US3819973A

US3819973A - Electroluminescent filament

Info

Publication number: US3819973A
Application number: US00303101A
Authority: US
Inventors: A Hosford
Original assignee: Individual
Current assignee: Individual
Priority date: 1972-11-02
Filing date: 1972-11-02
Publication date: 1974-06-25
Anticipated expiration: 1991-06-25

Abstract

An electroluminescent filament of at least two wires made of electrical conductors each having an electrically insulating covering over the surface is provided. The wires are placed in abutment and covered with a phosphorescent material and the total thickness of the filament is controlled. Helically wound wires are used wherein the distance between the helical loop centers is controlled for best performance.

Description

United States Patent 1191 Hosford June 25, 1974 5 ELECTROLUMINESCENT FILAMENT 3.069579 12/1962 Berg et al. 3 l3/l08 A [76] Inve to onzo L o o 30 S 3,571,647 3/l97l Robinson 3l3/l08 A Brentwood Dr., Moorestown, NJ. 1 08057 Primary Exammer-James W. Lawrence Assistant ExaminerWm. H. Punter [22] Filed: Nov. 2, 1972 Attorney, Agent, or Firm-Thomas A. Lennox, Esq. [21] Appl. No.: 303,101

[57] ABSTRACT 521 US. Cl. ..313/498, 313/345- electroluminescent filament of at least two Wires [51] Int. Cl. .lj.'.;.'....l.ii65323 made of electrical conductors each having electri- [58] n w of Search 313/108 A, 108 R, 92 p cally insulating covering over the surface is provided. 313/108 B, 344445; 250/225 The wires are placed in abutment and covered with a phosphorescent material and the total thickness of the [56] References Cited filament is controlled. Helically wound wires are used UNITED STATES PATENTS wherein the distance between the helical loop centers 2 684 450 7/1954 Mager at al 313/108 A is controlled for best performance. 1052:1212 9/1962 Dow 313/108 A 12 Claims, 3 Drawing Figures ELECTROLUMINESCENT FILAMENT BACKGROUND OF INVENTION Many electroluminescent devices have been proposed, but few, if any, have proved a sufficiently effective light source for mass commercial marketing. Deficiencies include low efficiency of light output, short life, inability to color the light effectively and pennanently, low capacity, inapplicable to low cost continuous production, and others.

Electroluminescent phosphors exhibit luminescence in the presence of electric fields. While it is known that higher voltage and/or higher frequency of alternating current yields higher brightness, these inputs seriously reduce the life of the electroluminescent device. In common practice, the electric fields are generated by alternating current which may be either a direct field or a fringing field. Therefore, it is most desirable to construct a filament which could be used alone or combined with other filaments to make strands which would provide efficient light output and long life at moderate voltage and frequencies, such as ordinary house current.

The present invention relates to an electroluminescent filament that uses a fringing electric field surrounding at least two electrical conductors separated by an electrical insulator. A phosphor is applied to the outer surface of the wires and caused to luminesce by an electrical current applied across the conductors.

Prior art devices have been described of this general type such as in U.S. Pat. No. 2,684,450 to E. L. Mager, et al., July 20, 1954, wherein conductors were wrapped around an insulator, covered with phosphor. Also, in U.S. Pat. No. 3,052,812 to F. w. Dow, Sept. 4, 1962, wherein two wires were wound in various configurations to form relatively large diameter strands, generally with only one wire insulated. Also, in U.S. Pat. No. 3,571,647 to Bessie A. Robinson, Mar. 23, 1971, insulated wires were twisted together without details. Attempts to construct these devices either provided filaments that fail almost immediately or yield an almost imperceptible glow under conditions that yield a reasonable life.

A particular difficulty arises from the use of commercially available wire, such as magnet wire, in that the surface of the smaller gauge wire has relatively large raised imperfections, which, when coated with a dielectric, provide points of weakness in the insulation and limit the life or performance of an electroluminescent device constructed from them. These hot spots on the surface make all prior electroluminescent devices using insulation on only one wire, essentially useless.

