Method for inhibiting significant oxidation of a film on a substance during heating

The present invention relates to a method for inhibiting significant oxidation of a film on a substrate during heating of the substrate. The method includes providing a metal or metal oxide film on a substrate and providing a material adjacent to the film. The substrate is then heated to a temperature sufficient to cause the substrate to bend and the material adjacent to the film reacts in such a way as to protect the metal or metal oxide film on the substrate from further significantly oxidizing.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a method for inhibiting significant 
oxidation of a film on a substrate. According to one embodiment, this 
invention relates to a method of inhibiting significant oxidation of films 
of electrochromic materials comprising a non-stoichiometric, oxygen 
deficient metal oxide film provided by pyrolytic deposition techniques 
wherein the non-stoichiometry of the metal oxide film on the glass is 
maintained during heating and bending of the glass. 
2. Discussion of the Related Art 
Electrochromic devices are devices in which a physical/chemical change 
produced in response to the induced electrical field results in a change 
in the reflective (or transmissive properties) of the device with respect 
to electromagnetic radiations, e.g., UV, IR and visible radiation. Such 
devices generally comprise a film of electrochromic material. The 
electrochromic film usually comprises an inorganic metal oxide most 
commonly a transition metal oxide, in particular, tungsten oxide film; 
more particularly non-stoichiometric tungsten oxide film provided 
according to the teachings of U.S. Pat. No. 4,960,324, assigned to Ford 
Motor Company. 
One of the problems solved by the teachings in U.S. Pat. No. 4,960,324 is 
that it teaches a method which is suitable for coating large areas such as 
would be necessary if, e.g., sunroofs or windshields of automobiles were 
to be made as electrochromic devices. It also teaches a sequential process 
suitable for providing multiple layers of the various films required for 
an electrochromic device. As would be apparent, it would be advantageous 
to make sunroofs or windshields electrochromic devices which could be 
colored to desired intensity to keep out radiation like UV, IR and visible 
transmissions at will. For example, it might be desirable to "color" the 
sunroof and the windows to allow minimum transmittance when the automobile 
is parked to prevent the interior of the automobile from heating up on a 
sunny day. In another embodiment, the windshield might be colored to an 
intensity which allows operation of the automobile yet reduces the amount 
of visible, UV, and IR transmission through the windshield. 
Non-stoichiometric, oxygen deficient tungsten oxide films have been 
observed to show excellent electrochromism. Electrochromism is also known 
to occur in several transition metal oxides. The characteristics of 
electrochromism are manifested by a reversible color change, usually 
switching from an uncolored state to a colored state, or vice versa, as a 
result of an applied electric current. From a building energy efficiency 
viewpoint in regards to using electrochromic glazings, the ability to 
dynamically control incoming solar radiation either in the visible or near 
infrared spectral regions is very attractive. Electrochromism also has an 
important future in automotive glazings. The properties of certain 
non-stoichiometric metal oxide films, more particularly 
non-stoichiometric, oxygen deficient tungsten oxide film is very important 
to the development of large area optical shutters which may be used as 
information displays or as windows for motor vehicles. 
However, the glass which serves as a support for such electrochromic 
non-stoichiometric metal oxide films is usually subjected to a bending 
process to bend the glass part to conform with the shape and form of 
automotive glazing. In the event that the non-stoichiometric, oxygen 
deficient metal oxide film is to be provided on the glass support prior to 
bending, the subsequent bending of the glass/metal oxide film system leads 
to a diminished electrochromic character of the non-stoichiometric oxygen 
deficient metal oxide film. It is believed that since the bending process 
is normally performed in air at temperatures of about 1200.degree. F., the 
diminished electrochromic character of the non-stoichiometric metal oxide 
film is caused by the oxidation of a non-stoichiometric metal oxide film 
before bending, to a stoichiometric metal oxide film after bending the 
glass support. Present methods for providing the electrochromic layer are 
incapable of providing a non-stoichiometric metal oxide layer which can 
then be subjected to the bending and fabrication processes required to 
transform the non-stoichiometric metal oxide layer on glass to the 
required shapes and sizes for sunroofs or windshields without structurally 
changing the layer. 
