Stock material or miscellaneous articles – Composite – Of polycarbonate
Reexamination Certificate
2000-05-18
2001-09-25
Boykin, Terressa M. (Department: 1711)
Stock material or miscellaneous articles
Composite
Of polycarbonate
C219S635000, C219S678000
Reexamination Certificate
active
06294258
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to windows used in appliances. More particularly, this invention relates to appliance windows which are coated with a thermochromic polymer dispersed liquid crystal material.
Many appliances in use today have a clear glass window for allowing consumers to see what is going on inside the appliance. Unfortunately, the transparent nature of the glass window also detracts from the aesthetics of the appliance because the window does not match the design of the rest of the appliance which is usually of a particular color.
Windowless appliances, while perhaps aesthetically pleasing, have the major disadvantage of requiring consumers to open the door of the appliance to see what is going on inside. This results in a loss of heat.
Thus, it is desirable to provide an appliance window which will allow consumers to see what is going on inside the appliance without requiring the consumer to open the appliance door and further without detracting from the overall appearance of the appliance.
The use of thermochromic materials in connection with appliances is known in the art. Reference is made, for example, to U.S. Pat. Nos.: 4,983,810 (Balderson); 6,037,572 (Coates, et al.); 5,451,932 (Wunderlich et al.); and 5,326,174 (Parker). However, none of these references teaches the use of a thermochromic coating on the appliance window.
U.S. Pat. No. 5,337,727 (Borens et al.) mentions the possibility of using in an appliance window thermochrome panes the radiation permeability of which decreases as the temperature increases. However, the Borens et al. patent then teaches away from the use of such panes because “this impairs the view through the window” (col. 1, lines 56-59). Thus, Borens et al. teaches away from using thermochrome materials in an appliance window if it is desired that the view through the window not be impaired.
In recent years, certain polymer-dispersed liquid crystal (“PDLC”) materials have been used as thermochromic (also referred to as temperature-responsive) materials. These particular PDLC thermochromic materials represent an improvement over previously used thermochromic materials because the PDLC materials have greater thermal stability and provide better visual contrast between the opaque and the clear states.
U.S. Pat. Nos. 4,688,900 (Doane et al.) and 4,685,771 (West et al.) each teach the use of temperature-responsive PDLC materials for use in displays but not on windows, particularly windows for use in appliances. U.S. Pat. Nos. 4,890,902 (Doane et al.); 4,994,204 (Doane et al.); 5,240,636 (Doane et al.); and 5,004,323 (West) teach the use of PDLC materials for use on windows but these materials are activated by electrical or magnetic means (i.e., these materials are “electro-responsive” or “magneto-responsive” rather than temperature-responsive) and, further, the windows on which these materials are applied are not appliance windows.
The use of temperature-responsive materials, rather than electro-responsive or magneto-responsive materials, in an appliance window is desirable because the temperature-responsive materials will be activated by the thermal energy released by the appliance during operation thereof. In other words, instead of requiring the active application of an electrical or magnetic stimulus to the material, the temperature-responsive material will be activated passively by the appliance's release of thermal energy.
Thus, it would be desirable to provide an appliance window coated with a thermochromic PDLC material.
In accordance with the foregoing, a primary object of this invention is to provide an appliance window which allows a consumer to see what is going on inside an appliance without opening the appliance door and which does not detract from the overall appearance of the appliance.
A further object of this invention is to provide an appliance window which is coated with a thermochromic material that allows a consumer to see what is going on inside an appliance without opening the appliance door and which does not detract from the overall appearance of the appliance.
Another object of this invention is to provide the aforementioned coated appliance window wherein the thermochromic material is a polymer-dispersed liquid crystal material having good thermal stability and which is capable of providing a good visual contrast between the opaque and transparent states of the material.
A still further object of this invention is to provide an appliance having a window coated with the thermochromic material having the features described in the foregoing objects.
These and other objects are achieved in the present invention.
SUMMARY OF THE INVENTION
The present invention provides appliance windows coated with a PDLC thermochromic material. The invention also provides appliances containing windows coated with such material.
The PDLC material used in the present invention is composed of phase-separated droplets of liquid crystal in a light-transmissive resin matrix and is capable of being thermally activated to cause the material to be reversibly switched between a light-scattering mode and a light-transmissive mode. The liquid crystal used in the present invention has an optical index of refraction in the isotropic phase that is similar to the refractive index of the resin and an index of refraction in the liquid crystalline phase that is mismatched with the refractive index of the resin.
The liquid crystal may contain a suitable dye to render the thermochromic material and the window in which it is disposed the same color as the rest of the appliance.
Non-limiting examples of appliances which can contain an appliance window coated with the aforementioned thermochromic material include baking ovens, toasters, clothes dryers, and the like.
The appliance window provided by the present invention differs from conventional appliance windows in that the window of this invention is only visible when it is at or above a certain temperature. When the appliance containing the window of this invention is below a certain temperature, the window will blend in with the color of the rest of the appliance. However, when the appliance is in operation and starts to heat up, the window will become transparent when a certain, predetermined temperature is reached. When the window becomes transparent, the consumer will be able to look inside the appliance without opening the door of the appliance as long as the temperature stays at or above the predetermined level. Once the temperature drops below the predetermined value, the window will turn back to the color of the appliance.
Therefore, the appliance window of this invention does not detract from the overall aesthetic appeal of the appliance and allows the consumer to view the inside chamber of the appliance without opening the appliance door.
REFERENCES:
patent: 4685771 (1987-08-01), West et al.
patent: 4688900 (1987-08-01), Doane
patent: 4890902 (1990-01-01), Doane et al.
patent: 4983810 (1991-01-01), Balderson
patent: 4994204 (1991-02-01), Doane et al.
patent: 5004323 (1991-04-01), West
patent: 5240636 (1993-08-01), Doane et al.
patent: 5326174 (1994-07-01), Parker
patent: 5337727 (1994-08-01), Borens et al.
patent: 5404245 (1995-04-01), Chahroudi
patent: 5451932 (1995-09-01), Wunderlich et al.
patent: 5589958 (1996-12-01), Lieb
patent: 6001487 (1999-12-01), Ladang et al.
patent: 6037572 (2000-03-01), Coates et al.
patent: 6039390 (2000-03-01), Agrawal et al.
Boykin Terressa M.
Patton & Boggs LLP
Tutco, Inc.
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