Method for depositing titanium oxide coatings on flat glass and the resulting coated glass

Method for depositing a titanium oxide coating on plate glass and glass coated therewith

The present invention relates to a method for depositing a titanium oxide coating on a flat glass substrate and to a glass thus coated. In particular, the present invention uses a coating precursor gas mixture containing titanium tetrachloride and an organic oxidant, chemical vapor deposition for forming a titanium oxide coating on a plate glass it's about how

Titanium oxide coatings have been proposed for use on glass containers such as bottles to improve the mechanical strength of the containers. It has also been proposed to use titanium oxide coatings on plate glass to change the characteristics of architectural glass, wherein titanium oxide coatings deposited under vacuum (by reactive sputtering) are sputtered multi-layer infrared reflecting coatings. coatings) have been used.

British Patent Specification No. 1 115 342 discloses good inherent properties by spraying a solution or dispersion of stannous chloride (i.e. tin tetrachloride) in an organic liquid, preferably isopropyl alcohol, from the manufacturing process into a vessel which is still hot from the manufacturing process. A method for making a glass container having strength and good abrasion resistance is disclosed. Small amounts of titanium chloride may be introduced as modifiers. On either side of the tunnel spanning the conveyor for the hot glass bottle to create a 'mist of liquid reagent' such that a liquid layer is formed on all exterior surfaces of the bottle which reacts to form a tin oxide layer. The liquid solution is supplied to an atomizer, which may be a variety of pressure jets disposed of.

British Patent Specification No. 1 187 784 discloses an improvement of the method disclosed in British Patent Specification No. 1 115 342, which is a glass article which does not affect the normal performance of the method and does not require additional monitoring. Methods well suited for incorporation into automated manufacturing processes are disclosed. The British Patent Specification No. 1 187 784 proposes to treat a glass container with a liquid solution of an organotin compound at a high temperature, wherein the organotin compound has the property of "decomposing into two substances by application of heat, One of the two materials is an organotin compound that has a high decomposition temperature to react with the glass surface to create a diffuse layer of tin oxide within the glass surface, and the other is an organotin compound with a vapor of a substantial portion of the compound being produced in at least one of the vessel's It is a volatile tin compound that heats the vessel so that a reaction occurs between the glass and the tin compound on the surface." Materials used to treat glass containers include tin tetrachloride and organic substances containing suitable active carbonyl groups, such as ethyl, n-propyl, isopropyl, n- with acetic acid, propionic acid and butyric acid. reaction with organic esters of butyl and isobutyl alcohol. The resulting solution can be sprayed in the form of a fine mist against a hot vessel under ambient atmosphere, for example before entering an annealing lehr after the vessel has exited the forming machine. British Patent Specification No. 1 187 783 discloses a method similar to British Patent Specification No. 1 187 784, wherein an organotanium compound is sprayed onto a hot glass vessel instead of an organotin compound. Organotanium compounds can be produced in a manner analogous to organotin compounds by reacting titanium tetrachloride with an organic ester, for example n-butyl acetate. Again, the resulting solution is sprayed onto the glass on a vessel production line in ambient atmosphere.

delete

Methods using reactants in gaseous form (called CVD or chemical vapor deposition) have some advantages over spraying methods for coating flat glass, especially when the reactants can be premixed before being applied to the glass. Unfortunately, tin tetrachloride readily reacts with water, so prior preparation is necessary to use tin tetrachloride and water vapor in gaseous form, by individually gassing the glass surface and mixing them in contact with the glass.

British Patent Specification No. 2 044 137A relates to a method in which separate laminar flows of each reactant are formed and released on a hot glass substrate by bringing these laminar flows together in mutual tangential contact on the glass. Titanium tetrachloride can be used as one of the gaseous reactants in place of tin tetrachloride to form a titanium oxide coating. British Patent Specification No. 2 044 137A also proposes to supply hydrogen to one of the gas streams to reduce the extreme reaction between tin tetrachloride and water vapor. This can be done by direct addition of hydrogen gas, or by addition of methanol reacting in conditions to produce the desired hydrogen gas.

delete

European Patent Specifications 0 365 239B1 and 0 376 240B1 disclose a method and apparatus for depositing a tin oxide coating on a high temperature glass ribbon. A first gas flow of tin tetrachloride in the preheated dry air flows along the surface of the hot glass ribbon running down the coating chamber, and a second turbulent flow of hydrofluoric acid and vapor is directed at the plane of the glass and in the direction of the first gas flow. and introduced into the coating chamber perpendicular to the , the mixed first and second gas streams flow through the coating chamber and over the glass under turbulent conditions. The apparatus and method may be used to apply a titanium oxide coating using titanium tetrachloride instead of tin tetrachloride.

