The present invention is in the field of overcoat protective layer for glass or similar surface. The Invention in particular provides an efficient overcoat protective layer that improves durability of the glass (particularly when the glass is thermally treated at high temperature) and improves mechanical, chemical and thermal properties of the glass or similar surface. The Invention also provides an article coated with the overcoat protective layer.

Background of the invention:
The following background discussion includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.

The performance of the glass is a concern for the glass industry, particularly when the glass is to be stored. The storage of glass under humid conditions after heat treatment degrades the performance of glasses. Storing of glasses in humidity chamber for more than 24 hours without the protective layer/ over coat layer results in damaging the quality of the film. The failure/s of glass performance is related to the optical, chemical and mechanical durability. The visual performance of the glass without the overcoat/ protective layer results in damaging functional layer (white spots) in the coated stack. The heat treatment of glass damages the stack of coatings, thus leading to the loss of its physical/chemical properties.

The existing provisions for protecting the glass coating are still not able to protect silver layer/s and not able to prevent its oxidation in the coated stack. Thus, the problem of reduced shelf life of the glass after heat treatment still persists and requires a technical solution as the existing technologies are not able to prevent oxidation of the silver layer in the coated stack and suffers with the problem of reduced shelf life of glass after heat treatment.

In view of the aforesaid, there exists need of an efficient overcoat/protective layer that improves durability of the glass, particularly when the glass is heated or thermally treated at high temperature. There is also a need of an efficient overcoat/protective layer that improves durability of the low emissivity coating stack. The Invention also provides an article coated with the overcoat protective layer.

There is a further need of a durable, stable and efficient low emissivity coating, having functional layer/s, with the overcoat protective layer. There is furthermore a need of an overcoat/protective layer for the glass that improves mechanical, chemical and thermal properties of the glass.

Object/s of the Invention:
Primary object of the present invention is to provide an overcoat protective layer that overcomes the limitation/drawback of the existing products as described above.
Another object of the present invention is to provide an overcoat protective layer providing improved durability to the glass during thermal/ heat treatment.
Another object of the present invention is to provide an overcoat protective layer that improves the mechanical durability and thermal stability of the coated stack.
Another object of the present invention is to provide an overcoat protective layer developed in the presence of oxygen and nitrogen with material composite target layer SiAlZrHfW providing enhanced chemical durability.
Another object of the present invention is to provide an overcoat protective layer comprising oxynitride of dielectric and corrosion resistant materials.
Another object of the present invention is to provide an overcoat protective layer comprising doped ZrO2 with elements of silicon and/or silicon oxide and/or aluminium and/ or aluminium oxide and/ or tungsten and/or Hafnium oxide and/or tungsten oxide.
Another object of the present invention is to provide an overcoat protective layer comprising silicon aluminium hafnium tungsten doped zirconium oxide layer (SiAlZrHfWOxNy)
Another object of the present invention is to provide a durable, stable and efficient low emissivity coating, having functional layer/s, with overcoat protective layer.
Another object of the present invention is to provide a method of developing the overcoat protective layer over the surface of an article.
Another object of the present invention is to provide a coated article comprising the overcoat protective layer of SiAlZrHfWNyOx as described above.
Summary of the Invention:
In an aspect, the Invention provides an overcoat protective layer comprising composite based on oxynitride of dielectric and corrosion resistant materials wherein said layer comprises a doped ZrO2 with elements of silicon and/or silicon oxide and/or aluminium and/ or aluminium oxide and/ or tungsten and/or Hafnium oxide and/or tungsten oxide;
wherein said layer comprises silicon aluminium hafnium tungsten doped zirconium oxide layer (SiAlZrHfWOxNy);
and wherein the layer comprises:
Silicon (Si) present in the amount ranging from 50 to 60 wt%;
Aluminium (Al) present in the amount ranging from 3 to 8 wt%;
ZrHf present in the amount ranging from 30 to 40 wt%;
Tungstun (W) present in the amount ranging from 3.5 to 4.5 wt%;
Trace elements comprising Fe, Mn, Hf present in an amount lesser than 0.1 to 0.5wt%;
In another aspect, there is provided a method of developing the overcoat layer as described above, over the surface of an article comprising:
a) Sputter depositing the coating of Silicon aluminium hafnium tungsten doped zirconium oxide layer (SiAlZrHfWOxNy) on said article at a base pressure ranging from 10-3 to 10-6 mbar in the presence of gases comprising Oxygen (Ox) and Nitrogen (Ny) in the inert atmosphere of argon gas;
wherein the layer comprises Silicon (Si) present in the amount ranging from 50 to 60 wt%; Aluminium (Al) present in the amount ranging from 3 to 8 wt%; ZrHf present in the amount ranging from 30 to 40 wt% with maximum trace material of zirconium; Tungstun (W) present in the amount ranging from 3.5 to 4.5 wt%;Trace elements comprising Fe, Mn, Hf present in an amount lesser than 0.1 to 0.5wt%;
b) Heating/thermally tempering the coated article obtained from step (a) at temperature ranging from 580 to 670 degree celsius, causing the deposited nitride layer in step (a) to oxygenate resulting in silicon aluminium hafnium tungsten doped zirconium oxide layer (SiAlZrHfWOxNy) coated on the article.
In another aspect, there is provided a coated article comprising the overcoat layer of SiAlZrHfWNyOx obtained from the method as described above.

