WO1999049447A1

WO1999049447A1 - Electroluminescent lamp including thermochromic shutters

Info

Publication number: WO1999049447A1
Application number: PCT/US1999/006214
Authority: WO
Inventors: Bryan D. Haynes
Original assignee: Add-Vision, Inc.
Priority date: 1998-03-24
Filing date: 1999-03-23
Publication date: 1999-09-30
Also published as: AU3108999A

Abstract

An electroluminescent lamp (100) having thermochromic shutters (105) is disclosed. The thermochronic shutters (105) comprise thermochromic ink segments (150) and heating elements (120, 122, 130, 140, 142). The heating elements (120, 122, 130, 140, 142) may be selectively activated to make the thermochromic ink segments (150) clear. If a heating element (120, 122, 130, 140, 142) is not activated then the thermochromic shutter (105) with which it is associated remains opaque. The thermochromic ink segments (150) allow portions of the lamp surface to be selectively blocked, allowing numerals, characters, or images to be displayed on the lamp (100).

Description

ELECTROLUMINESCENT LAMP INCLUDING THERMOCHROMIC SHUTTERS

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to electroluminescent displays. In particular, the invention relates to electroluminescent displays having thermochromic shutters which, in response to the local temperature, are opaque or clear, enabling formation of alphanumeric characters or other images.

2. Description of the Related Art

For displays such as signs and billboards, among other implementations, desirable display properties include low power consumption and high contrast between light and dark portions of the display. One way of increasing the contrast is to increase the display brightness, which unfortunately increases power consumption. Another desirable property is a long life for the display elements. However, increasing the display brightness can also decrease the life of the display elements.

Another desirable property is the ability to dynamically change the image displayed. One solution is to have a number of individually addressable display elements, which can be turned on or off depending upon the image to be displayed. However, this causes the various display elements to be active for different durations, which means that some will degrade before others.

A second solution to the problems of changing the image is to have shutters over portions of the display. The shutters can be opened or closed to give the appearance of different images. However, mechanical shutters require a large number of moving parts, increasing the display complexity, maintenance requirements, and cost.

A final desirable property includes having a relatively thin display profile. However, the above solutions to the image changing problem are all relatively thick in their profiles.

SUMMARY OF THE INVENTION The present invention addresses these and other problems of the prior art by providing an electroluminescent ("EL") lamp having thermochromic shutters.

The use of EL lamps by themselves provides a solution to some of the above problems because they are relatively long-lived, have a low power consumption, and emit bright light. The EL lamps can also be printed laminarly to give a relatively thin profile. However, to change the images using only EL lamp technology requires a number of EL elements, which leaves the nonuniform degradation problem unsolved. Thermochromic shutters by themselves provide another solution to some of the above problems because they can be substituted for a number of display elements. Thermochromic shutters use thermochromic ink, which becomes clear when warmed. A single display element can be covered with numerous thermochromic shutters instead of having multiple display elements. Because the single display element is either active or inactive, a uniform display brightness degradation results. The mechanical problems discussed above can be solved because thermochromic shutters are electrically controlled, not mechanically controlled. Thermochromic shutters can also be made relatively thin.

However, the problem with using thermochromic shutters for traditional display implementations is that the traditional types of lamps (incandescent, halogen, and fluorescent) when lit give off too much heat for the thermochromic ink to remain opaque, making it difficult to control the opening and closing of the shutters. The EL lamps, on the other hand, are cool enough for thermochromic shutters . According to a first preferred embodiment, a display according to the present invention includes an EL lamp and a plurality of thermochromic shutters. The plurality of shutters is arranged such that numerals, characters, or images can be formed by selective activation of the plurality of shutters.

The thermochromic shutter heaters in this embodiment have a trapezoidal shape; however, in a second preferred embodiment the heaters have a rectangular shape to provide more uniform heating of the thermochromic ink.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view of thermochromic shutters

configured as an alphanumeric display; FIG. 2 is a vertical cross-sectional view of an electroluminescent lamp with a thermochromic shutter; and

FIG. 3 is another schematic view of thermochromic shutters configured as an alphanumeric display.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 gives an exemplary illustration of a plurality of thermochromic shutters used to form numerals. FIG. 1 shows a set 100 of seven thermochromic shutters. Set 100, including thermochromic shutter 105, is on an insulator 110. The other shutters are similar to shutter 105.

