First surface mirror with DLC coating

Details First surface mirror with DLC coating First surface mirror with DLC coating

2002-03-21

2004-08-31

Dunn, Drew A. (Department: 2872)

Optical: systems and elements

Mirror

Fracture resistant

C359S838000, C359S884000

Reexamination Certificate

active

06783253

ABSTRACT:

This application is related to a mirror including a coating thereon that comprises diamond-like carbon (DLC). More particularly, certain example embodiments of this invention are related to such a mirror used in the context of a projection television (PTV) apparatus, or any other suitable application.
BACKGROUND OF THE INVENTION
Mirrors for various uses are known in the art. For example, see U.S. Pat. Nos. 5,923,464, 4,309,075, and 4,272,588 (all hereby incorporated herein by reference). Mirrors are also known for use in projection televisions and other suitable applications. In the projection television context, see for example U.S. Pat. Nos. 6,275,272, 5,669,681 and 5,896,236 (all hereby incorporated herein by reference).
One type of mirror is a second or back surface mirror (most common), while another type of mirror is a first or front surface mirror (less common). Back surface mirrors typically include a glass substrate with a reflective coating on a back surface thereof (i.e., not on the front surface which is first hit by incoming light). Incoming light passes through the glass substrate before being reflected by the coating. Thus, reflected light passes through the glass substrate twice in back surface mirrors; once before being reflected and again after being reflected on its way to a viewer. In certain instances, passing through the glass substrate twice can create ambiguity in directional reflection and imperfect reflections may sometimes result. Mirrors such as bathroom mirrors, bedroom mirrors, and architectural mirrors are typically back surface mirrors so that the glass substrate can be used to protect the reflective coating provided on the rear surface thereof.
In applications where more accurate reflections are desired, front surface mirrors are often used. In front surface mirrors, a reflective coating is provided on the front surface of the glass substrate so that incoming light is reflected by the coating before it passes through the glass substrate. Since the light to be reflected does not have to pass through the glass substrate in first surface mirrors (in contrast to rear surface mirrors), first surface mirrors generally have higher reflectance than rear surface mirrors and no double reflected image. Example front surface mirrors (or first surface mirrors) are disclosed in U.S. Pat. Nos. 5,923,464 and 4,780,372 (both incorporated herein by reference).
Many first surface mirror reflective coatings include a dielectric layer(s) provided on the glass substrate over a reflective layer (e.g., Al or Ag). Unfortunately, when the overcoat dielectric layer becomes scratched or damaged in a front surface mirror, this affects reflectivity in an undesirable manner as light must pass through the scratched or damaged layer(s) twice before reaching the viewer (this is not the case in back/rear surface mirrors where the reflective layer is protected by the glass). Dielectric layers typically used in this regard are not very durable, and are easily scratched or otherwise damaged leading to reflectivity problems. Thus, it can be seen that front/first surface mirrors are very sensitive to scratching or other damage of the dielectric layer(s) which overlie the reflective layer.
U.S. Pat. No. 6,068,379 discloses a dental mirror with a protective diamond-like carbon (DLC) layer thereon. Unfortunately, the type of DLC used in the '379 Patent is undesirable in that it (a) requires heating up to 2000 degrees F. for its application which tends to damage many types of undercoat layers, and (b) is not very dense which translates into the need for a very thick coating which tends to create an undesirable yellow-brown color that is clearly undesirable and can adversely affect reflective properties. This type of DLC also tends to delaminate rather easily. Thus, both the method for applying this type of DLC, and the type of DLC itself are undesirable. Moreover, the '379 Patent illustrates a rear surface mirror which does not have the problems associated with front surface mirrors discussed above.
It will be apparent from the above that there exists a need in the art for a first/front surface mirror that is less susceptible to scratching or other damage of dielectric layer(s) overlying the reflective layer. It will also be apparent that there exists a need in the art for a protective coating that can be applied at reasonably low temperatures, and/or which does not introduce significant yellow and/or brown color to the mirror (some small amount of yellow and/or brown color is permissible, but large amounts are undesirable).
BRIEF SUMMARY OF THE INVENTION
An object of this invention is to provide a mirror including a diamond-like carbon (DLC) coating thereon. The mirror may be used in projection televisions, copiers, scanners, bar code readers, overhead projectors, and/or any other suitable applications.
Another object of this invention is to provide a protective layer(s) comprising DLC over a reflective coating of a first surface mirror, wherein the DLC has a high density so that it can be applied at a rather small thickness so that it does not introduce significant discoloration to the mirror.
Another object of this invention is to provide a protective layer(s) comprising DLC over a reflective layer(s) of a first surface mirror, wherein the DLC can be applied at rather low temperatures so that underlying layer(s) are not significantly damaged during the application of the DLC.
Another object of this invention is to provide a first surface mirror with a protective layer including DLC, wherein the index of refraction value “n” and/or thickness of the DLC is/are adjusted based upon indices of other layers of the mirror in order to achieve good reflective and/or optical properties of the mirror.
Another object of this invention is to fulfill one or more of the above-listed needs and/or objects.
In certain example embodiments of this invention, one or more of the above listed objects and/or needs is/are fulfilled by providing a first surface mirror comprising: a glass substrate supporting a coating, wherein the coating includes at least a reflective layer, first and second dielectric layers, and a layer comprising amorphous diamond-like carbon (DLC), wherein the reflective layer is provided between the glass substrate and the dielectric layers, and the layer comprising DLC is provided over the reflective layer and the dielectric layers, wherein the first dielectric layer has an index of refraction value “n” greater than an index of refraction value “n” of the reflective layer and less than an index of refraction value “n” of the second dielectric layer, and the layer comprising DLC has an index of refraction value “n” less than the index of refraction value “n” of the second dielectric layer, and wherein the layer comprising DLC has an average density of at least about 2.4 gm/cm
3
and at least about 40% of carbon-carbon bonds in the layer comprising DLC are sp
3
type carbon-carbon bonds, and wherein the layer comprising DLC has an average hardness of at least about 10 GPa.
In other example embodiments of this invention, one or more of the above listed objects and/or needs may be fulfilled by providing a mirror comprising: a substrate supporting a coating, wherein the coating includes a reflective layer, at least a first dielectric layer, and a layer comprising diamond-like carbon (DLC) provided over the reflective layer and the first dielectric layer, and wherein the layer comprising DLC has an average density of at least about 2.4 gm/cm
3
and at least about 40% of carbon-carbon bonds in the layer comprising DLC are sp
3
type carbon-carbon bonds, and wherein the layer comprising DLC is from about 1-100 nm thick.
In still other example embodiments of this invention, one or more of the above listed objects and/or needs may be fulfilled by providing a projection television including a first surface mirror for reflecting at least red, blue and green light components from a source toward a lens so that an image can be viewed by a viewer, wherein the first surface mirror comprises:

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