In another aspect, there is provided a durable, low emissivity and solar control multi composite stack layer comprising the overcoat layer as described above, in the following manner:
a) at least an infrared reflecting layer sandwiched between atleast dielectric layers;
b) atleast a functional layer comprising single/multiple silver layer;
wherein said low emissivity coating comprises an over coat layer of silicon aluminium hafnium tungsten doped zirconium oxide layer (SiAlZrHfWOxNy)
Detailed description of Drawing/s:
The accompanying drawings, which are incorporated in and constitute a part of this disclosure, illustrate exemplary embodiments and, together with the description, explain the disclosed principles. The reference numbers are used throughout the figures to describe the features and components. Some embodiments of system and/or methods in accordance with embodiments of the present subject matter are now described, by way of example only, and regarding the accompanying figures, in which:
Fig. 1 and 2 illustrates a side cross-sectional view of the monolithic coated article of the layer stack (heat treated or not heat treated) with and without over coat layer illustrating reflective visible light from the coating stack
Fig. 3 illustrates a cross-sectional view of the monolithic coated article (heat treated or not heat treated) without over coat layer according to an embodiment of this invention
Fig. 4 illustrates a cross-sectional view of the monolithic coated article (heat treated or not heat treated) with over coat layer according to another embodiment of this invention
Fig. 5 illustrates the optical properties of the developed coating without protective over coat layer. It also shows the spectral curve of transmission value in the wavelength range of 250 to 2500 nm.
Fig. 6 illustrates output of the transmission in the visible region before and after thermal treatment, which shows variation of transmission value ranging from 75% to 82% at wavelength 500 nm
Fig. 7 illustrates Sample without protection layer and with protection layer. Figure 7 explains about the hardness of the protective layer stack by conducting a test name wet abrasion, under 500 cycles of repetitions via scrubber under industrial standards.

Detailed description of present Invention:
In the present document, the word "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any embodiment or implementation of the present subject matter described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments.
While the disclosure is susceptible to various modifications and alternative forms, specific embodiment thereof has been shown by way of example in the drawings and will be described in detail below. It should be understood, however that it is not intended to limit the disclosure to the specific forms disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternative falling within the spirit and the scope of the disclosure.
The terms “comprises”, “comprising”, “includes”, or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a setup, device or method that comprises a list of components or steps does not include only those components or steps but may include other components or steps not expressly listed or inherent to such setup or device or method. In other words, one or more elements in a system or apparatus proceeded by “comprises... a” does not, without more constraints, preclude the existence of other elements or additional elements in the system or method.
The Invention provides an overcoat protective layer based on thin film coating stack for protecting glasses and similar articles. The overcoat protective layer comprises following non-limiting technical advantages:
• Improved durability to the glass during thermal/ heat treatment
• Improves the mechanical durability and thermal stability of the coated stack
• Enhances chemical durability of the coated surface
In an embodiment, the invention provides coated article that include at least an infrared reflecting layer that is sandwiched between at least dielectric layers in a low emissivity coating. The coating in certain example embodiments, comprises at least one of the layer of the coatings of zirconium oxide (ZrO2) which may doped with Silicon (Si) and/or Aluminium (Al) and/or Hafnium (Hf) and/or Tungstun (W) and/or silicon aluminium tungsten oxide (eg., SiAlWOX) and/or silicon aluminium hafnium tungsten oxide (eg., SiAlHfWOX) and/or any silicon aluminium hafnium tungsten oxinitride (eg., SiAlHfWOXNy) or other stoichiometry.
The overcoat protective layer based on SiAlZrHfWO2 acts as the uppermost/ overcoat on the low emissivity stack and provides improved durability, humidity, chemical and heat stability to the glass layer. The developed uppermost/ over coated layer has applications in various areas comprising but not limiting to glass buildings, insulated glass window units, Glazing systems, vehicles, windows in interior and exterior of buildings or in other suitable applications. The coated layer stack are useful for applications such as monolithic/laminated windows, and/or the like.

