HK1116467B - Protective layers for optical coatings - Google Patents

Description

Protective layer for optical coatings

The present application is a divisional application of chinese patent application having application number 03802615.5, application date 2003, month 1, and day 27, entitled "protective layer for optical coating".

Background of the invention

Field of the invention

The present invention relates to a protective layer for an optical coating on a transparent substrate. The invention relates in particular to the use of a temporary carbon protective layer. In addition, the present invention relates to Scratch Propagation Blocker (SPB) protective layers for the outermost layers of various optical coatings.

Discussion of the background Art

Optical coatings are deposited on transparent substrates to reflect or alter the transmission of some or all of the radiation incident on the substrate. For example, the optical coating of the mirror is for reflecting visible light. Low emissivity optical coatings are used to reduce the transmission of infrared radiation. The optical coating typically comprises two or more distinct layers having thicknesses in the range of less than 1nm to greater than 500nm, respectively.

During shipping and handling, optical coatings are often damaged by scratching and exposure to corrosive environments. Low emissivity coatings based on silver have been plagued by corrosion problems especially since the introduction of the perforated market decades ago. In an attempt to improve the durability of optical coatings, the use of temporary protective layers, such as plastic adhesive backed films, has been involved. Other protective layers have been formed by applying and curing polymer-based solvents on glass.

However, the use of adhesive films and polymer films as protective layers on optical coatings presents a number of problems. The application of adhesive and polymer films to optical coatings requires expensive specialized equipment. When the adhesive film is torn off from the optical coating, the adhesive film runs the risk of taking away part of the optical coating. Even if a portion of the optical coating is not removed, the force exerted on the optical coating by the removal of the adhesive film can damage the optical coating. The solvent-based polymer film applied to the optical coating must be dried and the solvent removed in an environmentally friendly manner. Removal of the polymer film from the optical coating requires a specialized detergent that can easily damage the optical coating.

To protect against corrosion, silver-based low emissivity stacks are currently used in direct contact, and an isolating layer or cover layer is used on one side of the two silver layers. It is known in the art that various thin film layers can serve to isolate the movement of corrosive fluids, such as water vapor and oxygen. Metal layers are known to be particularly effective diffusion membranes due to their ability to physically and chemically inhibit the diffusion of corrosive fluids. Metal layers are more effective physical barriers to diffusion than dielectric layers, such as oxides, because evaporated and sputtered metal layers contain fewer pinhole defects than oxide layers. The metal layer also tends to chemically block diffusion by reacting with the fluid diffusing through the pin hole, stopping the movement of all chemically bound fluid molecules. The bound fluid molecules then restrict the passage of other fluids through the pinhole. More reactive metals are particularly effective for chemical blocking.

Tempering (tempering) greatly reduces the corrosion problems associated with silver-based low emissivity coatings. Tempering results in a restructuring of the atomic energy levels to lower energy states and a low tendency for silver to corrode. Tempering also improves the hardness and scratch resistance of the optical coating.

However, before the optical coating is tempered, the coating is still particularly vulnerable to scratching and corrosion. Even after tempering, the optical coating is not protected from scratches and corrosion.

Scratches in optical coatings are generally not visible until the coating is heated and tempered, which can cause the scratches to grow and propagate.

Carbon has been used as a protective coating on glass substrates. For example, U.S. patent No.6,303,226 discloses the use of amorphous diamond-like carbon (DLC) as a protective layer on a glass substrate.

There is a need for improved methods and protective layers for protecting optical coatings.

Summary of the invention

The present invention provides a method for making a transparent article having a reduced number of scratches and other surface defects. The transparent article includes an optical coating on a transparent substrate. According to the present invention, a protective layer that improves the durability and scratch resistance of an optical coating, particularly during production, is formed on the optical coating.

The protective layer may comprise a layer consisting essentially of carbon. A carbon protective layer is formed on the optical coating prior to tempering. The carbon layer acts as a low-friction scratch-resistant protective layer during transport and handling of the untempered optical coating. Heating and tempering the carbon-reactive optical coating and/or transparent substrate at atmospheric pressure consumes the carbon protective layer, thus eliminating any scratches or other surface defects in the carbon. The carbon protective layer is converted to a carbon-containing gas, leaving a relatively scratch-free optical coating.

