JPH0157061B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application] The invention comprises a thin, functional inorganic coating, such as a tin oxide coating forming a device for promoting infrared light reflection. The present invention relates to a glass structure whose thin coating reduces iridescence and has an improved appearance as a result.

[Conventional technology]

Glass and other transparent materials can be coated with transparent semiconductor films such as tin oxide, indium oxide or cadmium stannate to reflect infrared radiation. Such materials are useful for providing windows with increased insulation values (low thermal conductivity), for example in applications such as furnaces, architectural windows, etc. Coatings of these same materials also conduct electricity and are used as resistance heaters to heat vehicle windows to remove fog or ice.

One undesirable feature of these coated windows is that they exhibit interference colors (nacreousness) in reflected light and to a lesser extent interference colors in transmitted light. This nacre has been a significant barrier to widespread use of these coated windows (e.g. American Institute of Physics Conference Proceedings).
Prsceeding) No. 25, New York, 1975, No. 288
See page].

In some cases, when the glass is quite dark-toned (ie, has a light transmission of about 25% or less), this iridescence is attenuated and tolerable. However, in most architectural wall and window applications, nacreous effects for coatings smaller than about 0.75 microns are usually aesthetically unacceptable to many (see, e.g., U.S. Pat. No. 3,710,074 Stewart). ).

Nacreous color is a common phenomenon in transparent films in the thickness range of about 0.1 to 1 micron, especially thicknesses below about 0.85 micron. Unfortunately, it is precisely this range of thicknesses that is of practical importance in most commercial applications.

Semiconductor coatings thinner than about 0.1 micron do not exhibit interference colors, but such thin coatings have surprisingly poor infrared light reflectance and, moreover, surprisingly reduced current-carrying capacity. have.

Coatings thicker than about 1 micron also do not exhibit visible nacre in daylight illumination, but such thick coatings are extremely expensive to make because a larger amount of coating material is required, and the coating The time required to deposit the object is correspondingly longer. Furthermore, films thicker than 1 micron tend to exhibit haze, which results from light scattering from surface irregularities, and the irregularities are greater in such films. be. Also, such films exhibit a greater tendency to crack under thermal stress due to differential thermal expansion.

As a result of these technical and economic constraints,
Almost all current commercial products of such coated glass articles consist of films in the thickness range of about 0.1 to 0.3 microns, which exhibit a pronounced iridescent color. There is currently little architectural use of this coated glass, despite the fact that doing so would be cost effective in conserving energy. For example, infrared heat loss through glass areas of a heated building can approach about half the heat loss through an uncovered window. The presence of pearlescent color on these coated glass products is the main reason why these coatings are rejected for use.

US Application No. 782,542 discloses a means of reducing this iridescence to unobservably small values by additional layers superimposed on the main coating, including a gradient-type coating. The present disclosure is primarily directed to improved means for forming such graded nacre-resistant layers.

[Problem that the invention seeks to solve]

It is an object of the present invention to provide a glass product that eliminates visible pearlescence from semiconducting thin film coatings on glass and maintains their desirable properties of visible transparency, infrared reflectivity, and electrical conductivity. .

Another object of the present invention is to achieve the above objects without significantly increasing production costs over the conventional use of conventional nacreous films.

Another object of the present invention is to achieve the above objects in a manner that is continuous and fully compatible with current manufacturing methods in the glass industry.

Yet another object of the invention is to achieve the above objects in a product that is highly durable and stable to light, chemicals and mechanical abrasion.

Another objective is to achieve all of the above objectives using materials that are sufficiently plentiful and readily available to permit widespread use.

Another object of the invention is to provide a glass article that reduces the total amount of light reflected from the coated surface of the glass, thereby increasing the total transmission of light through the glass.

Another object of the invention is that the outer coating is formed from an infrared reflective surface of about 0.7 microns or less and that the inner coating (a) reduces haze on the coated glass, and simultaneously and independently (b) ) To provide a glass structure comprising a compound coating that forms a means for reducing iridescence in the glass structure.

