Title of Invention	SILVER-FREE LOW-E SOLAR CONTROL COATING
Abstract	A multi-layer, low-emissivity, solar control article comprises a dielectric substrate, a first dielectric metal oxide layer deposited on the substrate, a first highly conductive, silver- free metal oxide layer deposited on the first dielectric metal oxide, and a second dielectric metal oxide deposited on the first highly conductive, silver-free metal oxide layer. The aforementioned coating layer sequence may be repeated as necessary to achieve the desired properties. An iridescence suppressing interlayer may, optionally, be utilized in connection with the low-emissivity, solar control coating.

Title of Invention

SILVER-FREE LOW-E SOLAR CONTROL COATING

Abstract

A multi-layer, low-emissivity, solar control article comprises a dielectric substrate, a first dielectric metal oxide layer deposited on the substrate, a first highly conductive, silver- free metal oxide layer deposited on the first dielectric metal oxide, and a second dielectric metal oxide deposited on the first highly conductive, silver-free metal oxide layer. The aforementioned coating layer sequence may be repeated as necessary to achieve the desired properties. An iridescence suppressing interlayer may, optionally, be utilized in connection with the low-emissivity, solar control coating.

Full Text	SILVER-FREE LOW-E SOLAR CONTROL COATING BACKGROUND OF THE INVENTION Conventionally, solar control, low-e films made by various deposition processes, e.g., sputtering, have consisted of one or more layers of a conductive metal, such as silver, sandwiched between layers of dielectric materials. The dielectric materials isolate the conductive metal layer(s) and prevent, or at least minimize, undesirable oxidation of the conductive metal. While such film stacks, in various configurations, have been found to provide coatings exhibiting good low-emissivity and solar control properties, they are also known to have poor chemical and mechanical durability, thus increasing the risk of damage to the coating from exposure to atmospheric humidity or scratching from normal handling activities. Improvement of the physical and chemical durability of silver-containing films has been attempted by others. These effects include varying the composition of the dielectric layers, dividing individual dielectric layers into sub- layers of different dielectric materials, alloying the silver with other metals, and various methods of modifying so-called "sacrificial" layers between the silver and dielectric layers. Thus, those skilled in the art of thin film design and coated product manufacturing have continued to search for a thin film structure which has good emissivity and solar control properties, but which is superior in both chemical and mechanical durability. SUMMARY OF THE INVENTION The present invention comprises a low-emissivity, solar control coating deposited on a dielectric substrate, the coating comprising a first dielectric metal oxide layer deposited on the dielectric substrate; a first highly conductive, silver-free metal oxide layer deposited on the first dielectric metal oxide, the highly conductive metal oxide having an electrical conductivity greater than 10,000 ohm-1 cm-1; and a second dielectric metal oxide layer deposited on the first highly conductive, silver-free metal oxide layer. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention utilizes the well-known concept of induced transmission filters to form a thin film coating structure comprising one or more highly electrically conductive metal oxide layers, rather than onductive metal layers. The present structure further comprises a layer of a dielectric metal oxide on either side of the highly conductive metal oxide layer. This sequence of layers may be repeated as necessary to achieve the emissivity and solar control properties desired. The choice of the highly conductive metal oxides and the dielectric metal oxides, as well as the thickness of the layers in which such oxides are deposited, are important to achieving the sought-after combination of low- emissivity, high visible transmission, high IR reflection/absorption, mechanical durability, chemical stability, and in particular, good