Thin, durable electroluminescent lamp

Abstract

A high brightness, durable, thick film electroluminescent lamp includes a base having a thin layer of PET on a release layer and a transparent front electrode of ITO particles in a resin, a transparent rear electrode, and a reflective layer overlying the transparent rear electrode.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the invention can be obtained by considering the following detailed description in conjunction with the accompanying drawings, in which:

FIG. 1 is a cross-section of an EL lamp constructed in accordance with the prior art;

FIG. 2 is a cross-section of another EL lamp constructed in accordance with the prior art;

FIG. 3 is a cross-section of an EL lamp constructed in accordance with a preferred embodiment of the invention;

FIG. 4 is a cross-section of an EL lamp constructed in accordance with an alternative embodiment of the invention; and

FIG. 5 is a chart of the results of tests.

DETAILED DESCRIPTION OF THE INVENTION

The lamp illustrated in FIG. 1 is a standard (self-supporting) EL lamp known in the art and is used for comparison with lamps made in accordance with the invention. The lamp illustrated in FIG. 2, referred to as a “DFLX” lamp, is also used for comparison with other lamps described herein. None of the figures are drawn to scale, either within a figure or between figures.

In FIG. 1, transparent substrate 11 is a sheet of bi-axially oriented plastic such as polyester or polycarbonate, 5-7 mils thick. Transparent front electrode 12 overlies substrate 11 and is a thin layer of indium tin oxide or indium oxide. The transparent electrode is sputter deposited and the substrate with electrode are commercially available. Phosphor layer 15 overlies the front electrode and dielectric layer 16 overlies the phosphor layer. Layers 15 and 16 are combined in some applications. Overlying dielectric layer 16 is opaque rear electrode 18. An optional backing layer (not shown) may also be provided, e.g. for insulating the rear electrode. Coated phosphor particles are used, eliminating the need for a sealing layer.

Dielectric layer 16 can be made with particles of titania (TiO₂) barium titanate (BaTiO₃) in a suitable resin ink. A lamp type known as “HBC” sold by Durel Division of Rogers Corporation uses barium titanate as the dielectric and that is the designation herein for a lamp constructed as shown in FIG. 1.

FIG. 2 is a cross-section of an EL lamp constructed as described in the above-identified copending application. Lamp 20 includes release layer 21 with insulating layer 22 deposited thereon, e.g. by screen printing or other technique known in the art. The release layer is a coated paper or a plastic sheet, such as polyethylene terephthalate (PET), supplied in rolls, which facilitates handling the lamps and integrating the lamps into appliances or molding apparatus.

Electrode 23 is carbon bearing, conductive polymer that is screen printed on layer 22. Dielectric layer 25 overlies electrode 23 and phosphor layer 26 overlies the dielectric layer. Electrode 27 is made by screen printing a transparent conductive layer containing PEDOT (poly-3,4-ethylenedioxythiophene), such as available from Bayer or Agfa, on phosphor layer 26. Insulating layer 28 overlies electrode 27.

FIG. 3 is a cross-section of a lamp constructed in accordance with a preferred embodiment of the invention. Lamp 30 includes base 31, a conductive sheet commercially available from Sumitomo Metal Mining (SMM). Base 31 includes release layer 33, adhesive layer 34, substrate 35, and transparent front electrode 36.

Release layer 33 is 100μ PET. Adhesive layer 34 is a UV cured acrylic. Substrate 35 is a 6μ-50μ thick layer of PET, preferably having a thickness of 12μ-1μ. Electrode 36 is made with very fine (300-500 nm) particles (“nano particles”) of ITO in a UV cured resin. The PET substrate is dimensionally stable despite its relative thinness. Other stable substrates can be used instead.

The remaining layers of lamp 30 include insulating layer 41 around the perimeter of the lamp to prevent shorting along the edges, phosphor layer 43, dielectric layer 44, transparent rear electrode 45, reflective layer 46, and rear insulator 47. In FIG. 4, the alternative embodiment differs from FIG. 3 in that layers 46 and 47 are combined in layer 51.

Reflective layer 46 is not between the electrodes and does not affect the electrical operation of the lamp, which is sensitive to dielectric constant, susceptibility, and electrode spacing. Also because reflective layer 46 is not between the electrodes, one can choose a reflective layer for optical performance rather than for electrical performance. A layer having a reflectance of ninety percent or greater is preferred and the choice of materials is considerable. For example, of the materials specifically mentioned herein, layers containing barium titanate or titanium dioxide, each have a reflectance greater than ninety percent. The dielectric layer can be made thinner, which aids brightness, because one does not have to reflect all incident light with this layer.

FIG. 5 is a bar chart of the results of testing several of each type of sample. Each bar is an average of the results for the particular sample. Sample “A” is the present “DFLX” construction. This is a lamp that is not self-supporting and is subject to mechanical distortion. Sample “E” is a commercially available lamp. Sample “E” is much thicker than sample “A” and is much less flexible but is mechanically stable and slightly brighter than sample “A.” These lamps are representative of the state of the art in commercially available EL lamps.