U.S. Patent 4 590 096 discloses a coating solution comprising a solvent free mixture of organic tin chloride and a reactive organic fluorine compound dissolved in or mixed with organic tin chloride. A method is disclosed wherein the gas stream is introduced into a preheated carrier gas stream sufficiently containing water vapor wherein the relative humidity of the gas stream is from about 6% to about 100%. The resulting gas stream is passed over the hot glass surface to deposit a fluorine doped tin oxide coating on the hot glass. A wide range of organotin compounds can be used and the possibility of using tin tetrachloride is mentioned. Similarly, a wide range of organic fluorine compounds containing oxygen-containing compounds, for example trifluoroacetic acid and ethyltrifluoroacetate, can be used. Some fluorine-containing dopants limit the solubility in the organotin compounds used, and solubilizing agents are used, including but not limited to, acetic anhydride (acetic anhydride), ethyl acetate, hexane, methyl isobutyl ketone, and any dissolution aid may be used to increase the solubility of the fluorine dopant on the organotin compound, such as butyraldehyde. However, in common with other patent specifications that use a chemical vapor deposition method for depositing metal oxides from gaseous metal tetrachloride, this US patent uses water vapor as the oxygen source.

US Pat. No. 4 751 149 to Vijaykumar et al. on a heat sensitive photoconductor substrate by chemical vapor deposition at low temperatures (60° C. to 350° C., preferably 100° C. to 200° C.) It is proposed to deposit zinc oxide coatings from organic zinc compounds with oxygen containing organic compounds such as esters and oxides which may be inert carrier gases. Although this US patent is not entirely clear, it is clear that it is proposed to introduce separate flows of organozinc compound and oxidant into the deposition chamber, and not to premix the components together prior to transfer to the coating chamber. U.S. Patent 5 401 305 discloses a mixture of a metal oxide precursor, a silicon dioxide precursor tetraethylorthosilicate, and an accelerator such as triethyl phosphite to form a metal oxide deposited on a glass substrate. A composition for glass coating by chemical vapor deposition with a reactive atmosphere or added oxygen, wherein organic tin chloride (defined to include tin tetrachloride) is used as the source of tin, and the organofluorine compound is an esteryl as the source of fluorine and, optionally, the ester stabilizes the liquid. In each case, the liquid composition is vaporized in an oxygen-containing carrier gas stream for transport to the hot glass, and the oxygen gas serves as the oxygen source for the creation of the tin oxide coating.

U.S. Patent No. 5 124 180 relates to a CVD method for producing a fluorine-containing metal oxide coating on a substrate and apparatus for use in the method, wherein a metal oxide precursor and water or alcohol as an oxygen source are vaporized in a coating chamber. They are individually transferred to the furnace and mixed just before deposition on the substrate. Use of a preliminary mixture of the corresponding metal tetrachloride and oxygen source as a low-cost reactant without premature reaction between the metal tetrachloride and the oxygen source (formerly water) to form metal oxides in the coating apparatus and thus lead to problems and inefficiencies Therefore, it is advantageous to provide a method of depositing a titanium oxide coating by a CVD method applied to a high temperature plate glass. A method of depositing a coating at a high rate that can be deposited to the required coating thickness on a moving glass ribbon during the glass manufacturing process is particularly advantageous.