solar control. In this connection, dielectric metal oxides useful for the present invention include, oxides of tin, titanium, zinc, bismuth, and alloys of such oxides. Nitrides of silicon may also be useful for the present invention. Layer thicknesses of such dielectric metal oxides suitable for the invention are in the range of 200 to 400A, preferably, 250-350A. The highly conductive metal oxides useful for the present invention include simple oxides such as oxides of rhenium, ruthenium, iridium, chromium and molybdenum perovskite type mixed oxides, including CaRuO3, SrRuO3, SrVO3, SrCrO3, SrFeO3, SrTiO3, SrMoO3, CaVO3, LaTiO3, Sr2VMoO6; spinel type mixed oxides, such as NiCo2O4; heavily doped tungsten oxide bronzes, such as NaxWO3 (where x+>0.40). Layer thicknesses of the aforementioned highly conductive metal oxides suitable for the invention are less than 1000A, preferably less than 500A. Table 1 shows some exemplary electrical resistivity and electrical conductivity values for commonly used highly conductive metals, i.e., Ag and Cu, as well as highly conductive metal oxides suitable for use in connection with the present invention, i.e., ReO3, Na0.8WO3 and RuO2. Although the conductivities of the exemplary highly conductive metal oxides are substantially lower than the conductivities of Ag and Cu, the metal oxides shown in Table 1 have been found to perform satisfactorily from an electrical conductivity viewpoint, and to display the other desired properties discussed herein which make such oxides superior to Ag and Cu for the applications of the present invention. More specifically, highly conductive metal oxides having a conductivity > 10,000 ohm-1 cm-1, and preferably a conductivity >50,000 ohm-1 cm-1, are suitable for the present invention. The conductivities of the highly conductive metal oxides are clearly superior to conventional doped metal oxides, such as fluorine-doped tin oxide and tin-doped indium oxide, as can be seen in Table 1. The films formed according to the present invention will, generally, have stoichometry corresponding to the stoichometric oxide of the corresponding metal, e.g., SnO2, TiO2, etc., however, films which are slightly oxygen deficient may also be produced, and may be useful. Thin film structures utilizing a combination of the above-described dielectric and highly conductive metal oxides in a three-layer sequence have been found to exhibit an emissivity of transmittance >70%, and a total solar energy transmittance of Preferably, the thin film structure will have a total solar energy transmittance 45%. The chemical durability of the above-described thin film structures is significantly improved over conventional structures as, without wishing to be bound by any theory, the inventors believe the highly conductive metal oxide replacing the silver significantly reduces reaction of the film with ambient humidity, atmospheric contaminants, and the like. The inventors believe that replacement of the silver with a less reactive metal oxide improves the chemical stability of the film stack. Similarly, the inventors believe that the mechanical durability of the thin film structure will be improved by replacing the ductile, malleable silver layer with a rigid, stiff metal oxide layer. The thin film or coating of the present invention may be deposited on any suitable dielectric substrate material. A transparent glass, made by the float glass process, particularly a soda-lime-silica glass has been found to be suitable. Some tinted glasses may also be suitable. The films of the present invention may be deposited on the aforementioned substrates by any suitable method, including various types of sputtering or CVD techniques. In particular, an on-line deposition process occurring during the float-glass manufacturing process is considered suitable. A particularly preferred on-line deposition process for the present invention is atmospheric pressure chemical vapor deposition. An apparatus, useful for the on-line production of the coated glass article of the present invention, generally comprises a float section, a lehr, and a cooling section. The float section has a bottom which contains a molten tin bath, a roof, sidewalls, and end walls, which together