The protective layer may also comprise a thin protective layer of Scratch Propagation Blocker (SPB) material. During tempering, the SPB material inhibits the propagation of scratches into the brittle, glassy, outermost layer of various optical coatings. SPB materials such as Ti, Si, Zn, Sn, In, Zr, Al, Cr, Nb, Mo, Hf, Ta and W, and oxides and nitrides thereof are suitable for use In silicon nitride (e.g., Si-based nitride, Nb-based nitride, and Si-based nitrideSuch as Si₃N₄) On the outermost layer of (a). The SPB layer can be formed by: depositing a diffusion barrier layer of at least one metal, metal suboxide or metal subnitride of Ti, Si, Zn, Sn, In, Zr, Al, Cr, Nb, Mo, Hf, Ta or W on the outermost layer of the optical coating; the diffusion barrier is then reacted with an oxygen-containing atmosphere, such as air, to form a TiO-containing layer₂、SiO₂、ZnO、SnO₂、In₂O₃、ZrO₂、Al₂O₃、Cr₂O₃、Nb₂O₅、MoO₃、HfO₂、Ta₂O₅And WO₃A metal oxide SPB layer of at least one of (1). The SPB layer may be used with or without a carbon protective layer on the SPB layer.

The use of a temporary carbon protective layer in the production of transparent articles having an optical coating significantly reduces the number and severity of scratches introduced into the optical coating by the production process. The carbon layer does not affect the optical properties of the optical coating because it is removed during tempering. Although the SPB layer is not removed during tempering and may affect the optical properties of the optical coating, the SPB layer is particularly useful for protecting the brittle, glassy outermost layer of the optical coating from the formation of visible scratches by inhibiting the propagation of scratches. Metals, metal suboxides or metal subnitrides are particularly suitable for providing corrosion protection prior to tempering and can be converted to a metal oxide SPB layer that is substantially transparent to visible light by tempering in an oxygen-containing atmosphere.

Brief description of the drawings

Preferred embodiments of the present invention are described in detail with reference to the following drawings.

FIGS. 1A-1C show a carbon protective layer deposited on an optical coating on a glass substrate and the subsequent removal of the carbon protective layer.

Figure 2 shows a glass substrate coated with an optical coating, a scratch propagation blocker layer and a carbon protective layer.

FIG. 3 shows scratch propagation through Si₃N₄And (3) a layer.

Fig. 4A-4C show a metal layer deposited on an optical coating on a glass substrate, and the metal layer is subsequently converted to a metal oxide scratch propagation blocker layer.

Figure 5 compares glass substrates with the same optical coating with or without a carbon protective layer when scratched.

Figure 6 compares glass substrates with the same optical coating with or without a carbon protective layer when scratched.

Detailed description of the preferred embodiments

The present invention provides a protective coating deposited on an optical coating on a transparent substrate to inhibit the formation of scratches on the optical coating and corrosion of the optical coating.

The transparent substrate may be plastic or glass. Preferably, the transparent substrate is glass that can be tempered by heating and quenching.

In an embodiment, the protective coating comprises a carbon protective layer. Carbon is a typical low friction material. Even if the abrasive initially scratches the carbon, the abrasive is typically coated with carbon. Subsequent contact between the carbon-coated abrasive and the carbon is characterized by the lowest coefficient of friction, μ_Quiet≈μ_{Movable part}0.1-0.2. Thus, carbon coated abrasives tend to slip off of the carbon without further damage to the carbon. Carbon is also inert in many corrosive environments and exhibits good resistance to bases and most acids. Thus, the carbon layer on the optical coating can protect the optical coating from scratches and environmental corrosion during handling.

Fig. 1A-1C illustrate embodiments of the invention in which a temporary carbon layer is formed over the optical coating to protect the optical coating from scratches and environmental corrosion during the manufacturing process. Fig. 1A shows a glass substrate 1 coated with an optical coating 2. Fig. 1B shows the deposition of a carbon protective layer 3 on the optical coating 2 in order to protect the optical coating from scratches and environmental corrosion during shipping and handling. Fig. 1C shows that after tempering the optical coating 2 and/or the glass substrate 1 at an elevated temperature in a reactive atmosphere of carbon, the carbon protective layer 3 is converted to a carbon-containing gas and any scratches or other damage already present in the carbon protective layer 3 is eliminated.