SUMMARY OF INVENTION More particularly, this invention relates to electroluminescent devices offering high brightness and efficiency at the voltage and alternating cycle chosen, a more efficient capacitance than prior devices, and extremely long service life. Further, this invention relates to electroluminescent devices which provide versatility and efficiency in allowing the inclusion of permanent color bodies into the phosphor. Further, the electroluminescent devices are extremely ductle and durable as compared to prior devices.

It is an object of my invention to provide an electroluminescent filament that has increased brightness at relatively low voltage and frequency and that can be commercially reliable without failing due to arcing between the conductors. It is a further object that the filament be able to be produced by continuous methods with reliability suitable for consumer use. It is the object that the filament be able to be formed, twisted or wound to fonn designs, such as signs, crafts and arts, digital readouts, and indicators of an ornate or decorative nature. It is also intended that the filaments be grouped to provide a higher light output for illumination of the object on which the filaments are attached, such as interior emergency lighting on fixtures, baseboards and the like.

Therefore, my invention is an electroluminescent filament of at least two wires with each wire being an electrical conductor covered with an electrical insulator on its surface. The wires are placed in an abutting relation along their length and a phosphor coating applied to both wires. The total thickness of the filament is less than 10 mils.

It should be realized that by using the term abutting it is intended to indicate that the insulation of the wires touch. However, in an embodiment of the invention, where wire is helically wound around other wire, the looping wire touches the relatively straight wire, but the adjacent loops of the helical coil are preferably spaced a certain distance apart. When the embodiment of the invention employs two or more relatively parallel wires, their insulation touches for greatest efficiency.

DESCRIPTION OF PREFERRED EMBODIMENTS For the purpose of illustrating the invention, drawings and specific descriptions are provided, although it should be understood that the invention is not limited to these specific embodiments.

FIG. 1 illustrates an embodiment of the present invention.

FIG. 2 is a perspective view of a second embodiment of the invention.

FIG. 3 is a transverse sectional view of the embodiment of FIG. 2.

I have found that the total thickness of the filament is critical to performance. The thickness is required to be less than 10 mils, and best performance is obtained if the total thickness is 8 mils or less. There is no minimum thickness until there is insufficient conductive material in the wire to carry the current required to excite the phosphor. The present state of the art limits the total thickness of the filament since copper wire presently produced less than about 2 mils in thickness is generally insufficient to efficiently carry the current and provide long life to the filament. Therefore, the use of copper presently limits the thickness of the filament to greater than about 4 mils depending upon the configuration of the filament. Of course, other more conductive material will allow thinner filaments.

As stated above, the wires are placed in an abutting relationship. When two or more wires are placed in parallel, it is necessary that they touch. However, as stated above, when wires are helically wound around relatively straight wire, it is preferred that the helically wound loops not touch. In fact, I have discovered that a specific pitch between the loops provides particularly efficient illumination. This pitch is dependent somewhat upon the total thickness of the filament, but is within the range of about 5 to 12 mils. The pitch is preferably controlled in the range of 6 to l0 mils. Most preferred filaments are obtained by controlling the pitch to the range of 7 to 9 mils. This pitch distance is measured between loops of the same wire or between loops of different wires in multi-loop constructions.

This invention is not limited to the number of wires in the construction and may include any number of essentially parallel wires and any number of helically wound wires wound around parallel, twisted or helical wires. The wires may be of differing colors and may be connected in pairs or groups to achieve various effects.

Considering the drawings in detail, there is shown in FIG. I, an electroluminescent filament designated 10. In this embodiment wire 11 consisting of copper conductor l2 and polymeric electrical insulator 13 and wire 15 consisting of copper conductor 16 and polymeric electrical insulator 17 are laid in abutment in a roughly parallel configuration. The wires may be twisted, intertwined or even entangled together depending on the effect desired as long as they are in abutment. A phosphor 20 is located primarily in the crevices between wires 11 and 15 but also to a lesser degree over the entire surface of the wires. A light transparent or at least highly translucent polymeric coating 21 covers and protects the entire filament from damage due to hard use.