According to the present invention, a chemical vapor deposition method for disposing a titanium oxide coating on a high temperature glass substrate using a precursor gas mixture containing an organic oxygen source and titanium tetrachloride, without the need to introduce water vapor and without the risk of premature reaction. is to provide

The present invention is

(a) preparing a precursor gas mixture containing titanium tetrachloride and an organic oxygen-containing compound as an oxygen source for producing titanium oxide;

(b) maintaining the precursor gas mixture at a temperature below the temperature at which titanium tetrachloride reacts to form titanium oxide, while transferring the mixture onto a hot glass phase into an open coating chamber;

(c) introducing a precursor gas mixture into the coating chamber, whereby the mixture is heated to cause deposition of titanium oxide containing oxygen from the organic compound on the hot glass surface. To provide a method for depositing a coating.

delete

Surprisingly, a wide range of oxygen-containing organic compounds that do not require the presence of oxygen in the water vapor or gaseous state, including compounds such as alcohols, which are usually considered reducing agents rather than oxidizing agents, can be used as oxygen sources. However, preferred organic compounds are carbonyl compounds which are esters, and particularly good results are obtained using esters having an alkyl group containing beta hydrogen. Alkyl groups containing beta hydrogens typically contain from 2 to 10 carbon atoms.

It is preferred to use organic compounds containing 2 to 10 carbon atoms, especially esters, because of the tendency of larger molecules to lower volatility and somewhat inconvenient for use in the CVD process of the present invention.

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

The method of the present invention is practiced in connection with the formation of a continuous glass ribbon substrate, for example, during a float glass manufacturing process. However, the method of the present invention can be used to coat other flat glass substrates either online or offline.

The present invention involves the preparation of a precursor gas mixture containing titanium tetrachloride and an organic oxygen-containing compound, and a carrier gas or diluent such as nitrogen, air or helium may usually be included in the gas mixture. Since the pyrolysis of the organic oxygen-containing compound can initiate metal oxide deposition reactions at a high rate, the precursor mixture is maintained at a temperature below the pyrolysis temperature of the organic oxygen compound to prevent the formation of metal oxides and the prereaction of the gaseous mixture. It is preferable to be

The gaseous mixture is maintained at a temperature below the temperature at which it reacts to form a metal oxide, and transferred to a location adjacent to a plate glass substrate to be coated, wherein the substrate is at a temperature above the reaction temperature (and organic oxygen compounds in the precursor gas mixture) temperature above the decomposition temperature of

The precursor gas mixture is then introduced into the vapor space directly above the substrate. Heat from the substrate raises the precursor gas temperature to a temperature above the thermal decomposition temperature of the organic oxygen compound. The organic oxygen compound then reacts and decomposes with the metal tetrachloride to create a metal dioxide coating on the substrate.

The present invention allows a titanium oxide coating to be deposited on hot glass at high deposition rates of 130 angstroms per second (A) or greater, and in a preferred embodiment greater than 250 angstroms per second.

The deposition rate depends on the specific organic oxygen-containing compound used, the concentrations of both the organic oxygen-containing compound and the metal chloride, and the temperature of the glass. For any particular combination of mixtures, the optimum concentration (especially the optimum ratio of organic oxide containing compound to metal tetrachloride) and flow rate for rapid coating deposition can be determined by simple experimentation. However, the use of higher concentrations of reactants and high gas flow rates is likely to result in an overall insufficient conversion of reactants into the coating, so that optimal conditions for industrial operation may differ from those that provide the highest deposition rates. It will be understood that there is

Preferably, the organic oxygen-containing compound may be at a concentration of about 0.5 times the concentration of the volume of metal chloride, in particular 1 to 5 times the concentration. The organic oxygen-containing compound may be used, usually in an amount of at least 30% by weight of the weight of the metal chloride.

The method of the present invention can produce a titanium oxide coating on a high temperature plate glass substrate at high speed online during the glass manufacturing process. Titanium oxide coatings can be made with a high refractive index (2.4 or higher) that can achieve desirable optical effects, especially when used in combination with other coating layers.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic view, in vertical section, of an apparatus for carrying out the manufacture of float glass comprising a gas distributor suitably arranged for practicing the method of the present invention;

2 is a partial cross-sectional view of an article coated in accordance with the present invention;

3 is an enlarged schematic view of a gas distributor beam suitable for use in practicing the present invention;

4 is an enlarged schematic view of an optional gas distributor beam that may be used to practice the present invention;

These and other advantages of the present invention will become apparent to those skilled in the art from the following detailed description of preferred embodiments, when considered in light of the accompanying drawings.

