Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
1999-07-26
2001-06-05
Epps, Georgia (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C324S435000, C429S090000, C429S008000, C359S265000
Reexamination Certificate
active
06243192
ABSTRACT:
TECHNICAL FIELD
The invention relates to progressively changing displays including such displays in which the progressive change is used to perform a timing function. In the displays contemplated by the invention, electrochemical reactions produce the progressive change; and these displays are preferably self-powered, irreversible, low cost, and formed in layers that can be printed on an in-line press.
BACKGROUND
Progressively changing displays can be used both to perform timing functions and to display the progress or results of the timing functions. Such displays that are arranged to mark the passage of time are particularly useful as attachments to products with a limited life, such as food, room deodorants, flea collars, roach traps, and other products whose usefulness or effectiveness decreases over time. The progressive changes in these displays can also be equated to the service lives of other products such as batteries or filters, where service life is determined more by usage.
Various mechanisms have been used to effect such progressive changes in displays including physical migration, chemical reactions, and electrochemical reactions. Among the latter are displays that include electrochromic materials and voltaic or electrolytic cells.
For example, U.S. Pat. No. 4,804,275 to Kang et al. discloses a self-powered electrochromic timing device in which a color change boundary in an electrochromic material is advanced by a gradual dissolution of an electrode. Kang et al.'s electrochromic reactions, however, require a strong acid and other materials that add cost and pose problems for both manufacture and use.
U.S. Pat. No. 5,339,024 to Kuo et al. discloses a self-powered charge indicator cell connected in parallel with a main cell. An anode layer carried on a conductive substrate of the indicator cell is gradually oxidized (i.e., eroded) to reveal a message written in ink on an underlying layer. The thickness of the anode layer is tapered or stepped to regulate its rate of disappearance. Another embodiment arranges the anode and cathode layers side-by-side and fashions the electrolyte layer as a porous film straddling both electrode layers. The anode layer erodes under the electrolyte film in a direction away from the cathode layer. Both of Kuo et al.'s embodiments are subject to “islanding”, however, where portions of the anode layer become electronically isolated from the cathode layer and prevent the anode layer's more complete disappearance.
U.S. Pat. No. 5,418,086 to Bailey discloses an electrolytic type battery charge indicator powered by the monitored battery. One electrode layer is dissolved and redeposited on another electrode layer as an indication of battery usage. The rate of dissolution and redeposition is controlled by tapering or stepping electrolyte layer thickness between the electrode layers. Like in Kuo et al., the dissolving electrode layer is also subject to islanding, which limits further dissolution of the electrode layer. Another embodiment positions the two electrode layers side-by-side on a common substrate and fills a space between them with electrolyte. The exchanges between electrode layers are expected to grow increasingly irregular with variations in distance between them. Also, the electrolysis operations are at least partially reversible, which can be a problem if more permanent change is desired.
SUMMARY OF INVENTION
We have discovered that thin-film electrodes of electrochemical display cells can be more cleanly eroded for purposes of both measurement and display by linking the erosion of the thin-film electrodes to an expanding boundary of electrolyte. The erosion of the thin film is substantially complete and permanent behind the expanding boundary of electrolyte, and a clear demarcation is provided between the eroded and non-eroded portions of the thin film at the electrolyte boundary. For purposes of this invention and its further description, the term “erode” is regarded as synonymous with the terms “oxidize”, “dissolve”, “clear”, and “disappear” as they pertain to the systematic removal of thin-film electrodes.
According to one expression of our invention, an electrochemical display cell is arranged as a voltaic cell with two electrode layers having different electrode potentials. An electrolyte layer overlaps a first of the electrode layers and has a boundary in contact with a second of the electrode layers for completing an ionically conductive pathway between the two electrode layers. In response to a flow of current between the two electrode layers, the electrolyte boundary moves together with a boundary of the second electrode layer extending the ionically conductive pathway from the first electrode layer. The moving boundary of the second electrode layer provides for changing a visible appearance of the display.
The second electrode layer recedes rapidly at first until the boundary of the electrolyte layer is reached and then the recession slows considerably but continues through the remaining portion of the second electrode layer that was not initially in contact with the electrolyte layer. This surprising result is produced by an accompanying migration of the electrolyte that is apparently drawn along with the receding boundary of the second electrode layer by the interplay of one or more such mechanisms as capillary action, surface tension, diffusion, or electric field effects on ions of the electrolyte layer. More complete clearing of the second electrode layer takes place because erosion is limited to an interface formed by contiguous moving boundaries of the second electrode and electrolyte layers.
The second electrode layer is preferably a thin film capable of undergoing an electrochemical reaction that results in the progressive disappearance of the second electrode layer behind the moving boundary of the electrolyte layer. For example, the second electrode can be made of a thin film of aluminum or zinc deposited onto a transparent substrate, which provides a viewing window for observing the orderly disappearance of the thin film. The transparent substrate is preferably not conductive to avoid interfering with ion migration between the electrode layers across the portion of its surface exposed by the disappearing thin film.
Another expression of our invention features an electrochemical cell that has two electrode layers and an electrolyte layer occupying distinct areas of a substrate. The electrolyte layer is in contact with the two electrode layers for completing an ionically conductive pathway between them. An electronically conductive pathway between the electrode layers supports an electrochemical reaction that progressively increases the area of the substrate occupied by the electrolyte layer and progressively decreases the area of the substrate occupied by one of the electrode layers. The progressively increasing area of the electrolyte layer and the progressively decreasing area of the one electrode layer provide an irreversible indication of change at a rate governed by the electrochemical reaction.
Preferably, the progressively increasing area of the electrolyte layer corresponds to the progressively decreasing area of the one electrode layer. The area of the substrate occupied by the other electrode preferably remains substantially constant throughout the electrochemical reaction.
Though spatially and electronically separated, the first and second electrodes can have an irregular-shaped interface prior to the start of erosion. The irregular-shaped interface, such as a saw-tooth pattern, appears to enhance the electrochemical interaction between the electrode layers. Also, the second electrode layer is preferably funnel-shaped with its wide end adjacent to the first electrode layer to further increase the length of the irregular-shaped interface and to promote the migration of electrolyte in the direction of its advancing boundary. The narrow end of the second electrode layer is elongated to channel the erosion at a faster pace along a predetermined pathway.
The pace of erosion of the second
Good David M.
Mitchell, Jr. Chauncey T.
Parker Robert
Shadle Mark A.
Verschuur Gerrit L.
Epps Georgia
Eugene Stephens & Associates
Lester Evelyn A.
Ryan Thomas B.
Timer Technologies, LLC
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