Coatings on glass

Description: TECHNICAL FIELD [Detailed description of the invention]

The present invention relates to a coating, particularly a method of forming a lower layer that is useful for suppressing iridescence and protecting the alkali metal ion sensitive upper layer from the movement of alkali metal ions from the underlying glass surface. UK Pat. No. 2,031,756 relates to a thin transparent infrared reflective semiconductor coating, which is useful and conductive to improve the insulation of windows. This coating is, for example, ice or condensation from windows. It is useful as a resistance heater for removing liquid. According to British Patent No. 2,031,756, the use of such coatings has been limited in order for the coating to exhibit an iridescence color, especially in reflected light. Such iridescence effects are widely considered aesthetically unsatisfactory, and changes in iridescence color caused by slight variations in coating thickness exacerbate the problem. UK Pat. No. 2,031,756 proposes to solve the problem of iridescence by depositing an appropriate underlayer that reduces iridescence under the semiconductor coating, with a refractive index of 1.7-1.8 as the preferred underlayer. , A layer with a thickness of 64 to 80 nm is recommended. According to British Patent No. 2,031,756, the lower layer co-deposits a component mixture calculated to give the required index of refraction, for example a mixture of 84 ± 3% silicon nitride called silicon oxynitride and the rest of the silica ( It can be generated by making it codepositing). Such a silicon oxynatride film is a silicon source (eg SiH) on hot glass at a temperature of 500-600 ° C.₄, (CH₃)₂SiH₂, (C₂H₅)₂, (CH₃)₄Si, SiCl₄, SiBr₄), Oxygen source (eg O₂, H₂O, N₂O,) and nitrogen sources (eg N)₂H₄, NH₃, HN₃, CH₃NHNH₂, (CH₃)₂NNH₂, Or both oxygen and nitrogen sources (eg NO, NH₂OH, N₂H₄H₂It can be formed from O) by a chemical vapor deposition method. Appropriate underlayers that reduce iridescence are required, but the underlayers proposed in UK Pat. No. 2,031,756 have not been used extensively commercially. This is because there are various difficulties in producing a lower layer having sufficient quality and thickness by a known method, and a particularly long vapor deposition time is required. British Patent Publication No. 2,163,146 relates to forming a barrier coating on the glass surface to prevent the transfer of alkali metal ions from the glass into an alkali metal ion sensitive upper layer, such as indium chinoxide. This UK Patent Publication has good light transmittance and excellent barrier properties by thermally decomposing silane on the glass surface at about 600 ° C or higher in the presence of a gaseous compound which is an electron donor. It is described to manufacture a barrier coating. It was found that the presence of the electron donor compound causes oxygen to be mixed from the glass into the coating, resulting in the formation of a transparent barrier coating with a thickness of 50 nm or less on the glass surface. The electron donor compound used in the method described in British Patent Publication No. 2,163,146 is a compound containing an electron bonded state or a lone electron pair that can be donated in the electronic structure of a suitable acceptor molecule. is there. Using the electron donor compound, it was found that oxygen from the glass combined with silicon from the silane to form a clear barrier coating on the glass. Although this mechanism has not been elucidated, it is possible that the electron donor compound is adsorbed on the glass surface. As the electron donor compound, a compound that does not contain an oxygen atom, such as ethylene, or a compound that contains some oxygen atoms but is generally considered to be reducing, such as carbon monoxide and alcohols, is used. Since the clear barrier coating can be formed in the absence of free oxygen and compounds commonly considered oxidants, the barrier coating is on a float glass ribbon, on the molten metal on which it is formed. Can be adhered as the metal moves forward, and there is no great danger of the molten metal being oxidized. The use of oxygen atom-free electron donor compounds reduces the risk that the silane will oxidize before reaching the glass surface and that the reactant gas will oxidize the molten metal that supports the glass ribbon. Unfortunately, there is only insufficient oxygen available from the glass to form a relatively thick underlayer that reduces iridescence as recommended in UK Pat. No. 2,031,756. Relatively thick layers can be made by using electron donor compounds containing oxygen atoms, such as carbon dioxide, but the combined use of silane and carbon dioxide produces a thin coating with poor