The carbon protective layer is a layer consisting essentially of carbon. The term "consisting essentially of excludes other elements and compounds not specifically indicated which remain as solid residues when carbon is fully reacted with a reactive atmosphere to form a carbon-containing gas, while excluding unavoidable impurities. In an embodiment, the carbon layer consists of carbon and unavoidable impurities.

The carbon layer may be deposited on the optical coating by vapor deposition. Techniques and methods for vapor deposition of carbon are well known in the art. Suitable vapor deposition methods include evaporation and plasma deposition methods such as plasma chemical vapor deposition, ion implantation and sputtering. The sputtering may be DC or RF. An inert gas such as Ar with or without small amounts of other gases such as hydrogen and nitrogen may be used in the plasma deposition process to form the carbon layer. The presence of 1-10% nitrogen in the inert gas aids in the deposition of graphitic carbon. Nitrogen in the inert gas may be used to dope the carbon with nitrogen.

The carbon layer may include one or more carbon phases such as graphite, diamond, and amorphous phases of carbon. The carbon layer may also include diamond-like carbon. Carbon in graphite having sp²And (4) combining. Carbon in diamond has sp³And (4) combining. Amorphous carbon generally comprises sp²And sp³Combined, but long-range disorder. The diamond-like carbon further includes sp²And sp³Combine and exhibit a hardness similar to diamond.

The carbon layer is typically 1-10nm thick. Carbon layers less than 1nm thick do not provide adequate scratch resistance. A carbon layer more than 10nm thick becomes difficult to completely remove in a reactive atmosphere of carbon.

The reactive atmosphere used to convert the carbon protective layer into a carbon-containing gas may include various gases reactive with carbon as known in the art. For example, the reactive atmosphere may include hydrogen gas, which is capable of converting carbon to methane gas. Halogens, such as fluorine or chlorine, can be used to form tetrahalomethane gases, such as CF, at elevated temperatures₄Or CCl₄. Oxygen in the reactive atmosphere can be used to form carbon monoxide and carbon dioxide gases. Since optical coatings and glasses typically contain various oxides that are inert in oxygen, the reactive atmosphere of carbon preferably contains oxygen. Due to air (containing O)₂) Cheap and readily available, more preferably the reactive atmosphere is air.

Tempering is a process that involves heating the material to an elevated temperature and then quenching. Tempering is known to significantly increase the strength and toughness of glass and optical coatings on glass. The glass may be tempered by heating to a temperature range of 400-650 ℃ followed by quenching to room temperature. Optical coatings containing Ag layers can be tempered by heating to a temperature range below 960 ℃ below the melting point of Ag, followed by quenching to room temperature. For example, a low emissivity optical coating comprising a silver layer may be tempered by heating to about 730 ℃ for several minutes, followed by quenching. The glass and optical coating are preferably tempered at a temperature of at least 400 ℃. In an embodiment of the invention, both the glass and the optical coating are tempered in an oven maintained at an elevated temperature. In other embodiments, to avoid having to heat the entire glass, only the optical coating is tempered. For example, rather than heating in an oven, the optical coating may be heated by a flame lamp or high intensity lamp to a temperature sufficient to temper the optical coating and burn off the carbon protective layer.

Thus, tempering the optical coating covered by the carbon protective layer in a reactive atmosphere of carbon enables the carbon to form a carbon-containing gas and leave the surface of the optical coating. Any scratches in the carbon layer disappear with the carbon layer. Preferably, the reactive atmosphere tempering removes all of the carbon protective layer from the optical coating.

The carbon protective layer can protect the optical coating from scratches caused during the production of the coating, for example, by shipping and handling. In addition, the carbon protective layer may also protect the optical coating from a corrosive environment that may occur when the optical coating with the carbon protective layer is stored in air for one or more days or washed. Preferably, the number of scratches in the optical coating immediately after the carbon protective layer is removed is no more than 110% of the number of scratches in the optical coating immediately before the carbon is deposited on the optical coating.

In embodiments of the present invention, an SPB layer may be formed between the carbon protective layer and the optical coating. Preferably, the SPB layer has a uniform composition and is completely uniform. The SPB layer is made of a material having properties that inhibit propagation of scratches and cracking to the outermost layer of the optical coating during tempering. Different outermost layers require different materials in the SPB layer. The material forming the SPB layer should be less brittle and glassy than the outermost layer of the optical coating. Preferably, the SPB material has a higher fracture toughness than the outermost layer.