Another object of the invention is to provide a glass structure having the above-mentioned nacreous properties, the structure being characterized by a gradual change in coating composition between the glass and the outer coating. It is.

[Means for solving problems]

The present invention is a transparent glass structure without a substantially nacreous appearance having a glass substrate having a coating that is substantially homogeneous in each plane parallel to the surface of the glass substrate, comprising: The coating includes: (a) a first composition closest to the substrate containing a relatively high proportion of a first component to a second composition more distant from the substrate containing a relatively large proportion of a second component; (b) an upper sheath having a refractive index substantially the same as the refractive index of the second component; the mole fraction of the first component of the lower coating band varies substantially proportionally to the distance from the glass substrate, the first component being SiO ₂ and the second component being SnO ₂
and the upper coating is fluorine-doped tin oxide, and the material forming the lower coating contains an amount of tin of not more than 40% at the interface of the lower coating closest to the glass substrate. The present invention relates to the above glass structure containing an oxide.

The present invention utilizes the formation of a layer of transparent material between the glass and the semiconductor film. These layers have refractive indices that are intermediate between those of glass and semiconductor film. By proper selection of the thickness and refractive index value of these interlayers, the pearlescent color can be made so faint that most people cannot detect it, and yet certainly have widespread commercial use even in the architectural field. It has been found that the iridescent color can be weakened so as not to interfere. Suitable materials for these intermediate layers as well as methods of forming these layers are also disclosed herein.

In a preferred form of the invention, these interlayers intersect together in succession so that their refractive index is comparable to the refractive index of the glass (as it changes through the layer from the glass towards the semiconductor coating). A graded layer is formed that changes, preferably smoothly, from the value at the glass surface to a refractive index that is comparable (at the point closest to the overcoat semiconductor film) to the refractive index of the overcoat semiconductor film.

A coating having a reflectance that varies through its thickness can be produced by the method disclosed herein, in which a gaseous mixture with components of different reactivity is transferred to a moving glass substrate. Flows along the surface of the material.

Due to the essential nature of color sensing, it would be desirable to present a discussion of the methods and assumptions used to evaluate the invention disclosed herein. Most applications of the theory described below should be acknowledged to be retrospective in nature, since the information is necessarily provided in hindsight, i.e., in one's possession of the knowledge disclosed herein. It is.

In order to provide a suitable quantitative evaluation of various possible structures for suppressing nacreous colors, the intensity of such colors was calculated using optical and light sensing data. In this study, the film layers are assumed to be flat, with uniform thickness and uniform refractive index within each layer. It is believed that the refractive index change is steeper at flat interfaces between adjacent film layers. Continuously varying refractive index can be modeled as a series of many extremely thin layers with closely spaced refractive indices.

The true refractive index is used, corresponding to negligible absorption losses within the layers. Amplitude reflectance is determined for a normally incident plane wave of unpolarized light.

Using the above assumptions, the amplitudes for reflection and transmission from each interface are calculated from the Fresnel equations. These amplitudes are then summed taking into account layer differences caused by propagation through the associated layers. These results are based on the airy theory of multiple reflections and interference in thin films.
It has been found that the equations (eg, Optics of Thin Films, F. Knittl, Wiley & Sons New York, 1976) are equivalent when these equations are applied in the same case.

The calculated intensity of the reflected light is observed to vary with wavelength, thus being more intense for some colors than others. In order to calculate the reflected color seen by an observer, it is desirable to first determine the spectral distribution of the incident light. For this purpose,
International lighting approximating normal daylight lighting
Commitment on Illumination Standard Illuminant C (the International
Commission on Illumination Standard
Illuminant C) can be used. The spectral distribution of the reflected light is a product of the calculated amplitude reflectance and the spectrum of illuminant C. The hue and color saturation seen in the reflection by a human observer is then calculated from this reflection spectrum using homogeneous color scales known in the art. One useful scale is that disclosed by Hunter in 1967 in Food Technology, Vol. 21, pp. 100-105. This scale was used to derive the relationships disclosed herein.

