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Coated substrate with high reflectanceRelated Patent Categories: Stock Material Or Miscellaneous Articles, Composite (nonstructural Laminate), Of Quartz Or Glass, Next To Metal Or Compound ThereofCoated substrate with high reflectance description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070190339, Coated substrate with high reflectance. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] The present invention relates to a coated substrate with relatively high reflectance and photocatalytic properties. It is especially concerned with transparent glass substrates bearing a coating comprising a main layer of oxides of tin, (eventually doped with antimony and/or fluorine) and an outer layer mainly of titanium oxide and with the use of such substrates in exterior glazing panels for buildings or for the automotive industry. [0002] Although architects seeking glazing panels for use in buildings have traditionally tended to favour panels with low levels of reflection, a changing perception of the aesthetic appeal has led to increasing demands for panels with higher levels of reflection but without the glare as viewed from outside which is associated with very high levels of reflection. The panels may also be required to have other qualities such as providing protection for occupants of the building against solar radiation and the associated overheating (solar screening properties). [0003] There is also increasing search to provide glazing with additional functions such as self-cleaning properties and hydrophilic properties. Some materials called "photocatalytic" and based on particular metal oxides are known for their ability to degrade contamination upon exciting radiations, in particular UV radiations. [0004] The panels comprise at least one sheet of a transparent substrate material, typically soda-lime glass, with a thin coating on one or more of the sheet faces to modify, amongst other, the opto-energetic and physico-chemical properties of the sheet and the panel as a whole. A huge variety of prior proposals have been made for the coating, according to the specific properties sought. The coating may comprise a stack of several discrete layers chosen with appropriate compositions and thicknesses to complement their respective effects. A persistent problem in choosing the respective layers is that a layer adopted for one purpose may adversely change the effect of other layers. [0005] Tin oxide (SnO.sub.2) has been widely used as a coating material, often in combination with other metal oxides. Coatings comprising tin oxide with a small proportion of antimony oxide have proved especially attractive for anti-solar purposes. [0006] Our GB patent 1455148 teaches a method for pyrolytically forming a coating of one or more oxides (e.g. ZrO.sub.2, SnO.sub.2, Sb.sub.2O.sub.3, TiO.sub.2, Co.sub.3O.sub.4, Cr.sub.2O.sub.3, SiO.sub.2) on a substrate, primarily by spraying compounds of a metal or silicon, so as to modify the light transmission and/or light reflection of the substrate. Our GB patent 2078213, which relates to a method for pyrolytically forming a coating by two separate sprays to achieve high rates of coating build-up, discloses tin oxide coatings doped with fluorine or antimony. Our GB patent 2200139 relates to forming a pyrolytic tin oxide coating from a precursor containing at least two additives such as oxidising agents, sources of fluorine and sources of metal. [0007] The use of a tin oxide coating with a small proportion of antimony oxide has been found to offer several advantageous combinations of optical and energy properties. Our GB patent applications 2302101 ('101) and 2302102 ('102) describe anti-solar glazing panels comprising a pyrolytic coating layer of oxides of tin and antimony in which the Sb/Sn molar ratio is from 0.01 to 0.5. The '101 coating is applied by liquid spray and has a thickness of at least 400 nm, a luminous transmittance of less than 35% and a selectivity of at least 1.3. The '102 coating is applied by chemical vapour deposition (CVD) and has a solar factor below 70%. [0008] The use of pyrolysis to form a coating on a substrate generally has the advantage of producing a hard coating with durable abrasion-resistant and corrosion-resistant properties. It is believed that this is due in particular to the fact the process involves deposition of coating material on to a substrate which is hot. Pyrolysis is also generally cheaper than alternative coating processes such as sputtering, particularly in terms of the investment in plant. [0009] Properties of the coated substrate discussed herein are based on the standard definitions of the International Commission on Illumination--Commission Internationale de l'Eclairage ("CIE"). The illuminant for the tests was illuminant C, which represents average daylight having a colour temperature of 6700 K and is especially useful for evaluating the optical properties of glass intended for use in buildings. [0010] The "luminous