In an embodiment, the protective overcoat layer comprises Silicon, Aluminium, Zirconium, Hafnium and Tungsten (SIALZrHfW).

In an embodiment, the protective overcoat layer comprises an alloy of ZrHf with maximum amount of zirconium and minimal amount of Hafnium in it.

In an embodiment, the Invention provides an article e.g. glass, coated with the over coat protective layer comprising oxynitride of dielectric and corrosion resistant materials.

In an embodiment, the overcoat protective layer comprises composite based on oxynitride of dielectric and corrosion resistant materials. The layer comprises a doped ZrO2 with elements of silicon and/or silicon oxide and/or aluminium and/ or aluminium oxide and/ or tungsten and/or Hafnium oxide and/or tungsten oxide. The layer comprises silicon aluminium hafnium tungsten doped zirconium oxide layer (SiAlZrHfWOxNy). Particularly, the layer comprises the components in the following range:
• Silicon (Si) present in the amount ranging from 50 to 60 wt%;
• Aluminium (Al) present in the amount ranging from 3 to 8 wt%;
• ZrHf present in the amount ranging from 30 to 40 wt%;
• Tungstun (W) present in the amount ranging from 3.5 to 4.5 wt%;
• Trace elements comprising Fe, Mn, Hf present in an amount lesser than 0.1wt% to 0.5wt%;
The beneficial properties imparted by the overcoat protective layer is due to its single layered composite structure and the amount in which the components are present. It has been seen that if the amount of these components are varied/ disturbed from the above mentioned, the beneficial properties will not be achieved.

The overcoat layer (SiAlZrHfWOxNy) improves the quality of coating against humidity over a time period for approx. 48 to 72 hours and particularly 24 to 48 hours.

In Figure 1, layer 106 is the overcoat protective layer of silicon aluminium hafnium tungsten doped zirconium oxide layer (SiAlZrHfWOxNy).

Figure 2 illustrates another embodiment of the present invention where layer 108 indicates different layers of the durable, low emissivity and solar control multi composite stack layer.

Figure 3 illustrates layer stack of low emissivity coating over which the overcoat protective layer as the top layer is coated.

In an embodiment, the product comprises six layers of thin films as shown in figure 4. Figure 4 illustrates that layer 106 is the overcoat protective layer of silicon aluminium hafnium tungsten doped zirconium oxide layer (SiAlZrHfWOxNy) while layers 101 to 105 illustrates different layers of the durable, low emissivity and solar control multi composite stack layer. In such embodiment, layers 101 to 105 comprises layers of Si3N4, NiCrOx (or) NiCr, Ag, NiCrOx (or) NiCr, Si3N4 while the overprotective layer provided by the present invention is indicated by layer 106. The overprotective layer 106 provides protection, durability and strength against humidity to the low emissivity coating on the glass.

In an embodiment, the coated article comprises stack of Glass/Si3N4/NiCrOx (or) NiCr/ Ag/NiCrOx (or) NiCr/Si3N4/SIAlZrHfWOx.

In an embodiment, the coated article comprises stack of Glass/Si3N4/NiCrOx (or) NiCr/ Ag/NiCrOx (or) NiCr/ Si3N4/SIAlZrHfWOxNy

The coated protective layer has transmission color in neutral shade before and after muffle treatment at 650 degrees.

