Patent Application
20060214577
An electroluminescent lamp (EL) includes a layer of electroluminescent phosphor powder and a dielectric sandwiched between two electrodes. At least one of these electrodes is transparent. On application of a voltage, the electroluminescent phosphor emits light. The electroluminescent phosphor layer may be patterned in the form of a desired image, such as a corporate logo, so that when the EL lamp is turned on, illumination occurs in the form of the desired image. Typically, patterning the luminescent material in the form of a desired image is accomplished by a screen-printing process. However, the screen-printing process is cost effective only for large production runs of a given image. That is, where just a small number of EL lamps are desired to be made with a given image, the screen-printing process can be cost prohibitive.
The drawings referenced herein form a part of the specification. Features shown in the drawing are meant as illustrative of only some embodiments of the invention, and not of all embodiments of the invention.
In the following detailed description of exemplary embodiments of the invention, reference is made to the accompanying drawings that form a part thereof, and in which is shown by way of illustration specific exemplary embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. Other embodiments may be utilized, and logical, mechanical, electrical, electro-optical, software/firmware and other changes may be made without departing from the spirit or scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims.
A material is inkjet-printed or otherwise deposited onto a substrate of the EL lamp in accordance with a desired image (102). The material as inkjet printed is not substantially tacky, sticky, or otherwise adhesive. The material may also be deposited onto the substrate in ways other than inkjet-printing, such as via screen-printing or other conventional or novel techniques. The material may be a mixture, a solution, or another type of material. In one embodiment, the material includes a solvent in which one or more ultraviolet light-curable monomers and a photoiniator has been dissolved. For example, the solvent may be an alcohol such as methanol, ethanol, or propanol, the ultraviolet light-curable monomers may be hydroxyl ethylmethacrylate (HEMA) and glycerol dimethacrylate (GDMA), and the photoiniator may be benzoin methyl ether (BME), where the ratio of alcohol to HEMA to GDMA to BME is 30:50:15:5. In another embodiment, the solvent may be an alcohol such as methanol, ethanol, or propanol, the ultraviolet light-curable monomers may be HEMA and GDMA, and the photoiniator may be 2-hydroxy-2-methyl propiophenone (HMP), where the ratio of alcohol to HEMA to GDMA to HMP is 45:20:20:15. In another embodiment, the material can include a colloidal suspension of a polymer resin, such as polyurethane or cellulose, in a solvent. The following additives may also be included in the inkjet printed material: plasticizers, such as adipate or phthalate esters; adhesion promoters, such as silane coupling agents; and, humectants, such as 2-pyrollidinone.
Referring back to
The partial curing performed in 106 is one type of action that is performed to render the material inkjet-printed on the substrate at least partially tacky. Thus, this action may include exposure of the material to ultraviolet or another type of light to partially cure the material. In another embodiment, the material may be subjected to an elevated temperature to render it tacky (i.e., thermal activation), or the material may be chemically activated to render it tacky. Embodiments of the invention are not restricted by the type of action that is to be performed to render the material that was inkjet-printed on the substrate in a non-tacky state into a tacky state.
Next, a electroluminescent powder is deposited onto the substrate (108). Deposition of the electroluminescent powder may be accomplished by spraying the electroluminescent powder onto the substrate as the substrate passes relative to a spray gun, by releasing the electroluminescent powder from a vibratory hopper as the substrate passes underneath the hopper, or by another approach. The electroluminescent powder adheres to the substrate substantially where the material has been previously inkjet-printed or otherwise deposited on the substrate. Thereafter, excess electroluminescent powder that has not adhered to the substrate is removed (110). For instance, vibration, brushing, airflow, vacuum, or another approach may be used to remove excess electroluminescent powder.
In one embodiment, the inkjet-printing of the material 202 onto the substrate 200 off the EL lamp is accomplished in lieu of inkjet-printing the electroluminescent powder 302 itself directly onto the substrate 200 owing to the characteristics of the electroluminescent powder 302. The size of the electroluminescent powder 302 may be substantially larger than what can be usually ejected using typical inkjet-printing mechanisms. For example, copper-doped zinc sulfide phosphor particles have a particle size range between 5 and 35 microns, which is too large to be reliably dispensed through the nozzles of commercially available inkjet-printing mechanisms. Reducing the size of the phosphor particles may be impractical, since doing so reduces the lifetime of the phosphor, and thus the lighting life of the resulting EL lamp. Furthermore, the viscosity of an ink containing a suspension of phosphor powder particles in the quantity to form a continuous light-emitting layer may be too great to eject from commercially available inkjet-printing mechanisms.