Thermochromic shutter 105 is comprised of bus bars 120 and 122, resistive ink segment 130, trace leads 140 and 142, and thermochromic ink segment 150. Bus bars 120 and 122 are on insulator 110. Resistive ink segment 130 is on insulator 110 between each pair of bus bars 120 and 122. Trace leads 140 and 142 form a circuit from bus bar 120 through resistive ink segment 130 to bus bar 122. Thermochromic ink segment 150 is on top of resistive ink segment 130.

Although FIG. 1 illustrates how the thermochromic shutters can be arranged to form numerals, many other arrangements are possible. For instance, the shutters could be arranged to form letters or images. An example of insulator 110 is DuPont Membrane Switch Composition #5018. Other insulative materials can be substituted.

Bus bars 120 and 122 may be made of silver. Other conductive materials can be used in place of silver, as long as their resistance is lower than that of resistive ink segment 130.

Resistive ink segment 130 may be made of DuPont Carbon Black Ink #7144. Alternatively, resistive ink segment 130 may be made of Acheson indium-tin oxide ("ITO") ink #SS- 24823. Preferably, resistive ink segment 130 is made of 112- 48 Conductive Ink from Creative Materials Inc., Tyngsboro, Massachusetts. Other resistive materials can be used, as long as they generate enough heat to activate thermochromic ink segment 150.

Trace leads 140 and 142 may be made of silver. Other conductive materials can be substituted for silver, as long as their resistance is lower than that of resistive ink segment 130. Thermochromic ink segment 150 may be made of a thermochromic ink such as ChromaZone ink from Davis Liquid Crystals, Inc., San Leandro, California. This ink becomes clear at about 32°C. The ChromaZone ink as used in this embodiment is black, but other ink colors are also available.

More preferably, thermochromic ink segment 150 may be made of Dynacolor Thermochromic UV Screen Ink from Chromatic Technologies, Inc., Colorado Springs, Colorado. This ink becomes clear at about 31°C. The DynaColor brand is preferred over the ChromaZone brand because it is more amenable to printing processes.

The thermochromic shutters shown in FIG. 1 operate as follows. Initially thermochromic ink segment 150 is cool (i.e., below a temperature at which it becomes clear), which causes the ink to be opaque. To make thermochromic ink segment 150 clear, a current travels to bus bar 120 through trace lead 140. This current passes through resistive ink segment 130 to bus bar 122, increasing the temperature of resistive ink segment 130. This warms thermochromic ink segment 150 to a temperature above which it becomes clear. The current completes the circuit from bus bar 122 through trace lead 142.

Different alphanumeric characters or other images can be created by controlling which shutters in the set are opaque and which are clear.

FIG. 2 illustrates a vertical cross-section of a portion of an EL lamp with a thermochromic ink shutter. The EL lamp 200 is preferably an EL lamp as described in U.S. Patent Application No. 08/910,724 entitled

"Electroluminescent Lamp Designs", commonly owned by the assignee of the present application, the disclosure of which is incorporated herein by reference. More preferably, EL lamp 200 is Assembly #300-0000-00 from Precision Printing Inc. of Grass Valley, California.

Although this description references a single EL lamp, similar principles can be applied to create a display comprising a plurality of EL lamps, each having thermochromic shutters. The EL lamp 200 comprises a rear dielectric layer 210, a rear electrode 215, a dielectric layer 220, a phosphor layer 225, and an ITO layer 230. Each of these layers may be a few mils in thickness, making a very thin light source. Light may be emitted from EL lamp 200 toward the left of FIG. 2 from the front of the lamp.

Materials making up these layers are as follows, but similar materials can be substituted if desired. ITO layer 230 is comprised of a printable ITO conductor, such as DuPont #7160 or Acheson #SS-24823, sputtered on polyethylene terepthalate . Phosphor layer 225 is DuPont Membrane Switch Composition #7155 or Osram Sylvania EL Phosphor Type 30. Dielectric layer 220 is DuPont Dielectric Composition #7153. Rear electrode 215 is DuPont Membrane Switch Composition #5025. Rear dielectric layer 210 is DuPont UV curable sealant #5818.