FIG. 2 shows an embodiment of the invention in which an SPB layer 4 is sandwiched between a carbon protective layer 3 and the outermost Si layer of an optical coating 2₃N₄Between the layers 2 a. Both the SPB layer 4 and the carbon protective layer 3 provide scratch protection for the optical coating 2. In particular, the SPB layer 4 inhibits the carbon protective layer 3 from going down and into Si₃N₄Propagation of layer 2 a.

It is preferable that the outermost layer of silicon nitride has a uniform composition and is completely uniform. In the case of tempered, preference is given to optical coatings on glass substratesOutermost layer (e.g. amorphous Si)₃N₄)。No phase change is effected upon heating to the temperature required for tempering the glass. In addition to this, the present invention is,is the same before and after tempering, so tempering does not leave stress on the silicon nitride and its layersThe interface of the remaining optical coating causes delamination.

Haze formation in the optical coating is also suppressed. When the materials are mixed together to form a two-phase system, cloudiness occurs, causing the refractive index to change as a function of the state of the entire layer. Haze in the optical coating with the outermost layer of silicon nitride is reduced after tempering due to the phase stability of the silicon nitride preventing mixing.

Since the silicon nitride remains amorphous, the atomic movement at the interface between the optical coatings is less than would occur if the phases were altered, which allows the original adhesion between the layers to be better preserved.

In optical coatingsOne problem with the outermost layer is that the covalent bonding and amorphous structure of the silicon nitride creates a hard material with crack propagation characteristics similar to glass. Very small cracks are easily propagated through hard vitreous materials.

Fig. 3 illustrates a possible mechanism by which cracks can propagate through optical coating 2 having an outermost layer of silicon nitride. Small scratches are initially shallow and are not detectable by the "naked eye" inspection method used in most tempering lines. This is because the scratches do not pass completely through the outermost layer of silicon nitride. However, small cracks propagate through the silicon nitride by heating to the underlying layer, e.g., Ag. Upon exposure to cracking, Ag coalesces on its unconstrained surface. When the Ag coalesces, cracking becomes visible and part of the product must be rejected.

In the embodiment shown in fig. 2, cracking in the optical coating with the outermost layer of silicon nitride after tempering is minimized by depositing the SPB layer on the silicon nitride and the C layer on the SPB layer prior to tempering. The SPB/C combination and optical coating can be deposited on the glass using the same deposition equipment.

As noted above, carbon provides a typically low friction surface, and even when the abrasive initially scratches the carbon, the abrasive becomes coated with carbon, resulting in a very low friction carbon-carbon slip.

If the abrasive continues to penetrate the carbon overcoat, the abrasive will encounter the SPB layer. However, most scratches or cracks formed by the abrasive will not propagate through the SPB layer upon tempering. Although the SPB layer remains after tempering unlike the carbon protective layer, most scratches in the SPB remain invisible to the naked eye.

Materials suitable for forming the SPB layer include metals such as Ti, Si, Zn, Sn, In, Zr, Al, Cr, Nb, Mo, Hf, Ta, and W, oxides of these metals, and nitrides of these metals.

The term "oxide" as used herein includes stoichiometric oxides, peroxides containing more than a stoichiometric amount of oxygen, and suboxides containing less than a stoichiometric amount of oxygen. The term "metal suboxide" as used herein includes metals doped with small amounts of oxygen, for example 0.1 to 10 atomic percent oxygen.

The term "nitride" as used herein includes stoichiometric nitrides, supernitrides containing more than a stoichiometric amount of nitrogen, and subnitrides containing less than a stoichiometric amount of nitrogen. The term "metal subnitride" as used herein includes metals doped with small amounts of nitrogen, e.g., 0.1-10 atomic%.

Stoichiometric oxides suitable for forming the SPB layer include TiO₂、SiO₂、ZnO、SnO₂、In₂O₃、ZrO₂、Al₂O₃、Cr₂O₃、Nb₂O₅、MoO₃、HfO₂、Ta₂O₅、WO₃. Stoichiometric nitrides suitable for forming the SPB layer include TiN. TiO 2₂Particularly excellent in suppressing scratches. The SPB layer can be formed by vapor deposition techniques known in the art.