Referring in more detail to the drawings, a float glass installation used as a means for carrying out the method of the present invention is shown generally by reference numeral 10 in FIG. 1 . The float glass apparatus in particular comprises a canal section 12 through which molten glass 14 is conveyed from a melting furnace (not shown) to a float bath section 16, and a continuous glass ribbon 18 ) is formed by a known float process. The glass ribbon 18 travels from the bath portion 16 through an adjacent annealing furnace (lehr) 20 and a cooling portion 22 . The continuous glass ribbon 18 serves as a substrate on which a metal oxide coating is deposited in accordance with the present invention.

The float bath portion 16 includes a bottom portion 24 having a molten tin bath 26 therein, a roof 28 , opposing sidewalls 30 , and endwalls 32 . Roof 28, sidewall 30, and endwall 32 together define an enclosure 34 in which a non-oxidizing atmosphere is maintained to prevent oxidation of the molten tin.

Accordingly, the gas distributor beams 64 , 66 , 68 are positioned within the bath portion 16 . The gas distributor beams 64, 66 in the bath can be used to apply an additional coating on the substrate prior to applying the titanium oxide coating according to the method of the present invention. Additional coatings may include silicone and silica.

In operation, molten glass 14 flows in a controlled amount along a duct 36 below a regulating tweel 38 and downstream on the surface of a tin bath 26 . On a tin bath, the molten glass develops laterally under the influence of any mechanical and gravity and surface tension, and runs across the bath to form a ribbon 18 . The ribbon is conveyed over a lift out roll 40 and then through an annealing furnace 20 and a cooling section 22 on an aligned roll 42 . The application of the coating of the present invention is applied to the float bath section 16 or along the production line, for example in the space between the float bath and the annealing furnace or in an annealing furnace.

A suitable non-oxidizing atmosphere, typically nitrogen or a nitrogen-rich mixture of nitrogen and hydrogen, is maintained within the bath enclosure 34 to prevent oxidation of the tin bath. Atmospheric gas enters through conduit 44 operatively coupled to distribution manifold 46 . The non-oxidizing gas is introduced at a rate sufficient to compensate for the normal loss and maintained at a slightly positive pressure, about 0.001 atmospheres to about 0.01 atmospheres above ambient atmospheric pressure, to prevent infiltration of the outside atmosphere. Heat to maintain the desired temperature situation within the tin bath 26 and enclosure 34 is provided by radiant heaters 48 within the enclosure. The atmosphere in the furnace 20 is typically ambient air, while the cooling section 22 is not enclosed and the glass ribbon is open to the ambient atmosphere. Ambient air can be directed towards the glass ribbon by a fan 50 in the cooling section. A heater (not shown) may be provided in the annealing furnace to gradually decrease the temperature of the glass ribbon in accordance with a predetermined temperature situation as the ribbon is conveyed through the furnace.

1 illustrates the use of gas distributor beams 64, 66, 68 disposed within a float bath 16 to deposit various coatings on a glass ribbon substrate. Gas distributor beams are one type of reactor that can be used to practice the method of the present invention.

A preferred configuration for splitter beams suitable for supplying precursor material according to the invention is schematically illustrated in FIG. 3 . A generally inverted channel-like frame 70 formed by spaced inner and outer walls 72 , 74 defines enclosed cavities 76 , 78 . A suitable heat exchange medium is circulated through the enclosed cavities 76 and 78 to maintain the distributor beams at the desired temperature.

The precursor gas mixture is supplied through a fluid-cooled supply conduit 80 . A supply conduit 80 extends along the distributor beam and transports gas through spaced drop lines 82 along the supply conduit. A supply conduit 80 leads to a transfer chamber 84 in a header 86 supported by a frame. Precursor gases transported via drop line 82 are discharged from transport chamber 84 through passage 88 toward the coating chamber defining a vapor space opening for the glass, where these precursor gases are directed in the direction of the arrow in FIG. It flows along the surface of the glass 18 .

A baffle plate 90 for equalizing the flow of precursor material across the splitter beam to ensure that the material is emitted against the glass 18 in a smooth, laminar, uniform flow across the splitter beam may be provided within the transfer chamber 84 . The spent precursor material is collected and removed through an evacuation chamber 92 along the side of the distributor beam.

Various types of splitter beams used in chemical vapor deposition are suitable for the method of the present invention and are known in the art.

