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(11) | EP 0 172 985 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Electroluminescent lamp |
| (57) An electroluminescent apparatus comprises a substrat (12); a first conductor (14)
fixed to the substrate (12) in a preselected pattern to form a first electrode; a
luminescent coating (16) covering a first portion (18) of the first conductor (14)
while leaving a second portion (20) of the first conductor uncovered; and a pair of
second conductors (22, 24) situated adjacent to, but separated from, each other on
the substrate (12), wherein one (22) of the pair of second conductors (22 and 24)
contacts a selected one of the group consisting of the luminescent coating (16) and
the first conductor (14), and wherein the other (24) of the pair of second conductors
(22, 24) contacts the unselected one of said group. A method of forming the electroluminescent
device is also described. |
[0001] This invention relates in general to electroluminescent cells, lamps, and panels, whicn devices generate light in response to an applied electrical signal. The invention particularly relates to such devices naving an integral shielding layer so as to permit use of the device in close proximity to other circuits whicn may be responsive to said applied electrical signal. The invention also pertains to a unique metnod for constructing electroluminescent devices having inherent manufacturing simplicity and superiority.
[0002] Electroluminescent devices in tne form of lamps or panels are themselves well known. A typical device comprises a finely divided phosphor dispersed in a binder and distributed in a thin layer between two plate or sneet electrodes, at least one of the electrodes being substantially transparent. The application of an electrical signal to tne two electrodes causes tne phosphor material to emit light, part of whicn is directed outwardly througn the substantially transparent electrode.
[0003] An electroluminescent apparatus of tne present invention includes a substrate with a first conductor or electrode fixed to substrate in a preselected pattern. A luminescent coating covers a first portion of tne first conductor leaving a second portion of tne first conductor uncovered. A pair of second conductors can be simultaneously situated in spaced adjacent relationship on the substrate. One of the second conductors extends over the luminescent coating wnile tne otner of the second conductors contacts the uncovered portion of tne first conductor. The pair of second conductors form leads leading from the luminescent area or oody of the device to a terminal portion where pin elements are affixed in a manner compatible with standard dimensioneu plugs.
[0004] Apparatus of tnis general type are typically powered by a supply having an output signal in the audio frequency range, preferably about 800 hertz. When sucn an apparatus is used in close proximity with audio amplifiers or other circuits which may be responsive to a signal of such a frequency, some shielding must be employed to prevent interference. While the shielding can be incorporated in separate physical structure, it is desirable to have the shielding be an integral part of tne electroluminescent lamp so as to insure reliability of performance. An integral incorporation of shielding witn the lamp permits a total lower cost construction and generally quicker assemoly tnan would be experienced witn a separateshield assembly.
[0005] The method used to form devices of the present invention utilizes a substrate whicn can be formed to include a body portion and a lead portion. Tne first conductor wnicn forms one of the electrodes is depositea on the body portion of tne substrate in a preselected pattern. The luminescent coating covers a first portion of the first electrode, tne first portion comprising only those areas which are intended to be excited by an applied electrical signal so as to emit lignt. A second portion, usually a peripheral portion, of the first conductor is left uncovered by the luminescent coating. A pair of second conductors can then be simultaneously deposited adjacent to eacn other. One of tne pair of second conductors extends over the luminescent coating to form the second electrode wnile tne other of tne pair of second conductors contacts only the first portion of the first electrode. Both of tne second conductors can unitarily extend from the body portion linearly along the lead portion of the substrate to form a two-conductor lead of preselected length whicn terminates at the distal end of the lead portion of tne substrate.
[0006] The entire apparatus is covered by an insulative coating. The insulative coating acts as a barrier to prevent later ingress of moisture or other elements wnicn, if not excluded, contribute to failure of the device. Tne insulative layer also permits tne device once formed to experience greater physical manipulation witnout failure. A shielding layer is then deposited over tne insulative layer. The shielding layer is substantially coextensive with the insulative layer but preferably extends over tne terminal portion of tne conductor leading to tne second electrode. Alternatively, tne shielding layer can be formed to include a third terminal preferably adjacent tne terminal portions of tne second conductors. Pin elements or other similar contacts are tnen attached to the ends of the pair of second conductors and snielding layer in a manner whicn assures uniform separation and tnus plug compatibility of the device so formed. An additional protective layer can be applied over tne snielding layer either before or after attachment of tne pin elements.
