 1. The relatively low growth rate achieved with methyl acetate will be discussed later.

Example 6

A float glass process was used to produce an endless glass ribbon 0.125 inch / 3 mm thick at a transfer rate of 434 inches / 11 meters per minute. The glass transition temperature was 1140 ° F / 615 ° C at the desired deposition point of the titanium oxide coating in the float bath section using a coating reactor similar to that shown in FIG. The temperature in the precursor tower was 400 ° F / 205 ° C and the temperature at the reactor bottom was 500 ° F / 260 ° C. Prior to carrying out the process of this invention, a silicon dioxide coating had been applied to the glass substrate in the float bath section at a thickness of about 339 Å. The same vapor deposition method as described in Example 1 was used to apply the silica coating. The application of the silica is not part of the invention.

The precursor gas mixture comprising titanium tetrachloride and ethyl acetate in a helium carrier gas was developed. As a result of previous examples, which indicated that the coating reaction was not sensitive to the oxygen concentration, no oxygen was used in the precursor. The precursor mixture was prepared by simultaneously passing the three components through a manifold system. The volumetric composition of the precursor mixture was 0.6% titanium tetrachloride, 1.8% ethyl acetate and 97.5% helium. The flows of the components were 480.0 l / min of helium, 3.0 l / min of titanium tetrachloride and 9.2 l / min of ethyl acetate. The total flow of the precursor mixture was 492.2 l / min.

The thickness of the resulting titanium oxide coating was 684 Å. The carbon content of the coating was less than 2 atomic percent. The growth rate of the coating was 309 Å per second.

Example 7

In this example, the same procedure as in Example 6 was carried out. The substrate comprised coatings of silicon and then silicon dioxide on the glass substrate. The coatings were applied by a known vapor deposition method in the float bath section. The silicon coating was deposited by CVD of monosilane with a non-oxidizing carrier gas. Thereafter, the silica coating was applied to the silicon coating using the same procedure as described in Example 1.

The titanium oxide coating precursor comprised titanium tetrachloride and ethyl acetate in a helium carrier gas. The volumetric composition of the precursor was 0.5% titanium tetrachloride, 1.9% ethyl acetate and 97.6% helium. The respective flows of the components were 480.0 l / min of helium, 2.4 l / min of titanium tetrachloride and 9.2 l / min of ethyl acetate. The total flow of the precursor mixture was 491.6 l / min.

The obtained coated product 52 is illustrated in FIG. The glass substrate 54 is shown as having a multilayer structure 56. The coatings comprise a layer of silicon 58, a layer of silica 60, and thereon a titanium oxide coating 62 as a topcoat of the product. The titanium oxide coating on the resulting product had a thickness of 836 Å. The optical properties of the obtained layer structure included an observed light transmittance under standard illuminant C of 13.1% and an observed light reflectance under standard illuminant C of 82.5%. The growth rate of the titanium oxide coating was 378 Å per second. Table 1

Examples 8 to 13

In this series of experiments, a laboratory static coating apparatus was used to apply a tin oxide coating to a float glass substrate bearing a color-suppressing silica layer prepared as described in European Patent EP 0 275 662 B.

The float glass to be coated was supported on a nickel block in a reactor vessel and the block was heated from below starting by electrical heating elements to obtain a glass transition temperature of 1085 ° F / 585 ° C. Above the glass and parallel to it, a flat graphite plate was placed at a distance of about 0.4 inch / 10 mm to provide a gas flow path of 0.4 inch / 10 mm depth between the silica surface bearing glass surface and the graphite plate ,

A precursor gas mixture containing tin tetrachloride and an organic oxygen source was introduced in air and with a small amount of additional nitrogen as the carrier gas through a gas line maintained at a temperature of 435 ° F ± 25 ° F / 225 ° C ± 15 ° C and provided with a fish tail nozzle orifice was delivered into the gas flow path over the hot glass in a general direction parallel to the glass surface. The total carrier gas flow was 13 m³ / h. The flow of tin tetrachloride and the nature and flow of the organic compound used were as shown in Table 2. In Examples 9 and 11, small amounts of 40% hydrogen fluoride were incorporated into the precursor gas mixture to fluorine-dope the resulting tin oxide coating as shown in the table.

The gas stream containing the gaseous reactants was applied for about 8 seconds, after which time the coating apparatus and coated glass were allowed to cool under a 345 ° F / 225 ° C air stream. After disassembling the coating apparatus, the gas supply line, the nozzle and the plate which formed the gas flow path over the glass were in any case free of deposits, indicating the absence of any undesirable pre-reaction. In either case, the glass had a tin oxide coating applied to the silica, with the thickness of the coating varying with the distance from the fishtail nozzle. The largest thickness and corresponding growth rate for each precursor gas mixture are listed in Table 2. Emissivities, resistivities and haze of samples prepared using hydrogen fluoride to incorporate fluorine as a dopant (Examples 9 and 11) were measured and the results summarized in Table 2.

