Appeal No. 2006-0037
Application No. 09/874,371
Heat loss through a window may arise from a
convective/conductive/emissive process, for example,
where interior hot air raises the temperature of the
glass, by convection, the thermal energy is distributed
throughout the glass, by conduction, and some of the
thermal energy is emitted or radiated, by emission, to
the exterior. Heat loss by emission can be ameliorated
by reducing the emissivity of the window glass, for
example, by introducing a low emittance or "low E" (for
infrared) coating (which is typically a thin metal film).
Emissivity or emittance refers to the propensity of a
surface to emit or radiate radiation of a specified
wavelength, and is quantified as the ratio of radiant
flux per unit area emitted by body to that of a blackbody
radiator at the same temperature and under the same
conditions. Thus, a perfect blackbody has an emissivity
of 1.0. Ordinary window glass has an infrared emissivity
of about 0.84. Window glass with a "low E" coating has a
much lower infrared emissivity, often as low as 0.15, and
heat loss through such a window is greatly reduced.
Optical coatings have found widespread application
in the field of glazing, particularly as a means to
control heat loss and/or heat gain. In many
applications, optical coatings are used to "block" the
transmission of electromagnetic radiation (e.g., infrared
radiation, visible radiation, ultraviolet radiation) to
some degree. In some applications, it is desirable to
block some or all of the electromagnetic radiation of a
particular wavelength band while transmitting some or all
of the electromagnetic radiation of another particular
wavelength band.
Thus, in one [common] application, an optical
coating is employed to substantially block infrared
electromagnetic radiation while substantially
transmitting visible electromagnetic radiation. Such
optical coatings are often referred to as “heat mirrors,”
“hot mirrors,” or “thermal control films.” For glazing
applications, it is usually desirable that these optical
coatings also be substantially visibly transparent
[column 1, line 61, through column 2, line 41].
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