The result of the calculation for each combination of layer refractive index and thickness is a pair of numbers: "a" and "b.""a" indicates the shade of red (if positive) or green (if negative), while "b" indicates the shade of yellow (if positive) or blue (if negative). These shade results are useful in checking calculations for the observable color of samples including those of the present invention.
The single number “c” stands for “color saturation”.
c = (a ² + b ² ) ^1/2 This color saturation index, "c", is directly related to the eye's ability to detect hard pearlescent hues. The value at which the saturation index is One cannot see any color in the reflected light when: The value of this initial saturation of observability depends on the particular homogeneous color scale used, and on the viewing conditions and level of illumination. (For example, see The Measurement of Color Scale Reviews.
Appearance (The Measurement of
(See Wiley and Sons, New York 1975.) To establish a baseline for comparison of structures, an initial series of calculations was performed to mimic a single semiconductor layer on glass. The refractive index of the semiconductor layer is taken as 2.0, which is a value close to that of tin oxide, indium oxide, or cadmium stannate film.
A value of 1.52 was used for glass substrates. These are typical values for commercially available window glass. The calculated color saturation values are plotted in FIG. 1 as a function of semiconductor film thickness. Color saturation is 0.1 in thickness range
It is found that the reflection from ~0.5μ films is high. For films thicker than 0.5μ, color saturation decreases with increasing thickness. These results are consistent with qualitative observations of actual films. pronounced
oscillations) due to the eye's varying sensitivity to different spectral wavelengths. Each peak corresponds to a particular color as shown in the curve (R=red, Y
= yellow, G = green, B = blue).

Using these results, the minimum observed value of color saturation was established by the following experiment. Tin oxide films with thicknesses varying continuously up to about 1.5μ were deposited on glass plates by oxidation of tetramethyltin vapor. The thickness profile was established by varying the temperature across the glass surface from approximately 450°C to 500°C. The thickness profile was then measured by observing interference fringes under monochromatic light. When viewed under diffused sunlight, the film
The interference colors were shown in the correct position shown in the figure.
Portions of the film with a thickness greater than 0.85μ did not exhibit observable interference colors in diffused sunlight. The green peak, calculated to be 0.88μ thick, was not seen. Therefore, the "threshold" of visibility is eight or more of these color units.
Similarly, the calculated blue peak at 0.03μ was not seen, so the "beginning" is 11 color units greater than the value calculated for this peak. However, a weak red peak at 0.81μ under good observation conditions.
For example, a black velvet background can be used to view the reflected field without any colored obstructions, so the "start" is less than 13 color units calculated for this color. From these studies, the “beginning” for observing reflected colors is 11~
between 13 color units and thus represent the “beginning” for the observability of reflected color under daylight viewing conditions.
A value of 12 units was adopted. In other words, color saturations above 12 units appear as visibly colored pearlescent, while color saturations below 12 units are seen as neutral. There would be little objection to the commercialization of products with color saturation values of 13 or less. However, it is highly preferred that the value is 12 or less, and as will be explained in more detail below, the most advantageous products according to the invention, such as those characterized by a completely colorless surface, i.e. below about 8. There appears to be no practical reason why it cannot be produced economically.

A value of 12 or less indicates a reflection that does not distort the color of the reflected image in an observable manner. This "starting" value of 12 units can be taken as a quantitative standard and with which the success or failure of various multilayer designs in suppressing nacreous color can be evaluated.

Coatings with a thickness of 0.85μ or more have color saturation values below this "start" of 12, as seen in FIG. Experiments demonstrate that these thicker coatings do not exhibit undesirable pearlescent colors in daylight illumination.