A preferred embodiment is depicted in FIGS. 2 and 3 of an electroluminescent filament designated 10. It includes wire 11' helically wound around wire The wire 11 is shown the same size as wire 15' but this is not necessary even within this preferred embodiment. It should be understood that the wires can be of the same size or the straight wire can be larger or smaller than the helical wire if manufacturing procedures permit. Wire 11 consists of a copper conductor 12 covered with an insulator 13'. The insulator I3 is a dielectric material such as enamel or Paralyne C and N as disclosed below. The wall of the insulator 13' should be as thin as possible in accordance with the principles set forth below. Although the conductor 16 is illustrated as having a round cross section, the conductor and indeed the entire wire 15' can be square, rectangular or any shape in cross section as desired. The wire 15' includes a conductor 16' and an insulator 17'. The conductor 16 is preferably smaller in cross-sectional dimension than the conductor 12 so that it can be more readily would about it. However, this is not a necessary requirement. Otherwise, the conductor 16' is the same as the conductor 12. The insulator 17' is the same as the insulator 13', but may, of course, be of different thickness.

In FIG. 2, the coils of the wire 11' are shown spaced apart. This distance apart 25 between the coils as measured from wire center to wire center is referred to herein as the pitch." As stated above it is preferred that this distance be in the range of'6 to 12 mils.

The wires 11 and 15' are covered with a powdered phosphor material 20' mixed with an appropriate polymeric binder such as thermoplastic resins, epoxy resin, and the like, to make the phosphor adhere to the insulating coating on the wires 11 and 15. The phosphor coating is placed over and mostly between the wires to the extent possible. The phosphor may, for example, include any one of the following or a mixture thereof:

1. Sylvania Type 523 phosphor consisting of zinc sulfide and manganese which generates a yellow color at 60, 400 and 6,000 Hz with a peak wavelength of 580 nm and has Fisher sub-sieve sizer number of 19.4.

2. Sylvania Type 723 phosphor consisting of zinc sulfide and copper which generates a green color at 60 Hz, bluegreen at 400 Hz, and blue at 6,000 Hz with a peak wavelength of 497 nm and has Fisher sub-sieve sizer number of 20.0.

3. Sylvania Type 814 phosphor consisting of zinc sulfide and copper which generates a blue color at 60, 400 and 6,000 Hz with a peak wavelength of 452 nm and has a Fisher sub-sieve sizer number of 24.0.

Each of the above phosphors is available from the Sylvania Division of General Telephone and Electronics. Of course, other phosphors available on the market can be substituted for those disclosed above. If desired, fluorescent materials can be added to the phosphor to give it color in its unexcited states; that is, in ambient light. Such fluorescent materials may include fluores- 7 cent paints available on the market. One such fluorescent paint in varying colors is available from the Illinois Bronze Powder and Paint Co., Lake Zurich, Ill. and sold under the trademark DAZ-L.

If desired, wires 11' and 15 together with the phosphor material 20 may be enclosed within a coating of light transparent material such as a flexible polymeric. The coating permits the light to be emitted by the filament 10' while at the same time protecting the phosphor coating. The transparent coating may contain color bodies in the form of dye or translucent particles.

In accordance with known principles of electroluminescence, filaments 10 and 10' are energized by connecting a voltage source to the conductors. Such voltage source may, for example, be an alternating current at 60 Hz and the voltage at or 220 volts. A fringe electric field is developed that excites the phosphors to luminesce.

An example of a filament 10' which produces an enhanced luminescence consists of the following:

Wire 15' includes a No. 44, 2 mil, copper wire having an 0.05 mil enamel insulating coating. The wire 11' is also a No. 44 copper conductor with an 0.05 mil insulator coating. The wire 11 is would on the wire 15 at the density of turns per inch for a pitch of 8 mils to yield an overall diameter of the filament of 6 mils as desired. Measurements indicate that such a wire yields more than 0.4 foot lambert when excited with a 110 volt alternatingcurrent at 60 Hz..There is a substantial increase in brightness at 220 volts and 60 Hz since the brightness in foot lamberts is proportional to the square of the voltage. Experiments with known electroluminescent filaments produce substantially lower brightness levels.

