Low-emissivity, soil-resistant coating for glass surfaces

Abstract

A glass article that has a water-sheeting coating and methods of applying coating to a substrate are described. In certain embodiments, a water-sheeting coating 20 comprising silica is sputtered directly over a pyrolytic dielectric film over a glass sheet. In some cases, the exterior face of this water-sheeting coating is substantially non-porous but has an irregular surface. The water-sheeting coating causes water applied to the coated surface to sheet, making the glass article easier to clean and helping the glass stay clean longer. One embodiment provides an IG unit having a low-emissivity coating on its #2 surface, and having on its #4 surface a sputtered silica film over a pyrolytic dielectric layer.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] The present application is a continuation of U.S. patent application Ser. No. 09 / 868,543 (the contents of which are incorporated herein by reference), which was filed 15 Jan. 2002 and was a U.S. national stage filing under 35 USC 371 of International application PCT / US99 / 17876 (the contents of which are incorporated herein by reference), which was filed 6 Aug. 1999 and claimed priority to U.S. patent application 60 / 113,259 (the contents of which are incorporated herein by reference), filed 21 Dec. 1998, U.S. patent application 60 / 134,705 (the contents of which are incorporated herein by reference), filed 18 May 1999; and International application PCT / US99 / 02208 (the contents of which are incorporated herein by reference), filed 2 Feb. 1999.FIELD OF THE INVENTION [0002] The present invention provides a coating for glass substrates and the like which resists accumulation of dirt and water stains. Coated glass substrates of the invention c...

AI Technical Summary

Benefits of technology

[0018] In one aspect, the present invention provides a glass article that has a low-emissivity water-sheeting coating and a method of applying such a coating. In one embodiment, the invention provides a coated glass article having an exterior surface bearing a low emissivity water-sheeting coating thereon. The coating includes a first pyrolytically applied dielectric layer carried by the exterior surface of the glass article. An exterior layer of silica is sputtered directly onto the outer surface of the first layer, the low emissivity water-sheeting coating reducing the contact angle of water on the coated exterior surface of the glass article below about 15° and causing water applied to the coated exterior surface of the pane to sheet.

[0019] A second embodiment of the invention provides an automobile windscreen including an outer pane of glass having an exterior surface and a first bonded surface, an inner pane of glass having an interior surface and a seconded bonded surface, and a tear-resistant polymeric layer disposed between the first bonded surface and the second bonded surface. A low emissivity water-sheeting coating is carried by the exterior surface of the outer pane, the exterior coating including a first dielectric layer pyrolytically applied directly to the exterior surface and an exterior layer of silica sputtered directly onto the outer surface of the first layer, the low emissivity water-sheeting coating reducing the contact angle of water on the coated exterior surface of the glass article below about 15° and causing water applied to the coated exterior surface of the pane to sheet.

Problems solved by technology

Keeping windows and other glass surfaces clean is a relatively expensive, time-consuming process.

While cleaning any individual window is not terribly troublesome, keeping a larger number of windows clean can be a significant burden.

For example, with modern glass office towers, it takes significant time and expense to have window washers regularly clean the exterior surfaces of the windows.

First, the water itself can deposit or collect dirt, minerals or the like onto the surface of the glass.

Obviously, dirty water landing on the glass will leave the entrained or dissolved dirt on the glass upon drying.

Even if relatively clean water lands on the exterior surface of a window, each water droplet sitting on the window will tend to collect dust and other airborne particles as it dries.

As a result, the glass that underlies a drying water droplet will become a little bit rougher by the time the water droplet completely dries.

In storing and shipping plate glass, the presence of water on the surfaces between adjacent glass sheets is a chronic problem.

However, if the glass is stored in a humid environment, water can condense on the glass surface from the atmosphere.

This becomes more problematic when larger stacks of glass are collected.

Large stacks of glass have a fairly large thermal mass and will take a long time to warm up.

Due to limited air circulation, any moisture which does condense between the sheets of glass will take quite a while to dry.

This gives the condensed moisture a chance to leach the alkaline components out of the glass and adversely affect the glass surface.

While such photocatalytic coatings may have some benefit in removing materials of biological origin, their direct impact on other materials is unclear and appears to vary with exposure to ultraviolet light.

As a consequence, the above-noted problems associated with water on the surface of such coated glasses would not be directly addressed by such photocatalytic coatings.

Such “water repellent” coatings do tend to cause water on the surface of the glass to bead up.

However, in more quiescent applications, these droplets will tend to sit on the surface of the glass and slowly evaporate.

As a consequence, this supposed “water repellent” coating will not solve the water-related staining problems noted above.

To the contrary, by causing the water to bead up more readily, it may actually exacerbate the problem.

In so doing, it seems probable that the problems associated with the long-term residence of water on the glass surface would be increased.

While heat would still be lost by convection, limiting heat loss as infrared radiation may keep the glass sufficiently warm to avoid having the glass cooler than the “dew point” and thereby limit or even prevent the precipitation of dew or frost on the surface.

Most conventional sputtered infrared-reflective films are inadequately durable to be carried on an external glass surface.

However, they are insufficiently durable to weather indefinite exposure to the elements and usually are assembled in IG assemblies or windshields where they are shielded from the ambient atmosphere by another pane of glass.

Unfortunately, pyrolytic coatings have other drawbacks that have limited their widespread commercial adoption for such purposes.

It apparently tends to adversely affect bonding of the glass to the tear-resistant plastic sheet in such windshield laminates, requiring that it be used as either the external surface (i.e., facing the ambient environment) or the internal surface (i.e., facing the cabin of the vehicle) of the windshield.

Applied to the external surface, the pyrolytically applied coating does not appear to be sufficiently durable to withstand the rigors of many years of chemical exposure to the elements and the physical abrasion such a surface must endure.

In addition, it has been observed that this coating is notably more difficult to clean when it becomes dirty and tends to become dirty more readily than standard, untreated glass.

As a result, it is not deemed an optimal choice for the external surface of an automobile windshield and it has achieved limited success in the marketplace for this application.

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