In an embodiment, the invention provides overcoat layer as single layer film deposited on the low emissivity coating stack with multi composite materials which include silicon, aluminium, hafnium, Zirconium and tungsten in the presence of oxygen and oxy nitride.

In an embodiment, the invention provides multi composite materials composed to form a single layer can be used as an overcoat protective layer stack for the Low e and solar control stacks with single and double infrared materials (material like Ag, Nb, NiCr, CrN and Au) in presence of oxygen and oxynitride.

Figure 5 shows the optical properties of the developed coating without protective over coat layer. Figure 5 also shows the spectral curve of transmission value in the wavelength range from 250 to 2500 nm.

Figure 6 shows optical properties of the developed coating with protective over coat layer. It also shows the spectral curve of transmission value in the wavelength range from 250 to 2500 nm. Figure 6 shows that output of the transmission in the visible region before and after thermal treatment has a variation of transmission value ranging from 75% to 82% at wavelength 500 nm. The figure depicted in the figure 6 shows enlarged view of the coated film optical spectral curve in the visible region of wavelength range 380 to 780 nm.

In an embodiment, the invention also provides coated article including the low emissivity coatings with single/multiple layer of silver as a functional layer in the coated stack. The coated article is used in large scale glass industries for the applications of laminated and double glazing window/ aesthetic glazing applications.

The protective overcoat layer is developed in the presence of oxygen (Ox) and nitrogen (Ny) with a target consists of corrosion resistant materials like Silicon, Aluminium, Zirconium, Hafnium and Tungsten (SiAlZrHfW).

In another aspect, there is provided a method of developing the overcoat layer as described over the surface of an article comprising the steps of:
a) Sputter depositing the coating of Silicon aluminium hafnium tungsten doped zirconium oxide layer (SiAlZrHfWOxNy) on said article at a base pressure ranging from 10-3 to 10-6 mbar in the presence of gases comprising Oxygen (Ox) and Nitrogen (Ny) in the inert atmosphere of argon gas;
b) Heating/thermally tempering the coated article obtained from step (a) at temperature ranging from 580 to 670 degree celsius, causing the deposited nitride layer in step (a) to oxygenate resulting in silicon aluminium hafnium tungsten doped zirconium oxide layer (SiAlZrHfWOxNy) coated on the article.
The Invention also provides the coated article comprising the overcoat layer of SiAlZrHfWNyOx obtained from the method as described above.

In an embodiment, the product was fabricated by Physical Vapour Deposition (PVD) technique using RF/DC magnetron sputtering coating system. The process fabrication of layer coating is developed under low pressure vacuum via controlled environment.

In an embodiment, the float clear glass substrates comprising 2440 x 1220 mm and 3660 x 2440 mm, 2440 x 1830 mm and 2440 x 1080 mm dimension with 4 mm, or 6 mm, or 8 mm thickness was used. The glasses were cleaned via washer for approx. 5 minutes to remove all the surface impurities, prior to the coating step. All the coating chambers are evacuated via turbo molecular pump to attain a base pressure of 10-6 mbar. Once the base pressure reaches to 10-6 mbar, the actual deposition is carried out thereafter, at a pressure ranging from 10-3 to 10-4 mbar.

Importantly, Oxygen (Ox) and Nitrogen (Ny) gases or mixture of reactive and inert (Ar) gas environment were used/carried in a controlled SCCM via Mass flow controllers to obtain/achieve desirable beneficial property of the layer composition and for maintaining the layer stoichiometry.

In another embodiment, the layer of silicon aluminium zirconium hafnium tungsten (SiAlZrHfW) is deposited in the presence of Oxygen (Ox) and Nitrogen (Ny). After deposition of layer of the coated stack, and upon heating, the deposited nitride layer becomes oxygenated and results in Silicon aluminium hafnium tungsten doped zirconium oxide layer. The resulting layer is further used as a protective/ over coat layer for various embodiments of the present invention. For an instance, the developed invention may be used as an overcoat/ protective layer in single silver low emissivity coating. The Low emissivity coating may comprise of infrared (IR) reflecting layer of silver and other alternative materials in certain other embodiments. Other IR reflecting material layer like Nickel, chromium, Niobium, gold alloys and thereof etc.