The SPB layer may be 2-8nm thick. When the SPB layer is a stoichiometric oxide or nitride, the SPB layer is preferably 2-8nm, more preferably 3-6nm thick. When the SPB layer is a metal, the SPB layer is preferably 4-8nm, more preferably 4-6nm thick. If the stoichiometric oxide or nitride SPB layer is thinner than 2nm, or the metal layer is thinner than 4nm, the tendency of the SPB layer to suppress scratch propagation appears to be reduced. The advantage of SPB layer thicknesses of more than 8nm is small because the inhibition of scratch propagation by the SPB layer saturates at a thickness of about 8nm and the effect of the SPB layer on the optical characteristics of the optical coating increases with the thickness of the SPB layer, which must be taken into account. However, as described above, the metal, metal suboxide and metal subnitride used as the diffusion barrier layer (after oxidation during tempering, a substantially invisible metal oxide SPB layer may be formed) may be thicker than 2 nm.

As described above, in embodiments, the SPB layer may be combined with a carbon protective layer on top of the SPB layer. In other embodiments, the SPB layer may form the only protective layer on the optical coating. The SPB layer helps prevent scratches and scratch propagation during processing even without a carbon protective layer.

In embodiments of the invention, the SPB layer may be formed by oxidizing a diffusion barrier layer used to provide corrosion protection to the optical coating prior to tempering. The diffusion barrier layer is a metal, metal suboxide or metal subnitride material comprising a metal element selected from the group consisting of Ti, Si, Zn, Sn, In, Zr, Al, Cr, Nb, Mo, Hf, Ta and W. A diffusion barrier layer is deposited on the outermost layer of the optical coating prior to tempering the optical coating. Tempering the optical coating in an oxygen-containing atmosphere converts the diffusion barrier layer to a metal oxide SPB layer. Preferably, the diffusion barrier layer contains Ti, Zr or Al, which can be converted into the metal oxide TiO, respectively, by heating in air₂、ZrO₂Or Al₂O₃The SPB layer of (a). Preferably, the metal suboxide contains about 80% or less of the oxygen present in the most fully oxidized stoichiometric oxide of the metal. Metal suboxide deposits that are substantially oxidized by about 80% or less as compared to reactive deposited films that are substantially oxidized by greater than about 80%The film tends to form a better diffusion barrier.

As mentioned above, metallic layers are known to be particularly effective barriers to the diffusive movement of corrosive fluids. Metal suboxides and metal subnitrides act like metals as diffusion barriers. Metal suboxides and metal subnitrides tend to form dense layers when sputtered or evaporated, and chemically inhibit oxygen and water vapor diffusion to a greater extent than the corresponding fully oxidized metals.

The metal suboxide and metal subnitride may be formed by vapor deposition methods known in the art. For example, metal suboxides and metal subnitrides can be formed by vapor depositing metals in an atmosphere containing controlled amounts of oxygen and nitrogen.

Metal suboxides and subnitrides tend to optically absorb and reduce the visible light transmission of the optical coating until it is heated and reacted to a fully oxidized state.

In metal subnitrides, the bond between nitrogen and the metal is generally not as strong as the bond between oxygen and the metal in metal suboxides. The metal subnitride is heated in an oxygen-containing atmosphere, typically to convert the metal subnitride to the corresponding metal oxide or at least to a substantially transparent metal oxynitride.

The diffusion barrier layer may be 4-8nm thick, preferably 4-6nm thick. If the thickness of the metal is 2nm or less, the reactive metal layer is generally sufficiently oxidized in air at room temperature. The thicker metal layer typically oxidizes to a depth of 2nm while the rest of the layer remains metallic. The oxidation process can proceed deeper if the metal is exposed to an energy source, such as heat or an environment that is more chemically reactive than air. In an embodiment of the invention, the diffusion barrier layer is deposited thicker than would be fully oxidized at room temperature. In this way, the layer remains as metal and acts as an effective corrosion barrier before tempering. In order to provide the above described scratch propagation resistance prior to oxidation, it is preferred that the deposited diffusion barrier layer be 4nm or thicker. To ensure that the diffusion barrier layer is sufficiently oxidized during annealing, the diffusion barrier layer is deposited to a thickness of 8nm or less, preferably 6nm or less.

When a 4-6nm thick metal, metal suboxide or metal subnitride is sufficiently oxidized, it tends to have a small amount of optical effect on the optical stack. Since metal oxides are more transparent to visible light than metals, metal suboxides, and metal subnitrides, sufficient oxidation of the diffusion barrier layer produces an effective optically invisible metal oxide SPB layer.