The test series demonstrates that an organic source of oxygen can be used as part of a premixed precursor gas mixture comprising tin tetrachloride to apply a tin oxide coating without a significant undesirable pre-reaction which would adversely affect the coating process, for example, by deposition of tin oxide in the gas feeds. In addition, if desired, a source of a dopant such as hydrogen fluoride may be incorporated into the gaseous premix to reduce emissivity and resistivity of the coating while still avoiding significant adverse prereaction.

Example 14

In this example, a coating distribution nozzle as schematically illustrated in Fig. 4 was used in a float bath to apply a coating of tin oxide by the method of the present invention. The speed of the glass ribbon was about 233 inches per minute / 350 minutes per hour and the glass thickness was 0.05 inches / 1.2 mm. The glass transition temperature was about 1170 ° F / 630 ° C. The temperature of the gas supply line 101 serving as a mixing chamber for the primary gas was maintained at 300 ° F / 150 ° C and that of the "static" diverting gas distributor 105 at about 645 ° F / 340 ° C. The tin tetrachloride and butyl acetate vapors were supplied to the gas supply line 101 by bubbling nitrogen through the liquids held in gas wash bottles at 175 ° F / 80 ° C and then through separate heated lines. The vapors mixed in the main chamber flowed through the baffled gas distributor and then under laminar flow conditions. Table 2

It will be understood that various changes and modifications may be made to specific details of the invention as illustrated in the preceding example without departing from the spirit and scope thereof as defined in the claims. In its essential details, the invention is a continuous vapor deposition process for depositing titanium oxide coatings on a glass substrate at high deposition rates through the use of titanium tetrachloride and an organic compound used as an oxygen source in a premixed precursor gas mixture.

Because of the availability and cost of the starting materials, metal tetrachlorides are the preferred sources of the respective metals.

It has been found that, in particular, when titania tetrachloride titanium oxide coatings are applied to form the metal oxide at the optimum deposition rate, it is desirable to employ an oxygen-containing organic compound which is an ester, especially an ester in which the organosilicon compounds of U.S. Pat Alcohol-derived group is an alkyl group with a β-hydrogen. Furthermore, the decomposition temperature of the ester should not be higher than the reaction temperature of the precursor gas mixture for the coating at the desired deposition site. Esters used in the precursor gas mixture, having a β-hydrogen and a suitable decomposition temperature, deposit the coatings at high deposition rates. The preferred ester group used in the practice of the invention includes the group consisting of ethyl formate, ethyl acetate, ethyl propionate, isopropyl formate, isopropyl acetate, n-butyl acetate, and tertiary butyl acetate.

In general, an ester decomposes in a continuous manner over a given temperature range. In the present invention, the thermal decomposition temperature of the ester is defined as the temperature at which the monomolecular decomposition rate constant of the ester is 0.01 / sec. The one-molecular decomposition rate constants of conventional esters, such as ethyl acetate and tert-butyl acetate are known and can be found in the chemical literature. For ethyl acetate and tert-butyl acetate, the thermal decomposition temperature using this definition is 935 and 650 ° F, respectively (500 ° C and 344 ° C, respectively). Those skilled in the art will appreciate that the selection of the ester and the specific deposition temperature used will determine the optimum growth rate of the coating. Reaction temperatures below the defined thermal decomposition temperature, but within the decomposition range of the chosen ester, result in lower growth rates of the coating.

In the present invention, the alkyl group of an ester used in the precursor gas mixture for the coating may be a carbon compound having 2 to 10 carbon atoms. The lower limit of this range is determined by the requirement of the β-hydrogen in the alkyl group. The upper limit is to avoid problems of ignitability and volatility that occur when the alkyl group contains more than 10 carbon atoms.

In carrying out the process of the invention, a gas distributor may be used to connect and control the individual gas streams for the formulation of the precursor gas mixture for the coating. A common supply line may be used to deliver the precursor gas mixture from the gas distributor to the gas distribution nozzle. A static mixer arranged in the gas supply line can be used to ensure a homogeneous gas mixture in the gas supply line. Additionally, baffles as illustrated in FIG. 3 or a gas restrictor as described with reference to FIG. 4 may be provided in the gas distribution nozzle to mix the precursor gas in the reactor stage.

In many of the examples, oxygen was incorporated into the coating precursor gas mixture. However, the deposition rate of the metal oxide coating was not sensitive to the oxygen concentrations, therefore, in Example 6 or 7, no gaseous oxygen was used, showing that the addition of oxygen is unnecessary.

The concentration of the reactive components of the precursor gas mixture for the coating can be selected to obtain the optimum growth rate of the coating. The concentration of metal tetrachloride is generally 0.1 to 5.0 volume percent in the precursor gas mixture. The concentration of metal chloride is based on the amount of metal required to give the desired thickness of the coating within the available residence time. Thus, the concentration of metal tetrachloride is adjusted according to process parameters such as transport speed of the glass ribbon in a float glass process.