Use of a Progressive Index Interlayer The film interposed between the glass substrate and the semiconductor layer can be comprised of a gradient composition, for example a composition that gradually changes from a silica film to a tin oxide film. Such films can be depicted as consisting of a large number of intermediate layers. Calculations were made of the reflected color saturation for the change in refractive index profile between a glass with a refractive index of n=1.52 and a semiconductor coating with a refractive index of n=2.0. For interlayers thicker than about 0.15μ, the calculated color saturation index is typically 12
Below, it is neutral to the eye,
For interlayers larger than about 0.3μ no color can always be detected. The precise shape of the refractive index profile has little effect on these results, provided only that the change through the gradient layer is gradual.

Materials that may be used A wide variety of transparent materials are among those that may be selected to create a product that satisfies the above criteria by forming a nacre-resistant basecoat layer. Various metal oxides and metal nitrides, and mixtures thereof, have the right optical properties of transparency and refractive index. Table A
List some mixtures with the correct refractive index range between glass and tin oxide or indium oxide films. The required weight percent can be read from the measured refractive index versus composition curve or calculated from the normal Lorenz-Lorenz law for the refractive index of mixtures using the measured refractive index for the pure film [Z, Knittle ( Knittl),
Optics of Thin Films
of Thin Films), Wiley and Sons, New York, 976, No. 473
page〕. Although this mixing law generally provides a sufficiently accurate interpolation method for optical studies, the calculated refractive index is often slightly lower than the measured value. Film refractive index also varies somewhat with deposition methods and conditions of use.

FIG. 3 shows a typical curve of refractive index versus composition for the important case of silicon dioxide-tin dioxide mixtures.

_Table A Some combinations _{of compounds resulting in} transparent mixtures _{whose refractive index ranges from} 1.5 _{to 2.0} Method of Formation) Films can be formed by simultaneous vacuum evaporation of suitable materials in suitable mixtures. For coating large areas such as window panes, chemical vapor deposition (CVD) at normal atmospheric pressure is more convenient and less expensive. However, CVD methods require appropriate volatile compounds to form each material.
Silicon dioxide can be deposited by CVD from gases such as silane, SiH ₄ , dimethylsilane (CH ₃ ) ₂ SiH ₂ and the like. Liquids that are sufficiently volatile at room temperature are almost as useful as gases. Tetramethyltin is a source for CVD of such tin compounds; while (C ₂ H ₅ ) ₂ SiH ₂ and SiCl ₄ are volatile liquid sources for silicon.

A continuous gradient layer of mixed silicon-tin oxide can be created in a continuous CVD coating process on a continuous ribbon of glass by the following procedure. For example, below (or above) the thermal glass ribbon, as shown in Figure 4.
, the gas mixture is flowed in a direction parallel to the glass flow. The gas mixture contains an oxidizable silicon compound, an oxidizable tin compound, and oxygen or other oxidizing gas. The compound was chosen in such a way that the silicon compound is oxidized slightly faster than the tin compound, so that when the gas mixture hits the heated glass surface first, the oxide deposited on the glass contains only a small percentage of tin dioxide. Contains silicon dioxide. The proportions of silicon and tin compounds in the gas phase are adjusted so that this initially deposited material has a refractive index comparable to that of the glass itself. Then, as the gas continues in contact with the glass surface, the proportion of tin oxide in the deposited film increases until the silicon compounds are almost completely used up in the gas mixture at the exhaust end of the deposition region and are formed there. The resulting deposit increases until it is almost pure tin oxide.

Since the glass also progresses continuously from a relatively silicon-rich (initial) deposited region to a relatively tin-rich (final) region, the glass undergoes a coating and its gradient index of refraction increases across the thickness of the coating. , which starts at the glass surface with a value comparable to the refractive index of glass and ends at its outer surface with a value comparable to the refractive index of tin oxide. The subsequent deposition region shown in FIG. 3 can then be used to create a further layer of pure tin oxide or, for example, a layer of fluorine-doped tin oxide.