The formation of the metal oxide SPB layer from the diffusion barrier layer using a tempering process on a temperable low-emissivity optical coating both protects the coating from corrosion prior to tempering and eliminates many of the undesirable optical effects associated with the diffusion barrier layer as an SPB layer on the low-emissivity optical coating after tempering. In further embodiments, a carbon layer may be deposited as a diffusion barrier layer on the temperable low-emissivity optical coating as additional protection for the optical coating. The optical coating is then tempered by heating in air, both burning off the carbon layer and converting the diffusion barrier layer into a transparent metal oxide SPB layer.

Fig. 4A-4C illustrate embodiments of the invention in which a metal oxide SPB layer is formed by depositing a metal onto an optical coating and then oxidizing the metal in an oxygen-containing atmosphere to form an oxide. Fig. 4A shows a glass substrate 1 provided with an optical coating 2. Fig. 4B shows a metal layer 5 deposited on the optical coating 2. Fig. 4C shows that by heating the metal layer 5 in an oxygen-containing atmosphere, such as air, the metal layer 5 is converted into the metal oxide scratch propagation blocker layer 4.

Examples

The following examples serve to further illustrate the invention, but do not limit the scope of use as defined in the appended claims.

Example 1

FIGS. 5(1) -5(4) are graphs obtained by depositing a temporary carbon protective layer on the optical layer before tempering according to the present inventionOptical microscope pictures on the coating and subsequent removal of the carbon protective layer by tempering in a reactive atmosphere show a significant reduction of scratches. Each sample had the same optical coating. The optical coating comprises multiple layers of Zn, Ag and NiCr, with a 36nm thick outermost layer of Si. A 1nm thick carbon protective layer was deposited on the optical coating of the samples shown in fig. 5(1) and 5(2), but not on the optical coating of the samples shown in fig. 5(3) and 5 (4). Then using the same commercially available grinding wheel under the same conditions (Wheel) scratch the sample. Fig. 5(1) and 5(2) show different areas of the carbon protection sample representing the most severe scratches. The scratches in FIG. 5(1) are about 10-15nm wide. Fig. 1 and 5(3) show scratch samples before tempering. Fig. 5(2) and 5(4) show scratch samples after tempering at 730 c for 4 minutes in air. During tempering in air, the width of the scratch is approximately doubled. The carbon protective layer on the sample shown in fig. 5(2) burns off with most of the scratches during the tempering process.

Fig. 5 shows that the presence of a carbon protective layer on the optical coating before tempering greatly reduces the number of scratches that appear on the optical coating after tempering in air when the carbon layer is burned off.

Example 2

Figure 6 shows the effect of different carbon overcoat thicknesses on the scratches remaining on the optical coating after tempering for the comparative 9 samples (reference numerals 1-9). Each sample had the same optical coating. The optical coating comprises multiple layers of Zn, Ag and NiCr, with a 36nm thick outermost layer of Si. Table 1 below shows that carbon protective layers of different thicknesses were deposited on the samples. Samples 1-2 did not contain a carbon protective layer.

TABLE 1

Sample (I)	Thickness of carbon (nm)
		1	Is free of
2	Is free of
		3	1
4	1.2
		5	1.8
6	5
		7	5
8	10
		9	15

Using the same commercially available grinding wheel under the same conditions (Wheel) scratch the sample. The 9 samples were tempered in air at 730 ℃ for 4 minutes. Fig. 6 shows samples 1-9 after tempering.

As shown in fig. 6, samples 3-9 including the temporary carbon overcoat after tempering in air had significantly fewer scratches than samples 1-2 without the carbon overcoat. The color of samples 3-8 after tempering was the same as the color of samples 1-2 before tempering, indicating that the carbon layer on samples 3-8 was completely removed. A small amount of carbon remained on sample 9 after tempering.

Example 3

Protective layers of various SPB materials and carbon were deposited on the same optical coating on glass. Using the same commercially available grinding wheel under the same conditions (Wheel) scratch the sample. Table 2 shows the relative ability of each SPB material and carbon to reduce scratch damage.

TABLE 2

Protective layer (SPB or C)	Thickness (nm)	Damage (%)
			Unprotected (Standard)	-	100
SiO2	2	60
			TiN	2	30
TiO2	2	30
			ZnO	2	10
C	1	10
			C	10	2

In table 1, "damage%" is the approximate number of scratches per unit length in the direction perpendicular to the rubbing tool.