Another problem encountered with the electrochromic non-stoichiometric 
metal oxide layer is that when the layer is subjected to glass bending 
processes which comprise heating and bending, the layer becomes 
stoichiometric because of oxidation and therefore the layer loses its 
electrochromic efficiency. This is particularly problematic if the metal 
oxide layer is to be used in a device that requires many cycles to keep 
out undesirable radiation, as would be intended by a sunroof or windshield 
of an automotive vehicle or a window of a building. 
Still another problem of such metal oxide layers is the introduction of 
micro cracks in the layer due to film stress when the layer oxidizes from 
a non-stoichiometric metal oxide layer to a stoichiometric metal oxide 
layer during the bending and fabrication process. These micro cracks in 
the metal oxide layer are undesirable because they are partly responsible 
for degradation of the layer. 
It is desirable to have a method which could maintain the sub-stoichiometry 
of the electrochromic metal oxide film on glass during bending of the 
glass. This would help guarantee that such a metal oxide layer, when used 
in an electrochromic device, is capable of switching for a prolonged 
period of time without significantly changing its electrochromic activity. 
It would also be advantageous if the method for maintaining the 
electrochromic metal oxide sub-stoichiometry would be simple and 
commercially suitable for applying to large areas easily. 
SUMMARY OF THE INVENTION 
The invention disclosed herein is capable of overcoming the above mentioned 
problems of prior art electrochromic layers. The present invention is 
directed toward a method of inhibiting significant oxidation of a film on 
a substrate. One embodiment of the present invention includes a method of 
inhibiting significant oxidation of a non-stoichiometric metal oxide film 
on glass during heating and bending of the glass. This method comprises 
bending a "matching pair" of glass/film substrates with powdered material 
by, placing the "matching pair" on a bending fixture, and introducing the 
"matching pair" on the bending fixture into a bending lehr via a conveyer. 
The glass/film substrates comprise a pair of glass substrates and 
preferably therebetween: one electrode layer, a metal or metal oxide 
layer, powder material, a counter electrode layer and another electrode 
layer, in that order, wherein the metal or metal oxide layer preferably 
comprises a non-stoichiometric, oxygen deficient, variable oxidation state 
metal oxide film. Thus, when the pair of glass sheets is subjected to the 
bending process, the powdered material is capable of producing reducing or 
neutral gases between the matching pair of glass sheets to prevent the 
oxidation of the film during the bending process. 
The powdered materials are compounds which can be selected from groups that 
are capable of producing reducing or neutral gases during decomposition. 
The glass that requires bending is placed on a bending fixture, fabricated 
to allow the glass to bend to a predetermined shape. The bending fixture 
with the glass is introduced into the horizontal furnace at such a 
conveyer speed so as to allow the glass to heat up to its softening point, 
and then bend (sag) due to gravity on the bending fixture, until it 
assumes its predetermined shape. The bending lehr is essentially a 
horizontal furnace with temperatures ranging from 72.degree. F. to 
1200.degree. F. and having a conveyer with variable speed ranging from 2 
in./min. to 500 in./min. The glass having a film substrate is introduced 
into the bending lehr using the bending fixture and is conveyed on the 
bending fixture by the conveyer through the bending lehr. 
It has been found that preferred embodiments of the present invention are 
capable of substantially preventing oxidation of the non-stoichiometric, 
oxygen deficient, variable oxidation state metal oxide. Additionally, the 
method of the present invention provides films which remain durable after 
bending of the glass substrates. It has also been found that when the 
method of the present invention was applied to the non-stoichiometric, 
oxygen deficient films, the films maintained their electrochromic 
character.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 illustrates an overall view of a pair of glass substrates having 
films deposited thereon and powdered material included therebetween prior 
to any heating and/or bending of the glass substrates. This arrangement is 
generally identified by reference numeral 10. This arrangement 10 includes 
a glass substrate 12 shown in FIG. 2 with a transparent electrode film 14 
pyrolytically deposited thereon. It is also possible to deposit this film 
by chemical vapor deposition or other known methods well known to one of 
ordinary skill in the art. Pyrolytically deposited on top of transparent 
electrode 14 is an electrochromic layer preferably a non-stoichiometric 
metal oxide film such as tungsten oxide. This metal oxide film is 
generally indicated by reference numeral 16. 
FIG. 3 discloses the other half of the arrangement 10 wherein the glass 
substrate 20 includes a transparent electrode 22 deposited pyrolytically 
or by chemical vapor deposition as described above. Electrode 22 can 
further include an optional counter electrode layer 24 which can be 
deposited pyrolytically or by other well known means. 