For the tests, all lamps had the same shape and area. Each lamp was driven by the same inverter from a three volt supply. The phosphor used was the same in all samples and the dielectric layer was the same in all samples. A reflector behind a transparent rear electrode substantially improved brightness in otherwise identical constructions. The base provides a much more dimensionally stable lamp, while also improving brightness.

In the following chart, “a-ITO” refers to acicular ITO and “s-ITO” refers to sputtered ITO. Acicular ITO is as a transparent conductor known in the art, see U.S. Pat. No. 5,580,496 (Yukinobu et al.), having ITO needles suspended in an organic resin.

		substrate	front electrode	rear electrode	reflector
A	DFLX	polyurethane	Orgacon	Carbon	none
B		SMM	N/A	Carbon	none
C		SMM	N/A	PEDOT	TiO2
D		SMM	N/A	a-ITO	TiO2
E	HBC	PET	s/ITO	Carbon	none
F	modified	PET	s/ITO	PEDOT	TiO2
	HBC

The invention thus provides a thin, thick-film, inorganic EL lamp that is not easily torn or distorted, is brighter than EL lamps of the prior art and is as environmentally stable as commercially available lamps.

Having thus described the invention, it will be apparent to those of skill in the art that various modifications can be made within the scope of the invention. For example, the phosphor layer can be divided into areas for containing phosphors producing different colors instead of or in addition to the cascading layer. More than one cascading layer can be used, e.g. by including dye in the front insulating layer. As illustrated in FIG. 1, lamp 20 is constructed back to front. Typically, building an EL lamp from front to back involves no more than reversing the order in which layers are deposited. Unless indicated otherwise, it is immaterial which way the lamp is assembled when constructing a lamp in accordance with the invention. Other layers could be added to the embodiment shown in FIG. 1, such as graphic overlays and protective layers. Any layer can be split to form a plurality of lamps in a single panel.

Claims

1. A durable, thin, thick-film, inorganic, electroluminescent lamp comprising: a transparent front electrode;a phosphor layer overlying said front electrode;a dielectric layer overlying said phosphor layer;a transparent rear electrode overlying said dielectric layer; anda reflective layer overlying the transparent rear electrode.

2. The lamp as set forth in claim 1 wherein said transparent front electrode is a layer including indium tin oxide.

3. The lamp as set forth in claim 1 wherein said transparent front electrode is a base having a transparent conductive layer including particles of indium tin oxide in a resin.

4. The lamp as set forth in claim 1 wherein said transparent rear electrode includes poly-3,4-ethylenedioxythiophene.

5. The lamp as set forth in claim 1 wherein said transparent rear electrode includes indium tin oxide.

6. The lamp as set forth in claim 1 wherein said reflective layer has a reflectance greater than ninety percent.

7. The lamp as set forth in claim 1 wherein said reflective layer consists essentially of titanium dioxide in a polymer binder.

8. The lamp as set forth in claim 1 wherein said transparent front electrode includes: a substrate containing polyethylene terephthalate and having a thickness of 6μ-50μ;a layer of resin containing particles of indium tin oxide.

9. The lamp as set forth in claim 8 wherein said layer of resin contains nano particles of indium tin oxide.

10. A high brightness, durable, thick film electroluminescent lamp comprising: a transparent front electrode, wherein said transparent front electrode includes a layer of resin containing particles of indium tin oxide;a phosphor layer overlying said front electrode;a dielectric layer overlying said phosphor layer;a transparent rear electrode overlying said dielectric layer; anda reflective layer overlying the transparent rear electrode and consisting essentially of titanium dioxide in a polymer binder.

11. The lamp as set forth in claim 10 wherein said transparent rear electrode includes poly-3,4-ethylenedioxythiophene.

12. The lamp as set forth in claim 10 wherein said transparent rear electrode includes acicular indium tin oxide.

13. The lamp as set forth in claim 10 wherein said transparent front electrode includes: a thin substrate containing polyethylene terephthalate; andsaid layer of said resin containing particles of indium tin oxide overlies said substrate.

14. The lamp as set forth in claim 13 wherein said particles of indium tin oxide are nano particles.

15. A high brightness, durable, thick film electroluminescent lamp comprising: a transparent front electrode including a substrate containing polyethylene terephthalate and a layer of resin containing nano particles of indium tin oxide;a phosphor layer overlying said front electrode;a dielectric layer overlying said phosphor layer;a transparent rear electrode overlying said dielectric layer; anda reflective layer overlying the transparent rear electrode and having a reflectance of greater than ninety percent.

16. The lamp as set forth in claim 15 wherein said transparent rear electrode includes poly-3,4-ethylenedioxythiophene.

17. The lamp as set forth in claim 15 wherein said transparent rear electrode includes acicular indium tin oxide.