Table 2 shows that the SPB layer helps prevent scratches and scratch propagation during handling even without a carbon protective layer. The combination of SPB and C layers is more effective in suppressing scratches. The thickness of each SPB and C layer can be varied as desired.

Example 4

Zr layers of different thicknesses were deposited on the same silver-based low-emissivity optical coating on a glass substrate. The Zr coated optical coating was left in room temperature air at 80% relative humidity for 24 hours. The optical coating is then tempered in air at 730 ℃. Zr layers 2nm and 3nm thick were found to provide no corrosion protection to the silver-based low emissivity coating. In contrast, Zr layers 4nm and 8nm thick were found to provide substantial corrosion protection for silver-based low emissivity coatings.

The present invention has been described in terms of specific embodiments without limitation to the specific details set forth, and also includes variations and modifications as would be apparent to a person skilled in the art, all of which are within the scope of the present invention as defined by the following claims.

Claims (21)

1. A method of making a transparent article comprising

Forming a temporary protective coating comprising a layer consisting essentially of carbon over the optical coating on the substrate;

heating the protective coating in a reactive atmosphere;

reacting the layer comprised of carbon with a reactive atmosphere to form a carbon-containing gas; and

removing the layer consisting essentially of carbon from the optical coating to form a transparent article.

2. The method of claim 1, wherein said forming comprises vapor depositing a protective coating.

3. The method of claim 2, wherein said vapor depositing comprises sputtering.

4. The method of claim 1, wherein the layer consisting essentially of carbon is 1-10nm thick prior to heating.

5. The method of claim 1, wherein the layer consisting essentially of carbon is doped with nitrogen.

6. The method of claim 1, wherein the layer consisting essentially of carbon consists of carbon and unavoidable impurities.

7. The method of claim 1, wherein the carbon comprises at least one form of carbon selected from the group consisting of diamond-like carbon and graphite in the layer consisting essentially of carbon.

8. The method of claim 1, wherein the reactive atmosphere is an oxygen-containing atmosphere.

9. The method of claim 8, wherein the oxygen-containing atmosphere is air.

10. The method of claim 1, wherein the carbon-containing gas comprises at least one compound selected from the group consisting of carbon monoxide and carbon dioxide.

11. The method of claim 1, wherein the heating comprises raising the temperature of the protective coating to at least 400 ℃.

12. The method of claim 1, wherein the heating tempers the optical coating.

13. The method of claim 1, wherein the heating tempers the substrate.

14. The method of claim 1, wherein the substrate comprises glass.

15. The method of claim 14, wherein the glass is transparent to visible light.

16. The method of claim 1, wherein the reacting removes all of the layer consisting essentially of carbon from the optical coating.

17. The method of claim 1, wherein the number of scratches in the optical coating after said removing is no more than 110% of the number of scratches in the optical coating immediately prior to said forming.

18. The method of claim 1, wherein the optical coating comprises a uniform outermost layer comprising silicon nitride furthest from the substrate.

19. The method of claim 18, wherein

The protective coating further comprises a scratch propagation blocker layer between the layer consisting essentially of carbon and the outermost layer; while

The scratch propagation blocker layer is a uniform layer comprising a material selected from the group consisting of:

ti, Si, Zn, Sn, In, Zr, Al, Cr, Nb, Mo, Hf, Ta and W; oxides of Ti, Si, Zn, Sn, In, Zr, Al, Cr, Nb, Mo, Hf, Ta and W; nitrides of Ti, Si, Zn, Sn, In, Zr, Al, Cr, Nb, Mo, Hf, Ta and W; and mixtures thereof.

20. The method according to claim 19, wherein the scratch propagation blocker layer is composed of unavoidable impurities and a material selected from the group consisting of:

ti, Si, Zn, Sn, In, Zr, Al, Cr, Nb, Mo, Hf, Ta and W; oxides of Ti, Si, Zn, Sn, In, Zr, Al, Cr, Nb, Mo, Hf, Ta and W; nitrides of Ti, Si, Zn, Sn, In, Zr, Al, Cr, Nb, Mo, Hf, Ta and W; and mixtures thereof.

21. The method of claim 19, wherein the thickness of the scratch propagation blocker layer is 2 to 8 nm.