Suitable gas mixtures for this purpose include silicon compounds which can be oxidised, preferably with tetramethyltin (Me ₄ Sn), 1,1,2,2-tetramethyldisilane (HMe ₂ SiSiMe ₂ H), 1,1, Includes 2-trimethyldisilane (H ₂ MeSiSiMe ₂ H) and/or 1,2-dimethyldisilane (H ₂ MeSiSiMeH ₂ ). It has been found that the initially deposited film is rich in silicon and has a refractive index close to glass, while the later portions of deposition are almost pure tin oxide.

The Si—H bonds in the silicon compounds mentioned above are extremely useful in this method because tetramethylsilane
Me ₄ Si or hexamethyldisilane
Compounds without Si--H bonds such as Me ₃ SiSiMe ₃ oxidize better and slower than tetramethyltin, so the initial deposit is mainly tin oxide and the later part of the deposit is mainly silicon dioxide. It is from. In such cases, i.e. when using compounds such as Me ₄ Si, the gas and glass can be flowed in opposite directions to obtain the desired refractive index gradient, provided that the gas flow is faster than the glass flow. be able to. However, a preferred embodiment is to use more easily oxidizable silicon compounds and matching gas and glass flow directions.

When forming a coating whose composition changes monotonically with distance from the base material, it is desirable that the silicon compound has Si--Si bonds and Si--H bonds. For example, dimethylsilane Me ₂ SiH ₂ , a compound containing Si-H bonds but no Si-Si bonds, together with tetramethyltin, forms an initial deposit of almost pure tin oxide, which then forms an intermediate deposit. (intermediate) becomes rich in silicon with time,
The end result is a tin-rich deposit.

Although applicants are not bound by theory, it is believed that the Si--Si--H arrangement is caused by an initial thermally induced decomposition in which the hydrogen is transferred to the adjacent silicon.
Facilitates rapid oxidation.

HMe ₂ Si—SiMe ₂ H→Me ₂ SiH ₂ +Me ₂ Si The reactive dimethylsilylene Me ₂ Si species is then rapidly oxidized, releasing free radicals such as hydroxyl (OH), which in turn removes hydrogen from the Si—H bond. is rapidly removed, thus creating more reactive silylene radicals and forming a chain reaction. Tetramethyltin is less reactive with these radicals and thus enters primarily into later stages of oxidation.
Me ₂ SiH ₂ lacks a rapid initial decomposition step, thus some tetramethyltin decomposes to form radicals (CH ₃ , OH, O, etc.) that preferentially replace Me ₂ SiH ₂ at intermediate times. Me ₂ SiH ₂ cannot begin to oxidize until after Me ₂ SiH ₂ is consumed and subsequent tetramethyltin oxidation becomes dominant again. Disilanes with one methyl substituent or without methyl substituents are susceptible to spontaneous combustion in air and thus must be premixed with an inert gas such as nitrogen.

Other hydrocarbon radicals such as ethyl, propyl, etc. may replace methyl in the above compounds, but methyl is more volatile and is preferred.

Higher partially alkylated polysilanes, such as polyalkyl-substituted trisilanes or tetrasilanes, function similarly to disilanes. However, higher polysilanes are difficult to synthesize and have lower volatility than disilane, which is why disilane is preferred.

The initial deposit of silica-tin oxide film is approx.
When containing less than 40% tin oxide, little or no haze will occur at the interface between the glass substrate and the coating thereon. If for some reason it is desired to initiate a tin oxide gradient of greater than about 30%, it is preferred to coat the glass with an anti-blur layer, silicon dioxide. Such a blurring prevention layer is extremely thin, for example 25~
The thickness is similar to 100 Å.

This will be explained below with reference to the drawings.