Referring back to
The method 100 that has been described is amenable to the construction of EL lamps in short production runs. Whereas the screen-printing process of patterning a desired image into a luminescent material layer of an EL lamp is an analog process that is cost prohibitive for short production runs, the inkjet-printing process of the method 100 is a digital process that is cost effective even for short production runs. Expensive and complex screens, for instance, do not have to be fabricated to pattern a luminescent material layer of an EL lamp with a desired image in the method 100. Rather, inkjet-printing is accomplished to define a desired image for the luminescent material of the EL lamp. The process is digital because the image is defined digitally, and the inkjet-printing of the image is performed by turning on and off an inkjet-printing mechanism in accordance with the image as the mechanism is moved over the substrate of the EL lamp.
When the substrate 200 passes under the inkjet-printing mechanism 410, the mechanism 410 ejects a first layer of the material 202 in accordance with the desired image. The inkjet-printing mechanism 410 may be or include an inkjet-printing cartridge, one or more inkjet-printing pens, and so on. The substrate 200 then passes under an ultraviolet light source 412 emitting ultraviolet light 414 to partially cure the material 202 to render it at least partially tacky. Thereafter, the substrate 200 passes under a electroluminescent powder release mechanism 416 that releases the electroluminescent powder 302 at least substantially uniformly over the entirety of the substrate 200. The mechanism 416 may be or include a vibratory hopper, a spray gun, or another type of mechanism to release the electroluminescent powder 302 onto the substrate 200.
As the substrate 200 passes under an excess electroluminescent powder removal mechanism 418, the mechanism 418 removes the excess of the electroluminescent powder 302 that did not adhere to the substrate 200, as indicated by the arrows 420. For instance, the mechanism 418 may operate by vacuum, suction, vibration or another approach, such as by ejecting an air stream, and so on. The electroluminescent powder 302 adheres to the substrate 200 where the first layer of the material 202 has been previously inkjet-printed on the substrate 200, as has been described.
A second layer of the material 202 is applied to the substrate 200 in accordance with the desired image by another inkjet-printing mechanism 422, as the substrate 200 passes under the mechanism 422. The substrate 200 finally passes under another ultraviolet light source 424 emitting ultraviolet light 426 to fully cure the material 202, and thus to permanently affix the electroluminescent powder 302 to the substrate 200. As can be appreciated by those of ordinary skill within the art, just one layer of the material 202 may be inkjet-printed on the substrate 200, instead of the two layers depicted in
Next, a layer of dielectric 504 is deposited over the electroluminescent powder 302 as sandwiched by the layers of the material 202. The dielectric 504 may be barium titanate powder in a polyurethane binder, or another type of dielectric. An electromigration barrier 506, such as carbon, may be fashioned over the dielectric 504 to prevent the electroluminescent powder 302 from migrating through the EL lamp 500 during usage thereof. A busbar 508, such as silver, is deposited directly onto the ITO layer. The function of the busbar is to distribute the electrical power move evenly across the ITO coating. Finally, an electrode 510, which may also be silver, is deposited over the busbar 508, and an encapsulant 512 seals the entire EL lamp 500. The encapsulant 512 may be a fluoropolymer film, such as the clear and/or transparent moisture barrier film sold by Honeywell International Inc. under the trade name Aclar, or any other suitable type of encapsulant.
For usage of the EL lamp 500, a voltage source 514 is applied between the electrode 510 and the transparent conductor 502. Application of power in this manner causes the electroluminescent powder 302 to glow outwards through the transparent conductor 502 and the transparent substrate 200. Because the electroluminescent powder 302 has been formed in the desired image, the image itself illuminates.
A dielectric layer is deposited or otherwise formed or created onto the electroluminescent powder (606), and a carbon electromigration barrier is inkjet-printed thereon or otherwise formed or created or deposited (608). A busbar and a rear electrode may also be formed by inkjet-printing, or by another approach to form, create, or deposit the busbar and the rear electrode (610). Finally, the entire lamp is sealed with an encapsulant (612).
It is noted that, although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that any arrangement is calculated to achieve the same purpose may be substituted for the specific embodiments shown. This application is intended to cover any adaptations or variations of the present invention. Therefore, it is manifestly intended that this invention be limited only by the claims and equivalents thereof.