[0007] One feature of the present invention is tne coincident contact formed by tne superpositioning of tne terminal portions of one of the second conductors and tne shielding layer. Tne grounding of this contact assures an effective shielding of the electrical signal applied to the lamp thereby preventing interference witn desirable signals being processed by adjacent circuitry.
[0008] An advantage of tne present invention is that a number of devices can be simultaneously formed on a large single sheet of substrate whicn is tnereafter diecut to form the individual luminescent devices. Tne pin elements or other contact devices can be attaciied using conventional contact stapling techniques witn hign reliability of both dimensional tolerance and electrical continuity.
[0009] Additional features and advantages of tne invention will become apparent to tnose skilled in tne art upon consideration of the following detailed description of a prefered embodiment exemplying the best mode of carrying out the invention as presently preceived. Tne detailed description particularly refers to the accompanying figures in which:
Fig. 1 is a plan view snowing the substrate and first conductor deposited in a preselected pattern;
Fig. 2 is a plan view showing the positioning of the luminescent coating over the first conductor so as to leave at least one edge of tne first conductor uncovered;
Fig. 3 is a plan view snowing the deposition of the pair of second conductors adjacent to eacn other witn one conductor contacting tne luminescent coating and tne other conductor contacting the first electrode;
Fig. 4 is a plan view showing the insulative coating deposited over the entirety of tne apparatus except the terminal portions of tne pair of second conductors.
Fig. 5 is a plan view showing tne shielding layer deposited coextensively witn the insulative layer and extending over the terminal portion of one of tne second conductors.
Fig. 6 is a plan view similar to Fig. 5 snowing an alternative embodiment witn tne shielding layer forming a third terminal.
Fig. 7 is a sectional view taken along line 7-7 of Fig. 5.
Fig. 8 is a sectional view similar to Fig. 7 showing the addition of a protective overlayer and a terminal pin.
[0010] An electroluminescent device 10 in accordance witn the present invention is illustrated in tne various stages of its construction in Figs. 1 tnrougn 5 and in final form in Fig. 8. While eacn of tne Figs. 1-6 illustrate only a single device 10, it will be appreciated that a plurality of similar devices 10 can be formed simultaneously on a single substrate 12, tne devices being separated from eacn otner at a later stage in the manufacture. The device 10 comprises a substrate 12 onto which is deposited a first conductor or electrode 14 wnicn can be deposited in a plurality of discrete areas. A luminescent coating 16 covers a first substantial portion 18 of the first conductor 14 while leaving a second generally peripheral portion 20 of the first conductor 14 uncovered. The luminescent coating is similarly positionable on a plurality of discrete areas. One portion 19 of tne luminescent coating 16 extends beyond an edge 13 of the first electrode 14.
[0011] A pair of second conductors 22 and 24 are deposited adjacent to each other. The second conductor 22 is deposited so as to contact portion 19 and substantially cover the luminescent coating 16 to form a second electrode 26 parallel to tne first electrode formed by first conductor 14. The second conductor 22 can form bridges 23 between various second electrodes 26. Tne second conductor 24 is deposited so as to contact only tne substrate 12 and tne first conductor 14 in the second or pheripheral portion 20. The second conductor 24 thus forms an electrical lead or bus 25 for the first electrode 14.
[0012] An insulative layer 32 is deposited or positioned over the second conductors 22 and 24 so as to cover substantially all of tne device 10. A shielding layer 38 is then deposited over substantially the entirety of tne insulative layer 32 except for a free edge 40 adjacent tne terminal end of one of the second conductors sucn as conductor 24. As shown in Fig. 5, tne snielding layer 38 extends over the terminal end of conductor 22 wnicn forms the second electrode 26. In an alternative emoodiment shown in Fig. 6, the shielding layer is extended to form a third terminal 44 adjacent to but insulated from conductors 22 and 24 by free edge 40 of insulative layer 32. A protective coating 42 can be applied over the shielding layer 38 as shown in Fig. 8 to protect it from abrasion and corrosion which might degrade its electrical performance.
