Electrode construction for flexible electroluminescent lamp

• US 4,020,389 A
• Filed: 04/05/1976
• Issued: 04/26/1977
• Est. Priority Date: 04/05/1976
• Status: Expired due to Term

• Current Assignee: Minnesota Mining and Manufacturing Co (3M Company)
• Original Assignee: Minnesota Mining and Manufacturing Co (3M Company)
• Inventors: Dickson, Arthur D., Pruitt, Laurie E.
• Primary Examiner(s): Demeo, Palmer C.
• Application Number:
  US05/673,680
• Time in Patent Office: 386 Days
• Field of Search: 313/509, 313/511, 313/512, 313/506, 313/112, 313/503, 427/66, 315/246, 29/25.13
• US Class Current: 315/246
• CPC Class Codes: H05B 33/22 characterised by the chemical or physical composition or the arrangement of auxiliary dielectric or reflective layers
• CPC Class Codes: H05B 33/28 of translucent electrodes

Abstract

A flexible electroluminescent lamp comprising a laminate of an opaque metal electrode, a flexible resin body having electroluminescent particles embedded therein and a transparent electrically conductive electrode. The transparent electrode comprises a polymeric substrate having a three layer sandwich thereon, which layers comprise a thin-film metal layer between outer dielectric layers having a relatively high index of refraction. The dielectric layers are formed to provide quarter-wavelength interference filters to result in a high degree of transmittance of the sandwich, while yet enabling the metal layer to be sufficiently thick to result in a low resistivity electrode.

Claims

1. A flexible electroluminescent lamp comprising a light transmitting flexible resin body member having opposing faces and a finely divided electroluminescent phosphor embedded therein and electrically conducting electrode layers, one of which is at least substantially transparent, affixed to the opposing faces of the body member, the improvement wherein said substantially transparent electrode layer comprises a transparent polymeric substrate having on a surface thereof a three layer sandwich of a layer of a thin-film of a metal selected from the group including gold, silver, and copper between layers of thin-film dielectric materials generally exhibiting an index of refraction in excess of two, the outer dielectric layer being positioned adjacent the body member, wherein the metal layer has resistivity of less than 30 ohms/square and a thickness in the range between 70 and 180 A, and each of the layers of the thin-film dielectric material have a thickness in the range between 400 and 600 A., wherein the transmissivity of said transparent electrode layer to radiation to be emitted by the phosphor is not less than 70% and wherein the reflectance of said transparent electrode layer to visible radiation is less than 15%, whereby the transparent electrode layer enables the light source to operate at frequencies in excess of 400 Hz while maintaining substantially uniform brightness over the entire transparent electrode layer.

2. A flexible electroluminescent lamp according to claim 1, wherein the dielectric materials are selected from the group consisting of sulfides of zinc, cadmium, mercury, tin, lead, antimony and bismuth;

chlorides, bromides and iodides of copper, silver and lead; and

oxides of titanium and bismuth.

3. A flexible electroluminescent lamp according to claim 1, wherein the three layer sandwich of the transparent electrode layer comprises a thin-film of silver between thin-films of zinc sulfide, the resistivity of the silver film being less than approximately 10 ohms/square and the transmissivity of the sandwich being greater than approximately 80% to light of 5500 A.

4. A lamp according to claim 1, further comprising a substantially moisture impregnable sheet hermetically enclosing the flexible resin body member.

5. A system for producing light by electroluminescence including

a flexible electroluminescent lamp which comprises a light transmitting flexible resin body member having opposing faces and a finely divided electroluminescent phosphor embedded therein and electrically conducting electrode layers, one of which is at least substantially transparent, affixed to the opposing faces of the body member, and

means for applying an electrical potential to said electrode layers, which potential periodically alternates at a frequency in excess of 400 Hz,

the improvement wherein said substantially transparent electrode layer comprises a transparent polymeric substrate having on a surface thereof a three layer sandwich of a layer of a thin-film of a metal selected from the group including gold, silver and copper between layers of thin-film dielectric materials generally exhibiting an index of refraction in excess of two, the outer dielectric layer being positioned adjacent the body member, wherein the metal layer has resistivity of less than 30 ohms/square and a thickness in the range between 70 and 180 A., and each of the layers of the thin-film dielectric material have a thickness in the range between 400 and 600 A., wherein the transmissivity of said transparent electrode layer to radiation to be emitted by the phosphor is not less than 70% and wherein the reflectance of said transparent electrode layer to visible radiation is less than 15%, whereby the low resistivity of the transparent electrode layer enables the light source to efficiently emit light when energized by said alternating potential and to exhibit substantially uniform brightness over the entire transparent electrode layer.

6. A method of making a flexible electroluminescent lamp comprising the steps of

forming a sheet having a coating of electroluminescent particles embedded in an organic binder on a flexible electrically conductive substrate,

forming a substantially transparent electrically conductive sheet according to the sub-steps of

providing a transparent polymeric sheet as a substrate,

forming a first thin-film dielectric layer on a surface of the polymeric sheet, said first dielectric layer generally exhibiting an index of refraction in excess of two and having a thickness in the range between 400 and 600 A.,

forming a layer of a thin-film of a metal selected from the group consisting of gold, silver and copper on the exposed surface of the first dielectric layer, said metal layer having a thickness in the range between 70 and 180 A. and a resistivity of less than 30 ohms/square, and

forming a second thin-film dielectric layer on the exposed surface of the metal layer, said second dielectric layer generally exhibiting an index of refraction in excess of two and having a thickness in the range between 400 and 600 A.,

bonding the transparent conductive sheet to the sheet having a coating of electroluminescent particles by positioning the sheets such that the exposed surface of the electroluminescent particle coating is in contact with the second thin-film dielectric layer and heat-fusing the two sheets together to form a homogeneous integral construction, and

securing electrical contacts to the electrically conductive substrate and to the metal layer.

7. A method according to claim 6, further comprising the step of hermetically sealing said integral construction within a substantially moisture impregnable enclosure.