Any one of these alternative splitter beam shapes is schematically illustrated in FIG. 4 . Using this distributor, shown generally by reference numeral 100 (as detailed in European Patent EP 0 305 102B), the precursor gas mixture is cooled by means of a cooling fluid circulated through ducts 102 , 103 . It is introduced via the supply duct 101 . The gas supply duct 101 opens into the gas flow restrictor 105 through the expansion hole 104 .

A gas flow restrictor 105 is of the kind detailed in British Patent Specification GB 1 507 996, a plurality of longitudinally corrugated waves in the form of a sine wave and vertically mounted in adjacent relation to each other so as to extend along the length of the distributor. of metal strips. Adjacent corrugated metal strips are placed "out of phase" to define a plurality of vertical channels therebetween. Since these vertical channels have a cross-sectional area that is less than the cross-sectional area of the gas supply duct 101 , the gas is discharged from the gas flow restrictor 105 at substantially positive pressure along the length of the distributor.

The coating gas flows from the gas flow restrictor into a substantially U-shaped guide channel 106 comprising an inlet leg 107 , a coating chamber 108 open onto the hot glass substrate 110 to be coated, and an outlet leg 109 . is discharged into the inlet side 107 of the , whereby the used coating gas is withdrawn from the glass. The rounded edges of the block defining the coating channels promote a uniform laminar flow of coating parallel to the glass surface across the glass surface to be coated.

The following examples (gas volumes are presented under standard conditions, i.e. one atmospheric pressure and ambient temperature without being brought to another state) are presented to illustrate and explain the present invention, and are not to be construed as limitations of the present invention.

<u>Examples 1 to 5</u>

In a series of examples, a bidirectional coating reactor of the type shown in FIG. 3 may be used in a laboratory to deposit titanium oxide coatings.

In Examples 1-3, the glass is heated on a conveyor hearth to mimic the coating reaction conditions of a float glass process to test the method of the present invention. The furnace uses in-line rollers to transport the glass substrate through the heating zone prior to carrying out the method of the present invention. In Example 1, the glass substrate was initially float glass with a silica coating. Silica coatings are deposited on float glass via known chemical vapor deposition methods using precursors of monosilane in an oxygen containing atmosphere. Silica deposition does not form part of the present invention.

According to the present invention, a titanium oxide coating is deposited on a silica coated substrate. The substrate temperature is 630° C. (1170° F.) and the substrate line speed is 300 in. (8 m) per minute.

To deposit titanium oxide, the precursor gas mixture includes titanium tetrachloride, ethyl acetate, oxygen, and helium. Helium is included in the precursor mixture as a carrier for the reactants. The precursor mixture is prepared by simultaneously introducing all four gas streams through a manifold system. An in-line static mixer is used to ensure a homogeneous precursor mixture. The volume percent composition of the precursor mixture was 0.7% titanium tetrachloride, 17.2% ethyl acetate, 7.2% oxygen, and 74.9% helium, and the flow rates for the components in the manifold are shown in the attached Table 1.

The temperature of the precursor mixture is maintained above 150° C. (350° F.) to prevent the addition reaction of titanium tetrachloride with ethyl acetate. In addition, the precursor temperature is maintained below the pyrolysis temperature range of ethyl acetate of 510°C to 610°C (950°F to 1130°F) to prevent the mixture from pre-reacting.

The precursor mixture is introduced into the reactor directly above the moving substrate. The temperature in the precursor tower is 120° C. (250° F.). The temperature at the reactor side is 175°C (350°F). Higher substrate temperatures initiate thermal decomposition of ethyl acetate resulting in the deposition of titanium oxide.

The resulting coated glass was cooled in air to analyze this coating. This coating was found to be titanium oxide with a carbon content of 2.5 to 3.5 atomic percent. The thickness of the titanium oxide coating was measured to be 490 Angstroms, and this thickness and growth rate (150 Angstroms per second) is shown in Table 1. The optical properties of the obtained product have an observed Illuminant C transmittance (10° observatory) of 62.3% and an observed Illuminant C reflectivity of 35.6%. The extinction coefficient was 0.008 at 550 nm, and the refractive index of the titanium oxide coating was 2.44.