form a seal such that there is provided an enclosed zone, wherein a non-oxidizing atmosphere is maintained, as hereinafter described in greater detail, to prevent oxidation of the tin bath. During operation of the apparatus, molten glass is cast onto a hearth, and flows therefrom under a metering wall, then downwardly onto the surface of the tin bath, from which it is removed by lift-out rolls and conveyed through the lehr, and thereafter through the cooling section. A non-oxidizing atmosphere is maintained in the float section by introducing a suitable gas, such as for example one composed of 99 percent by volume nitrogen and 1 percent by volume hydrogen, into where the coating WE CLAIM 1. A low-emissivity, solar control coating to be deposited on a dielectric substrate, the coating comprising: a first dielectric layer deposited over the dielectric substrate; a first highly conductive silver-free metal oxide layer deposited over the first dielectric layer and having an electrical conductivity greater than 10,000 ohm-1 cm-1; a second dielectric layer deposited over the highly conductive, silver-free metal oxide layer; and wherein each dielectric layer is formed of a metal oxide chosen from the group consisting of oxides of tin, titanium, zinc, bismuth and alloys thereof, or a nitride of silicon. 2. The solar control coating defined in claim 1, wherein the first highly conductive metal oxide has an electrical conductivity greater than 50,000 ohm-1 cm-1. 3. The solar control coating defined in claim 1, wherein the dielectric material comprises Si3N4. 4. The solar control coating defined in claim 1, wherein the highly conductive silver-free metal oxide is chosen from the group consisting of oxides of rhenium, ruthenium, iridium, chromium, molybdenum and mixed oxides, CaRuO3, SrRuO3, SrVO3, SrCrO3, SrFeO3, SrTiO3, SrMoO3, LaTiO3, Sr2VMoO6, NiCo2O4, and NaxWO3. 5. The solar control coating defined in claim 1, wherein a second highly conductive silver-free metal oxide layer is deposited over the second dielectric metal oxide layer, and a third dielectric metal oxide layer is deposited over the second highly conductive silver-free metal oxide layer. 6. A coated glass article comprising: a dielectric substrate; a first dielectric metal oxide layer deposited on the dielectric substrate; a first highly conductive silver free metal oxide layer deposited on the first dielectric metal oxide the highly conductive metal oxide so deposited having an electrical conductivity greater than 10,000 ohm-1 cm-1; and a second dielectric metal oxide layer deposited on the conductive, silver- free metal oxide layer; wherein the coated glass article has an emissivity of 0.3, a visible light transmittance >70%, and a total solar energy transmittance of 7. The coated glass article defined in claim 6, wherein the emissivity is 8. The coated glass article defined in claim 6, wherein: the first dielectric metal oxide layer comprises TiO2; the first highly conductive silver free metal oxide layer comprises ReO3; and the second dielectric metal oxide layer comprises TiO2. 9. The coated glass article defined in claim 6, wherein: the first dielectric metal oxide layer comprises SnO2; the first highly conductive silver free metal oxide layer comprises RuO2; and the second dielectric metal oxide layer comprises SnO2. 10. The coated glass article defined in claim 6, wherein: the first dielectric metal oxide layer comprises TiO2; the first highly conductive silver free metal oxide layer comprises RuO2; and the second dielectric metal oxide layer comprises TiO2. ABSTRACT Title : SILVER-FREE LOW-E SOLAR CONTROL COATING A multi-layer, low-emissivity, solar control article comprises a dielectric substrate, a first dielectric metal oxide layer deposited on the substrate, a first highly conductive, silver- free metal oxide layer deposited on the first dielectric metal oxide, and a second dielectric metal oxide deposited on the first highly conductive, silver-free metal oxide layer. The aforementioned coating layer sequence may be repeated as necessary to achieve the desired properties. An iridescence suppressing interlayer may, optionally, be utilized in connection with the low-emissivity, solar control coating.