durability, or Attempts to increase the thickness of the coating have been found to produce white, hazy deposits. Moreover, in the case of attempting to produce a barrier coating with extremely high transparency (for example, the light transmittance is not more than 2% smaller than that of the base glass) in combination with silane and ethylene in accordance with British Patent Publication No. 2,163,146, The barrier properties of the coating have been found to be inadequate in some application areas. There is a demand for methods suitable for commercial operation in float glass production lines that can produce lower layers that reduce iridescence as recommended in UK Pat. No. 2,031,756. There is also a demand for a method suitable for commercial operation in float glass production lines, which can produce a coating that is effective as a barrier to the movement of alkali metal ions from the glass. In the present invention, these demands are met by applying a mixed gas of silane, ethylene-based unsaturated hydrocarbons and carbon dioxide to the surface of hot glass to deposit a coating containing silicon and oxygen on the surface of the glass. I found that I could do it. In the present invention, a mixed gas of silane, an unsaturated hydrocarbon compound and carbon dioxide is applied to the surface of hot glass at a temperature of 600 to 750 ° C to deposit a transparent layer containing silicon and oxygen on the glass surface. Provided is a method for forming a useful underlayer on a glass surface. The lower layer produced by the method of the present invention acts as a barrier to the movement of alkali metal ions from the glass, and the upper layer sensitive to the movement of alkali metal ions from the glass is directly or indirectly adhered onto the lower layer. It is useful for. According to another aspect of the invention, the method of the invention further comprises the step of depositing a layer sensitive to the movement of alkali metal ions from the glass onto the underlying layer. To produce a coating with low iridescence that has at least one of infrared reflectivity and conductivity, a layer with at least one of infrared reflectivity and conductivity is deposited on top of the underlying layer. Thus, in yet another aspect of the invention, the method of the invention further comprises the step of depositing a layer having at least one of infrared reflectivity and conductivity over the underlayer. This upper layer can be made from a semiconductor metal oxide, such as tin-doped tin oxide or tin oxide, especially fluorine-doped tin oxide. Both the lower layer and the upper layer can be adhered to the float glass in the float glass production line. In this case, the underlying layer is from a solid (eg, as described in UK Pat. No. 2,156,386) and from a liquid (eg, as described in UK Pat. No. 1,523,991). Alternatively, it can be a fluorine-doped tin oxide deposited by thermal decomposition from a vapor source (eg, gaseous stannic chloride in the presence of steam and hydrogen fluoride). This decomposition can be performed at the entrance to the slow cooling machine. When the coating needs to be used as an infrared reflective coating, the thickness of the infrared reflective layer is usually 200-500 nm. A thicker thickness, for example 1000 nm or less, can be used if desired, but this is usually unnecessary in terms of lower iridescence reduction. When the coating needs to be currented, for example in a resistance heater or liquid crystal disc play, the thickness of the coating depends on the required conductivity, but is typically 100-1000 nm. As a silane, monosilane (SiH)₄) Is preferred, but other gaseous substituted or unsubstituted silanes, eg (CH), are desired.₃)₂SiH₂And disilane Si₂H₆Can be used. As the unsaturated hydrocarbon, an ethylene-based unsaturated hydrocarbon compound, an acetylene-based unsaturated compound (for example, acetylene) or an aromatic compound (for example, toluene) can be used, but it is usually gaseous under ambient conditions. It is most convenient to use unsaturated hydrocarbons. As the unsaturated hydrocarbon, an olefin is preferable, and an olefin having 2 to 4 carbon atoms is preferable. Ethylene is particularly preferable. The proportion of the component gas present in the mixed gas and the flow rate of the mixed gas on the glass can be adjusted to provide a lower layer having the desired thickness and refractive index. Since carbon dioxide acts as an oxygen source, the use of oxygen from the glass surface is limited, but it is easy to achieve a transparent layer with a thickness of 80 nm or less as taught by UK Pat. No. 2,031,756. Can be done. Moreover, by appropriately adjusting the relative ratio of the existing component gases, the