Patent Grant
7202600
This invention relates to a thick-film, inorganic, electroluminescent (EL) panel and, in particular, to an EL panel assembled on a release layer and, after separation from the release layer, an EL panel that does not substantially curl or distort.
As used herein, and as understood by those of skill in the art, “thick-film” refers to one type of EL lamp and “thin-film” refers to another type of EL lamp. The terms only broadly relate to actual thickness and actually identify distinct disciplines. In general, thin film EL lamps are made by vacuum deposition of the various layers, usually on a glass substrate or on a preceding layer. Thick-film EL lamps are generally made by depositing layers of inks on a substrate, e.g. by roll coating, spraying, or various printing techniques. The techniques for depositing ink are not exclusive, although the several lamp layers are typically deposited in the same manner, e.g. by screen printing. A thin, thick-film EL lamp is not a contradiction in terms and such a lamp is considerably thicker than a thin film EL lamp.
In the context of a thick-film EL lamp, and as understood by those of skill in the art, “inorganic” refers to a crystalline, luminescent material that does not contain silicon or gallium. The term does not refer to the other materials from which an EL lamp is made.
As used herein, an EL “panel” is a single sheet including one or more luminous areas, wherein each luminous area is an EL “lamp.” An EL lamp is essentially a capacitor having a dielectric layer between two conductive electrodes, one of which is transparent. The dielectric layer can include phosphor particles or there can be a separate layer of phosphor particles adjacent the dielectric layer. The phosphor particles radiate light in the presence of a strong electric field, using relatively little current.
EL phosphor particles are typically zinc sulfide-based materials, including one or more compounds such as copper sulfide (Cu2S), zinc selenide (ZnSe), and cadmium sulfide (CdS) in solid solution within the zinc sulfide crystal structure or as second phases or domains within the particle structure. EL phosphors typically contain moderate amounts of other materials such as dopants, e.g., bromine, chlorine, manganese, silver, etc., as color centers, as activators, or to modify defects in the particle lattice to modify properties of the phosphor as desired. The color of the emitted light is determined by the doping levels. Although understood in principle, the luminance of an EL phosphor particle is not understood in detail. The luminance of the phosphor degrades with time and usage, more so if the phosphor is exposed to moisture or high frequency (greater than 1,000 hertz) alternating current.
Various colors can be produced by mixing phosphors having different dopants or by “color cascading” phosphors. A copper-activated zinc sulfide phosphor produces blue and green light under an applied electric field and a copper/manganese-activated zinc sulfide produces orange light under an applied electric field. Together, the phosphors produce what appears to be white light. It has long been known in the art to color-cascade phosphors, i.e. to use the light emitted by one phosphor to stimulate another phosphor or other material to emit light at a longer wavelength; e.g. see U.S. Pat. No. 3,052,810 (Mash). It is also known to doubly cascade light-emitting materials. U.S. Pat. No. 6,023,371 (Onitsuka et al.) discloses an EL lamp that emits blue light coated with a layer containing fluorescent dye and fluorescent pigment. In one example, the pigment absorbs blue light and emits green light, while the dye absorbs green light and emits red light.
A modern (post-1985) EL lamp typically includes transparent substrate of polyester or polycarbonate material having a thickness of about 7.0 mils (0.178 mm.). A transparent, front electrode of indium tin oxide or indium oxide is vacuum deposited onto the substrate to a thickness of 1000 Å or so. A phosphor layer is screen printed over the front electrode and a dielectric layer is screen printed over phosphor layer. A rear electrode is screen printed over the dielectric layer. It is also known in the art to deposit the layers by roll coating.
The inks used include a binder, a solvent, and a filler, wherein the filler determines the nature of the ink. A typical solvent is dimethylacetamide (DMAC). The binder is typically a fluoropolymer such as polyvinylidene fluoride/hexafluoropropylene (PVDF/HFP), polyester, vinyl, epoxy, or Kynar 9301, a proprietary terpolymer sold by Atofina. A phosphor layer is typically screen printed from a slurry containing a solvent, a binder, and zinc sulphide particles. A dielectric layer is typically screen printed from a slurry containing a solvent, a binder, and particles of titania (TiO2) or barium titanate (BaTiO3). A rear (opaque) electrode is typically screen printed from a slurry containing a solvent, a binder, and conductive particles such as silver or carbon.
As long known in the art, having the solvent and binder for each layer be chemically the same or chemically similar provides chemical compatibility and good adhesion between adjacent layers; e.g., see U.S. Pat. No. 4,816,717 (Harper et al.). It is not easy to find chemically compatible phosphors, dyes, binders, fillers, solvents or carriers and to produce, after curing, the desired physical properties, such as flexibility, and the desired optical properties, such as color and brightness.
An EL lamp constructed in accordance with the prior art is relatively stiff, even though it is typically only seven mils thick, making the lamp unsuited to some applications requiring greater flexibility, such as keypads. Layer thickness and stiffness are not directly related. The material from which the layer is made affects stiffness. Typically, EL lamps are made from the materials listed above. An EL lamp backlighting a keypad, for example, typically has holes under the keys to avoid affecting the actuation of a key. Simply reducing the thickness of the substrate does not provide the desired flexibility.
Relatively flexible EL lamps are known in the art. U.S. Pat. No. 5,856,030 (Burrows) discloses an EL lamp made on a UV-cured urethane layer on a release paper. The release paper provides substantial structural support while the lamp layers are applied from an ink containing a vinyl gel. Unlike panels made on substrates that are seven mils thick, or so, EL panels made on thin sheets from flexible materials, e.g. urethane one to five mils thick, do not keep their shape but bend or curl. This makes it extremely difficult to automate the assembly of panels into end products, e.g. a keypad for a cellular telephone or as the luminous structure in a three dimensional molded object.