The concentration of the oxygen-containing organic compound in the precursor gas mixture for the coating is generally one to five times the concentration of the metal tetrachloride and is selected within this range based on the deposition temperature. When an ester is used, lower deposition temperatures result in slower ester decomposition rates, therefore, higher concentrations of the ester are required to react with the metal tetrachloride. In Examples 6 and 7, the optimum ethyl acetate concentration in the precursor gas mixture is one to three times the concentration of titanium tetrachloride. Concentrations above or below the optimum range yield metal oxide coatings with slower growth rates of the coating.

The temperature of the precursor gas mixture is critical to controlling the reaction, particularly to avoid undesirable pre-reaction or adduct formation resulting from the formation of a non-volatile product in the precursor lines. In a preferred embodiment, which is particularly applicable when using an ester, the temperature in the precursor gas lines is maintained above 300 ° F / 150 ° C. The temperature of the precursor gas mixture is also preferably maintained below the thermal decomposition temperature of the oxygen-containing organic compound to prevent pre-reaction of the mixture.

In the process according to the invention, the heat from the substrate is used to trigger the coating reaction. In cases within a production line, such as the float glass process, the substrate is formed at extremely high temperatures. Therefore, the method of the present invention can be applied to a float glass process where the substrate temperature has dropped but is still above the temperature at which the coating forms (and preferably, after the glass ribbon has substantially ceased to expand) is called below 1380 ° F / 750 ° C). Discontinuous applications of the process of the invention require heating the substrate to a temperature above the decomposition temperature of the ester.

When carrying out the process according to the invention in the float glass process, the preferred deposition site is in the float bath section. The temperature range at the deposition site of the coating usually ranges from about 1100 to 1320 ° F / 590 to 715 ° C. Temperature is an important operating parameter as it affects the concentration of organic compound used in the precursor gas mixture.

The temperatures of the substrate in the float bath section are relatively stable and therefore have only slight fluctuations at the deposition site. In Examples 6 and 7, in which ethyl acetate was used, the preferred substrate temperature range was 1100 to 1250 ° F / 590 to 680 ° C.

Due to the heat of the substrate, the temperature of the precursor gas mixture rises above the temperature required for the formation of the coating (and when the ester is used as the organic compound, above the thermal decomposition temperature of the ester). The metal deposition reaction can be initiated by decomposition of the oxygen-containing organic compound. When titanium tetrachloride is used together with an ester having an alkyl group with a β-hydrogen, the titanium oxide coating is formed on the substrate at a decomposition rate ten times higher than that of known coating methods. When used in a production line in a process for producing a float glass ribbon, it passes under the gas distribution nozzle at a relatively high speed. The metal oxide coating is applied to the float glass ribbon as it passes under the gas distribution nozzle.

The following theory is proposed by the inventors in terms of the chemical reaction that can take place when an ester having an alkyl group with a β-hydrogen is used. However, it is not intended to limit the invention to only this possible explanation, and therefore it merely provides an aid to understanding the results of the method according to the invention.

It is suggested by the inventors that as the ester decomposes, the carbon-hydrogen bond of one of the β-hydrogen atoms breaks down and the hydrogen changes to the carbonyl group, which cleaves an alkene and forms a carboxylic acid. The hydrolysis reaction occurs simultaneously between the carboxylic acid and the metal tetrafluoride, resulting in the formation of the metal oxide coating on the substrate.

In general, the resulting product obtained according to the present invention comprises a substrate having a titanium oxide coating. In this case, the coating can be applied directly to the substrate or as a layer within a plurality of layers on a substrate. The deposition rate of the metal oxide coating is influenced by the rate of decomposition of the oxygen-containing organic compound. At a constant reaction temperature, different oxygen-containing organic compounds give different growth rates of the coating due to the difference in decomposition temperatures. Therefore, the desired growth rate for a metal oxide coating in a given system is selected by matching a particular oxygen-containing organic compound to the temperature of the precursor gas mixture and to the substrate temperature at the deposition site.

The deposition rate of the titanium oxide coating according to the invention may be ten times higher than the deposition rates in known deposition processes. The process of the present invention allows deposition rates in excess of 130 Å per second, with some deposition rates well in excess of 300 Å per second. The higher deposition rates for titanium oxide result in a coating having a refractive index greater than 2.4.

Another advantage of the invention is that it uses, in addition to the high rates of deposition, precursor compounds for the metal at low cost, and that, especially when the precursor gas mixture is directed to the substrate under the preferred laminar flow conditions, it is high Turnover (of metal tetrachloride) allows.

According to the invention, the resulting oxide coating contains little residual carbon from the decomposition of the oxygen-containing organic compound, especially when an ester is used. Carbon is an undesirable by-product of the coating reaction because high carbon levels of the deposited coatings cause absorption problems in them. The focus of using an oxygen-containing organic compound in the precursor gas mixture for the coating is that the decomposition does not result in carbon contents that affect the absorption properties of the finished glass. The carbon content of coatings made by the process of the invention showed less than four atomic percent of carbon in the measurement. This low carbon content does not appreciably affect the absorption properties of the coating.