FIG. 4 illustrates a cross section of a rare in a float glass line. The structure of the rhea itself is not shown for clarity. Hot glass 10, for example at about 500 DEG -600 DEG C., is conveyed through the lair onto rollers 12, 14 and 16. Gas duct assembly 18 consisting of a gas introduction duct 20 and a gas discharge duct 22
is located between rollers 12 and 14. A duct 25 forming a means for conveying a heat exchange fluid is separated from the ducts 22 and 20 by a heat exchange wall muntin 24, which heat exchange fluid in turn carries the exhaust gases from the duct 22. Means are provided for cooling and for heating the gas flowing through the duct 20. The temperature of the heat exchange fluid is maintained sufficiently low that coating does not occur on the surfaces of the inlet duct.

Gas entering inlet 20 travels through slit-like holes 28 and thence along a reaction zone formed by the top surface 30 of duct assembly 18 and the lower surface of glass sheet 10. Upon reaching the second slit-like hole 32, the remaining gas is exhausted through the duct 22. in that the gradient coating varies along the length of the attachment zone between rollers 12 and 14;
It is during the passage of gas along the lower surface of glass sheet 10 that one of the reactants is selectively depleted.

In the device shown in Fig. 4, the second gas duct assembly 3
8 is used to complete the coating deposition, for example by adding a fluorine-doped tin oxide coating to a previously deposited gradient coating. Again, it is convenient to have the gas enter the upstream port 28a and exit the downstream port 32a.

The ducting is preferably formed from a corrosion-resistant steel alloy and includes a thermally insulating jacket 50.
Consisting of

Hereinafter, it will be explained in detail using examples.

Example 1 Glass heated to about 580°C was moved across the apparatus shown in Figure 4 at a speed of 10 cm/sec. The temperature of the gas introduction duct was maintained at approximately 300° C. by blowing suitably heated or cooled air through a temperature control duct. The first deposition area reached by the glass was fed with a gas mixture of the following composition (mol %):

1,1,2,2-tetramethyldisilane 0.7% Tetramethyltin 1.4% Bromotrifluoromethane 2.0% Dry air balance The second deposition area was supplied with a gas mixture having the following composition (mol %):

Tetramethyltin 1.6% Bromotrifluoromethane 3.0% Dry air remainder
It was adjusted to be 0.2 seconds.

The resulting coated glass of the invention had a color-neutral appearance under reflected sunlight. That's 15
% visible reflectance with no visible blurring. The infrared reflectance was 90% at 10μ wavelength. Electrical resistance was 5 ohms/square.
The coating was approximately 0.5 microns thick.

Example 2 The deposition described in Example 1 was repeated, the only difference being the composition of the gas mixture supplied to the first deposition area.

1,2-dimethyldisilane 0.4% 1,1,2-trimethyldisilane 0.3% 1,1,2,2-tetramethyldisilane
Approximately 0.02% Tetramethyltin 1.5% Bromotrifluoromethane 2.0% Dry air remainder The properties of the product obtained were indistinguishable from those of Example 1.

Samples of these coated glasses were subjected to ion evaporation-etching as well as auger chemical analysis of the coating composition to determine their chemical composition as a function of thickness. FIG. 5 shows the resulting chemical composition profile of deposits over regions of varying chemical composition. Near the glass surface, the deposits are primarily silicon dioxide, with approximately 1 in 8 silicon atoms replaced by tin. As we move away from the glass surface, the tin concentration increases and the silicon concentration decreases;
As a result, at a distance of 0.18μ or more from the glass surface, the deposit becomes tin oxide, and approximately 1.5% of oxygen is replaced by fluorine. According to FIG. 3, the silicon-tin composition profile is converted to a refractive index distance profile, which is also plotted in FIG. These results demonstrate the ability of the present method to produce desired changes in refractive index through the thickness of the deposited film.