[0013] The substrate 12 is shown to comprise a body portion 28 and a lead portion 30. While lead portion 30 is shown to extend outside the general peripnery of tne body portion 28, devices can be formed having lead portions within the periphery of the body portion 28. Tne substrate is preferably formed of a flexible transparent sheet material composed of a polymeric resin wnicn is sufficiently form stable to prevent any mechanical stretching wnich might destroy the continuity of tne various coated layers placed on that substrate. An example of a satisfactory material is a polyester sucn as biaxially oriented polyethelene terephtnalate (PET). Tne body portion 28 and lead portion 30 are unitary and in general are cut from a single sheet of about 0.005 to 0.007 inch thickness subsequent to the deposition of tne various layers disclosed herein.
[0014] The first conductor 14 comprises generally a substantially transparent metal oxide film whicn is spaced inwardly from the edge of substrate 12. Suitable metal oxide films can be formed of tin oxide, indium oxide, or nickel oxide with indium tin oxide being preferred. Metal oxide films having an optical transmittance of 60% or greater can be achieved while maintaining electrical ' continuity throughout the layer, the layer having a sheet resistance of less than about 2000 ohms per square. Tne metal oxide film is preferably formed oy silK screening a solvent solution of a polyester resin containing tne metal oxide on to the substrate 12. Alternatively, tne metal oxide film may be formed in accordance with the general practices of U.S. Pat. 3,295,002.
[0015] Tne luminescent coating 16 is shown to cover substantially the whole of the first conductor 14 leaving only an edge portion 20 of tne first conductor 14 exposed. The luminescent coating 16 generally comprises a light emitting layer 15 and an insulative, lignt reflecting layer 17 as shown in Fig. 7. Tne lignt emitting layer 15 generally comprises a mixture of a phosphor and a binder. The phosphor may be an inorganic compound sucn as zinc sulfide or zinc oxide combined witn suitable activators such as copper, manganese, lead or silver. Alternatively, the phosphor may be an organic luminescent agent such as anthracene, naptnalene, butadiene, acridine or other similar material. Tne phosphor is mixed with a suitable binder which is selected to be compatible witn the phospnor. Examples of suitable binders are polyvinyl chlorides, cellulose acetate, epoxy cements, and other similar materials. Particularly useful binders include cyanoethyl cellulose and etnyl hydroxyethyl cellulose.
[0016] Tne light reflective layer 17 is generally a mixture of a light reflective opacifier in a matrix whicn is itself a dieletric. The layer preferably has a dielectric constant of about 10 or greater, and a breakdown strength of at least 800 volts/mil. Tne reflective opacifier is generally a metal oxide powder such as titanium oxide, lead oxide or barium titanate in a resin matrix of acrylic, epoxy, or other suitable resin. The relative positioning of layers 15 and 17 is sucn that light is emitted from the device 10 through tne substrate 12.
[0017] Tne pair of second conductors 22 and 24 are deposited, preferably simultaneously, so as to be positioned side by side on the lead portion 30 of the substrate 12. One of the second conductors 22 unitarily extends on top of the luminescent coating 16 so as to form the second electrode 26. The other second conductor 24 extends merely over the second portion 20 of the first conductor 14 which was left uncovered by the luminescent coating 16. The second conductor 24 is spaced from tne luminescent coating by a distance sufficient to insure electrical isolation of the first electrode 14 and second conductor 24 from the second electrode 26. The second conductors 22 and 24 including the second electrode portion 26 of second conductor 22 are formed of a particulate metal in colloidal form which is deposited in combination with an evaporable medium leaving benind a conductive film of particulate metal. A suitable material is a silver conductive coating material commercially available from Atcheson Colloids Company, Port Huron, Michigan, under part name Electrodag 426SS. Other types of fluid silver conductive materials are commercially available which may perform satisfactorily.
[0018] An insulative coating 32 is applied over the top of the various layers previously described to cover tne entirety of the device as shown in Fig. 4. The insulative coating 32 preferably has a low dielectric constant of less than about 4 whicn acts to minimize the capactive coupling from the circuit formed ny tne various layers 14, 16, 22, and 24 to the shielding layer 38. While low to medium density polyethylene and polymethylpentine materials generally may be satisfactory to form this layer, a particularly advantageous material is a biaxially oriented PET film coated on one side with about 0.001 inch of a cross-linking acrylic adhesive sucn as 3-M No. 467.
