Solar control coated substrate with high reflectance

Details Solar control coated substrate with high reflectance Solar control coated substrate with high reflectance

1999-11-22

2002-05-14

Jones, Deborah (Department: 1775)

Stock material or miscellaneous articles

Composite

Of quartz or glass

C065S017100, C065S060100

Reexamination Certificate

active

06387514

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a solar control coated substrate with high-reflectance and to a process for making such a coated substrate.
2. Description of the Related Art
Transparent solar control panels have become much in demand for use as exterior glazing for buildings. In addition to having aesthetic appeal they offer advantages in providing protection against solar radiation and its dazzling effects, giving occupants of the building a screen against overheating and glare.
The panels comprise at least one sheet of a transparent substrate material, typically soda-lime glass, carrying a coating to provide the specific properties required. The solar control requirement is that the panel shall not pass too great a proportion of total incident solar radiation, thereby resisting overheating of the building interior. The transmission of total incident solar radiation may be expressed in terms of the “solar factor” (FS). As used herein, the term “solar factor” means the sum of the total energy directly transmitted and the energy which is absorbed and re-radiated on the side away from the energy source, as a proportion of the total radiant energy incident on the coated substrate.
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 high levels of reflection, while retaining a low solar factor.
Properties of the coated substrate discussed herein are based on the standard definitions of the International Commission on Illumination—Commission Internationale de l'Eclairge (“CIE”).
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 “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).
The “purity” (p) of the colour of the substrate refers to the excitation purity in transmission or reflection measured with Illuminant C. It is specified according to a linear scale on which a defined white light source has a purity of zero and the pure colour has a purity of 100%. Illuminant C represents average daylight having a colour temperature of 6700° K.
The term “refractive index” (n) is defined in the CIE International Lighting Vocabulary, 1987, page 138.
The “dominant wavelength” (&lgr;
D
) is the peak wavelength in the range transmitted or reflected by the coated substrate.
A number of techniques are known for forming coatings on a vitreous substrate, including pyrolysis. Pyrolysis generally has the advantage of producing a hard coating, precluding the need for a protective layer. The coatings formed by pyrolysis have durable abrasive- 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.
A wide variety of coating materials have been proposed for modifying the optical properties of glazing panels. Tin oxide (SnO
2
) has been widely used, often in combination with other materials such as other metal oxides.
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 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.
The use of a tin oxide coating with a small proportion of antimony oxide has been found to offer several advantageous combinations of optical 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%.
It is an object of the present invention to provide a pyrolytically formed coated substrate which imparts solar screening properties and a high reflectance.
SUMMARY OF THE INVENTION
We have discovered that this and other useful objectives can be achieved by including certain defined additives when applying to a substrate a pyrolytic coating comprising tin and antimony oxides.
Thus, according to a first aspect of the present invention, there is provided a transparent substrate carrying a pyrolytically-formed coating layer containing oxides of tin and antimony in a Sb/Sn molar ratio of from 0.01 to 0.5, characterised in that the coating layer further contains an additive comprising one or more of aluminium, chromium, cobalt, iron, manganese, magnesium, nickel, vanadium, zinc and zirconium and is free from fluorine, whereby the so-coated substrate has a reflectance (RL) of at least 10%.
The invention further provides a method of forming a transparent coated substrate comprising the pyrolytic deposition from a reactant mixture onto the substrate of a coating layer containing tin oxide and antimony in a Sb/Sn molar ratio from 0.01 to 0.5, said reactant mixture comprising a source of tin and a source of antimony, characterised in that the reactant mixture further contains an additive comprising one or more of aluminium, chromium, cobalt, iron, manganese, magnesium, nickel, vanadium, zinc and zirconium and is free from fluorine, whereby the so-coated substrate has a reflectance (RL) of at least 10%.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
It has been found that a coating of oxides of tin and antimony modified by an additive as described above (referred to herein as a “modified tin oxide/antimony coating”) retains the anti-solar properties of the coating without the additive but also can display a much higher level of reflectance.
A coated substrate according to the invention may be employed as a single-sheet glazing panel or alternatively in a multiple glazed or laminated so panel assembly. In a multiple glazing or laminated assembly it is preferred that just one of the constituent sheets carries 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.
Because coatings produced by pyrolysis generally have a greater mechanical resistance than coatings produced by other methods the choice of location of the coating can be made according to the obtained properties of the panel rather than for reasons of protecting the coated surface against exposure to wear or corrosion.
Coated substrate sheets according to the invention preferably have a low solar factor of around 70% or less, more preferably at most 65%. In the case of multiple glazing, locating the coating on the outer face, i.e. towards the energy source, generally improves the solar factor over that achieved with the coating facing away from the energy source.
The Sb/Sn molar ratio in the coating layer is preferably at least 0.03, most preferably at least 0.05. This assists in ensuring a high level of absorption. On the other ha

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