Patent Application
20150037569
The present invention generally relates to coating compositions and methods. More particularly this invention relates to reflective coating systems suitable for use in reflector lamps.
Reflector lamps have various applications, nonlimiting examples of which include spot lights and head lamps. Particular examples of reflector lamps include PAR (parabolic aluminized reflector) 38 and PAR 64 lamps available from various manufacturers. Reflective coatings are often deposited on the interior surface of a glass substrate housing of a reflector lamp to improve reflectance of the lamp. U.S. Pat. No. 6,773,141 describes reflector lamps and reflective coatings, and the contents of this patent relating thereto are incorporated herein by reference.
In recent years, considerable emphasis has been placed on increasing energy efficiency in reflector lamps. Energy efficiency is measured in the industry in lumens produced by a lamp per watt (LPW) of electricity input to the lamp. Lamps with higher LPW are more energy efficient than those with lower LPW. Consequently, improvements are often sought to maintain or enhance the LPW of lamps in cost-effective ways without compromising efficiency and aesthetics. As an example, a lamp can employ a reflective coating to reduce light absorption by the lamp housing and/or increase the lumens of light transmitted through a lens or other transparent section of the lamp, offering the potential to increase the efficiency of the lamp. Reflectance is typically indicated as a ratio of the total amount of light reflected by a surface to the total amount of radiation incident on the surface.
In the lighting industry, commonly used reflective coatings include aluminum and silver metallic films (coatings). Methods of achieving these coatings are described in U.S. Pat. No. 6,773,141 and elsewhere and therefore will not be described in any detail here. Silver metallic films may require protection to prevent certain undesirable consequences, including oxidation at lamp operating temperatures and chemical attack. For this reason, protective coatings have been developed which include, but are not limited to, silicon dioxide (SiO2) films. Reflective silver metallic films may also require a sufficient thickness to survive harsh manufacturing conditions. Because reflective coatings that contain silver can significantly increase the cost of a reflector lamp due to the high cost of silver, there is an ongoing desire for reflective coatings that are less expensive than relatively thick silver reflective coatings. Further, any new reflective coating would desirably maintain the reflectance and the cosmetic appearance of the lamp when viewed from within and outside the lamp. Thus a need exists for reflective coatings capable of achieving reflectance comparable to silver films while reducing material costs and maintaining the overall cosmetic appearance of a reflector lamp.
The present invention provides reflective coating systems suitable for use in lamps, such as, but not limited to, PAR lamps, as well as methods of forming such coating systems. Embodiments of this invention further relate to lamps that include such reflective coating systems.
According to a first aspect of the invention, a substrate is provided with a reflective coating system comprising an intermediate metallic layer that overlies the substrate and consists of nickel, chromium, or a Ni—Cr alloy, a reflective metallic layer that contains silver and overlies the intermediate metallic layer, and a protective layer that overlies the reflective metallic layer. In this aspect of the invention, the intermediate metallic layer constitutes at least 20 percent of a combined thickness of the intermediate metallic layer and the reflective metallic layer.
According to a second aspect of the invention, a lamp is provided with a substrate and a reflective coating system on the substrate. The reflective coating system comprises an intermediate metallic layer that overlies the substrate and consists of nickel, chromium, or a Ni—Cr alloy, a reflective metallic layer that contains silver and overlies the intermediate metallic layer, and a protective layer that overlies the reflective metallic layer. The intermediate metallic layer constitutes at least 20 percent of a combined thickness of the intermediate metallic layer and the reflective metallic layer.
According to a third aspect of the invention, a method is provided for producing a lamp to have a reflective interior surface. The method comprises depositing an intermediate metallic layer consisting of nickel, chromium, or a Ni—Cr alloy to overlie a substrate of the lamp, depositing a reflective metallic layer containing silver to overlie the intermediate metallic layer, and depositing a protective layer to overlie the reflective metallic layer. The intermediate metallic layer constitutes at least 20 percent of a combined thickness of the intermediate metallic layer and the reflective metallic layer.
A technical effect of the invention is the capability of reflective coatings of this invention to achieve reflectance properties and cosmetic appearances that are substantially similar to certain prior art reflective coatings, while also potentially reducing material costs.