transmittance" (TL) is the luminous flux transmitted through a substrate as a percentage of the incident luminous flux. [0011] The "luminous reflectance" (RL) is the luminous flux reflected from a substrate as a percentage of the incident luminous flux. [0012] The "purity" (p) of the colour of the substrate refers to the excitation purity in transmission or reflection. [0013] The "dominant wavelength" (.lamda..sub.D) is the peak wavelength in the transmitted or reflected range. [0014] The "solar factor" (FS), referring to the transmission of total incident solar radiation through the coated substrate, is the sum of the total energy directly transmitted (TE) and the energy which is absorbed and re-radiated on the side of the coated substrate away from the energy source, as a proportion of the total incident radiant energy. [0015] The "selectivity" of a coated substrate for use in a building glazing panel is the ratio of the luminous transmittance to the solar factor (TL/FS). [0016] It is an object of the present invention to provide a pyrolytically formed coating on a substrate to impart self-cleaning properties possibly combined with solar screening properties and a relatively high reflectance to the substrate. [0017] We have discovered that this and other useful objectives can be achieved by depositing a coating stack comprising a defined overcoat layer on a main layer comprising mainly tin oxide. [0018] According to the invention there is provided a transparent substrate carrying a coating stack comprising a pyrolytically-formed main layer containing oxides of tin possibly doped with antimony and/or fluorine, characterised in that the stack includes an outer layer comprising titanium oxide and having a refractive index in the range 2.0 to 2.8, whereby the so-coated substrate has a reflectance (RL) of more than 10%. [0019] The presence of the outer layer creates an increase of the luminous reflectance (RL) of the coated substrate, increasing the reflectance from the coated side, from less than 10% to more than 10%. According to the present invention, the claimed substrate advantageously has a reflectance greater than 14% but lower than 30%, and preferably lower than 25%. Moreover these increases are achieved without taking the other optical properties of the substrate beyond acceptable limits. The outer layer is also beneficial in further improving the abrasion and corrosion resistance of the coating. [0020] Furthermore, it has been discovered that the presence of the TiO.sub.2 outer layer according to the invention induces photocatalytic properties to the coated surface. In particular, the photocatalytic activity is greater than 2.10.sup.-3 cm.sup.-1 min.sup.-1 and preferably greater than 5.10.sup.-3 cm.sup.-1 min.sup.-1. One of the more common method for measuring this activity is based on the degradation of stearic acid. According to this method, the samples are dipped in a solution of stearic acid in methylic alcohol at room temperature. Then the samples are irradiated by ultraviolet radiations of a frequency of 340 nm in a "QUV Accelerated Weatherin Tester" for 5 minutes with a power of 40 watt/m.sup.2 with lamps of the type UVA 340. The FTIR (Fourrier Transform Infrared Spectrophotometer) spectra are obtained every 5 minutes until cumulative time reaches 20 minutes. The slope of the linear regression of the curve "integrated intensity versus UV irradiation time" gives the photocatalytic activity. [0021] It has also been discovered that the presence of the TiO2 layer according to the invention induces hydrophilic properties after UV irradiations. In particular the contact angle with water after 3 hours of irradiation at the temperature of 40.degree. C. in a "QUV Accelerated Weathering Tester" with lamps of the type UVA 340, is lower than 10.degree., preferably lower than 5.degree.. [0022] Although the invention is described herein primarily with reference to glazing panels for buildings, panels according to the invention are suitable for other applications such as vehicle windows, in particular vehicle sunroofs. [0023] According to some embodiment of the present invention, the outer layer may contain, in addition to the titanium oxide, an oxide of one or more of nickel, tin, zinc and zirconium. [0024] It has been discovered that when the outer coating contains oxide of titanium together with oxide of tin, this confers to the coating a better abrasion and chemical resistance. Such enhancement of the abrasion and chemical resistance is principally important when the coating is applied by liquid pyrolisis. Such a coating contains most preferably at least 50% by volume of tin oxide and at least 30% by volume of titanium oxide. Continue reading about Coated substrate with high reflectance... Full patent description for Coated substrate with high reflectance Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Coated substrate with high reflectance patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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