To the outside of EL lamp 200 are added insulator 110; one or more thermochromic ink segments 150; and for each thermochromic ink segment, resistive ink segment 130, trace leads 140 and 142, and bus bars 120 and 122. FIG. 2 shows one thermochromic ink shutter on EL lamp 200, but additional shutters can be added.

The layers added to EL lamp 200 are formed as follows. Thermochromic ink segment 150 is applied, e.g., by screen printing, in a desired shape to the front surface of EL lamp 200. The ink segment may be in any shape consistent with the character or image to be formed, but a shape having protrusions may be more difficult to heat uniformly. If desired, a picture can be placed on the front surface before thermochromic ink segment 150. This picture may be visible with reflected ambient light even when EL lamp 200 is off.

Resistive ink segment 130 may be screen-printed as a thin film along the back of EL lamp 200 aligned with each thermochromic ink segment 150. Each screen-printed pass makes a film about 1 mil thick, which is then cured. Successive passes create thicker layers. A thin layer will heat more quickly when powered, but a thick layer will generate more heat.

In an alternative embodiment, resistive ink segment 130 may contain conductive components, such as aluminum or copper. This embodiment would further comprise a heat sink to evenly distribute heat over resistive ink segment 130.

Bus bars 120 and 122 may be printed beside resistive ink segment 130 on the back of EL lamp 200, covered by insulator 110. Insulator 110 on the back of EL lamp 200 separates resistive ink segment 130 and bus bars 120 and 122 from trace leads 140 and 142. This separation allows the trace leads 140 and 142 to pass beneath the bus bars and the ink segment instead of threading between the ink segments. Insulator 110 may have an opening for trace lead 140 to connect to bus bar 120 at a desired location, and another for trace lead 142 to connect to bus bar 122 at a desired location. Trace leads 140 and 142 may be printed on the insulator 110 and are connected to a power source.

When EL lamp 200 is on, it has a low temperature,

e.g., about 23°C, which is only a few degrees above

ambient room temperature. Depending upon the thermochromic ink selected, this temperature may be low enough to avoid triggering the thermochromic ink segment to become clear. The low heat output from the lamp allows the use of thermochromic inks in bright-light applications which would be otherwise impossible with traditional incandescent, fluorescent, or halogen lamps because of the relatively large amount of heat they emit.

10 As mentioned above, the layers of EL lamp 200 may be made very thin. This thinness allows the resistive ink segment 130, bus bars 120 and 122, and trace leads 140 and 142 to be placed on the back of the lamp and the heat generated thereby to heat thermochromic ink segment 150 on the front of the lamp. Thus, the front of EL lamp 200 need contain none of the heating components, and the light emitted by EL lamp 200 need not be obscured thereby. Although the description so far has described a portion of EL lamp 200 having one thermochromic shutter, similar principles may be applied to provide a plurality of shutters on the lamp.

The EL lamp 200 can be thin enough that the heater for one thermochromic ink segment does not significantly affect adjacent thermochromic ink segments. That is, because the heat is generated on one side of the lamp and the thermochromic ink is on the other, the heat passes through the lamp to affect only the ink in an ink segment directly above the heater. If the lamp were thicker, the lamp structure might conduct the heat to other parts of the lamp and affect other ink segments. A thinner lamp allows a closer spacing of thermochromic ink

11 segments than a thicker lamp while permitting selective control of which ink segments are triggered and which remain opaque by control of heat conduction.

The apparatus shown in FIG. 2 operates as follows when EL lamp 200 is not emitting light, for example, during daytime. Bus bars 120 and 122 are initially unpowered, allowing thermochromic ink segment 150 to remain opaque. Ambient light reflects off the surface of the lamp. A viewer perceives a contrast differential between the part of ITO layer 230 not covered by the opaque thermochromic ink segment and the opaque thermochromic ink segment itself. If a picture has been added on the surface of the lamp, a viewer sees the parts of the picture that are not covered by the opaque thermochromic ink segment. Thus, a plurality of opaque thermochromic ink segments can be used to form numerals, characters, or images against the background of the ITO layer 230 or of a picture on the ITO layer.