Example 3 Tin oxide coatings were applied to glass substrates at various thicknesses. (The glass substrate was first coated with an ultra-thin film of silicon dioxide to provide an amorphous, anti-blurring surface.) Thickness of tin oxide Nacreous Visibility 0.3μ High 0.6μ Sharp but weaker 0.9 μ 1.3μ barely detectable except for fluorescence Even fluorescence is weak The latter two materials are not aesthetically objectionable for architectural applications, and the visible color saturation scale has been used for design evaluation. confirm.

To provide the most effective suppression of pearlescent color, it is desirable that the refractive index of the initial deposit be approximately comparable to that of the glass substrate, preferably within ±0.04, more preferably within ±0.02 refractive index units. It is desirable that there be. To obtain such a refractive index, the parameters of the deposition, in particular the ratio of tin to silicon atoms in the introduced gas, are varied. As an example of such a change, Figure 6 shows tetramethyltin and 1,1,2,
Figure 3 shows the change in refractive index in an initial deposit from a gas mixture with 2-tetramethyldisilane as a function of gas composition. Other parameters for these deposits were fixed as in Example 1. For example, FIG. 6 shows that an initial deposit with a refractive index of 1.52 (close to commensurate with the refractive index of a typical window glass) is produced by a gas composition of equal numbers of silicon and tin atoms. When the gas composition is kept between 47 and 52 atomic percent tin, a balance of 1.52±0.02 is obtained. These exact numbers will vary slightly for other deposition conditions, such as other temperatures or other compounds, but in order to obtain a suitable balance of refractive index between the substrate and the initially deposited coating composition, It is a routine experimental problem to establish a calibration curve such as .

The reflection of light from the surface of the coated product of Example 3 is about 16-17%, i.e., less than the reflection from the coated glass of Examples 1 and 2 (which has a gradient basecoat according to the invention). It should be noted that it is 10% higher.

[Brief explanation of drawings]

FIG. 1 is a diagram illustrating the calculated color intensity changes for various colors with respect to semiconductor film thickness. FIG. 2 is a schematic cross-sectional view of a non-nacreous coated glass made according to the present invention with a nacreous interlayer of continuously varying composition according to the present invention. FIG. 3 is an ideal, typical gradient refractive index diagram representing a gradual change from 100% SiO ₂ to 100% SnO ₂ . FIG. 4 is a slightly simplified cross-section for ease of explanation of a convenient type of apparatus for manufacturing the glass products of the present invention. Fifth
The figure shows experimental measurements of the chemical composition gradient of the silica-tin oxide gradient zone of the glass article of the invention. Figure 6 shows the change at the glass surface as a function of glass composition.
Figure 3 shows the observed change in refractive index for the initial deposition of _SiO2 -- _SnO2 .

Claims (1)

[Scope of Claims] 1. A glass substrate having a coating that is substantially homogeneous in each plane parallel to the surface of the glass substrate,
a transparent glass structure without a substantially nacreous appearance, the coating comprising: (a) a first composition proximate to the substrate containing a relatively high proportion of the first component; (b) a lower covering zone consisting of a material formed from at least two components characterized by a gradual change from said substrate to a second composition more remote from said substrate containing a relatively large proportion of; an upper cladding having a refractive index substantially the same as the refractive index of the two components, the mole fraction of the first component of the lower cladding varying substantially proportionally to distance from the glass substrate; The first component is SiO ₂ and the second component is SnO ₂
and the upper coating is fluorine-doped tin oxide, and the material forming the lower coating contains an amount of tin of not more than 40% at the interface of the lower coating closest to the glass substrate. The above glass structure containing an oxide. 2. The lower coating zone contains at least about 30% tin oxide at the interface of the lower coating zone closest to the glass substrate;
A glass structure according to claim 1, having a 100 Å anti-blur layer of silicon dioxide. 3. The glass according to claim 1 or 2, wherein the visible reflectance of the structure is about 15%, the color of the structure is neutral, and the structure is free of visible blur. Structure. 4. A glass structure according to claim 1 or 2, wherein the refractive index of the glass substrate is within ±0.04 refractive index units of the refractive index of the coating material of the lower coating band.