Published PCT application WO 02/103718 alludes to “selected” layers of an EL structure being made from UV-curable inks. No basis for selection is described nor is any layer described that is not made from a UV-curable ink. U.S. Pat. No. 5,565,733 (Krafcik et al.) discloses an EL lamp made from solvent based materials and including a UV-curable dielectric layer overlying portions of conductive traces that are not connection points for the EL lamp. U.S. Pat. No. 5,770,920 (Eckersley et al.) discloses a UV-curable insulating layer overlying the rear electrode of an EL lamp made with solvent based materials. U.S. Pat. No. 5,780,965 (Cass et al.) discloses a polyurethane acrylic protective layer for an EL lamp. In general, the industry has followed the layers-having-similar-chemistry maxim pronounced in the Harper et al. patent, particularly for the lamp layers (between and including the electrodes).
In view of the foregoing, it is therefore an object of the invention to provide a thin, thick-film, inorganic EL panel that does not curl or distort when removed from a release layer.
Another object of the invention to provide a flexible EL lamp that is more stable dimensionally than urethane based EL lamps of the prior art.
A further object of the invention is to provide a flexible EL lamp that does not require similar chemistry for adjacent lamp layers.
Another object of the invention is to provide an EL lamp made from solvent based inks on a removable substrate or release layer.
A further object of the invention is to provide a flexible EL lamp that is brighter than flexible EL lamps of the prior art.
Another object of the invention is to provide a flexible EL lamp suitable for keypads.
The foregoing objects are achieved in this invention in which an electroluminescent panel includes a release layer, a first insulating layer on the release layer, a plurality of lamp layers on the first insulating layer, and a second insulating layer overlying the lamp layers. In accordance with a first aspect of the invention, the first insulating layer and the second insulating layer include low molecular weight PVDF/HFP resin. In accordance with a second aspect of the invention, at least one of the lamp layers includes a UV-cured resin and the remaining lamp layers include a heat cured resin.
A more complete understanding of the invention can be obtained by considering the following detailed description in conjunction with the accompanying drawings, in which:
Electrode 23 is carbon/PEDOT/PSS (Poly-3,4-ethylenedioxythiophene/polystyrenesulfonic acid) (Orgacon™ EL-P 4010; Agfa-Gevaert N.V.), a conductive polymer composite 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 PEDOT/PSS ink (Orgacon™ EL-P 3040; Agfa-Gevaert, N.V.) on phosphor layer 26. Electrode layers 23 and 27 can be patterned to define lit areas of the lamp in a graphic design. Insulating layer 28 overlies electrode 27.
The embodiments of
Other layers could be added to the embodiment shown in
In accordance with one aspect of the invention, materials have been found that enable one to make bright, flexible, long-life, thin, thick-film EL lamps with adjacent UV-curable and heat-curable (solvent based) layers. In one embodiment of the invention, referring to
By way of example only, the following data describes the construction of an EL lamp in accordance with the invention. References are to
Layer 38 rear insulator, for example, Kolorcure Lustercure Special Release Liner C.
In
In
To make a simple two-electrode lamp, like the one illustrated in
Taking the materials in order used in the above sequence, the following examples are presented as viable, compatible materials for making an EL panel in accordance with the invention. The examples are not intended to be exhaustive of combinations or proportions. The three white formulations produce different shades of white.
Front Insulator
The preferred front insulator includes a resin solution described in U.S. Pat. No. 6,445,128 (Bush et al.), the contents of which are incorporated by reference herein. Panels made with this ink were thinner than panels made in accordance with Example 1 yet had better dimensional stability (stayed flatter) and were more elastic.
The Kyx solution used in the phosphor layer is a resin solution having the following composition.
The various combinations represented in
The invention thus provides a thin, thick-film, inorganic EL panel that does not curl or distort when removed from a release layer and is more stable dimensionally than urethane-based EL lamps of the prior art. The panel can be stretched and will return to its original shape when released. The panel does not require similar chemistry for adjacent lamp layers and the panel can be made from solvent based inks on a removable substrate or release layer. The resulting panel is brighter than flexible EL panels of the prior art and is well suited for keypads and other applications where non-destructive flexibility is necessary.
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.
| Number | Name | Date | Kind |
|---|---|---|---|
| 5565733 | Krafcik et al. | Oct 1996 | A |
| 5770920 | Eckersley et al. | Jun 1998 | A |
| 5780965 | Cass et al. | Jul 1998 | A |
| 5856030 | Burrows | Jan 1999 | A |
| 5882806 | Mori | Mar 1999 | A |
| 6198216 | Kosa et al. | Mar 2001 | B1 |
| 6413676 | Munshi | Jul 2002 | B1 |
| 6445128 | Bush et al. | Sep 2002 | B1 |
| 6503432 | Barton et al. | Jan 2003 | B1 |
| 6749650 | Gonzalez et al. | Jun 2004 | B2 |
| 6771019 | Wu et al. | Aug 2004 | B1 |
| 6787993 | Bush et al. | Sep 2004 | B2 |
| 20040145089 | Burrows | Jul 2004 | A1 |
| Number | Date | Country |
|---|---|---|
| WO 02103718 | Dec 2002 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 20050194895 A1 | Sep 2005 | US |