[0019] A shielding layer 38 is applied on top of and substantially coextensive with tne insulative coating 32 as shown in Figs. 5-8. In one preferred embodiment snown in Fig. 5, the shielding layer 38 extends over tne terminal portion of conductor 22. In anotner embodiment shown in Fig. 6, the shielding layer 38 includes a separate terminal 44 whicn can be attached to an appropriate ground to effect the desired shielding. In eitner embodiment the shielding layer can comprise a metal foil or metalized plastic film which can be cut to snape and directly applied, or a particulate metal in colloiaal form which is deposited in a manner similar to conductors 22 and 24. A suitable metalized plastic film is available in conjunction with easily handled release sheets from Flexcon, Inc. of Spencer, Mass. under part MM-100. A suitable particulate metal colloid is that indicated previously for conductors 22 and 24.
[0020] As shown in Fig. 8, a protective overcoat 42 can be applied over the shielding layer 38. Tne overcoat 42 is preferably abrasion resistant and moisture proof. While curable silicone materials generally may be satisfactory to form this layer, a particularly advantageous material is tne polyester resins dissolved in a suitable carrier to be applied by overprinting.
[0021] Tne overcoat layer 42 can also be formed using the adhesively coated PET film disclosed for insulative layer 32. The PET or other similarly suitable polymeric film can include a second adhesive layer 46 and a removable release sheet 48 as shown in Fig. 7. Tne release sheet 48 is adapted to be removed to expose tne adhesive layer 46 so as permit mounting of tne finished product on other apparatus witn whicn tne device is intended to be used.
[0022] The completed assembly is easily die cut to tae final desired configuration witn a multiplicity of devices 10 being cut from a single substrate 12 and pin connectors 36 applied. In the emoodiment shown in Fig. 8, tne pin connector acts to electrically connect tne shielding layer 38 to tne conductor 22 whicn is tnen connected to a suitable ground. A suitable connector is AMP 88997-2.
[0023] The metal connectors 36 can be attacnea to tne terminal portions of conductors 22 and 24 by stapling or other appropriate means. Tne spacing between the connector pins or elements 36 are set by tne attacning equipment and by the spacing between tne two second conductors 22 and 24 as well as on terminal 44 wnere present as a separate terminal element. Wnen tne two conductors 22 and 24 are simultaneously formed, the distance between the two conductors is uniformly maintained and hence tne connection with tne snielding layer 38 and spacing of the pin connectors 36 can also be similarly maintained with very high reliaoility.
1. An electroluminescent apparatus comprising a substrate,
a first conductor fixed to tne sudstrate in a preselected pattern to form a first electrode,
a luminescent coating covering a first portion of the first conductor leaving a second portion of tne first conductor uncovered; and
a pair of second conductors situated adjacent to, but separated from, eacn other on tne substrate, one of the pair of second conductors contacting a selected one of the group consisting of the luminescent coating and the first conductor, the other of tne pair of second conductors contacting the unselected one of said group.
2. The apparatus of claim 1 wnerein tne substrate comprises a flexible transparent
sneet composed of a polymeric resin.
3. The apparatus of claim 1 tne first conductor comprises a transparent metal oxide
film spaced inwardly from the edge of tne substrate.
4. The apparatus of claim 1 wherein the luminescent coating covers suostantially tne
wnole of tne first conductor leaving at least one edge of tne first conductor uncovered.
5. Tne apparatus of claim 4 wnerein one of said pair of second conductors extends
along said at least one edge of the first conductor.
6. The apparatus of claim 4 wherein tne substrate comprises a body portion and a lead
portion, said first conductor being confined to said body portion.
7. The apparatus of claim 6 wnerein said pair of second conductors extend along said
lead portion parallel to each other from said body portion to a terminal and remote
therefrom.
8. The apparatus of claim 7 furtner comprising a pair of pin elements attached to
the terminal end of said pair of second conductors remote from said body portion.
9. The apparatus of claim 1 furtner comprising a water vapor impervious coating extending
over the entirety of the luminescent coating and all but an end portion of the pair
of second conductors.
10. The apparatus of claim 1 wnerein the luminescent coating comprises a light-emitting
layer and an opaque, light-reflecting layer.
ll. The apparatus of claim 10 wnerein the opaque layer comprises a metal oxide power
in a matrix.