Full Text

SILVER-FREE LOW-E SOLAR CONTROL COATING
BACKGROUND OF THE INVENTION
Conventionally, solar control, low-e films made by various deposition
processes, e.g., sputtering, have consisted of one or more layers of a
conductive metal, such as silver, sandwiched between layers of dielectric
materials. The dielectric materials isolate the conductive metal layer(s) and
prevent, or at least minimize, undesirable oxidation of the conductive metal.
While such film stacks, in various configurations, have been found to provide
coatings exhibiting good low-emissivity and solar control properties, they are
also known to have poor chemical and mechanical durability, thus increasing
the risk of damage to the coating from exposure to atmospheric humidity or
scratching from normal handling activities.
Improvement of the physical and chemical durability of silver-containing
films has been attempted by others. These effects include varying the
composition of the dielectric layers, dividing individual dielectric layers into sub-
layers of different dielectric materials, alloying the silver with other metals, and
various methods of modifying so-called "sacrificial" layers between the silver
and dielectric layers.
Thus, those skilled in the art of thin film design and coated product
manufacturing have continued to search for a thin film structure which has good
emissivity and solar control properties, but which is superior in both chemical
and mechanical durability.
SUMMARY OF THE INVENTION
The present invention comprises a low-emissivity, solar control coating
deposited on a dielectric substrate, the coating comprising a first dielectric
metal oxide layer deposited on the dielectric substrate; a first highly conductive,
silver-free metal oxide layer deposited on the first dielectric metal oxide, the
highly conductive metal oxide having an electrical conductivity greater than
10,000 ohm-1 cm-1; and a second dielectric metal oxide layer deposited on the
first highly conductive, silver-free metal oxide layer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention utilizes the well-known concept of induced
transmission filters to form a thin film coating structure comprising one or more
highly electrically conductive metal oxide layers, rather than onductive metal
layers. The present structure further comprises a layer of a dielectric metal
oxide on either side of the highly conductive metal oxide layer. This sequence
of layers may be repeated as necessary to achieve the emissivity and solar
control properties desired.
The choice of the highly conductive metal oxides and the dielectric metal
oxides, as well as the thickness of the layers in which such oxides are
deposited, are important to achieving the sought-after combination of low-
emissivity, high visible transmission, high IR reflection/absorption, mechanical
durability, chemical stability, and in particular, good solar control.
In this connection, dielectric metal oxides useful for the present invention
include, oxides of tin, titanium, zinc, bismuth, and alloys of such oxides.
Nitrides of silicon may also be useful for the present invention. Layer
thicknesses of such dielectric metal oxides suitable for the invention are in the
range of 200 to 400A, preferably, 250-350A.
The highly conductive metal oxides useful for the present invention
include simple oxides such as oxides of rhenium, ruthenium, iridium, chromium
and molybdenum perovskite type mixed oxides, including CaRuO3, SrRuO3,
SrVO3, SrCrO3, SrFeO3, SrTiO3, SrMoO3, CaVO3, LaTiO3, Sr2VMoO6; spinel
type mixed oxides, such as NiCo2O4; heavily doped tungsten oxide bronzes,
such as NaxWO3 (where x+>0.40). Layer thicknesses of the aforementioned
highly conductive metal oxides suitable for the invention are less than 1000A,
preferably less than 500A.
Table 1 shows some exemplary electrical resistivity and electrical
conductivity values for commonly used highly conductive metals, i.e., Ag and
Cu, as well as highly conductive metal oxides suitable for use in connection
with the present invention, i.e., ReO3, Na0.8WO3 and RuO2. Although the
conductivities of the exemplary highly conductive metal oxides are substantially
lower than the conductivities of Ag and Cu, the metal oxides shown in Table 1
have been found to perform satisfactorily from an electrical conductivity

viewpoint, and to display the other desired properties discussed herein which
make such oxides superior to Ag and Cu for the applications of the present
invention.
More specifically, highly conductive metal oxides having a conductivity
> 10,000 ohm-1 cm-1, and preferably a conductivity >50,000 ohm-1 cm-1, are
suitable for the present invention.
The conductivities of the highly conductive metal oxides are clearly
superior to conventional doped metal oxides, such as fluorine-doped tin oxide
and tin-doped indium oxide, as can be seen in Table 1.

The films formed according to the present invention will, generally, have
stoichometry corresponding to the stoichometric oxide of the corresponding
metal, e.g., SnO2, TiO2, etc., however, films which are slightly oxygen deficient
may also be produced, and may be useful.
Thin film structures utilizing a combination of the above-described
dielectric and highly conductive metal oxides in a three-layer sequence have
been found to exhibit an emissivity of transmittance >70%, and a total solar energy transmittance of Preferably, the thin film structure will have a total solar energy transmittance 45%.

The chemical durability of the above-described thin film structures is
significantly improved over conventional structures as, without wishing to be
bound by any theory, the inventors believe the highly conductive metal oxide
replacing the silver significantly reduces reaction of the film with ambient
humidity, atmospheric contaminants, and the like. The inventors believe that
replacement of the silver with a less reactive metal oxide improves the
chemical stability of the film stack.
Similarly, the inventors believe that the mechanical durability of the thin
film structure will be improved by replacing the ductile, malleable silver layer
with a rigid, stiff metal oxide layer.
The thin film or coating of the present invention may be deposited on
any suitable dielectric substrate material. A transparent glass, made by the
float glass process, particularly a soda-lime-silica glass has been found to be
suitable. Some tinted glasses may also be suitable.
The films of the present invention may be deposited on the
aforementioned substrates by any suitable method, including various types of
sputtering or CVD techniques. In particular, an on-line deposition process
occurring during the float-glass manufacturing process is considered suitable.
A particularly preferred on-line deposition process for the present invention is
atmospheric pressure chemical vapor deposition.
An apparatus, useful for the on-line production of the coated glass article
of the present invention, generally comprises a float section, a lehr, and a
cooling section. The float section has a bottom which contains a molten tin
bath, a roof, sidewalls, and end walls, which together form a seal such that
there is provided an enclosed zone, wherein a non-oxidizing atmosphere is
maintained, as hereinafter described in greater detail, to prevent oxidation of
the tin bath. During operation of the apparatus, molten glass is cast onto a
hearth, and flows therefrom under a metering wall, then downwardly onto the
surface of the tin bath, from which it is removed by lift-out rolls and conveyed
through the lehr, and thereafter through the cooling section.
A non-oxidizing atmosphere is maintained in the float section by
introducing a suitable gas, such as for example one composed of 99 percent by
volume nitrogen and 1 percent by volume hydrogen, into where the coating