All the developed coatings were characterized and tested in terms of optical, colour, mechanical, elemental properties via UV-VIS-NIR Spectrophotometry, Hunter, Wet abrasion, and x-ray fluorescence spectroscopy.

The coated article herein used in the context of large scale glass industries for the applications of laminated and double glazing window/ aesthetic glazing applications, for industrial and socio economic areas, for residential and commercial building development agencies.

Technical advantage of the layer provided by the present invention:
• The overcoat protective layer provides increased durability against stress as deposited, stress upon thermal treatment, thermal tempering and the like.
• The overcoat/ uppermost layer has improved the coated stack under mechanical durability and thermal stability.
• The overcoat layer in presence of oxygen and nitrogen with material composite target layer SiAlZrHfW provides better chemical durability
In another aspect, there is provided a durable and stable low emissivity coating comprising following components:
c) at least an infrared reflecting layer sandwiched between atleast dielectric layers;
d) at least a functional layer comprising single/multiple silver layer;
e) at least an over coat layer of silicon aluminium hafnium tungsten doped zirconium oxide layer (SiAlZrHfWOxNy)
The Infrared layer comprises layers of silver, nickel, chromium, niobium, gold alloys and like.

The Invention is further described with the help of non-limiting examples:
Example 1a:
A coated article was developed based on the process as defined below and the characteristic values were measured.
A Dielectric layer stack with over coat top coat layer of SiAlZrHfWOxNy was sputter deposited directly on the coated stack of soda lime silica glass substrate. The coating layer stack deposited in the presence of oxygen and also nitrogen in the inert atmosphere of argon gas. The protective over coated layer on the base layer stack of the glass substrate was then thermally tempered at a temperature 580 to 670 degree celsius, which transforms the layer into scratch and corrosion resistant layer with improved humidity. The visible transmission of the coated article is also increased due to the coated layer. The table below shows physical parameters/characteristics before and after the thermal tempering / heat treatment of coated layer stack on the glass substrate. The Haze value before and after heat treatment was no more than 0.1 to 0.5%.

The Tr (y) represents the Transmission and Rg (y) stands for glass side reflection (a*g thus stands for glass side reflective color of a* vlaue) and Rf (y) stands for film side reflection (a*f thus stands for film side reflective color of a* value).

The below table shows that after tempering the transmission in the coated glass is increasing and the color a* and b* remains same, as desired. The humidity of the low emissivity coating stack with the overcoat protective layer is durable for more amount of time. Generally, the humidity of the conventional low emissivity coating stack degrades in less than 1 day, however the glass coated with the overprotective layer and low emissivity coating stack provided by the present invention has enhanced durability of the humidity. Accordingly, the lifetime of the low emissivity coating stack is increased by the overprotective layer. The color of the glass after tempering does not change and remains same. The conventional coatings tends to change the color.

In the below table a* is relative to the green–red opponent colors, with negative values toward green and positive values toward red. The b* represents the blue–yellow opponents, with negative numbers toward blue and positive toward yellow. A* is 0 to -3 and b* is 0 to -8 for neutral shade.

Color/optical characteristics of over coated layer on the glass substrate before tempering

Before Tempering
Broader range preferred most preferred

Transmission- Tvis (Tr Y) 35-50 40-48 42-45%
a* T (Transmission color) -0.5 to -5 -0.75 to -2.5 -1.0 to '-3.0
b* T -0.75 to -4.5 -1 to -4 -1.5 to '-3.5
Rg (Y) Reflection color of glass side 3 to 6 5 to 6 5.5 to 6.5
a* g -0.5 to -4 -0.75 to -3.75 -1.0 to '-3.0
b* g -3 to -8 -4 to -6 -4.5 to '-6.5
Rf (y) Reflection color of film side 3 to 8 3.5 to 5 4.0 to 6.0
a* f -0.5 to 4.5 -0.75 to 2 1.0 to 3.0
b*f 6 to 12 7 to 11 8.0 to 10.0

Table - A
Color/optical characteristics of over coated layer on the glass substrate after tempering