Other aspects and advantages of this invention will be better appreciated from the following detailed description.
Embodiments described herein generally relate to reflective coatings employed in reflector lamps such as, but not limited to, PAR 38 and PAR 64 lamps. In particular, combinations of metallic reflective coating layers and optional intermediate and protective coating layers are described in order to achieve a desired level of reflectivity, maintain a desirable cosmetic appearance, and reduce the cost of materials for such coatings. While the invention will be described in reference to reflector lamps, those skilled in the art will appreciate that the teachings of this invention will find applications in products and technologies other than lamps.
The present invention is discussed below in reference to
Referring again to
In preferred embodiments of the invention for the coating system 14 of
The intermediate metallic layer 28 preferably constitutes at least 20 percent of the combined thickness of the intermediate and reflective metallic layers 28 and 30, and in some embodiments may constitute 75 percent or more of the combined thickness of the intermediate and reflective metallic layers 28 and 30. A preferred thickness for the intermediate metallic layer 28 is in a range of about 50 to about 400 nm, more preferably about 100 to about 200 nm, and nominally about 200 nm. A preferred thickness for the reflective metallic layer 30 is about 60 to about 400 nm, more preferably about 100 to about 200 nm, and nominally about 150 nm. The protective layer 32 may have a thickness of about 10 to about 200 nm, more preferably about 30 to about 200 nm, and nominally about 30.
The intermediate metallic layer 28 preferably functions as an opaque barrier layer within the coating system 14 and may be less reflective than the reflective metallic layer 30, yet reduces the thickness required of the reflective metallic layer 30 to survive harsh manufacturing conditions of the type often involved in deposition processes, for example, when depositing the layers 28, 30 and 32 of the coating system 14. As a result, the thickness of the reflective metallic layer 30 can be considerably less than that of reflective metallic layers of the prior art, with the result that the overall material cost of the lamp 10 may be reduced. Thus, use of the above mentioned set of metallic layers 28 and 30 can provide a cost advantage in the fabrication of the reflective coating system 14 for the lamp 10. Evaluations have shown that reflectances of parabolic reflector lamps provided with coating systems l4 of the type represented in
At the thicknesses disclosed above, when disposed between the intermediate metallic layer 28 and the substrate of the housing 12, the interior metallic layer 34 is preferably capable of an ornamental function by concealing the intermediate metallic layer 28 from view if the lamp housing 12 is formed of glass (or another transparent material) and observed from the exterior of the lamp 10. Evaluations have shown that the reflectance and cosmetic appearance of a parabolic reflector lamp provided with the coating system 14 of
Methods of producing coating systems 14 in accordance with the embodiments discussed above can be achieved by sequentially depositing the optional interior metallic layer 34, the intermediate metallic layer 28, and then the reflective metallic layer 30 on the substrate of the reflector housing 12. Suitable deposition techniques include sputtering, thermal evaporation, ion-assisted deposition (IAD), physical vapor deposition (PVD), or chemical vapor deposition (CVD) and other known processes such as dip coating, with sputtering and thermal evaporation believed to be preferred. The protective layer 32 can also be deposited by conventional techniques, for example, sputtering, thermal evaporation, and CVD, particularly plasma-enhanced chemical vapor deposition (PECVD). The as-coated reflector housing 12 is then preferably heated to a temperature at which oxygen is able to diffuse into the protective layer 32 to fill voids and increase the density of the protective layer 32. For example, during manufacture of the lamp housing 12 the protective layer 32 may be subjected to a temperature within a range of about 100 to about 300° C., at which oxygen from the surrounding ambient air is available to diffuse into the protective layer 32.
In view of the above, it is believed that the embodiments described here for the reflective coating systems 14 are advantageously capable of reducing material costs without compromising, or at minimum not significantly compromising, the reflectance, energy efficiency and cosmetic appearance of lamps utilizing the coating systems 14. It should be noted that it may be possible to use different material sets or different thicknesses for the layers 28, 30, 32, and 34 described above, yet achieve similar results.
While the invention has been described in terms of specific embodiments, it is apparent that other forms could be adopted by one skilled in the art. Therefore, the scope of the invention is to be limited only by the following claims.