WE CLAIM
1. A low-emissivity, solar control coating to be deposited on a dielectric
substrate, the coating comprising:
a first dielectric layer deposited over the dielectric substrate;
a first highly conductive silver-free metal oxide layer deposited over the
first dielectric layer and having an electrical conductivity greater than
10,000 ohm-1 cm-1;
a second dielectric layer deposited over the highly conductive, silver-free
metal oxide layer; and
wherein each dielectric layer is formed of a metal oxide chosen from the
group consisting of oxides of tin, titanium, zinc, bismuth and alloys
thereof, or a nitride of silicon.
2. The solar control coating defined in claim 1, wherein the first highly
conductive metal oxide has an electrical conductivity greater than 50,000
ohm-1 cm-1.
3. The solar control coating defined in claim 1, wherein the dielectric material
comprises Si3N4.
4. The solar control coating defined in claim 1, wherein the highly
conductive silver-free metal oxide is chosen from the group consisting of
oxides of rhenium, ruthenium, iridium, chromium, molybdenum and mixed
oxides, CaRuO3, SrRuO3, SrVO3, SrCrO3, SrFeO3, SrTiO3, SrMoO3, LaTiO3,
Sr2VMoO6, NiCo2O4, and NaxWO3.

5. The solar control coating defined in claim 1, wherein a second highly
conductive silver-free metal oxide layer is deposited over the second dielectric
metal oxide layer, and a third dielectric metal oxide layer is deposited over
the second highly conductive silver-free metal oxide layer.
6. A coated glass article comprising:
a dielectric substrate;
a first dielectric metal oxide layer deposited on the dielectric substrate;
a first highly conductive silver free metal oxide layer deposited on the first
dielectric metal oxide the highly conductive metal oxide so deposited
having an electrical conductivity greater than 10,000 ohm-1 cm-1; and
a second dielectric metal oxide layer deposited on the conductive, silver-
free metal oxide layer; wherein the coated glass article has an emissivity
of 0.3, a visible light transmittance >70%, and a total solar energy
transmittance of 7. The coated glass article defined in claim 6, wherein the emissivity is 8. The coated glass article defined in claim 6, wherein:
the first dielectric metal oxide layer comprises TiO2;
the first highly conductive silver free metal oxide layer comprises ReO3;
and
the second dielectric metal oxide layer comprises TiO2.

9. The coated glass article defined in claim 6, wherein:
the first dielectric metal oxide layer comprises SnO2;
the first highly conductive silver free metal oxide layer comprises RuO2;
and
the second dielectric metal oxide layer comprises SnO2.
10. The coated glass article defined in claim 6, wherein:
the first dielectric metal oxide layer comprises TiO2;
the first highly conductive silver free metal oxide layer comprises RuO2;
and
the second dielectric metal oxide layer comprises TiO2.

ABSTRACT

Title : SILVER-FREE LOW-E SOLAR CONTROL COATING
A multi-layer, low-emissivity, solar control article comprises a
dielectric substrate, a first dielectric metal oxide layer
deposited on the substrate, a first highly conductive, silver-
free metal oxide layer deposited on the first dielectric metal
oxide, and a second dielectric metal oxide deposited on the
first highly conductive, silver-free metal oxide layer. The
aforementioned coating layer sequence may be repeated as
necessary to achieve the desired properties. An iridescence
suppressing interlayer may, optionally, be utilized in
connection with the low-emissivity, solar control coating.

SILVER-FREE LOW-E SOLAR CONTROL COATING

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