After Tempering
General preferred most preferred
Transmission- Tvis (Tr Y) 70 to 80% 71 to 77% 73-76%
a* T -2 to -6 -2.75 to -5 -3.0 to '-4.5
b* T -1 to -5 -2.5 to -4 -2.00 to '-3.5
Rg (Y) Reflection color of glass side 3 to 8 3.5 to 7 4.0 to 6.0
a* g -0.25 to 3.5 -0.75 to '-2.5 -0.1 to '-1.5
b* g -3 to -8 -4 to -7 -5.0 to '-6.5
Rf (y) Reflection color of film side 2 to 7 3 to 6 4.0 to 5.0
a* f 1.0 to 7.0 2 to 6 3.0 to 5.0
b*f 1.0 to 7.0 2 to 7 4.0 to 6.0
Table - B

The above tables (A and B) shows properties of the coated glass with overprotective layer before tempering and after tempering. It is clear from the data in Table A and B that transmission increases, which is desired, after tempering while the color properties remains same because the overcoat protective layer protects the low emissivity coating.
The target power and the gas flow values were maintained as below in the experiments to obtain the best results with respect to the deposition of the overcoating protective layer. The results of the experiments are illustrated in examples 1 to 4.
Power (KW) Ar gas (SCCM) nitrogen gas (SCCM) oxygen gas (SCCM)
15 to 25
(used in Example 1) 200 to 400 500 to 700 15 to 25

20 to 30
(used in Example 2) 200 to 400 500 to 700 20 to 30

25 to 35
(used in Example 3) 200 to 400 500 to 700 25 to 35

35 to 45
(used in Example 4) 200 to 400 500 to 700 35 to 45

Various experiments (mentioned in examples 1 to 4) have been performed by varying the power range. The below experiments demonstrate/s impact of the variation of power in terms of the change in the color of glass, change in transmission etc.
Example 1: Measurements of example (pre and post HT)

The below experiment was performed when power varied in the range of 15 to 25KW while argon gas (SCCM) ranges from 200 to 400, Nitrogen gas (SCCM) ranges from 500 to 700, Oxygen gas (SCCM) ranges from 15 to 25. It can be seen from the results mentioned in the below example 1 that the transmission is increasing after heat treatment and the glass color is in neutral range, even after when the glass is heated.

Tvis R-glass side R-film side
T (Transmission) a* (color properties) b* (color properties) R (Reflection) a*(color properties) b*(color properties) R(Reflection) a*(color properties) b*(color properties)
As coated 70.55 -2.56 -3.45 5.20 -1.73 -5.08 5.91 1.6 10.52
Post Heat treatment (HT) 75.23 -3.1 -3.49 4.66 -0.25 -5.64 5.14 2.55 5.79

EXAMPLE 2: Measurements of example (pre and post HT)

The below experiment was performed when power varied in the range of 20 to 30KW while argon gas (SCCM) ranges from 200 to 400, Nitrogen gas (SCCM) ranges from 500 to 700, Oxygen gas (SCCM) ranges from 20 to 30. It can be seen from the results mentioned below that the transmission is increasing after heat treatment and the glass color is in neutral range, even after when the glass is heated.

Tvis R-glass side R-film side
T a* b* R a* b* R a* b*
As coated 70.88 -2.6 -3.36 5.30 -1.92 -5.31 5.50 1.8 10.23
Post Heat treatment (HT) 75.66 -3.14 -3.33 4.75 -0.62 -6.07 4.83 2.71 5

EXAMPLE 3: Measurements of example (pre and post HT)
The below experiment was performed when power varied in the range of 25 to 35KW while argon gas (SCCM) ranges from 200 to 400, Nitrogen gas (SCCM) ranges from 500 to 700, Oxygen gas (SCCM) ranges from 25 to 35. It can be seen from the results mentioned below that the transmission is increasing after heat treatment and the glass color is in neutral range, even after when the glass is heated.

Tvis R-glass side R-film side
T a* b* R a* b* R a* b*
As coated 71.72 -2.66 -2.88 5.95 -2.29 -6.11 4.56 2.56 6.89
Post Heat treatment (HT) 76.30 -3.05 -2.97 5.19 -1.08 -6.87 4.09 2.61 1.84

EXAMPLE 4: Measurements of example (pre and post HT)

The below experiment was performed when power varied in the range of 35 to 45KW while argon gas (SCCM) ranges from 200 to 400, Nitrogen gas (SCCM) ranges from 500 to 700, Oxygen gas (SCCM) ranges from 35 to 45. It can be seen from the results mentioned below that the transmission is increasing after heat treatment and the glass color is in neutral range, even after when the glass is heated.