A material 18 is then applied to either the metal oxide film 16, as shown 
in FIG. 2, or to the counter electrode 24. If there is no counter 
electrode 24, the material 18 can be applied to electrode 22. This 
material 18 is preferably in the form of a powder and it is applied to the 
surface of the film such that when the arrangement is assembled, the 
powdered material 18 will be adjacent to the metal oxide film 16. 
The transparent electrodes layers 14 and 22 are individually selected from 
electrode materials consisting essentially of doped or undoped (a) tin 
oxide, (b) indium oxide, (C) indium tin oxide, (d) zinc oxide, and (e) 
mixtures of any of them. 
The electrochromic non-stoichiometric metal oxide film 16 can be selected 
from tungsten oxide, molybdenum oxide, copper oxide, nickel oxide, cobalt 
oxide and mixtures of any of them. The optional counter-electrode layer 24 
is selected from vanadium oxide, titanium oxide, copper oxide, niobium 
oxide and mixtures of any of them. 
The powdered material 18 is selected so that when the arrangement 10 is 
heated, the powdered material is capable of producing reducing or 
inert/neutral gases adjacent to the metal oxide film 16 thereby inhibiting 
significant oxidation of the metal oxide film on the substrate. Exemplary 
of powdered materials capable of producing reducing or neutral gases 
include carbonyl, carbonates, hydrides, formate, borohydrides, sulfates, 
sulfites, ammonia compounds and hydrazine. Reducing elements such as W, V, 
Cu, Fe, Pb etc. may also be included in the composition. It is not 
necessary that the material 18 necessarily be a powdered material. It is 
also contemplated that the material may be a liquid including a gel 
formulation of materials outlined above as long as the material produces a 
reducing or neutral gas adjacent to the metal oxide film substantially 
inhibiting significant oxidation of the film. 
In another embodiment, it is also contemplated that material 18 need not be 
adjacent the film. In such a case one would provide a gaseous environment 
adjacent the metal oxide film during heating and bending of the glass 
substrates and this gas would be capable of providing a reducing or 
neutral environment adjacent the film during the heating of the substrate. 
The gases employed according to this invention include inert gases or 
reducing gases including, but not limited to gases such as nitrogen, argon 
and hydrogen and other gas mixtures of the like. Other gas mixtures could 
also be utilized and those gases would be selected from those well known 
in the art. The optimal amount of inert or reducing gas or reducing agent 
which could be employed according to this invention is that which would 
inhibit significant oxidation of the film during heating. Selection of 
optimal amounts of such material (e.g., inert gas and/or reducing agents) 
will be apparent to those skilled in the art in view of the present 
disclosure. 
FIG. 4 discloses the arrangement 10 disposed on a bending fixture 30 which 
can be placed on a conveyor which leads into a horizontal lehr wherein the 
arrangement 10 is heated to temperatures of about 1200.degree. F. At this 
temperature, the glass substrates which have been placed horizontally, 
begin to bend via gravity and conform to the exact shape of the bending 
fixture as shown in FIG. 5. 
If a powdered material or other material 18 is used adjacent to the metal 
oxide film, this material must produce a reducing gas or inert atmosphere 
adjacent to the film thereby inhibiting significant oxidation of the film 
during the heating and bending process. In the preferred embodiment of the 
invention the powdered material will sublime to produce the gaseous 
environment adjacent to the metal oxide film and thereby protect it from 
significant oxidation. 
Following the bending process the arrangement 10 is removed from the 
bending fixture 30 and the two glass substrates 12, 20, are separated and 
any residual powder or reactant material is cleaned from the surface of 
the metal oxide film 16 or other exposed surfaces. 
The substrates 12 and 20 have now been bent into a substantially identical 
shape such that they are termed a "matching pair" in the art and this 
matching pair can then be assembled into an electrochromic device with the 
addition of an ion conductive material therebetween and any sealing of the 
edges which may be needed. 
