Electric lamp and discharge devices – With luminescent solid or liquid material – Solid-state type
Reexamination Certificate
2001-06-25
2004-12-21
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
With luminescent solid or liquid material
Solid-state type
C313S498000, C313S509000, C313S511000, C427S066000
Reexamination Certificate
active
06833669
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to electroluminescent panels and deals more particularly with a method and related apparatus for continuous processing to produce large-scale foil-back electroluminescent lamp material. The invention further relates to split-electrode and parallel plate electroluminescent lamps and strip lamps made from the large-scale foil-back electroluminescent lamp material.
BACKGROUND OF THE INVENTION
Lamps and processes for making individual lamps from electroluminescent material are known in the electroluminescent (EL) lamp art. Typical EL lamps are relatively small in illuminated surface area and are known as “parallel plate lamps” that are produced from a number of processes including screen-printing, lamination and other processes known in the EL lamp art. The generic construction of most EL lamps can be described as being built up layer-by-layer from the front substrate having: 1) a transparent front substrate; 2) a transparent conductive front electrode; 3) a phosphor/organic binder layer; 4) a barium titanate layer and 5) a rear electrode layer formed from a conductive coating such as nickel acrylic or conductive silver ink.
An alternate generic construction uses an aluminum foil substrate to form the rear electrode, in which case there is no front substrate because the lamp is built up layer-by-layer from the rear. Also, in the generic construction described above a portion of the front electrode is not coated with the phosphor/organic binder layer and is left exposed to permit attachment of an electrical connector to the front electrode. Inherently, clear conductors are fragile and cannot support connection and often a conductive ink, such as a silver ink, is used to support the termination and distribute the power applied thereto more evenly.
A disadvantage of EL lamps constructed as described above is the limited size or area that can be powered to maintain uniform brightness across the EL lamp. The transparent front electrode in these EL lamps is characteristically not a perfect conductor and exhibits a significant electrical resistance. This electrical resistance produces voltage drops that manifest as decreasing and lower relative brightness as the distance from the point of power connection increases. An EL lamp with a continuous silver conductor around its periphery is often used to obtain shorter connection distances to distribute current in a parallel plate EL lamp in an attempt to overcome the effects of voltage drops; however, the center of the EL lamp will become lower in brightness compared to the brightness at the periphery as the lamp area size increases.
D'Onofrio (U.S. Pat. No. 4,534,743) discloses a process for continuously manufacturing flexible electroluminescent lamps by applying the materials throughout the course of the process on a carrier strip, which carrier strip itself becomes part of the lamp and wherein the termination method does not use the front electrode. In the '743 patent, the rear electrode is scored or “scribed” into two substantially equal areas so that the rear electrode areas are electrically isolated from each other. The terminations are then subsequently placed on the two rear electrode halves and connected to an AC voltage or power source. This type of construction is known as a “split-electrode” EL lamp construction and the two rear electrode areas function electrically as a voltage divider, therefore twice the normal operating voltage is required compared to a “parallel plate” EL lamp construction to achieve the equivalent brightness. The brightness, however, in a split-electrode EL lamp is obtained at a reduced current. The primary advantage of a split-electrode EL lamp compared to a parallel plate EL lamp is that most of the current, particularly for large surface area EL lamps, is distributed through the more conductive rear electrodes, which may be, for example, nickel acrylic paint or conductive silver ink. The front transparent electrode, typically indium tin oxide (ITO), carries a small amount of the current, which only powers a local region of the EL lamp. The “split electrode” construction allows the fabrication of larger surface area EL lamps before any reduction in brightness occurs. A further advantage of the “split electrode” construction is the ability to utilize higher volume and automated manufacturing techniques, particularly web-to-web processing, than would otherwise be possible with other EL lamp constructions which are built to a given specification provided beforehand. That is, continuous rolls of EL lamp material can be coated using standard converting equipment, which provides the advantage that the specific lamp size does not have to be predefined prior to the manufacturing of a roll of EL lamp material.
U.S. Pat. No. 5,019,748, assigned to the same assignee as the present invention, discloses a method for making an electroluminescent panel in a continuous fashion using a continuously moving carrier strip that becomes part of the electroluminescent panel or lamp to provide a highly reflective rear electrode that may be split in accordance with the “split-electrode” construction techniques described in U.S. Pat. No. 4,534,743. The method described in the '748 patent for making the electroluminescent panel includes depositing a reflective metallic layer on a smooth finished surface dielectric layer to provide a highly reflective rear electrode. The high reflectivity is a result of controlling the smoothness gloss of the second cured dielectric adhesive layer which causes significantly increased reflectivity of light from the rear to the front of the lamp in operation. The carrier strip can then be coiled after the lamp layers are formed thereon for subsequent payout in a production line that may, for example, die cut lamp shapes from the coil and split the rear electrode. Attachment of electrical conductors to the split rear electrode areas is then made for example, as disclosed in U.S. Pat. No. 5,045,755, assigned to the same assignee as the present invention. Although the '748 patent describes a method for making an EL lamp using an ultraviolet (UV) curable binder and electrostatic deposition of phosphor particles to provide an EL lamp that is superior to the EL lamp production methods and EL lamps of the prior art, the lamp produced in accordance with the method of the '748 patent is not entirely satisfactory. The EL lamp produced in accordance with the '748 patent requires two separate coating and curing operations for the binder to encapsulate the phosphor particles, which are electrostatically deposited in a separate operation and a further third coating and curing operation to add a rear electrode. The structure thus produced is more costly than it need be resulting from the numerous separate operations required to produce the EL lamp material. Additionally, the EL lamp so manufactured has some performance limitations as well. These limitations may be manifested as lower total brightness resulting from a thick second binder coating and lack of rear barium titanate to impedance layer, and limited overall total size due to limited conductivity of the rear electrode.
Accordingly, it is an object of the present invention to reduce the cost of manufacturing EL lamp material by reducing the number of process steps in production.
It is a further object of the present invention to improve the performance of the EL lamp itself made from the EL lamp material by increasing its brightness and substantially removing limitations in the size or surface area of an EL lamp.
It is yet a further object of the present invention to provide apparatus for the continuous production of two primary substrates that are laminated together to create the large-scale foil-back EL lamp material in continuous rolls.
It is a still further object of the present invention to provide an improved foil-back EL lamp material and an EL lamp that reduces the time to make a product by eliminating registration and artwork requirements.
It is an additional object
Appelberg Gustaf T.
George Douglas A.
E-Lite Technologies, Inc.
Leurig Sharlene
Patel Nimeshkumar D.
Ware Fressola Van Der Sluys & Adolphson LLP
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