lower layer of the refractive index of 1.7 to 1.8 taught by British Patent No. 2,031,756 can be achieved. In a suitable aspect of the present invention, a lower layer having a thickness of 60 to 80 nm and a refractive index of 1.6 to 1.8 is deposited. In another example of the present invention, the proportion of the component gas present in the mixed gas used to deposit the lower layer and the flow rate of the mixed gas on the hot glass are adjusted so that the light transmittance of the glass coated with the lower layer is adjusted. An underlayer is deposited that has a thickness and refractive index within 2% of the light transmittance of the uncoated glass and serves as an effective barrier to the movement of alkali metal ions from the glass. The light transmittance of the coated glass is preferably within 1% of the light transmittance of the base glass. Here, "effective barrier" means that the lower layer is Gasura 1dm when tested by the method described here.²100 mg or less per unit, preferably 60 mg or less of Na₂It means to allow the passage of Na expressed as O. Generally, the higher the ratio of unsaturated hydrocarbons to silanes, the thinner the coating and the lower the index of refraction. Normally, operations are performed with unsaturated hydrocarbon: silane ratios of 2: 1 to 5: 1 by volume, but ratios outside this range, such as 1: 1 to 8: 1 (or larger ratios), are also used. be able to. Since unsaturated hydrocarbons are thought to act by being adsorbed on the glass surface, the more strongly unsaturated hydrocarbons are adsorbed on the glass, the more the ratio of unsaturated hydrocarbons to silanes required to achieve a given effect. Is usually smaller. The carbon dioxide to silane ratio is preferably 2: 1 to 8: 1 by volume, but ratios outside this range, such as 1: 1 to 20: 1 (or larger), can also be used. .. High ratios should only be used when operating at extremely high silane concentrations. Usually, the mixed gas contains a certain amount, for example, 10 to 90% by volume of the mixed gas, an inert carrier gas such as nitrogen gas. As the total flow rate of the mixed gas having a predetermined composition increases, the thickness of the lower layer increases as expected as a result. It was also found that the refractive index of the lower layer increased. The temperature of the glass is preferably 630 to 720 ° C. The method of the present invention acts as a barrier to the movement of alkali metal ions and facilitates online production of an iridescence-reduced lower layer with extremely high transparency to visible light. Moreover, since the reactant used does not have a strong oxidizing action, the method of the present invention can be applied to the float glass ribbon when the glass ribbon advances on the molten metal on which the float glass ribbon is formed. There is no great danger of the molten metal being oxidized. Next, an example of the present invention will be described. In the examples, the percentages are all volume% unless otherwise specified, and the gas flow rate is a value measured at about 20 ° C and 60 kPa (10 psi). The values of refractive index and thickness used for the lower layer were calculated from the magnitude and wavelength of the maximum reflectance of the lower layer by applying the thin film theory. The light transparency of the coated glass was expressed in dT. This is the difference between the light transmittance of the glass coated with the lower layer and the light transmittance of the glass not coated. The effect of the lower layer as a barrier layer on the movement of alkali metal ions was determined by the following method. 10 cm each from coated glass²The wall formed by the coated surface of the glass and the inner surface of the silicone rubber ring, which is cut out of two samples and tightened together with an annular silicone rubber ring with an inner diameter of 8.5 cm sandwiched between these samples. Form a cylindrical cell with. This cell is filled with deionized water through a hole in a silicone rubber ring, the hole is closed, and the closed cell is immersed in a hot water bath at 96 ° C for 48 hours. The solution is taken out and analyzed for sodium by flame light emission spectroscopy. Glass 1dm exposed to water in cells for sodium extraction²Na per₂Expressed as Oμg. Example 1 A 6 mm float glass ribbon that advances at a slow cooling rate of 322 m / hour supplies a mixed gas to the upper surface of the glass at a glass temperature of approximately 645 ° C as the glass ribbon advances over the float bath. By coating the lower layer. The mixed gas consisted of 11% monosilane, 23% ethylene, 23% carbon dioxide and 44% nitrogen as a carrier gas. The mixed gas was flowed in the traveling direction of the glass