In the example described above, the insulatordielectric for the wires 1 l and 15' is enamel. If desired, the insulator could be Parylene C and N coated on the conductors in accordance with the process available from Union Carbide Corporation. The advantage of using Parylene C and N is that it reduces the size of the insulator-dietectric on the wires. The reduction in the total thickness of the insulator-dietectric using the same size core conductors 12' and 16, enhances the fringe field and hence the excitation of the phosphors.

Similarly, the filament 10 may be constructed using No. 40, 3 mil, copper wire with 0.1 mil coating as wire 15 while retaining No. 44 insulated copper wire with an 8 mil pitch as the winding. The overall thickness of the filament is about 7 A mils and yields almost the same light output under the same excitation as the device above.

In a third construction of the filament the core wire is No. 37 (4 is mil) copper wire with an 0.15 mil insulation, wrapped again with insulated No. 44 wire on an 8 mil pitch to produce a filament about 9 mils thick. The illumination obtained is somewhat poorer than obtained with the first construction.-

Similar constructions to filament 10' yield the following results:

Measurements of capacitance on filament 10' yield a C-Factor of about 86 phase angle as compared to a perfect capacitor which would yield 90. This high efficiency is favorable as compared to prior filament devices.

The prior examples are merely illustrative of my invention and are not intended to limit the scope of the patent grant. My invention is limited only by the appended claims.

1 claim:

1. An electroluminescent filament comprising:

at least two wires,

each wire comprising an electrical conductor and an electrically insulating covering on the surface of the conductor,

the wires being in abutting relation along their length,

a phosphor coating overlying the wires, and

the total thickness of the filament including the insulators covering the conductors being less than 10 mils.

2. An electroluminescent filament in accordance with claim 1 wherein the total thickness of the filament is less than about 8 mils.

3. An electroluminescent filament in accordance with claim 1 wherein the total thickness of the filament including the phosphor coating, which is essentially all between the wires except where the wires are in abutment, is less than 10 mils.

4. An electroluminescent filament in accordance with claim 3 wherein the total thickness is less than 8 mils.

5. An electroluminescent filament as set forth in claim 1 wherein at least two wires are in parallel abutting relation.

6. An electroluminescent filament in accordance with claim 1 wherein the wires are interwound each upon the other.

7. An electroluminescent filament in accordance with claim 1 wherein at least one of the wires is helically wound around at least one of the other wires so that the wires are in abutting relation along their length.

8. An electroluminescent filament in accordance with claim 7 wherein the distance between centers of each loop of helically wound wire and the next adjacent loop of helically wound wire is in the range of about 6 mils to about 12 mils.

9. An electroluminescent filament in accordance with claim 8 wherein the total thickness of filament is less than about 8 mils and the distance between centers of each loop is about 7 to about 9 mils.

10. An electroluminescent filament in accordance with claim 1 including a light transparent coating overlying the wires and the phosphor.

11. An electroluminescent filament comprising:

at least two wires, each wire comprising an electrical conductor and an electrically insulating coating on the surface,

at least one of the wires being helically wound around one of the other wires so that the wires are in abutting relation along their length,

a phosphor coatingoverlying the wires,

the total thickness of the filament including the insulators covering the conductors and the phosphor coating being less than 10 mils, and

the distance between centers of each loop of helically wound wire and the next adjacent loop of helically wound wire being in the range of about 6 mils to about 12 mils.

12. An electroluminescent filament in accordance with claim 11 wherein the total thickness of the filament is in the range of about six to about nine mils and the distance between helically loops is about 7 to 9 mils.

Claims

1. An electroluminescent filament comprising: at least two wires, each wire comprising an electrical conductor and an electrically insulating covering on the surface of the conductor, the wires being in abutting relation along their length, a phosphor coating overlying the wires, and the total thickness of the filament including the insulators covering the conductors being less than 10 mils.

11. An electroluminescent filament comprising: at least two wires, each wire comprising an electrical conductor and an electrically insulating coating on the surface, at least one of the wires being helically wound around one of the other wires so that the wires are in abutting relation along their length, a phosphor coating overlying the wires, the total thickness of the filament including the insulators covering the conductors and the phosphor coating being less than 10 mils, and the distance between centers of each loop of helically wound wire and the next adjacent loop of helically wound wire being in the range of about 6 mils to about 12 mils.