While the preferred embodiment has been described in conjunction with 
forming the matching pair of two substrates 12 and 20 with the respective 
films thereon, this invention also contemplates that this process can be 
applicable to only one substrate 12 with a respective film or films 
thereon. The invention also contemplates that the film can have a metal or 
metal oxide as the outermost coating wherein this coating has the 
opportunity of oxidizing when the substrate is heated. In this case, it is 
possible to apply the material 18 to the metal or metal oxide film 16 such 
as is shown in FIG. 2 and then place this substrate with its respective 
films onto the bending fixture 30 and commence the bending process. As 
described earlier, it is also possible to omit the material 18 adjacent to 
the metal or metal oxide film and provide an inert atmosphere adjacent to 
the metal or metal oxide film to inhibit significant oxidation of the 
film. 
While the preferred embodiment has also been described in conjunction with 
non-stoichiometric metal oxide film such as WO.sub.3-x, it is also 
contemplated that this invention is useful for preventing or inhibiting 
significant oxidation of a metal oxide film which is stoichiometric and 
has the possibility of further oxidation. One example contemplated by this 
invention is the oxidation of the film of vanadium oxide (VO.sub.2) into 
the further oxidized state V.sub.2 O.sub.5. Other such metal oxide films 
which can be further oxidized into other stoichiometric arrangements are 
also contemplated and are well known to those skilled in the art. 
It is also contemplated that this invention is useful for preventing or 
inhibiting significant oxidation of a metal film that has the possibility 
of oxidation upon heating. For example, an Al film when heated may oxidize 
to AlO.sub.2 which can be undesirable. Therefore, the material 18 can be 
added to this Al film prior to heating to protect the film from 
significant oxidation. Other metals contemplated by the present invention 
include Al, Ag, Cu, Ta, Zr, Mo, Zr, Mo, Zn, Sn, Ti, Cr, In, W, Mg, Ni, Fe 
and mixtures of any of them. As described herein, silicon is considered a 
metal within the context of this application. 
While the present invention has been described in conjunction with a 
non-stoichiometric metal oxide film usable in an electrochromic device, 
other films are also capable of being applied to the substrates such as 
other electrochromic layers, etc. 
The invention will be further understood by referring to the following 
detailed examples which exemplify embodiments of the present invention. It 
should be understood that the specific examples are presented by way of 
illustration and not by way of limitation. 
EXAMPLE 1 
An electrochromic device was made of a first 58 cm.sup.2 glass substrate 
which had pyrolytically deposited thereon a transparent electrode made of 
fluorine-doped tin oxide film and applied thereto was a non-stoichiometric 
oxygen deficient tungsten oxide (WO.sub.3-x) film having a thickness of 
270 nm. A second 58 cm.sup.2 substrate had a fluorine-doped tin oxide 
transparent electrode pyrolytically deposited thereon and these two 
substrates were then spaced parallel to each other and the edges were 
sealed with a silicon resin to form a cavity between the transparent 
electrode of the second substrate and the non-stoichiometric tungsten 
oxide film of the first substrate. An electrolytic solution comprising one 
molar lithium perchlorate in propylene carbonate was injected into the 
cavity to provide an ion conductor therefor. This then completed the 
electrochromic device. There was no bending or heating of the substrates 
containing the films in this example. 
The visible light transmission of the device in the "bleached" (uncolored) 
state was measured by a transmittance meter. The results are shown in 
Table 1. A copper wire was connected to each electrode. A direct biasing 
voltage of 3 V was applied for 5 minutes across the electrode with the 
electrode nearest the WO.sub.3-x film being of negative polarity. 
Application of this voltage caused the electrochromic non-stoichiometric 
tungsten oxide (WO.sub.3-x) film in the device to change from colorless to 
a blue color (colored state). The light transmission of the device in the 
colored state was also measured by a transmittance meter. This result is 
also shown in Table 1. 
EXAMPLE 2 
A matching pair of glass substrates was prepared for bending which included 
a first glass substrate of 58 cm.sup.2 having a pyrolytically deposited 
fluorine-doped tin oxide film and a pyrolytically deposited 
non-stoichiometric tungsten oxide film having a thickness of 270 nm. The 
other glass substrate of 58 cm.sup.2 included a fluorine-doped tin oxide 
film electrode which was pyrolytically deposited thereon. These substrates 
were then placed together such that the non-stoichiometric tungsten oxide 
film contacted the film of the other substrate. No powder material was 
added to this combination. This device was then placed in a bending 
fixture and was subjected to a bending process which included placing it 
on a conveyor which fed the device through the horizontal lehr having a 
temperature of 1200.degree. F. At this point the substrates conformed to 
the shape of the fixture and the bent arrangement was then removed from 
the horizontal lehr. The two substrates with the included films were then 
separated and assembled into an electrochromic device including the 
electrolytic solution disclosed above in Example 1. 