parallel to the glass surface under laminar flow conditions. At this time, as the device, the device described in British Patent No. 1,507,966 was modified to extend the moving path of the mixed gas on the glass surface to about 0.2 m. The mixed gas flow rate was 22 / min per 1 m of coated glass width. A transparent, substantially cloudless underlayer was formed on the glass surface, with a thickness of 76.1 nm and a refractive index of 1.77. Examples 2 and 3 The operation of Example 1 was repeated with the flow rate ratio of ethylene and carbon dioxide larger than that of Example 1. As a result, both the thickness and the refractive index of the formed layer were slightly reduced. The conditions used and the results obtained are shown in Table 1 for comparison with the corresponding results of Example 1. Examples 4-8 Using a mixed gas different from that of Example 1, the operation of Example 1 was repeated by changing the ratio of ethylene to carbon dioxide while keeping both the ratio of monosilane: ethylene + carbon dioxide and the total gas flow rate constant. It was. The conditions used and the results obtained are shown in Table 2. As a result of using large ethylene: silane ratios as in Examples 4 and 5, a very thin underlayer (less than 55 nm) was formed. When the ethylene: silane ratio was reduced and the carbon dioxide: silane ratio was increased, the thickness of the lower layer increased (Examples 6 and 7). However, as the carbon dioxide: silane ratio increased to 8: 1, the thickness of the lower layer became thinner. Examples 9 to 13 The operation of Example 1 was repeated using a mixed gas consisting of 10% monosilane, 25% ethylene, 25% carbon dioxide and 40% nitrogen, and a total flow rate different from that of Example 1. The results are shown in Table 3 (Examples 9 to 11). Both the thickness of the lower layer and the index of refraction increased with increasing total flow rate. Using the same flow rates of silane, ethylene and carbon dioxide as in Example 9, the nitrogen flow rate was increased and the operation of Example 9 was repeated. The flow rates used and the characteristics of the generated lower layer are shown in Table 3 (Examples 9, 12 and 13). It was found that as the nitrogen flow rate increased, the thickness of the lower layer became thinner, but the refractive index increased. Examples 14-19 Examples 14 to 19 were carried out in the same manner as in Example 1 to form a lower layer on 6 mm float glass under the conditions shown in Table 4. The resulting lower layer was found to have the refractive index and thickness shown in Table 4. Then, when the float glass enters the slow cooling furnace, a fluorine-doped tin oxide layer is placed on the lower layer on the float glass ribbon by a chemical vapor deposition method from a mixed gas of stannic chloride, water and hydrogen fluoride. Was deposited. The thickness of tin oxide was measured, and the color coordinates of the light reflected from the coating side of the glass (CIEI lluminant C) were measured. In the case of Examples 14 to 17, there was no lower layer. Compared with the color coordinates of the light reflected from a similar fluorine-doped tin oxide coating in the case. (The use of color coordinates to reveal colors is "The Measusment of Appearances" by Earl S. Hunter (1975) (published by John Willy and Sons). The results obtained are shown in Table 5. From Table 5, it can be seen that the action of the lower layer is to suppress the reflected color of the tin oxide layer. Examples 20-23 A mixed gas consisting of 10% silane, 20% ethylene, 30% carbon dioxide and 40% nitrogen was used, and the mixed gas was coated on a 2.1 mm glass ribbon advancing at a slow cooling rate of 1130 m / hour. The operation of Example 1 was repeated with a flow rate of 50 / min per 1 mm. The mixed gas was passed over the glass at a position where the glass temperature was about 645 ° C. The glass was coated with a layer of high transparency, and the light transmittance of this coated glass was only 1.1% less than that of the uncoated glass. The effect of the layer as a barrier to the movement of alkali is glass 1dm²90 μg of Na per₂Measured as O. The operation was repeated with different gas compositions on 6 mm and 4 mm glasses. Table 6 shows the glass temperature at the coating station, the slow cooling rate of the glass ribbon, the glass composition and flow rate used, along with the properties of the coated product. Comparing Examples 21 and 22, increasing the glass temperature, increasing the silane concentration, and reducing the ratio of ethylene and carbon dioxide to silane reduces the gas flow rate (from 55 / min / m to 22 / min / m). ), And it can be seen that the thickness of the coating formed in