Tvis R-glass side R-film side
T a* b* R a* b* R a* b*
As coated 70.98 -2.63 -3.16 5.59 -2.03 -5.8 5.06 2.11 8.92
Post Heat treatment (HT) 75.89 -3.13 -3.19 4.92 -0.79 -6.41 4.48 2.58 3.87

The results of the experiments performed in examples 1 to 4 discloses following essential technical features:

a) The coated layer of SiAlZrHfWOx, has refractive index in the range of 1.85 to 1.90 and most preferably to 1.9 to 2.2
b) The heat treatment causes the transmission (Tvis) of the coated article to increase by at least 4% (more preferably by at least 6% and most preferably by 7%). The transmission (Tvis) of the coated article comprising protective ZrOx layer increases from 1.8 to 2.23
c) The heat treated coated article has visible transmission of approx. 75% to 77%
d) The coated article of examples 1 to 4 include a layer of silver sandwiched between atleast first and second dielectric layers on the glass substrate, which remains protected due to the overcoat protective layer provided by the present invention. The glass substrate comprises protective over coat layer of SiAlZrHfWOXNy
e) The coated article after the heat treatment has no major color variation
f)The coated layer comprising SiAlZrHfWOxNy layer comprises physical thickness in the range of 5 to 30 nm.
g) The thermal tempering is performed at temperature in the range of 580 to 670 degrees celsius

Example 5:
The coating layer comprises following components:

Example 6:
The coating layer obtained in example 5 has following dimensions:
Length BT l/D BT O/D Target O/D Step width Groove Weight (kg)
Standard in Industry 2886 (±1.0) ? 125
±0.2 ? 132.5
(+0.1/ -0.3) ? 139 (+1.0/0) 21 ±1.0 ? 128.5 (0/-0.3)

Glass layer- 1 coated with overprotective layer 2886.00 125.02 132.46 139.92 140.00 21.00 128.28 50.0
Glass layer- 2 coated with overprotective layer 2885.80 125.06 132.52 139.62 139.84 20.84 128.34 50.2

Example 7:
Further, the glass layers provided in the above examples from 1 to 4 were examined for the humidity. The results are illustrated below.
Table 3 shows durability of the coating towards the humidity environment with the time interval span from 2 hours to 36 hours. In the below mentioned Table 3, the experimental result of 1st example shows that without the protective layer, the durability of the developed product is lost within 2 hours span whereas the glass with the coated layer withstand/ resistant for more than 2 hours of time.
Sr. NO Power
(KW) test condition 2 Hrs 8 Hrs 14 Hrs 20 Hrs 36 Hrs
1 No top coat provided by the present invention Humidity pass fail fail fail fail
2 15 to 20 pass pass fail fail fail
3 20 to 25 pass pass fail fail fail
4 25 to 30 pass pass fail fail fail
5 30 to 35 pass pass pass pass fail
6 35 to 40 pass pass pass pass fail
7 40 to 50 pass pass pass fail fail

Table 3
Further, Table 4 shows durability of the coating towards the flower test environment for the time interval span from 2 hours to 36 hours in pre thermal treatment. The experimental result of 1st example shows that the without the protective layer the durability of the developed product is lost within 2hours of span whereas the glass with the coated layer withstand for more than 2 hours of time.

Sr. NO Power
(KW) test condition 2 Hrs 8 Hrs 14 Hrs 20 Hrs 36 Hrs
1 No top coat Flower pass fail fail fail fail
2 15 to 20 pass pass fail fail fail
3 20 to 25 pass pass fail fail fail
4 25 to 30 pass pass fail fail fail
5 30 to 35 pass pass pass pass fail
6 35 to 40 pass pass pass pass fail
7 40 to 50 pass pass fail fail fail

Table 4
Example 8:
The experiment was performed to evaluate the Color/optical characteristic properties of the coated sample and its variation against pre and post thermal treatment against to change in the cathode power of the top coat layer. The results are provided in the below table. It explains the variation of the Color properties of a* and b* in reflection film side, reflection glass side and transmission. The color properties should remain same in the ideal/ desirable condition. BM indicates before muffle reflection while AM indicates after muffle reflection.