The same procedure for measuring the light transmittance described in 
Example 1 was then utilized and the electrochromic device was measured in 
the bleached and the colored states. Table 1 lists the results including a 
greatly increased transmission for the colored state. This higher 
transmission value is believed to represent the diminished electrochromic 
character of the tungsten oxide film. It is believed that the 
non-stoichiometric tungsten oxide film was allowed to oxidize into a 
stoichiometric WO.sub.3 film after bending. 
EXAMPLE 3 
In this example, the two substrates were prepared as an Example 2, however, 
after the non-stoichiometric film was applied to the first substrate, a 
powdered material of CaCO.sub.3 was applied to the tungsten oxide film. 
The other substrate was then added on top of this such that its electrode 
contacted the CaCO.sub.3 powder. This sandwich was then placed on a 
bending apparatus and heated as described in Example 2. Following bending, 
the sandwich was separated and then assembled into an electrochromic 
device by adding an electrolytic solution described in Example 1. 
The transmission measurements were then obtained as described in Example 1 
for the bleached and colored states and the results are set forth in Table 
1. When the results of the Example 3 are compared to that of Example 2, it 
is seen that the inclusion of CaCO.sub.3 as a powdered material, provided 
a means capable of preventing or inhibiting significantly the oxidation of 
the non-stoichiometric tungsten oxide on the glass during bending of the 
glass. 
EXAMPLE 4 
This sample was prepared as set forth in the description outlined in 
Example 3, however, herein the powdered material which was adjacent to the 
non-stoichiometric tungsten oxide film was 75% CaCO.sub.3 and 25% 
W(CO).sub.6. 
The transmission measurements were taken after the device had been 
assembled following the bending processing outlined above. These 
transmission results are set forth in Table 1. 
EXAMPLE 5 
This sample was prepared as set forth in the description outlined in 
Example 3, however, herein the powdered material which was adjacent to the 
non-stoichiometric tungsten oxide film was 50% CaCO.sub.3 and 50% 
W(CO).sub.6. 
The transmission measurements were taken after the device had been 
assembled following the bending processing outlined above. These 
transmission results are set forth in Table 1. 
EXAMPLE 6 
This sample was prepared as set forth in the description outlined in 
Example 3, however, herein the powdered material which was adjacent to the 
non-stoichiometric tungsten oxide film was 25% CaCO.sub.3 and 75% 
W(CO).sub.6. 
The transmission measurements were taken after the device had been 
assembled following the bending processing outlined above. These 
transmission results are set forth in Table 1. 
EXAMPLE 7 
This sample was prepared as set forth in the description outlined in 
Example 3, however, herein the powdered material which was adjacent to the 
non-stoichiometric tungsten oxide film was W(CO).sub.6. 
The transmission measurements were taken after the device had been 
assembled following the bending processing outlined above. These 
transmission results are set forth in Table 1. 
As can be seen from Table 1, the higher the percentage of W(CO).sub.6 the 
lower the transmission percentage of the electrochromic device while the 
device was in the colored state following bending. 
TABLE 1 
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Visible Transmission (%) of non-stoichiometric 
WO.sub.x film in an electrode cell before and after 
bending process. 
(Applied Voltage: 3V; Time: 3 minutes) 
Transmission (%) 
Before Bending 
After Bending 
Powder Col- Col- 
Ex. Used Bleached ored Bleached 
ored 
______________________________________ 
1 None 74.2 30.5 -- -- 
2. None 76.8 43.3 
3. 100% CaCO.sub.3 
-- -- 75.5 41.7 
4. 75% CaCO.sub.3 76.6 40.5 
25% W(CO).sub.6 
5. 50% CaCO.sub.3 
-- -- 75.5 38.4 
50% W(CO).sub.6 
6. 25% CaCO.sub.3 
-- -- 76.0 36.1 
75% W(CO).sub.6 
7. 100% W(CO).sub.6 
-- -- 75.8 34.1 
______________________________________ 
In view of the disclosure, many modifications of this invention will be 
apparent to those skilled in the art. It is intended that all such 
modifications fall within the true scope of this invention be included 
within the terms of the appended claims.