In Example 2, ethyl formate was used as the organic oxygen source, and in Example 3, isopropanol was used as the organic oxygen source and uncoated glass (Silicone oxide coated glass of Examples 1 and 2) The coating procedure set in Example 1 was repeated in Examples 2 and 3, except that ) was used as the substrate. The gas flow rates used and the thickness and growth rate of the titanium oxide coating obtained in the case of Example 2 are shown in Table 1. In Example 3, isopropanol burned in the reactor leaves only titanium oxide particulates on the glass, with a corresponding deposition rate of 0 Angstroms per second.

The procedure of Examples 4 and 5 is the same as that used in the previous examples except that the substrate is static rather than dynamic (reactor temperature and substrate are the same as in Example 1). A static sample is placed under the reactor for 10 seconds. Under static conditions, the residence time of the substrate under the reactor is increased over dynamic conditions by five factors.

In Example 4, methyl acetate was used as the organic oxygen source and in Example 5, t-butyl acetate was used, in each case resulting in a titanium oxide coating. The gas flow rate, obtained titanium oxide coating thickness and coating growth rate are shown in Table 1. The relatively slow growth rates achieved using methyl acetate are described below.

<u>Example 6</u>

A float glass process was used to make continuous glass ribbons with a thickness of 3 mm (0.125 in) at a line speed of 11 m (434 in) per minute. The glass temperature at a given point in the float bath of the titanium oxide coating was 615° C. (1140° F.) using the same coating reactor as shown in FIG. 3 . The temperature in the precursor tower was 205°C (400°F) and the temperature at the reactor side was 260°C (500°F). Prior to practicing the method of the present invention, a silica coating was deposited on a glass substrate in a float bath to a thickness of about 339 Angstroms. The same chemical vapor deposition method as described in Example 1 was used to deposit the silica coating. Silica deposition does not form part of the present invention.

A precursor gas mixture was created containing titanium tetrachloride and ethyl acetate in a helium carrier gas. Oxygen was not used in the precursor as the coating reaction was indicated to be non-responsive to oxygen concentration as a result of the previous example. The precursor mixture was prepared by simultaneously introducing the three components through a manifold system. The volume percent composition of the precursor mixture was 0.6% titanium tetrachloride, 1/8% ethyl acetate, and 97.5% helium. The flow rates of the components were helium 480.0 l/m, titanium tetrachloride 3.0 l/m, ethyl acetate 9.2 l/m. The total flow rate of the precursor mixture was 492.2 l/m.

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

<u>Example 7</u>

The same procedure as in Example 6 was used in this example. The substrate includes a silicon coating followed by a silica coating on a glass substrate. The coating was deposited by known chemical vapor deposition in a float bath. The silicon coating was deposited by CVD from monosilane with a non-oxidizing carrier gas. A silica coating was deposited on the silicone coating using the same procedure as described in Example 1.

The precursor for the titanium oxide coating contains titanium tetrachloride and ethyl acetate in a helium carrier gas. The volume percent composition of the precursor was 0.5% titanium tetrachloride, 1.9% ethyl acetate, and 97.6% helium. The flow rates corresponding to the above components were 480.0 l/m of helium, 2.4 l/m of titanium tetrachloride, and 9.2 l/m of ethyl acetate. The total flow rate of the precursor mixture was 491.6 l/m.

The resulting coated article 52 is shown in FIG. 2 . Glass substrate 54 is depicted as having a stack of a plurality of coatings 56 . The coating includes a silicon layer 58 , a silica layer 60 , followed by a titanium oxide coating 62 on top of the article. The titanium oxide coating on the obtained article had a thickness of 836 Angstroms. The optical properties of the resulting coating stack included an observed illuminant C transmittance of 13.1% and an observed illuminant C reflectance of 82.5%. The growth rate of the titanium oxide coating was 378 Å per second.

<tables id="1"><table colsep="0" frame="top" id="1" rowsep="0"><title /><tgroup align="left" cols="1" colsep="0" rowsep="0" xmlns="http://www.oasis-open.org/tables/exchange/1.0"><colspec align="left" char="0" charoff="0" colname="1" colnum="1" colsep="0" colwidth="10200" rowsep="0" /><tbody valign="top"><row rowsep="0" valign="middle"><entry align="left" morerows="0" nameend="1" namest="1"><img file="KR100493566B1_D0001.tif" /></entry></row></tbody></tgroup></table></tables>

delete

delete

delete

delete

delete

delete

delete

delete

delete

delete

It will be understood that various changes and modifications may be made from the specific details of the invention encompassed in the above-described embodiments without departing from the spirit and scope thereof as defined in the appended claims. In essential detail, the present invention is a continuous chemical vapor deposition method for depositing titanium oxide coatings on glass substrates at high deposition rates through the use of titanium tetrachloride and an organic compound used as an oxygen source in a pre-formed precursor gas mixture.