Example 22 is about twice that of the coating in Example 21. All of these examples showed good barrier performance, but the underlayer of Example 22 showed the highest light transmission (compared to the light transmission of uncoated glass). Examples 24 to 30 In Examples 24 to 30, butene was used as an unsaturated hydrocarbon together with silane and carbon dioxide to produce a color-suppressing lower layer and a barrier layer by the method of the present invention. These examples were carried out by the method described in Example 1, but only narrow glass strips were coated at the edges of the ribbon. The glass was 6 mm thick and was moved at a slow cooling rate of 360 m / hour and coated at a temperature of 685 ° C. The conditions used, gas composition and gas flow rate, and the characteristics of the formed lower layer are shown in Table 7. A layer that sufficiently suppresses color was generated. In Examples 25 to 27, the layer thickness was 60 nm to 80 nm, and the refractive index of the layer was 1.6 to 1.8 (in Example 24, it was extremely slightly out of these ranges). Examples 28 to 30 were carried out at a relatively low gas flow rate. As a result, a relatively thin coating having excellent barrier performance was produced, and the light transmittance of the coated glass was close to that of the uncoated glass. Comparing Examples 24-30 with earlier examples, it can be seen that a larger total gas flow rate is required to produce a coating of similar thickness. This is believed to be due, at least in part, to the methods of Examples 24-30 being performed on narrower glass strips, with large amounts of gas escaping from the sides of the coated glass strips. Examples 31-36 With a 10 x 10 cm 3 mm float glass sample stationary, the glass is heated in a quartz tube at about 650 ° C and a mixed gas of silane, carbon dioxide, unsaturated hydrocarbons and nitrogen is placed on the surface of the hot glass. It was coated in the laboratory by passing it through. The gas composition and treatment time used are shown in Table 8. Table 8 shows the measurement results of the light transmittance and barrier property of the coated product together. By using each unsaturated hydrocarbon, good barrier properties and high transparency (transparency within 1% of the transparency of uncoated glass) were achieved. Examples 37-40 The operation of Example 1 was repeated using a mixed gas composed of silane, ethylene and carbon dioxide in nitrogen, and a coating was applied to a 2 mm float glass advancing at a slow cooling rate of 1100 m / hour. The light transmittance of the glass was measured, the difference dT was obtained by comparing with the light transmittance of the uncoated glass, and the barrier performance of the glass was measured as described above. Since the thickness of the coating was so thin that it could not be measured by the above-mentioned optical method, it was measured by an argon ion etching technique. The coating conditions and the results obtained are shown in Table 9. All of Examples 37 to 40 showed the formation of a barrier layer, and the light transmittance of the coated glass was in the range of 1.5% (dT) from the uncoated glass. The final comparative example shows that the light transmittance is significantly smaller (dT = 2.3%) when carbon dioxide is not used, but the lower layer is thicker than the lower layer actually produced in Examples 38 and 40. Comparing Examples 37 and 38, when the ratio of the dopant (ethylene and carbon dioxide) to silane is increased, the thickness of the lower layer is reduced, and as a result, the light transmittance is improved, but the barrier performance is improved. It can be seen that it decreases. Comparing Examples 37 and 39, it can be seen that when the ratio of the dopant to the silane was slightly reduced, the light transmittance was reduced, but the thickness and barrier performance were not changed. In the case of Example 40 in which ethylene was significantly reduced and carbon dioxide was increased, the thickness was reduced and the light transmittance was increased, but the barrier performance was significantly reduced. In the above-described embodiment, the lower layer having a desired thickness and refractive index is obtained by adjusting the ratio of the component gas present in the mixed gas used in the method of the present invention and adjusting the flow rate of the mixed gas on the surface of the hot glass. Indicates that it can be generated. Therefore, the method of the present invention is not only useful for producing the color-suppressing underlayers of the types described in UK Pat. No. 2,031,756, but is also a color-suppressing underlayer known in the art. 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