To change the character or image, resistive ink segment 130 is heated by powering bus bars 120 and 122, causing heat to pass through the layers of EL lamp 200 to thermochromic ink segment 150. The thinness of EL lamp 200 allows a relatively close spacing between resistive ink segments without the heat from one resistive ink segment unintentionally heating the thermochromic ink segment of

12 another resistive ink segment. This heat causes thermochromic ink segment 150 to become clear. Ambient light then passes through thermochromic ink segment 150 and reflects off ITO layer 230, or off the picture if it is present. Thus, a plurality of thermochromic ink segments may be used to selectively form numerals, characters, or images on, or otherwise selectively obscure portions of, the ITO layer 230 or a picture on the ITO layer.

During low ambient light situations, such as nighttime, EL lamp 200 may be activated. To turn EL lamp 200 on, an alternating voltage may be applied across rear electrode 215 and ITO layer 230, creating an electric field. Phosphor layer 225 emits light which passes through ITO layer 230. Bus bars 120 and 122 are initially unpowered, allowing thermochromic ink segment 250 to remain opaque. The light emitted from the phosphorescent layer 225 beneath thermochromic ink segment 150 is blocked, allowing a viewer to easily differentiate between the opaque segment (s) over the lamp and the light generated by the lamp itself. If a picture has been added on the surface of the lamp, the light emitted can be low enough to illuminate the picture, or high enough to obscure easy viewing of the picture. A plurality of opaque thermochromic ink segments can be used to form

13 numerals, characters, or images against the background of the ITO layer 230, or of a picture on the ITO layer.

When bus bars 120 and 122 are powered, heat from resistive ink segment 130 causes thermochromic ink segment 150 to become clear, as described above. Light generated by EL lamp 200 then passes through thermochromic ink segment 150. Thus, a plurality of thermochromic ink segments can be used to selectively form numerals, characters, or images by obscuring the light emitted from EL lamp 200. FIG. 3 illustrates a second embodiment of an EL lamp with thermochromic shutters. Similar reference numerals are used to refer to features similar to those discussed previously with the addition of a suffix of "a" (e.g., thermochromic shutter 105a) . FIG. 3 shows a seven-segment alphanumeric display wherein the heating elements 130a are rectangular in shape. Use of such a rectangular shape has been found to be preferable when a more uniform heating of thermochromic ink segments 150a is desired. Bus bars 120a and 122a are shown on the short sides of heating elements 130a; however, they may also be placed along the long sides.

Otherwise, the EL lamp shown in FIG. 3 is constructed and operates similarly to that described above regarding FIGS. 1 and 2.

14 It should be understood that various alternatives to the embodiments of the invention described herein may be employed in practicing the invention. For example, other EL lamp structures, thermochromic shutter arrangements, and element positions will be readily apparent to those skilled in the art. Thus, the described embodiments are merely exemplary, and the invention is limited only by the scope of the appended claims.

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Claims

WHAT IS CLAIMED IS:

1. A display device (100) comprising: an electroluminescent lamp (200); and a thermochromic shutter (105) disposed proximate to the electroluminescent lamp (200) to selectively pass and block light emitted from the electroluminescent lamp (200) .

2. The display device (100) of claim 1, wherein: a portion (150) of the thermochromic shutter (105) having variable light transmissivity is disposed on the electroluminescent lamp (200) in a direction in which the electroluminescent lamp (200) is capable of emitting light so that the thermochromic shutter (105) controls the emission of light from the electroluminescent lamp (200) .

3. The display device (100) of claim 1, wherein the electroluminescent lamp (200) comprises: a rear dielectric layer (210) ; a rear electrode (215) disposed on the rear dielectric layer (210); a front dielectric layer (220) disposed on the rear electrode (215) ;

16 a phosphor layer (225) disposed on the front dielectric layer (220); an indium-tin oxide layer (230) disposed on the phosphor layer (225) .

4. The display device (100) of claim 3, wherein a portion (150) of the thermochromic shutter (105) having variable light transmissivity is disposed on a side of the indium-tin oxide layer (230) opposite the phosphor layer (225) , the front dielectric layer (220) , the rear electrode (215) and the rear dielectric layer (210) .

5. The display device (100) of claim 3, wherein a portion (120, 122, 130, 140, 142) of the thermochromic shutter (105) having fixed light transmissivity is disposed on a side of the rear dielectric layer (210) opposite the rear electrode (215) , front dielectric layer (220) , phosphor layer (225) and indium-tin oxide layer (230) .