Metal tetrachloride is a suitable source for each metal because of the availability and cost of the raw material.

When depositing a titanium oxide coating from titanium tetrachloride, it is preferable to use an ester, particularly an organic oxygen-containing compound in which the group derived from an alcohol is an ester in which the group derived from the alcohol is an alkyl group with β-hydrogen in order to form a metal oxide with an optimum deposition rate. found out that Additionally, the decomposition temperature of the ester should not be higher than the reaction temperature of the coating precursor gas mixture at the desired point of application. The ester used in the precursor gas mixture with β-hydrogen and an appropriate decomposition temperature will deposit the coating at a high deposition rate. Preferred ester groups used in practicing the present invention include the group consisting of ethyl formate, ethyl acetate, ethyl propionate, isopryl formate, isopryl acetate, n-butyl acetate, and t-butyl acetate.

Generally, esters decompose in a continuous manner over a range of temperatures. 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 monomolecular degradation rate constants of common esters such as ethyl acetate and t-butyl acetate are well known and can be found in chemical literature and the like. For ethyl acetate and t-butyl acetate, the pyrolysis temperatures using the above definitions are 500° C. and 344° C. (935° F. and 650° F.) respectively. Those skilled in the art will understand that the choice of ester and the specific deposition temperature used will determine the optimum coating growth rate. Reaction temperatures below the specified pyrolysis temperature or temperature ranges within the decomposition range of the selected ester will result in lower coating growth rates.

According to the present invention, the alkyl group of the ester used in the coating precursor gas mixture may be a carbon compound having a range from 2 to 10 carbon atoms. The lower limit of the range is determined by the condition of β hydrogen on the alkyl group. The upper limit avoids the problems of ignitability and volatility that occur when the alkyl group contains more than 10 carbon atoms.

In practicing the method of the present invention, a manifold may be used to connect and regulate the respective gas flows to compound the coating precursor gas mixture. A common transfer line may be used to transfer the precursor gas mixture from the manifold to the gas beam distributor. An in-line static mixer can be used in the transfer line to ensure a homogeneous gas mixture. In addition, the baffles in the gas distributor beam shown in FIG. 3 or the gas flow restrictor described with reference to FIG. 4 may provide additional mixing of the precursor gas at the reactor stage.

In some embodiments, oxygen is included in the coating precursor gas mixture. However, no oxygen gas was used in Examples 6 or 7, which showed that the deposition rate of the titanium oxide coating was not responsive to oxygen concentration, and that introduction of oxygen was unnecessary.

The concentration of the reactive components of the coating precursor gas mixture may be selected to obtain an optimal coating growth rate. The concentration of titanium tetrachloride is generally 0.1 to 5.0 volume percent in the precursor gas mixture. The concentration of titanium tetrachloride is based on the amount of titanium required to provide the desired coating thickness at the available residence time. Thus, the titanium tetrachloride concentration is controlled according to various processes such as the line speed of the ribbon in the float glass process.

The concentration of the organic oxygen compound in the coating precursor gas mixture is generally 1 to 5 times the concentration of titanium tetrachloride, and is selected within a range based on the deposition temperature. When using esters, lower deposition temperatures result in lower ester decomposition rates and thus require higher ester concentrations to react with titanium tetrachloride. In Examples 6 and 7, the optimum concentration of ethyl acetate in the precursor gas mixture is one to three times the concentration of titanium tetrachloride. Concentrations above or below the optimum range will produce a titanium oxide coating with a lower coating growth rate.

The temperature of the precursor gas mixture is important to control the reaction and is particularly important to avoid undesirable pre-reactions or adduct formation that lead to the formation of non-volatile articles in the precursor line. In one preferred embodiment, particularly when using esters, the temperature is maintained above 150° C. (300° F.) in the precursor gas line. In addition, the precursor gas mixture is preferably maintained below the thermal decomposition temperature of the organic oxygen compound in order to prevent a pre-reaction of the mixture.