12. The apparatus of claim 1 further comprising, an insulative layer opposite tne
substrate covering all but a terminal portion of tne conductors, and a conductive
shielding layer substantially coextensive witn tne insulative layer, tne snielding
layer including a terminal portion adapted to be connected to a suitable ground.
13. Tne device of claim 12 wnerein tne terminal portion of the shielding layer overlies
the terminal portion of one of the conductors and is electrically connected thereto.
14. The device of claim 13 further comprising a pin element connected to the terminal
portion of eacn of the conductors, one of the pin elements electrically connecting
the shielding layer to said one of the conductors.
15. The device of claim 12 wnerein tne terminal portion of tne shielding layer is
situated adjacent to and spaced from tne terminal portions of tne conductors, eacn
terminal portion further comprising a pin element connected tnereto in a preselected
spaced relation to eacn other pin element.
16. The device of claim 12 wnerein tne substrate comprises a body portion and a lead
portion, tne electrodes and electroluminescent layer being confined to the body portion,
the conductors extending form tne pody portion to a distal end of tne lead portion
where the terminal portion of the conductors are situated.
17. The device of claim 12 wnerein one of tne conductors is unitary witn one of the
electrodes tne conductor connected to tne other electrode extending along an edge
thereof to form a bus.
18. The device of claim 12 furtner comprising a protective overcoat of abrasion resistant,
water vapor impervious material lying on top of tne snielding layer.
19. The device of claim 18 furtner comprising an adhesive layer and a removable release
sneet situated on top of the overcoat, tne release sneet being adapted for later removal
to permit mounting of the device.
20. The method of forming an electroluminescent device comprising the steps of:
a) providing a substrate;
b) depositing a first conductor on the substrate in a preselected pattern to form a first electrode;
c) covering a first portion of tne first conductor with a luminescent coating while leaving a second portion of the first conductor uncovered; and
d) depositing simultaneously a pair of second conductors adjacent to each other, one of tne pair of second conductors contacting only the luminescent coating and the substrate, the other of tne pair of second conductors contacting only the first conductor and the substrate.
21. The method of claim 20 furtner comprising the step of forming the substrate to
include a body portion and a lead portion, the first conductor being deposited only
on the body portion.
22. The method of Claim 2l wnerein step d) includes depositing said pair of conductors
adjacent to each other on said lead portion of the substrate, said pair of conductors
contacting the first conductor and tne luminescent coating only on said body portion.
23. The method of claim 20 wherein step c) comprises the steps of depositing a mixture
of a pnospnor and binder on said first portion of the first conductor; and depositing
a mixture of a reflective opacifier in a matrix over the phosphor and binder.
24. Tne method of claim 20 furtner comprising the step of overcoating all but an end
portion of said pair of conductors witn a protective overcoat of water vapor impervious
material.
25. The method or claim 20 further comprising the step of attaching a pin element
to an end of eacn of the pair of second conductors.
26. The method of Claim 20 furtner comprising the step of cutting the substrate to
separate the formed device from adjacently formed devices.
27. The method of claim 20 further comprising tne steps of:
a) depositing an insulative film so as to cover the pair of second conductors; and
b) depositing a conductive snielding layer over the insulative film, tne shielding layer including a terminal portion adapted to be connected to a suitable ground.
28. Tne method of claim 27 wnerein tne terminal portion of the shielding layer is
deposited on top of a terminal portion of one of said pair of second conductors.
29. The method of claim 28 furtner comprising the step of attacning a pin element
to tne terminal portion of each of the pair of second conductors, one of the pin elements
electrically connecting tne terminal portion of the shielding layer to tne underlying
terminal portion of a second conductor.
30. The method of claim 27 wnerein tne terminal portion of the shielding layer is
deposited adjacent to the terminal portions of the pair of second conductors at a
preselected spacing tnerefrom.
31. The method of claim 30 further comprising the step of attaching a pin element
to tne end of eacn of the second conductors and the shielding layer at a preselected
spacing.
32. Tne method of claim 27 furtner comprising the step of applying a protective overcoat
over the shielding layer.
33. The method of claim 32 wherein tne protective overcoat includes an adhesive layer
and a removable release sneet.
34. The metnod of claim 27 furtner comprising tne step of cutting the device from
a sheet of tne substrate material.
35. Tne method of claim wnerein tne preselected pattern employed is one which forms
a plurality of devices simultaneously on a single suostrate.