6. The display device (100) of claim 1, wherein a portion (150) of the thermochromic shutter (105) having variable light transmissivity is disposed on a side of the electroluminescent lamp (200) opposite that of a portion

17 (120, 122, 130, 140, 142) of the thermochromic shutter (105) having fixed light transmissivity.

7. The display device of claim 1, further comprising an insulator (110) disposed between the electroluminescent lamp (200) and one of a portion (150) of the thermochromic shutter (105) having variable light transmissivity and a portion (120, 122, 130, 140, 142) of the thermochromic shutter (105) having fixed light transmissivity.

8. The display device (100) of claim 1, wherein the thermochromic shutter (105) comprises: a thermochromic segment (150); and a heater (120, 122, 130, 140, 142) for heating the thermochromic segment (150) to change its light transmissivity.

9. The display device (100) of claim 8, wherein the thermochromic segment (150) is thermochromic ink.

10. The display device (100) of claim 8, wherein the heater (120, 122, 130, 140, 142) comprises: a resistive segment (130);

18 a plurality of bus bars (120, 122) proximate to the resistive segment (130) and in electrical contact therewith; and a plurality of trace leads (140, 142) in electrical contact with the plurality of bus bars (120, 122) for conveying electrical energy to the bus bars (120, 122) .

11. The display device of claim 10, wherein the plurality of bus bars (120, 122) includes two bus bars (120, 122) substantially parallel to one another, one of the bus bars (120, 122) being longer than the other to give the heater (120, 122, 130, 140, 142) a trapezoidal shape.

12. The display device of claim 10, wherein the plurality of bus bars (120, 122) includes two bus bars (120, 122) substantially parallel to one another, the two bus bars (120, 122) being substantially equal in length to give the heater (120, 122, 130, 140, 142) a rectangular shape.

13. A display device (100) comprising: an electroluminescent lamp (200) ; and a plurality of thermochromic shutters (105) disposed proximate to the electroluminescent lamp (200) to

19 selectively pass and block light emitted from the electroluminescent lamp (200) .

14. The display device (100) of claim 13, wherein: a portion (150) of each of the thermochromic shutters (105) having variable light transmissivity is disposed on the electroluminescent lamp (200) in a direction in which the electroluminescent lamp (200) is capable of emitting light so that the thermochromic shutter (105) controls the emission of light from the electroluminescent lamp (200) .

15. The display device of claim 13, wherein a portion (150) of each the thermochromic shutters (105) having variable light transmissivity is disposed on a side of the electroluminescent lamp (200) opposite that of a portion

(120, 122, 130, 140, 142) of the thermochromic shutter (105) having fixed light transmissivity.

16. The display device (100) of claim 13, further comprising an insulator (110) disposed between the electroluminescent lamp (200) and one of portions (150) of the thermochromic shutter (105) having variable light transmissivity and portions (120, 122, 130, 140, 142) of the

20 thermochromic shutter (105) having fixed light transmissivity.

17. The display device (100) of claim 13, wherein each of the thermochromic shutters (105) comprises: a thermochromic segment (150) ; and a heater (120, 122, 130, 140, 142) for heating the thermochromic segment (150) to change its light transmissivity.

18. The display device (100) of claim 17, wherein the thermochromic segment (150) is thermochromic ink.

19. The display device (100) of claim 17, wherein the heater (120, 122, 130, 140, 142) comprises: a resistive segment (150); a plurality of bus bars (120, 122) proximate to the resistive segment (150) and in electrical contact therewith; and a plurality of trace leads (140, 142) in electrical contact with the plurality of bus bars (120, 122) for conveying electrical energy to the bus bars (120, 122).

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20. The display device (100) of claim 19, wherein the plurality of bus bars (120, 122) includes two bus bars (120, 122) substantially parallel to one another, one of the bus bars (120, 122) being longer than the other to give the heater (120, 122, 130, 140, 142) a trapezoidal shape.

21. The display device (100) of claim 19, wherein the plurality of bus bars (120, 122) includes two bus bars (120, 122) substantially parallel to one another, the two bus bars (120, 122) being substantially equal in length to give the heater (120, 122, 130, 140, 142) a rectangular shape.

22. The display device (100) of claim 13, wherein the plurality of thermochromic shutters (105) are disposed relative to one another so that they can be selectively activated to form information-bearing indicia.

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