The method of the present invention utilizes heat from the substrate to initiate the coating reaction. In an on-line state such as a float glass process, the substrate is formed at a very high temperature. Thus, the method of the present invention is a point in the float glass process at which the substrate temperature is lowered but remains above the temperature at which the coating is formed (preferably after the glass ribbon has substantially finished drawing, i.e., 750° C. (1380° F.) or less). can be applied in Off-line applications of the present invention require heating the substrate to a temperature above the decomposition temperature of the ester.

In practicing the method of the present invention in a float glass process, a preferred point of application is within the float bath. The temperature range at the point for applying the coating is about 590° C. to 715° C. (1100° F. to 1320° F.). Temperature is an important working factor as it affects the concentration of organic compounds utilized in the precursor gas mixture. The temperature of the substrate in the float bath is relatively stable, so there is little change at the point of application. In Examples 6 and 7 using ethyl ester, the preferred substrate temperature range is 590° C. to 680° C. (1100° F. to 1250° F.).

The heat from the substrate raises the temperature of the precursor gas mixture above the temperature required to produce the coating (and above the pyrolysis temperature of the ester when the ester is used in an organic compound). The titanium oxide deposition reaction can be initiated by decomposition of organic oxygen compounds. When titanium tetrachloride is used in combination with an ester having an alkyl group having ? hydrogen, a titanium oxide coating is formed on the substrate with a decomposition rate ten times higher than that of known coating methods. In an on-line application with a float glass ribbon process, the ribbon passes under the gas distributor beam at a relatively high speed. The titanium oxide coating is deposited on the float glass ribbon as the ribbon passes under the coater.

The present inventors propose the following theory with respect to the chemical reactions that may occur when using esters having an alkyl group with β hydrogen. However, the inventors do not wish to limit the present invention to only these possible descriptions, but only to help understand the results of the method of the present invention.

We propose that when the ester is cleaved, the carbon-hydrogen compound is broken on one of the β hydrogens, and the hydrogen is transferred to the carbonyl group which removes the alkene to form the carboxylic acid. The hydrolysis reaction takes place simultaneously between the metal tetrachloride and the carboxylic acid to produce a metal oxide coating on the substrate.

In general, the finished article produced according to the present invention comprises a substrate having a titanium oxide coating. The coating may be applied directly to the substrate or as a plurality of coating layers on the substrate. The deposition rate of the metal oxide coating is affected by the deposition rate of the organic oxygen compound. At a constant reaction temperature, different organic oxygen compounds will give different coating growth rates because of the difference with the decomposition temperature. Thus, the desired titanium oxide coating growth rate for a given system is selected by matching the specific organic oxygen compound to the substrate temperature and the precursor gas mixture temperature at the point of application.

The deposition rate of the titanium oxide coating of the present invention can be ten times higher than the deposition rate in known deposition methods. The process of the present invention allows deposition rates of 130 Angstroms per second or greater, with some deposition rates preferably measured at 300 Angstroms per second or greater. A higher deposition rate of titanium oxide results in a coating having a refractive index greater than 2.4.

In addition to being able to achieve high coating rates, an additional advantage of the present invention is the use of inexpensive metal precursor compounds, especially when the precursor gas mixture is directed onto the substrate under good laminar flow conditions (of metal tetrachloride). ) can achieve high conversion efficiency.

In the present invention, the oxide coating obtained hardly contains residual carbon from the decomposition of organic oxygen compounds, especially when esters are used. Carbon is an undesirable by-product of the coating reactants because high levels of carbon in deposition coatings create absorption problems for the coating. A consideration in the use of organic oxygen compounds in the coating precursor gas mixture is that decomposition results in carbon levels that adversely affect the absorption properties of the finished glass. It is indicated that the carbon content in the coating obtained from the process of the present invention is less than 4 atomic percent of carbon. This low level of carbon will not sufficiently affect the absorption properties of the coating.

The forms of the present invention shown and described herein may be taken identically to the illustrated embodiments, and various changes in process, as well as various changes in shape, size and arrangement of parts may be reconfigured without departing from the spirit of the present invention. It must be understood that there is