Example 10:
The experiment was performed to evaluate mechanical durability of the coated protective layer films. Particularly, hardness of the coating and its adherence property on the glass was evaluated. Figure 7 illustrates the results of the coating glass with and without protective coating layer. It is evident that muffling of the sample without overcoat protective layer was not durable and was hazy. However, the coated article, after muffling, demonstrated good durability. It shows that the hardness of the protective layer stack by conducting a test name wet abrasion, under 500 cycles of repetitions via scrubber under industrial standards.

WE CLAIM:

1. An overcoat protective layer for a glass surface comprising composite single layer based on oxynitride of dielectric and corrosion resistant materials;
where said layer comprises a doped ZrO2 with elements of silicon and/or silicon oxide and/or aluminum and/ or aluminium oxide and/ or tungsten and/or Hafnium oxide and/or tungsten oxide deposited in the presence of oxygen and oxynitride;
wherein said layer comprises silicon aluminium hafnium tungsten doped zirconium oxide layer (SiAlZrHfWOxNy);
said layer characterized by the components comprising:
Silicon (Si) present in the amount ranging from 50 to 60 wt%;
Aluminium (Al) present in the amount ranging from 3 to 8 wt%;
ZrHf present in the amount ranging from 30 to 40 wt% with maximum trace material of zirconium;
Tungstun (W) present in the amount ranging from 3.5 to 4.5 wt%;
Trace elements comprising Fe, Mn, Hf present in an amount lesser than 0.1 to 0.5wt%;
2. The layer as claimed in claim 1, comprises physical thickness in the range of 5 to 30nm.
3. The layer as claimed in claim 1, comprises refractive index present in the range of 1.85 to 1.90.
4. A method of developing the overcoat layer of claim 1 over the surface of an article comprising:
c) Sputter depositing the coating of Silicon aluminium hafnium tungsten doped zirconium oxide layer (SiAlZrHfWOxNy) on said article at a base pressure ranging from 10-3 to 10-6 mbar in the presence of gases comprising Oxygen (Ox) and Nitrogen (Ny) in the inert atmosphere of argon gas;
wherein the layer comprises Silicon (Si) present in the amount ranging from 50 to 60 wt%; Aluminium (Al) present in the amount ranging from 3 to 8 wt%; ZrHf present in the amount ranging from 30 to 40 wt% with maximum trace material of zirconium; Tungstun (W) present in the amount ranging from 3.5 to 4.5 wt%; Trace elements comprising Fe, Mn, Hf present in an amount lesser than 0.1 to 0.5wt%;

d) Heating/thermally tempering the coated article obtained from step (a) at temperature ranging from 580 to 670 degree celsius, causing the deposited nitride layer in step (a) to oxygenate resulting in silicon aluminium hafnium tungsten doped zirconium oxide layer (SiAlZrHfWOxNy) coated on the article.

5. The method as claimed in claim 4, wherein said deposition comprises physical vapour deposition (PVD) performed through magnetron sputtering coating system.
6. The method as claimed in claim 4, wherein the layer was deposited with power (KW) present in the range of 25 to 35, argon gas present in the range of 200 to 400 SCCM, nitrogen gas present in the range of 500 to 700 SCCM, oxygen gas present in the range of 25 to 35 SCCM.
7. A coated article comprising the overcoat layer of SiAlZrHfWNyOx obtained from the method as claimed in claim 4.
8. A durable, low emissivity and solar control multi composite stack layer comprising:
a) at least an infrared reflecting layer sandwiched between atleast dielectric layers;
b) atleast a functional layer comprising single/multiple silver layer;
wherein said low emissivity coating comprises an over coat layer of silicon aluminium hafnium tungsten doped zirconium oxide layer (SiAlZrHfWOxNy) of claim 1.
9. The low emissivity coating as claimed in claim 8, wherein said Infrared layer comprises layers of silver, nickel, chromium, niobium, gold alloys and like.
10. The low emissivity coating as claimed in claim 8, wherein the dielectric layer comprises silicon nitride or similar material.