Optical: systems and elements – Light interference – Produced by coating or lamina
Reexamination Certificate
1999-08-20
2003-11-18
Chang, Audrey (Department: 2872)
Optical: systems and elements
Light interference
Produced by coating or lamina
C359S577000, C359S589000, C359S359000, C359S360000
Reexamination Certificate
active
06650478
ABSTRACT:
BACKGROUND OF THE INVENTION
I. Field of the Invention
The present invention relates to an optical filter element which controls or limits the transmission of light so that only a portion of the total incident light passes through the optical filter element thereby making the element semi-transparent. The element is typically applied or adhered to a light transmissive substrate such as polymer or glass for ultimate use in the field of window manufacturing and particularly in the manufacturing of windows where control of light (e.g., control of absorbed light, reflected light, transmitted light and solar energy rejection) is important.
II. Background Information
Windows are conventionally manufactured with solar control elements or optical filters as a component thereof in order to provide desired coloration and advantageous levels of visible light transmission (VLT), visible light reflectance (VLR), solar energy absorption and total solar energy rejection. Such optical filters are often multi-layered coatings or laminates which are used in combination with a glass sheet or other optical glass device so that the light which passes through the glass also passes through the optical device to produce the desired effects. Typically the optical filter is incorporated in or on the glass or is positioned in close proximity to the glass (such as within the gas containing space between two glass sheets in a double glazed window). The optical filter may be coated or otherwise adhered to a suitable light transmissive substrate such as a polymer in order to produce a structure for combination with the glass. For example such optical filters are conventionally coated onto or otherwise adhered to a polymeric film such as polyethylene terephthalate (PET). Such polymer/optical filter films can be combined with the glass during the manufacturing steps of making a window for residential, automotive or other architectural applications. Alternatively the polymer/optical filter film can be retrofitted onto previously manufactured windows by adhering the film thereto. Such polymer/optical filter films are known as solar control films.
Windows which include an optical filter have characteristic levels of reflection on both sides (i.e., surfaces) of the filter. Thus, such windows which are installed in the walls of a building or vehicle will have a characteristic level of interior visible reflection and exterior visible reflection. Interior visible reflection is the reflection of visible interior incident light (interior light is light which is inside the building or vehicle) while exterior visible reflection is the reflection of visible exterior incident light. (exterior light is light which is outside the building or vehicle). Optical filters which have unequal exterior and interior visible light reflection are asymmetric reflectance (dual-reflectance) filters or films. It is highly desirable to use optical filters wherein the interior visible reflection is less than the exterior visible reflection. Also it is highly desirable to keep reflectance levels to 20% or less.
When optical filters are used for residential or architectural applications such as windows, it is desirable for the filter to have certain properties. Some of these properties include color that does not change hue or shade over time (i.e., color stability); visible light reflectance on both the exterior and interior that is not perceived as “mirrored ”(20% or less); visually appealing transmitted and reflected color; and the ability to significantly reduce solar heat gain (60% or greater solar energy rejection). Traditionally optical filters for windows (e.g., solar control films) are constructed either from dyed polymer film, clear polymer film coated with a single metal layer or multiple metal layers, or a hybrid structure which includes both dyed film and metallized film. However such traditional optical filters for windows do not provide all of the above desirable properties.
Dyes used in such optical filters have poor color stability and thus optical filters which contain a dyed layer will eventually fade and change color. Also, optical filters which utilize only dyed layers instead of metal layers have inferior solar heat rejection. Films with single or multiple metal layers are perceived as too reflective in the marketplace for films with visible light transmission levels of 35% or less. In other words, the problem with single or multiple layer metal films is that when the metal is thick enough to bring the light transmission to 35% or less, the visible reflectance becomes unacceptably high. The hybrid dyed/metal optical filters described above provide low visible reflectance but are still susceptible to color change and fading problems. In addition when dyed/metal films are constructed with a single dyed layer facing the window, the interior reflectance is excessive.
When optical filters, such as solar control window films, are in contact with a glass window additional thermal stress is induced into the glass. This occurs due to the fact that such filters absorb a portion of the incident solar energy. This absorbed solar energy in turn increases the temperature of the glass for the portion of the glass exposed to sunlight. This increased temperature induces additional thermal stress in the glass structure. If the thermal stress exceeds the tensile strength of the glass thermal stress breakage can occur. Thus it is imperative to produce optical filters and solar control window films which do not produce excessive thermal stress. This is accomplished by minimizing the solar absorption of such filters and films.
To minimize the occurrence of thermal stress breakage, and thus to manufacture commercially viable solar control products, the following limits of solar absorption are recommended by glass, window and solar control film manufacturers as an industrial standard:
Single-pane annealed glass: less than 65% total solar absorption
Dual-pane annealed glass: less than 50% total solar absorption
These absorption rates are measured with the optical filter applied to ⅛″ clear glass. This industrial standard exists as a safeguard against thermally induced breakage. Thus it would be highly desirable to meet this standard while providing the desirable color stability and light altering characteristics. It would also be desirable to meet this standard as described above while also limiting the visible light reflectance on both surfaces of the optical filter so that a window can be produced which has an exterior and interior visible light reflectance of 25% or less.
As noted above one of the parameters which is regulated by optical filters is the amount of solar energy rejection. The term “total solar energy rejection” (TSER) is a term of art which describes the percentage of incident solar heat rejected by a glazing system relative to the incident solar radiation. The TSER value equals the solar reflectance plus the portion of the solar absorption that is both re-radiated and conducted/convected to the outdoors. The TSER is expressed as a percentage between 0 and 100%. The higher a window's TSER the less solar heat is transmits.
Total solar energy rejection may also be expressed in terms of the solar heat gain coefficient (SHGC). The SHGC represents the solar heat gain through the window system relative to the incident solar radiation. SHGC is expressed as a number between 0 and 1. The lower a window's SHGC, the less solar heat is transmits. The sum of TSER (in decimal form) and SHGC value is 1. Thus if the TSER of a specified optical filter is 65% then the SHGC is 1 minus 0.65 which equals 0.35.
SUMMARY OF THE INVENTION
It is an objective of the present invention to provide an optical filter for a window or the like which has the desirable characteristics as outlined above. In particular it is an objective of the invention to produce a colored optical. filter with color stability without the use of dyes.
It is another objective of this invention to produce a color stable optical filter that provides increased or
DeBusk Steven
Maschwitz Peter
Bacon & Thomas
Chang Audrey
CPFilms Inc.
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