Stock material or miscellaneous articles – Composite – Of quartz or glass
Reexamination Certificate
1999-11-22
2002-07-23
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Composite
Of quartz or glass
C428S426000
Reexamination Certificate
active
06423414
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a coated substrate with high reflectance. It is especially concerned with transparent glass substrates bearing a coating of oxides of tin and antimony and with the use of such substrates in exterior glazing panels for buildings.
2. Description of the Related Arts
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).
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 the optical and physical 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.
Tin oxide (SnO
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.
Our GB patent 1455148 teaches a method for pyrolytically forming a coating of one or more oxides (e.g. ZrO
2
, SnO
2
, Sb
2
O
3
, TiO
2
, Co
3
O
4
, Cr
2
O
3
, SiO
2
) on a substrate, primarily by spraying compounds of a metal or silicon, so as to modify the light transmission and/or fight 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.
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 001 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%.
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 is 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.
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 rests 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.
The “luminous transmittance” (TL) is the luminous flux transmitted through a substrate as a percentage of the incident luminous flux.
The “luminous reflectance” (RL) is the luminous flux reflected from a substrate as a percentage of the incident luminous flux.
The “purity” (p) of the colour of the substrate refers to the excitation purity in transmission or reflection.
The “dominant wavelength” (&lgr;
D
) is the peak wavelength in the transmitted or reflected range.
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.
The “selectivity” of a coated substrate for use in a building glazing panel is the ratio of the luminous transmittance to the solar factor it is an object of the present invention to provide a pyrolytically formed coating on a substrate to impart solar screening properties and a high reflectance to the substrate.
SUMMARY OF THE INVENTION
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 tin and antimony oxides.
According to the invention there is provided a transparent substrate carrying a coating stack comprising a pyrolytically-formed main layer containing oxides of tin and antimony, characterised in that the main layer has a geometric thickness of at least 250 nm and in that the stack includes an outer reflective layer having a geometric thickness in the range 30 to 150 nm 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%.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The presence of the outer reflective creates an improvement in the luminous reflectance (RL) of the coated substrate, increasing the reflectance from less than 10% to more than 10%, and generally to at leas 15% and even to around 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.
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.
Preferably the outer reflective layer contains an oxide of one or more of nickel, tin, titanium, zinc and zirconium. These materials readily form by pyrolysis a coating with the required refractive index.
The outer reflective layer preferably comprises oxide of titanium. This gives a high luminous reflectance for a very thin coating thickness. Preferably, the coating contains oxide of titanium together with oxide of tin. This confers to the coating a better abrasion and chemical resistance. Such a coating contains most preferably at least 50% by volume of tin oxide and at least 30% by volume of titanium oxide. The preferred geometric thickness for a titanium oxide coating is in the range 45-55 nm. The preferred geometric thickness for tin/titanium oxide reflective layer is in the range 40 to 75 nm. Below 40 nm the layer may not be sufficient to modify the optical properties, especially the reflectance, of the coated product. Above 75 nm the level of luminous reflection may be unduly high and the optical effects of the overcoat will tend to mask the optical effects of the other layers in the stack. More preferably the said layer has a thickness in the range 60 to 75 nm. This range permits the attainment of good optical stability for the coating stack. Optical stability means that variations of the thickness of the layer, inherent in industrial production, do not cause significant changes of the optical properties, particularly of Hunter values a and b and purity in reflection. Optical st
Legrand Philippe
Tixhon Eric
Blackwell-Rudasill Gwendolyn
Glaverbel
Jones Deborah
Piper Rudnick LLP
Schneider Jerold I.
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